Showing papers in "Plant Physiology in 1987"
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TL;DR: All forms of catalase in tobacco show peroxidatic (measured as ethanol to acetaldehyde conversion) as well as catalatic activities, however, for both Nicotiana species the ratio per oxidatic/catalatic activity is at least 30-fold higher in peak 3 than in peaks 1 and 2.
Abstract: Leaf extracts of both Nicotiana tabacum and Nicotiana sylvestris contain multiple forms of catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) which are separable at different pH values by chromatofocusing columns. Marked changes in distribution of these catalases occur during seedling development and leaf maturation. The form of catalase eluting first (peak 1) was predominant during early seedling growth and present at all stages of development. Two more acidic forms (peaks 2 and 3) appeared later and comprised 29% of the total activity by 11 days postgermination. Mature leaves of N. tabacum contained peak 1 catalase, but peaks 2 and 3 represented 62% of the total activity. No interconversion of peaks 1, 2, and 3 was detected. The three forms of catalase differed in thermal stability with peak 1 > peak 2 ≫ peak 3. For N. sylvestris, t½ at 55°C was 31.5 and 3.0 min for peaks 1 and 3, respectively, and for N. tabacum, t½ was 41.5 and 3.2 min, respectively. All forms of catalase in tobacco show peroxidatic (measured as ethanol to acetaldehyde conversion) as well as catalatic activities. However, for both Nicotiana species the ratio peroxidatic/catalatic activity is at least 30-fold higher in peak 3 than in peaks 1 and 2. Chromatofocusing of extracts from spinach leaves separated at least four peaks of catalase activity, one of which had a 10-fold higher ratio of peroxidatic/catalatic activity than the others. Short-term growth (5 days) of tobacco seedlings under atmospheric conditions suppressing photorespiration (1% CO2/21% O2) reduced total catalase activity and caused a decline in peak 1 catalase and a substantial increase in the activity of peaks 2 and 3 relative to air-grown seedlings at the same stage.
771 citations
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TL;DR: Bjorkman et al. as discussed by the authors found that exposure of leaves of Populus balsamifera, Hedera helix, and Monstera deliciosa to excess excitation energy (high light, air; weak light, 2% O2, 0% CO2) led to massive formation of zeaxanthin and a decrease in violaxanthins.
Abstract: Comparative studies of chlorophyll a fluorescence, measured with a pulse amplitude modulated fluorometer, and of the pigment composition of leaves, suggest a specific role of zeaxanthin, a carotenoid formed in the xanthophyll cycle, in protecting the photosynthetic apparatus against the adverse effects of excessive light. This conclusion is based on the following findings: (a) exposure of leaves of Populus balsamifera, Hedera helix, and Monstera deliciosa to excess excitation energy (high light, air; weak light, 2% O2, 0% CO2) led to massive formation of zeaxanthin and a decrease in violaxanthin. Over a wide range of conditions, there was a linear relationship between either variable, Fv, or maximum fluorescence, Fm, and the zeaxanthin content of leaves. (b) When exposed to photoinhibitory light levels in air, shade leaves of H. helix had a higher capacity for zeaxanthin formation, at the expense of β-carotene, than shade leaves of M. deliciosa. Changes in fluorescence characteristics suggested that, in H. helix, the predominant response to high light was an increase in the rate of nonradiative energy dissipation, whereas, in M. deliciosa, photoinhibitory damage to photosystem II reaction centers was the prevailing effect. (c) Exposure of a sun leaf of P. balsamifera to increasing photon flux densities in 2% O2 and 0% CO2 resulted initially in increasing levels of zeaxanthin (matched by decreases in violaxanthin) and was accompanied by fluorescence changes indicative of increased nonradiative energy dissipation. Above the light level at which no further increase in zeaxanthin content was observed, fluorescence characteristics indicated photoinhibitory damage. (d) A linear relationship was obtained between the ratio of variable to maximum fluorescence, Fv/Fm, determined with the modulated fluorescence technique at room temperature, and the photon yield of O2 evolution, similar to previous findings (O Bjorkman, B Demmig 1987 Planta 170: 489-504) on chlorophyll fluorescence characteristics at 77 K and the photon yield of photosynthesis.
698 citations
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TL;DR: A Sprouting-resistant and a sprouting-susceptible wheat cultivar were utilized to examine the role of ABA levels and sensitivity responses in wheat embryonic germination and a new and sensitive ABA immunoassay revealed differences in sensitivity to ABA.
Abstract: A sprouting-resistant and a sprouting-susceptible wheat cultivar were utilized to examine the role of ABA levels and sensitivity responses in wheat embryonic germination. Endogenous embryonic ABA levels were measured in both cultivars throughout grain maturation utilizing a new and sensitive ABA immunoassay. Embryonic ABA levels of each cultivar were similar with the sprouting-susceptible cultivar having about a 25% lower ABA level than that of the sprouting-resistant cultivar. Larger differences between the cultivars were noted in sensitivity to ABA, as measured by capability of ABA to block embryonic germination. ABA inhibited embryonic germination much more effectively in the sprouting-resistant cultivar.
493 citations
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TL;DR: Investigation of cultured tobacco cells adapted to grow under osmotic stress revealed that osmotin is concentrated in dense inclusion bodies within the vacuole, and although antiosmotin did not label organelles, cell walls, or membranes, osmotins appeared sparsely distributed in the cytoplasm.
