Showing papers in "Plant Physiology in 1977"
TL;DR: Nine of the enzyme activities were eliminated with cyanide treatment suggesting that they may be cupro-zinc enzymes, whereas one was cyanide-resistant and may be a manganese enzyme.
Abstract: Shoots, roots, and seeds of corn (Zea mays L., cv. Michigan 500), oats (Avena sativa L., cv. Au Sable), and peas (Pisum sativum L., cv. Wando) were analyzed for their superoxide dismutase content using a photochemical assay system consisting of methionine, riboflavin, and p-nitro blue tetrazolium. The enzyme is present in the shoots, roots, and seeds of the three species. On a dry weight basis, shoots contain more enzyme than roots. In seeds, the enzyme is present in both the embryo and the storage tissue. Electrophoresis indicated a total of 10 distinct forms of the enzyme. Corn contained seven of these forms and oats three. Peas contained one of the corn and two of the oat enzymes. Nine of the enzyme activities were eliminated with cyanide treatment suggesting that they may be cupro-zinc enzymes, whereas one was cyanide-resistant and may be a manganese enzyme. Some of the leaf superoxide dismutases were found primarily in mitochondria or chloroplasts. Peroxidases at high concentrations interfere with the assay. In test tube assays of crude extracts from seedlings, the interference was negligible. On gels, however, peroxidases may account for two of the 10 superoxide dismutase forms.
4,882 citations
TL;DR: In this article, the quantum yields of C3 and C4 plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O2 and in 2% CO2.
Abstract: The quantum yields of C3 and C4 plants from a number of genera and families as well as from ecologically diverse habitats were measured in normal air of 21% O2 and in 2% O2. At 30 C, the quantum yields of C3 plants averaged 0.0524 ± 0.0014 mol CO2/absorbed einstein and 0.0733 ± 0.0008 mol CO2/absorbed einstein under 21 and 2% O2. At 30 C, the quantum yields of C4 plants averaged 0.0534 ± 0.0009 mol CO2/absorbed einstein and 0.0538 ± 0.0011 mol CO2/absorbed einstein under 21 and 2% O2. At 21% O2, the quantum yield of a C3 plant is shown to be strongly dependent on both the intercellular CO2 concentration and leaf temperature. The quantum yield of a C4 plant, which is independent of the intercellular CO2 concentration, is shown to be independent of leaf temperature over the ranges measured. The changes in the quantum yields of C3 plants are due to changes in the O2 inhibition. The evolutionary significance of the CO2 dependence of the quantum yield in C3 plants and the ecological significance of the temperature effects on the quantum yields of C3 and C4 plants are discussed.
727 citations
TL;DR: The onset of ripening correlates with the peroxide content of fruit tissues as occurring under normal conditions or as influenced by the treatments, indicating that Hydrogen peroxide may be involved in oxidative processes required in the initiation and the promotion of ripens.
Abstract: Endogenous peroxide levels in pear fruit (Pyrus communis) were measured using a titanium assay method, and were found to increase during senescence in both Bartlett and Bosc varieties. Application of glycolic acid or xanthine, serving as substrates for the formation of H2O2, increased the peroxide content of the tissue and accelerated the onset of ripening, as measured by increased softening and ethylene evolution. Application of ethylene also induced increased peroxide levels. Ripening processes were similarly promoted when peroxides were conserved by inhibiting the activity of catalase with hydroxylamine or potassium cyanide. By comparison, the inhibition of glycolate oxidase with alphahydroxy-2-pyridinemethanesulfonic acid decreased the peroxide content of the tissue and delayed the onset of ripening. These results indicate that the onset of ripening correlates with the peroxide content of fruit tissues as occurring under normal conditions or as influenced by the treatments. Hydrogen peroxide may be involved in oxidative processes required in the initiation and the promotion of ripening.
664 citations
TL;DR: Glutathione reductase activity is present in spinach chloroplasts and a possible role in chloroplastics is proposed and the pH dependence and substrate concentration for half-maximal rate are reported.