Abstract: Cultured tobacco (Nicotiana tabacum var Wisconsin 38) cells adapted to grow under osmotic stress synthesize and accumulate a 26 kilodalton protein (osmotin) which can constitute as much as 12% of total cellular protein. In cells adapted to NaCl, osmotin occurs in two forms: an aqueous soluble form (osmotin-I) and a detergent soluble form (osmotin II) in the approximate ratio of 2:3. Osmotin-I has been purified to electrophoretic homogeneity, and osmotin-II has been purified to 90% electrophoretic homogeneity. The N-terminal amino acid sequences of osmotins I and II are identical through position 22. Osmotin-II appears to be much more resistant to proteolysis than osmotin-I. However, it cross-reacts with polyclonal antibodies raised in rabbits against osmotin-I. Osmotin strongly resembles the sweet protein thaumatin in its molecular weight, amino acid composition, N-terminal sequence, and the presence of a signal peptide on the precursor protein. Thaumatin does not cross-react with antiosmotin. An osmotin solution could not be detected as sweet at a concentration at least 100 times that of thaumatin which could be detected as sweet. Immunocytochemical detection of osmotin revealed that osmotin is concentrated in dense inclusion bodies within the vacuole. Although antiosmotin did not label organelles, cell walls, or membranes, osmotin appeared sparsely distributed in the cytoplasm.
465 citations
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TL;DR: The observations that barley plants fail to complete their life cycle in the absence of Ni and addition of Ni to the growth medium completely alleviates deficiency symptoms in the maternal plants satisfies the essentiality criteria means Ni should be considered a micronutrient for cereals.
Abstract: Nickel was established as an essential micronutrient for the growth of temperate cereal crops. Grain from barley (Hordeum vulgare L. cv ;Onda'; containing 40 to 80 nanograms of Ni per gram dry weight) grown in solution culture with negligible Ni concentrations (< 30 nanograms of Ni per liter) exhibited greatly reduced germination rates (i.e. 50% less than grain from Ni-adequate plants) and seedling vigor of the viable grain was greatly depressed. Grain containing less than 30 nanograms per gram dry weight was inviable. Under Ni-deficient conditions, barley plants fail to produce viable grain because of a disruption of the maternal plant's normal grain-filling and maturation processes that occur following formation of the grain embryo. The observations that (a) barley plants fail to complete their life cycle in the absence of Ni and (b) addition of Ni to the growth medium completely alleviates deficiency symptoms in the maternal plants satisfies the essentiality criteria; thus, Ni should be considered a micronutrient for cereals. Because Ni is required by legumes, and is now established as essential for cereals, we conclude that Ni should be added to the list of micronutrients essential for all higher plant growth.
463 citations
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TL;DR: A fundamental difference in the ability of pea to reduce the destructive effects of free-radical and (1)O(2) production in chloroplasts during chilling in high light is suggested.
Abstract: Chilling temperatures (5°C) and high irradiance (1000 microeinsteins per square meter per second) were used to induce photooxidation in detached leaves of cucumber (Cucumis sativus L.), a chilling-sensitive plant. Chlorophyll a, chlorophyll b, β carotene, and three xanthophylls were degraded in a light-dependent fashion at essentially the same rate. Lipid peroxidation (measured as ethane evolution) showed an O2 dependency. The levels of three endogenous antioxidants, ascorbate, reduced glutathione, and α tocopherol, all showed an irradiance-dependent decline. α-Tocopherol was the first antioxidant affected and appeared to be the only antioxidant that could be implicated in long-term protection of the photosynthetic pigments. Results from the application of antioxidants having relative selectivity for 1O2, O2−, or OH indicated that both 1O2 and O2− were involved in the chilling- and light-induced lipid peroxidation which accompanied photooxidation. Application of D2O (which enhances the lifetime of 1O2) corroborated these results. Chilling under high light produced no evidence of photooxidative damage in detached leaves of chilling-resistant pea (Pisum sativum L.). Our results suggest a fundamental difference in the ability of pea to reduce the destructive effects of free-radical and 1O2 production in chloroplasts during chilling in high light.
463 citations
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TL;DR: The recombinant genes were transmitted to progeny and resistance to insects was maintained, thus demonstrating that the introduction of toxin genes into plants may be a practical method of providing protection against certain insect pests.
Abstract: The crystal proteins, or §-endotoxins, of Bacillus thuringiensis are specifically lethal to Lepidopteran insects. We utilized a truncated and modified portion of a cloned crystal protein gene to construct a chimeric gene capable of expression in plant cells. Using an Agrobacterium tumefaciens binary vector system, we then transferred the chimeric toxin gene into tobacco (Nicotiana tabacum cv Havana 425) cells and regenerated recombinant plants. One to several copies per cell of the toxin gene are routinely present in the recombinant plants. Hybridization experiments demonstrated that these plants had a new RNA species of the size expected for the truncated toxin mRNA, and a polypeptide having the mobility expected for the truncated toxin was detected by immunoblotting. Significant variation was found in the levels of toxin-specific RNA expression between different recombinants, but the levels of hybridizing RNA in transformants correlated with the level of toxicity demonstrated against Manduca sexta (tobacco hornworm), and other Lepidopteran insects. The recombinant genes were transmitted to progeny and resistance to insects was maintained, thus demonstrating that the introduction of toxin genes into plants may be a practical method of providing protection against certain insect pests.
434 citations
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TL;DR: Results indicate that phosphorus has specific roles in nodule initiation, growth, and functioning in addition to its involvement in host plant growth processes.