Abstract: Glutathione reductase (EC 1.6.4.2) activity is present in spinach (Spinacia oleracea L.) chloroplasts. The pH dependence and substrate concentration for half-maximal rate are reported and a possible role in chloroplasts is proposed.
594 citations
TL;DR: The superoxide dismutase activity per plant and per milligram water-soluble protein considerably increased during germination of oats and during greening and hook opening of peas.
Abstract: Superoxide dismutase was purified from pea (Pisum sativum L., cv. Wando) seeds and corn (Zea mays L., cv. Michigan 500) seedlings. The purified pea enzyme eluting as a single peak from gel exclusion chromatography columns contained the three electrophoretically distinct bands of superoxide dismutase characterizing the crude extract. The purified corn enzyme eluted as the same peak as the pea enzyme, and contained five of the seven active bands found in the crude extract. The similar molecular weights and the cyanide sensitivities of these bands indicated that they are probably isozymes of a cupro-zinc superoxide dismutase. One of the remaining corn bands was shown to be a peroxidase.Superoxide dismutase accounted for 1.6 to 2.4% of the water-soluble protein in seedlings of corn, peas, and oats (Avena sativa L., cv. Au Sable). The superoxide dismutase activity per plant and per milligram water-soluble protein considerably increased during germination of oats and during greening and hook opening of peas.
527 citations
TL;DR: The method is based on the destruction of pre-existing glucose and fructose, followed by the hydrolysis of sucrose and reduction of NADP+ by a series of coupled enzymic reactions.
Abstract: Procedures are described for measuring sucrose in plant extracts or freeze-dried tissue in the range between 10−7 and 10−14 moles. The method is based on the destruction of pre-existing glucose and fructose, followed by the hydrolysis of sucrose and reduction of NADP+ by a series of coupled enzymic reactions. Depending on the sensitivity required, the NADPH is determined directly with a spectrophotometer or a fluorometer, or is amplified as much as 30,000 times before fluorometric assay. The procedures suggested for the macro level are simpler than current methods, and those suggested for microanalysis are several orders of magnitude more sensitive.
With this technique, single palisade parenchyma cells and single spongy parenchyma cells of Vicia faba leaflets were each found to contain about 2.2 pmoles of sucrose.
488 citations
TL;DR: Chlorophyll determinations made for leaves harvested at intervals after an ozone treatment indicated that maximum chlorophyll reduction had occurred by 4 days, which should be useful in eliminating the human bias associated with visible estimates of injury.
Abstract: A simple, rapid procedure is described for evaluating ozone injury to leaves of Phaseolus vulgaris L. cv. Pinto. Leaf chlorophyll is extracted with ethanol and analyzed spectrophotometrically; the concentration is expressed on the basis of leaf dry weight. The per cent chlorophyll reduction of ozone-injured leaves was highly correlated with the per cent visible necrosis and chlorosis ( r = 0.96). The variability in injury estimates with chlorophyll analysis was slightly less than with visual evaluation. An evaluation of chlorophyll a and b concentrations separately showed that the chlorophyll a/b ratio decreased with increasing amounts of injury. Chlorophyll determinations made for leaves harvested at intervals after an ozone treatment indicated that maximum chlorophyll reduction had occurred by 4 days. This procedure for measuring ozone injury should be useful in eliminating the human bias associated with visible estimates of injury.
388 citations
TL;DR: Starch synthesis in leaves was increased by phosphate starvation or by treatments which decreased cytoplasmic orthophosphate levels (such as mannose feeding) and it is suggested that this control is exerted via the phosphate translocator and the known allosteric regulation of ADP-glucose pyrophosphorylase.