Abstract: The interactive effects of phosphorus supply and combined nitrogen (nitrate) on dry matter and nitrogen accumulation by nodulated soybean (Glycine max L. Merr.) plants, and the relative effects of phosphorus supply on nodule number, mass, and function in comparison to host plant growth were used to investigate the role of phosphorus in symbiotic dinitrogen fixation. Mixed positive and negative phosphorus by nitrogen source interactions indicated that severe phosphorus deficiency markedly impaired both host plant growth and symbiotic dinitrogen fixation and that symbiotic dinitrogen fixation has a higher phosphorus requirement for optimal functioning than either host plant growth or nitrate assimilation. In the whole plant phosphorus concentration range of 0.8 to 1.5 grams per kilogram dry weight, plants supplied with 20 millimolar nitrate accumulated significantly more dry matter and nitrogen than symbiotic plants without nitrate. This suggested that the higher phosphorus requirement for symbiotic dinitrogen fixation is internal rather than being associated with differences in the ability of roots in the two nitrogen regimes to absorb phosphorus from the external solution. Increasing the phosphorus concentration in plants solely dependent on dinitrogen fixation resulted in highly significant (P = 0.0001) increases in whole plant nitrogen concentration as well as highly significant increases (P = 0.0001) in whole plant dry matter and nitrogen accumulation. This indicated a greater responsiveness of symbiotic dinitrogen fixation than of host plant growth to improvement in phosphorus nutrition. The large increases in whole plant nitrogen concentration were associated with about 3.5-fold increases in the ratio of nodule mass to whole plant mass and about 2-fold increases in specific acetylene reduction (nitrogenase) activity of the nodules. The large increase in nodule mass (>30-fold) between the 0 and 2.0 millimolar phosphorus levels resulted from 11- and 3-fold increases in nodule number per plant and average mass of individual nodules, respectively. Root mass per plant over the same concentration range increased 3.5-fold. These results indicate that phosphorus has specific roles in nodule initiation, growth, and functioning in addition to its involvement in host plant growth processes.
402 citations
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TL;DR: Results demonstrate a greater photosynthetic N use efficiency in A. retroflexus than C. album and at any given N(a), it had a greater light saturated photosynthesis rate thanC.
Abstract: The effect of leaf nitrogen (N) on the photosynthetic capacity and the light and temperature response of photosynthesis was studied in the ecologically similar annuals Chenopodium album (C(3)) and Amaranthus retroflexus (C(4)). Photosynthesis was linearly dependent on leaf N per unit area (N(a)) in both species. A. retroflexus exhibited a greater dependence of photosynthesis on N(a) than C. album and at any given N(a), it had a greater light saturated photosynthesis rate than C. album. The difference between the species became larger as N(a) increased. These results demonstrate a greater photosynthetic N use efficiency in A. retroflexus than C. album. However, at a given applied N level, C. album allocated more N to a unit of leaf area so that photosynthetic rates were similar in the two species. Leaf conductance to water vapor increased linearly with N(a) in both species, but at a given photosynthetic rate, leaf conductance was higher in C. album. Thus, A. retroflexus had a greater water use efficiency than C. album. Water use efficiency was independent of leaf N in C. album, but declined with decreasing N in A. retroflexus.
376 citations
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TL;DR: The results provide direct evidence for the role of sucrose phosphate synthase and cytosolic fructose 1,6-bisphosphatase in regulating sucrose synthesis in leaves and also show that the phosphate translocator is kinetically limiting in vivo.
Abstract: The alterations of subcellular metabolite levels during the day in spinach leaves have been investigated using nonaqueous density gradient centrifugation to separate chloroplasts, cytosol, and vacuole. The results provide direct evidence for the role of sucrose phosphate synthase and cytosolic fructose 1,6-bisphosphatase in regulating sucrose synthesis in leaves and also show that the phosphate translocator is kinetically limiting in vivo.
370 citations
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TL;DR: Highly enriched plasma membrane fractions were isolated from leaves of nonacclimated (NA) and acclimated (ACC) rye and there were substantial differences in the molecular species.
Abstract: Highly enriched plasma membrane fractions were isolated from leaves of nonacclimated (NA) and acclimated (ACC) rye (Secale cereale L. cv Puma) seedlings. Collectively, free sterols, steryl glucosides, and acylated steryl glucosides constituted >50 mole% of the total lipid in both NA and ACC plasma membrane fractions. Glucocerebrosides containing hydroxy fatty acids constituted the major glycolipid class of the plasma membrane, accounting for 16 mole% of the total lipid. Phospholipids, primarily phosphatidylcholine and phosphatidylethanolamine with lesser amounts of phosphatidylglycerol, phosphatidic acid, phosphatidylserine, and phosphatidylinositol, comprised only 32 mole% of the total lipid in NA samples. Following cold acclimation, free sterols increased from 33 to 44 mole%, while steryl glucosides and acylated steryl glucosides decreased from 15 to 6 mole% and 4 to 1 mole%, respectively. Sterol analyses of these lipid classes demonstrated that free beta-sitosterol increased from 21 to 32 mole% (accounting for the increase in free sterols as a class) at the expense of sterol derivatives containing beta-sitosterol. Glucocerebrosides decreased from 16 to 7 mole% of the total lipid following cold acclimation. In addition, the relative proportions of associated hydroxy fatty acids, including 22:0 (h), 24:0 (h), 22:1 (h), and 24:1 (h), were altered. The phospholipid content of the plasma membrane fraction increased to 42 mole% of the total lipid following cold acclimation. Although the relative proportions of the individual phospholipids did not change appreciably after cold acclimation, there were substantial differences in the molecular species. Di-unsaturated molecular species (18:2/18:2, 18:2/18:3, 18:3/18:3) of phosphatidylcholine and phosphatidylethanolamine increased following acclimation. These results demonstrate that cold acclimation results in substantial changes in the lipid composition of the plasma membrane.
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TL;DR: The characteristics of these mutants conclusively demonstrate the major role of chloroplast glutamine synthetase in photorespiration and its associated nitrogen recycling.
Abstract: Eight mutants of barley (Hordeum vulgare cv Maris Mink) lacking the chloroplast isozyme of glutamine synthetase (EC 6.3.1.2.) were isolated by their inability to grow under photorespiratory conditions. The cytoplasmic isozyme of glutamine synthetase was present in the leaves of all the mutants, with activities comparable to the wild-type (10-12 nanokatals per gram fresh weight). The mutant plants developed normally and were fully fertile under conditions that minimize photorespiration. In 1% O2 the rate of CO2 fixation in leaves of one of the mutants, RPr 83/32, was the same as the wild-type, but in air this rate declined to 60% of the wild-type after 30 minutes. During this time the ammonia concentration in leaves of the mutant rose from 1 to 50 micromoles per gram fresh weight. Such ammonia accumulation in air was found in all the mutant lines. In back-crosses with the parent line, F1 plants were viable in air. In the F2 generation, nonviability in air and the lack of chloroplast glutamine synthetase co-segregated, in both the lines tested. These two lines and four others proved to be allelic; we designate them gln 2a-f. The characteristics of these mutants conclusively demonstrate the major role of chloroplast glutamine synthetase in photorespiration and its associated nitrogen recycling.
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TL;DR: The increased release of citrate may provide a mechanism by which P-stressed plants enhance the availability of P in the rhizosphere.
Abstract: Under certain stress conditions roots exude organic molecules, which may facilitate the uptake of nutrients. The objective of this research was to identify and measure the effect of low P upon the exudation of organic acids by roots of alfalfa (Medicago sativa L.) seedlings. Surface-sterilized alfalfa seeds were grown aseptically in sterile sand using an apparatus specially designed for the addition of ±P nutrient solutions and for the collection of root exudates. Citric, malic, and succinic acids were detected in the root exudates of 24-day-old alfalfa seedlings. Citrate exudation from the roots of P-stressed alfalfa was 182% that of plants receiving a complete nutrient solution. The increased release of citrate may provide a mechanism by which P-stressed plants enhance the availability of P in the rhizosphere.
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TL;DR: It is concluded that the protection of root growth from salt stress by supplemental Ca(2+) is related to improved Ca-status and maintenance of K(+)/Na(+) selectivity.
Abstract: High Na+ concentrations may disrupt K+ and Ca2+ transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca2+ levels often counteract these consequences of salinity. The effect of supplemental Ca2+ on influx of Ca2+, K+, and Na+ in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca2+. Sodium influx increased proportionally to increasing salinity. At high external Ca2+, Na+ influx was less than at low Ca2+. Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, 45Ca2+ influx increased in proportion to salt concentrations, especially with high Ca2+. Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca2+. The rate of K+ uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca2+ is related to improved Ca-status and maintenance of K+/Na+ selectivity.
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TL;DR: There appears to be fundamental differences between these species in the mechanism of sun-shade adaptation and N partitioning in the photosynthetic apparatus that result in significant differences in the N-use efficiency of photosynthesis between Phaseolus and Alocasia but similar RuBPCase:substrate:product ratios despite these differences.
Abstract: Effects of varying light intensity and nitrogen nutrition on photosynthetic physiology and biochemistry were examined in the sun plant Phaseolus vulgaris (common bean) and in the shade plant Alocasia macrorrhiza (Australian rainforest floor species). In both Phaseolus and Alocasia, the differing growth regimes produced large changes in photosynthetic capacity and composition of the photosynthetic apparatus. CO2-saturated rates of photosynthesis were linearly related to leaf nitrogen (N) content in both species but photosynthesis per unit leaf N was markedly higher for Phaseolus than for Alocasia. Photosynthetic capacity was also higher in Phaseolus per unit ribulose 1,5-bisphosphate (RuBP) carboxylase (RuBPCase) protein. The leaf content of RuBPCase was linearly dependent on leaf N content in the two species. However, the proportion of leaf N which was RuBPCase was greater in Phaseolus than in Alocasia and was more sensitive to growth conditions, ranging from 6% of leaf N at low light to 20% at high light. In Alocasia, this range was much less, 6 to 11%. However, chlorophyll content was much more sensitive to light intensity in Alocasia. Thus, the RuBPCase/chlorophyll ratio was quite responsive to N availability and light intensity in both species (but for different reasons), ranging from 6 grams per gram for Phaseolus and 2 grams per gram for Alocasia at high leaf N and 1.5 gram per gram for Phaseolus and 0.5 gram per gram for Alocasia at low leaf N. These large changes in the proportions of components of the photosynthetic apparatus had marked effects on the sensitivity of these species to photoinhibition. These environmental effects also caused changes in the absolute levels of metabolites of the photosynthetic carbon reduction cycle. Concentrations of RuBP and P-glycerate were approximately 2-fold higher in high light-grown than low light-grown Phaseolus and Alocasia when expressed on a leaf area basis. However, if metabolite pool sizes are expressed on the basis of the RuBPCase catalytic site concentration, then they were little affected by the marked changes in leaf makeup. There appears to be fundamental differences between these species in the mechanism of sun-shade adaptation and N partitioning in the photosynthetic apparatus that result in significant differences in the N-use efficiency of photosynthesis between Phaseolus and Alocasia but similar RuBPCase:substrate:product ratios despite these differences.
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TL;DR: The results indicate that pea has an endogenous mechanism(s) for the removal of toxic oxygen species prior to lipid peroxidation, and this mechanism breaks down in pea after 6 hours in the cold, light, and the presence of paraquat.
Abstract: Chilling-induced photooxidation was studied in detached leaves of chilling-sensitive (CS) cucumber ( Cucumis sativus L.) and chilling resistant (CR) pea ( Pisum sativum L.). The rates of photosynthesis and respiration, measured as O 2 exchange, were found to be comparable in the two species over a temperature range of 5 to 35°C. Chilling at 5°C for 12 hours in high light (1000 microeinsteins per square meter per second) decreased CO 2 uptake 75% in detached pea leaves whereas CO 2 uptake by cucumber was reduced to zero within 2 hours. Respiration was unaffected in either species by the chilling and light treatment. Although ultrastructural alterations were apparent in chloroplasts of both species, cucumber9s were affected sooner and more severely. The mechanism of photooxidative lipid peroxidation was investigated by following the production of ethane gas under a variety of conditions. Maximum ethane production occurred in the CS cucumber at low temperature (5°C) and high light (1000 microeinsteins per square meter per second). Atrazine, an inhibitor of photosynthetic electron transport, almost completely halted this chilling- and light-induced ethane production. These data, taken with those reported in an accompanying article (RR Wise, AW Naylor 1986 Plant Physiol 83: 278-282) suggest that the superoxide anion radical is generated in cucumber chloroplasts (probably via a Mehler-type reaction) during chilling-enhanced photooxidation. Parallel experiments were conducted on pea, a CR species. Detached pea leaves could only be made to generate ethane in the cold and light if they were pretreated with the herbicide parquat, a known effector of O 2 − production. Even so, pea showed no lipid peroxidation for 6 hours, at which time ethane production began and was at a rate equal to that for the chilled and irradiated cucumber leaves. The results indicate that pea has an endogenous mechanism(s) for the removal of toxic oxygen species prior to lipid peroxidation. This mechanism breaks down in pea after 6 hours in the cold, light, and the presence of paraquat.
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TL;DR: Xylem vessels in grapevines growing in New England contained air over winter and yet filled with xylem sap and recovered their maximum hydraulic conductance during the month before leaf expansion in late May, suggesting that the decrease in permeability with hydration is due to formation of water films across pores in intervascular pit membranes.
Abstract: Xylem vessels in grapevines Vitis labrusca L. and Vitis riparia Michx. growing in New England contained air over winter and yet filled with xylem sap and recovered their maximum hydraulic conductance during the month before leaf expansion in late May. During this period root pressures between 10 and 100 kilopascals were measured. Although some air in vessels apparently dissolved in ascending xylem sap, results indicated that some is pushed out of vessels and then out of the vine. Air in the vessel network distal to advancing xylem sap was compressed at about 3 kilopascals; independent measurements indicated this was sufficient to push air across vessel ends, and from vessels to the exterior through dead vine tips, inflorescence scars, and points on the bark. Once wetted, vessel ends previously air-permeable at 3 kilopascals remained sealed against air at pressures up to 2 and 3 megapascals. Permeability at 3 kilopascals was restored by dehydrating vines below −2.4 megapascals. We suggest that the decrease in permeability with hydration is due to formation of water films across pores in intervascular pit membranes; this water seal can maintain a pressure difference of roughly 2 megapascals, and prevents cavitation by aspirated air at xylem pressures less negative than −2.4 megapascals.
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TL;DR: The results indicate that feedback limitations can play a role in determining the diurnal carbon gain in the field as the CO(2) concentration in the atmosphere increases.
Abstract: The sensitivity of photosynthesis to O2 and CO2 was measured in leaves from field grown plants of six species (Phaseolus vulgaris, Capsicum annuum, Lycopersicon esculentum, Scrophularia desertorum, Cardaria draba, and Populus fremontii) from 5°C to 35°C using gas-exchange techniques. In all species but Phaseolus, photosynthesis was insensitive to O2 in normal air below a species dependent temperature. CO2 insensitivity occurred under the same conditions that resulted in O2 insensitivity. A complete loss of O2 sensitivity occurred up to 22°C in Lycopersicon but only up to 6°C in Scrophularia. In Lycopersicon and Populus, O2 and CO2 insensitivity occurred under conditions regularly encountered during the cooler portions of the day. Because O2 insensitivity is an indicator of feedback limited photosynthesis, these results indicate that feedback limitations can play a role in determining the diurnal carbon gain in the field. At higher partial pressures of CO2 the temperature at which O2 insensitivity occurred was higher, indicating that feedback limitations in the field will become more important as the CO2 concentration in the atmosphere increases.
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TL;DR: To determine which peroxidase isozymes from Nicotiana tabacum are involved in cell wall biosynthesis or other normal cellular functions and which respond to stress, plants were subjected to either wounding or infection with tobacco mosaic virus.
Abstract: Peroxidases (EC 1.11.1.7) have been implicated in the responses of plants to physical stress and to pathogens, as well as in a variety of cellular processes including cell wall biosynthesis. Tissue samples from leaf, root, pith, and callus of Nicotiana tabacum were assayed for specific peroxidase isozymes by analytical isoelectric focusing. Each tissue type was found to exhibit a unique isozyme fingerprint. Root tissue expressed all of the detectable peroxidase isozymes in the tobacco plant, whereas each of the other tissues examined expressed a different subset of these isozymes. In an effort to determine which peroxidase isozymes from Nicotiana tabacum are involved in cell wall biosynthesis or other normal cellular functions and which respond to stress, plants were subjected to either wounding or infection with tobacco mosaic virus. Wounding the plant triggered the expression of several cationic isozymes in the leaf and both cationic and anionic isozymes in pith tissue. Maximum enzyme activity was detected at 72 hours after wounding, and cycloheximide treatment prevented this induction. Infection of tobacco with tobacco mosaic virus induced two moderately anionic isozymes in the leaves in which virus was applied and also systemically induced in leaves which were not inoculated with virus.
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TL;DR: The relationships between leaf nitrogen content per unit area (N(a) and the initial slope of the photosynthetic CO(2) response curve, activity and amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate car boxylase (PEPC), and chlorophyll content were studied in the ecologically similar weeds Chenopodium album and Amaranthus retroflexus.
Abstract: The relationships between leaf nitrogen content per unit area (Na) and (a) the initial slope of the photosynthetic CO2 response curve, (b) activity and amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC), and (c) chlorophyll content were studied in the ecologically similar weeds Chenopodium album (C3) and Amaranthus retroflexus (C4). In both species, all parameters were linearly dependent upon leaf Na. The dependence of the initial slope of the CO2 response of photosynthesis on Na was four times greater in A. retroflexus than in C. album. At equivalent leaf Na contents, C. album had 1.5 to 2.6 times more CO2 saturated Rubisco activity than A. retroflexus. At equal assimilation capacities, C. album had four times the Rubisco activity as A. retroflexus. In A. retroflexus, a one to one ratio between Rubisco activity and photosynthesis was observed, whereas in C. album, the CO2 saturated Rubisco activity was three to four times the corresponding photosynthetic rate. The ratio of PEPC to Rubisco activity in A. retroflexus ranged from four at low Na to seven at high Na. The fraction of organic N invested in carboxylation enzymes increased with increased Na in both species. The fraction of N invested in Rubisco ranged from 10 to 27% in C. album. In A. retroflexus, the fraction of Na invested in Rubisco ranged from 5 to 9% and the fraction invested in PEPC ranged from 2 to 5%.
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TL;DR: 2-day-old wheat seedlings with 15-millimeter roots were transferred to solutions containing 0.4 millimolar CaCl(2) at pH 4.3 variously supplemented with AlCl(3) and additional amounts of a chloride salt, and competition between the cation and Al for external binding sites may account for most of the amelioration.
Abstract: Aluminum is a major constituent of most soils and limits crop productivity in many regions. Amelioration is of theoretical as well as practical interest because understanding amelioration may contribute to an understanding of the mechanisms of toxicity. In the experiments reported here 2-day-old wheat (Triticum aestivum L. cv Tyler) seedlings with 15-millimeter roots were transferred to solutions containing 0.4 millimolar CaCl2 at pH 4.3 variously supplemented with AlCl3 and additional amounts of a chloride salt. Root lengths, measured after 2 days in the test solutions, were a function of both Al activity and the cation activity of the added salt. Percent inhibition = 100 {Al3+}/({Al3+} + Km + α{C}β) where {Al3+} is the activity of Al3+ expressed in micromolar, {C} is the activity of the added cation expressed in millimolar, and Km (= 1.2 micromolar) is the {Al3+} required for 50% inhibition in the absence of added salt. For Ca2+, Mg2+, and Na+ the values of α were 2.4, 1.6, and 0.011, respectively, and the values for β were 1.5, 1.5, and 1.8, respectively. With regard to relative ameliorative effectiveness, Ca2+ > Mg2+ ≈ Sr2+ ≫ K+ ≈ Na+. Other cations were tested, but La3+, Sc3+, Li+, Rb+, and Cs+ were toxic at potentially ameliorative levels. The salt amelioration is not solely attributable to reductions in {Al3+} caused by increases in ionic strength. Competition between the cation and Al for external binding sites may account for most of the amelioration.
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TL;DR: The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.
Abstract: The partial purification and characterization of cell wall polysaccharides isolated from suspension-cultured Douglas fir (Pseudotsuga menziesii) cells are described. Extraction of isolated cell walls with 1.0 m LiCl solubilized pectic polysaccharides with glycosyl-linkage compositions similar to those of rhamnogalacturonans I and II, pectic polysaccharides isolated from walls of suspension-cultured sycamore cells. Treatment of LiCl-extracted Douglas fir walls with an endo-alpha-1,4-polygalacturonase released only small, additional amounts of pectic polysaccharide, which had a glycosyl-linkage composition similar to that of rhamnogalacturonan I. Xyloglucan oligosaccharides were released from the endo-alpha-1,4-polygalacturonase-treated walls by treatment with an endo-beta-1,4-glucanase. These oligosaccharides included hepta- and nonasaccharides similar or identical to those released from sycamore cell walls by the same enzyme, and structurally related octa- and decasaccharides similar to those isolated from various angiosperms. Finally, additional xyloglucan and small amounts of xylan were extracted from the endo-beta-1,4-glucanase-treated walls by 0.5 n NaOH. The xylan resembled that extracted by NaOH from dicot cell walls in that it contained 2,4- but not 3,4-linked xylosyl residues. In this study, a total of 15% of the cell wall was isolated as pectic material, 10% as xyloglucan, and less than 1% as xylan. The noncellulosic polysaccharides accounted for 26% of the cell walls, cellulose for 23%, protein for 34%, and ash for 5%, for a total of 88% of the cell wall. The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.
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TL;DR: The tobacco ALS gene was isolated from a line of tobacco which is resistant to the sulfonylurea herbicides due to an alteration in ALS, and codes for an ALS that is sensitive to the herbicides, as assayed by transformation of the gene into sensitive tobacco cells.
Abstract: Acetolactate synthase (ALS) is the first common enzyme in the biosynthetic pathways to valine, isoleucine, and leucine. It is the target of two structurally unrelated classes of herbicides, the sulfonylureas and the imidazolinones. Genomic clones encoding ALS have been isolated from the higher plants Arabidopsis thaliana and Nicotiana tabacum, using a yeast ALS gene as a heterologous hybridization probe. Clones were positively identified by the homology of their deduced amino acid sequences with those of yeast and bacterial ALS isozymes. The tobacco and Arabidopsis ALS genes have approximately 70% nucleotide homology, and encode mature proteins which are approximately 85% homologous. Little homology is seen between the amino acid sequences of the presumptive N-terminal chloroplast transit peptides. Both plant genes lack introns. The tobacco ALS gene was isolated from a line of tobacco which is resistant to the sulfonylurea herbicides due to an alteration in ALS. The tobacco gene which was isolated codes for an ALS that is sensitive to the herbicides, as assayed by transformation of the gene into sensitive tobacco cells.
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TL;DR: It is proposed that under high light and at suboptimal temperatures, A is limited by rate of utilization of triose phosphate; at optimal temperatures, by the availability of substrate (CO(2) and RuBP) under photorespiring conditions or utilization of Triose phosphate under nonphotoresp firing conditions.
Abstract: Net photosynthetic assimilation rate (A), extractable activities of three photosynthetic enzymes, and the concentrations of six metabolites were determined for wheat (Tricum aestivum L.) leaves as leaf temperature was varied under photorespiring (350 microliters per liter CO(2) and 21% O(2)) and under nonphotorespiring conditions (800 microliters per liter CO(2) and 2% O(2)). The extractable activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and fructose-1,6-bisphosphatase declined with increasing leaf temperature from 15 to 45 degrees C. Leaf concentrations of ribulose-1,5-bisphosphate (RuBP) declined slightly between 15 and 25 degrees C but increased to a level which is 4 to 5 times the binding site concentration of Rubisco at leaf temperatures of 35 and 45 degrees C. Leaf concentrations of 3-phosphoglycerate, fructose-6-phosphate, and glucose-6-phosphate all declined with increasing leaf temperature. Outside of the limitations imposed by photorespiration, it is proposed that under high light and at suboptimal temperatures, A is limited by rate of utilization of triose phosphate; at optimal temperatures, by the availability of substrate (CO(2) and RuBP) under photorespiring conditions or utilization of triose phosphate under nonphotorespiring conditions; and at supraoptimal temperatures, by the activation state of Rubisco.
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TL;DR: Results show that soybean calcium-dependentprotein kinase represents a new class of protein kinase which requires calcium but not calmodulin for activity.
Abstract: A calcium-dependent protein kinase activity from suspension-cultured soybean cells (Glycine max L. Wayne) was shown to be dependent on calcium but not calmodulin. The concentrations of free calcium required for half-maximal histone H1 phosphorylation and autophosphorylation were similar (≈2 micromolar). The protein kinase activity was stimulated 100-fold by ≥10 micromolar-free calcium. When exogenous soybean or bovine brain calmodulin was added in high concentration (1 micromolar) to the purified kinase, calcium-dependent and -independent activities were weakly stimulated (≤2-fold). Bovine serum albumin had a similar effect on both activities. The kinase was separated from a small amount of contaminating calmodulin by sodium dodecyl sulfate polyacrylamide gel electrophoresis. After renaturation the protein kinase autophosphorylated and phosphorylated histone H1 in a calcium-dependent manner. Following electroblotting onto nitrocellulose, the kinase bound 45Ca2+ in the presence of KCl and MgCl2, which indicates that the kinase itself is a high-affinity calcium-binding protein. Also, the mobility of one of two kinase bands in SDS gels was dependent on the presence of calcium. Autophosphorylation of the calmodulin-free kinase was inhibited by the calmodulin-binding compound N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7), showing that the inhibition of activity by W-7 is independent of calmodulin. These results show that soybean calcium-dependent protein kinase represents a new class of protein kinase which requires calcium but not calmodulin for activity.
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ARCO1
TL;DR: The small size of primary wall microfibrils in higher plants may well be due to the binding of xyloglucan to cellulose during synthesis which prevents fasciation of small fibrils into larger bundles.
Abstract: Since xyloglucan is believed to bind to cellulose microfibrils in the primary cell walls of higher plants and, when isolated from the walls, can also bind to cellulose in vitro, the binding mechanism of xyloglucan to cellulose was further investigated using radioiodinated pea xyloglucan. A time course for the binding showed that the radioiodinated xyloglucan continued to be bound for at least 4 hours at 40°C. Binding was inhibited above pH 6. Binding capacity was shown to vary for celluloses of different origin and was directly related to the relative surface area of the microfibrils. The binding of xyloglucan to cellulose was very specific and was not affected by the presence of a 10-fold excess of (1→2)-β-glucan, (1→3)-β-glucan, (1→6)-β-glucan, (1→3, 1→4)-β-glucan, arabinogalactan, or pectin. When xyloglucan (0.1%) was added to a cellulose-forming culture of Acetobacter xylinum, cellulose ribbon structure was partially disrupted indicating an association of xyloglucan with cellulose at the time of synthesis. Such a result suggests that the small size of primary wall microfibrils in higher plants may well be due to the binding of xyloglucan to cellulose during synthesis which prevents fasciation of small fibrils into larger bundles. Fluorescent xyloglucan was used to stain pea cell wall ghosts prepared to contain only the native xyloglucan:cellulose network or only cellulose. Ghosts containing only cellulose showed strong fluorescence when prepared before or after elongation; as predicted, the presence of native xyloglucan in the ghosts repressed binding of added fluorescent xyloglucan. Such ghosts, prepared after elongation when the ratio of native xyloglucan:cellulose is substantially reduced, still showed only faint fluorescence, indicating that microfibrils continue to be coated with xyloglucan throughout the growth period.
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TL;DR: Results indicate that glutathione is a substrate for phytochelatin synthesis, and the protein synthesis inhibitor cycloheximide does not affect the initial production of phytOChelatin.
Abstract: Cell suspension cultures of tomato, Lycopersicon esculentum Mill. cv VFNT-Cherry, produce phytochelatins (poly[γ-glutamylcysteinyl]glycines) when exposed to cadmium. The synthesis of these peptides is accompanied by a decline in cellular levels of glutathione. Buthionine sulfoximine, an inhibitor of glutathione synthesis, inhibits the sustained production of phytochelatins. However, phytochelatin synthesis can occur in the presence of buthionine sulfoximine provided that sufficient glutathione is available. These results indicate that glutathione is a substrate for phytochelatin synthesis. The protein synthesis inhibitor cycloheximide does not affect the initial production of phytochelatin.
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TL;DR: It is concluded that, in the presence of external hydrostatic gradients, water moves primarily in the apoplast, whereas in the absence of osmotic gradients this component is much smaller in relation to the cell-to-cell component (symplasmic plus transcellular transport).
Abstract: A root pressure probe has been used to measure the root pressure (Pr) exerted by excised main roots of young maize plants (Zea Mays L.). Defined gradients of hydrostatic and osmotic pressure could be set up between root xylem and medium to induce radial water flows across the root cylinder in both directions. The hydraulic conductivity of the root (Lpr) was evaluated from root pressure relaxations. When permeating solutes were added to the medium, biphasic root pressure relaxations were observed with water and solute phases and root pressure minima (maxima) which allowed the estimation of permeability (PSr) and reflection coefficients (σsr) of roots. Reflection coefficients were: ethanol, 0.27; mannitol, 0.74; sucrose, 0.54; PEG 1000, 0.82; NaCl, 0.64; KNO3, 0.67, and permeability coefficients (in 10−8 meters per second): ethanol, 4.7; sucrose, 1.6; and NaCl, 5.7. Lpr was very different for osmotic and hydrostatic gradients. For hydrostatic gradients Lpr was 1·10−7 meters per second per megapascal, whereas in osmotic experiments the hydraulic conductivity was found to be an order of magnitude lower. For hydrostatic gradients, the exosmotic Lpr was about 15% larger than the endosmotic, whereas in osmotic experiments the polarity in the water movement was reversed. These results either suggest effects of unstirred layers at the osmotic barrier in the root, an asymmetrical barrier, and/or mechanical effects. Measurements of the hydraulic conductivity of individual root cortex cells revealed an Lp similar to Lpr (hydrostatic). It is concluded that, in the presence of external hydrostatic gradients, water moves primarily in the apoplast, whereas in the presence of osmotic gradients this component is much smaller in relation to the cell-to-cell component (symplasmic plus transcellular transport).
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TL;DR: Red, far-red photoreversibility in the controlled environment study indicated involvement of phytochrome, and dry matter partitioning among plant components in the field was related to far- red/red light ratio received during growth and development.
Abstract: The influence of plant spacing and row orientation on spectral distribution of light received by growing soybean (Gylcine max [L.] Merr.) plants was measured under field conditions. Light absorption, reflection and transmission of individual leaves showed that most of the blue and red was absorbed while most of the far-red was either reflected or transmitted. Plants growing in the field received different ratios of far-red relative to red, depending on nearness and/or orientation of other vegetation. Plants grown in close-spaced rows, or high population densities, received higher far-red/red ratios than did those grown in wide rows, or sparse populations. Heliotropic movements of the leaves also contributed to the far-red reflection patterns associated with row orientation. Under field conditions, differences in far-red/red ratios associated with nearness of competing vegetation became more pronounced with low solar angle near the end of the day. Plants exposed to far-red for 5 minutes at the end of each day in controlled environments, and those grown in close-spaced rows in the field, developed longer internodes and fewer branches. Red, far-red photoreversibility in the controlled environment study indicated involvement of phytochrome. Dry matter partitioning among plant components in the field was related to far-red/red light ratio received during growth and development.
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TL;DR: At low N, low N C. album plants did not lose leaf area to necrosis and had a greater NAR and NUE at low applied N than A. retroflexus, so that leaf N did not decline as much.
Abstract: The effect of applied nitrogen (N) on the growth, leaf expansion rate, biomass partitioning and leaf N levels of Chenopodium album (C3) and Amaranthus retroflexus (C4) were investigated. At a given applied N level, C. album had 50% greater leaf N per unit area (Na) than A. retroflexus. Nitrate accumulated at lower Na in A. retroflexus than C. album. A. retroflexus was more productive than C. album at high N, but C. album was more productive at low N. At high applied N, nitrogen use efficiency (NUE), expressed either as net assimilation rate (NAR) per unit N or relative growth rate per unit N, was greater in A. retroflexus than C. album. However, at low applied N, C. album had a greater NUE on both an NAR and growth basis than A. retroflexus. The leaf area partitioning coefficient was similar in the species at high N, but was greater in A. retroflexus than C. album at low N. At low N, greater leaf area partitioning apparently lowered leaf N in A. retroflexus to levels at which necrosis occurred. In C. album by contrast, leaf area partitioning declined to a greater degree with declining N than it did in A. retroflexus, so that leaf N did not decline as much. Consequently, low N C. album plants did not lose leaf area to necrosis and had a greater NAR and NUE at low applied N than A. retroflexus.