Abstract: Starch synthesis in leaves was increased by phosphate starvation or by treatments which decreased cytoplasmic orthophosphate levels (such as mannose feeding). Usually less than 30% of the total carbon fixed during CO(2) assimilation was incorporated into starch in spinach (Spinacia oleracea L.), spinach beet (Beta vulgaris), and tobacco (Nicotiana tabacum) leaves.In isolated spinach chloroplasts, formation of starch from CO(2) was usually less than in leaves. In the absence of significant levels of 3-phosphoglycerate, concentrations of phosphate as low as 1 mm (in the medium) or 10 mm (in the stroma) almost completely inhibited starch synthesis. The inhibitory action of phosphate could be overcome by 3-phosphoglycerate. The controlling factor of starch synthesis appeared to be the ratio of phosphoglycerate to orthophosphate rather than the stromal hexose monophosphate concentration, and it is suggested that this control is exerted via the phosphate translocator and the known allosteric regulation of ADP-glucose pyrophosphorylase. Starch synthesis was also favored by the presence of dihydroxyacetone phosphate and by high light and high temperature. Oxygen was inhibitory, probably owing to carbon drain into glycolate. Starch formation by intact chloroplasts could not be promoted by added glucose or glucose 6-phosphate.Starch mobilization in the dark was promoted by orthophosphate and phosphate-dependent mobilization was inhibited by phosphoglycerate. The principal products of starch breakdown in the presence of phosphate were the transport metabolites dihydroxyacetone phosphate and 3-phosphoglycerate. Formation of these compounds from starch was stimulated by ATP or oxaloacetate. In a phosphate-independent reaction, starch was also converted to neutral products such as maltose and glucose. The rates of phosphate-dependent starch degradation phosphorolysis were very much higher than those of starch hydrolysis for which there was no phosphate requirement.
374 citations
TL;DR: Comparison of results on total cell wall composition and linkages of sugars as determined by a preliminary methylation analysis of unfractionated fiber walls indicates that the primary cell wall of cotton fibers is similar to that of primary cell walls of other dicotyledons and of gymnosperms as reported in the literature.
Abstract: The composition of the cell wall of the cotton fiber ( Gossypium hirsutum L. Acala SJ-1) has been studied from the early stages of elongation (5 days postanthesis) through the period of secondary wall formation, using cell walls derived both from fibers developing on the plant and from fibers obtained from excised, cultured ovules. The cell wall of the elongating cotton fiber was shown to be a dynamic structure. Expressed as a weight per cent of the total cell wall, cellulose, neutral sugars (rhamnose, fucose, arabinose, mannose, galactose, and noncellulosic glucose), uronic acids, and total protein undergo marked changes in content during the elongation period. As a way of analyzing absolute changes in the walls with time, data have also been expressed as grams component per millimeter of fiber length. Expressed in this way for plant-grown fibers, the data show that the thickness of the cell wall is relatively constant until about 12 days postanthesis; after this time it markedly increases until secondary wall cellulose deposition is completed. Between 12 and 16 days postanthesis increases in all components contribute to total wall increase per millimeter fiber length. The deposition of secondary wall cellulose begins at about 16 days postanthesis (at least 5 days prior to the cessation of elongation) and continues until about 32 days postanthesis. At the time of the onset of secondary wall cellulose deposition, a sharp decline in protein and uronic acid content occurs. The content of some of the individual neutral sugars changes during development, the most prominent change being a large increase in noncellulosic glucose which occurs just prior to the onset of secondary wall cellulose deposition. Methylation analyses indicate that this glucose, at least in part, is 3-linked. In contrast to the neutral sugars, no significant changes in cell wall amino acid composition are observed during fiber development. Compositional analyses of cell walls derived from culture-grown fibers indicate that these walls are remarkably similar to those derived from fibers grown on the plant, both in terms of composition and in terms of relative changes in composition during development. A comparison of our results on total cell wall composition and linkages of sugars as determined by a preliminary methylation analysis of unfractionated fiber walls indicates that the primary cell wall of cotton fibers is similar to that of primary cell walls of other dicotyledons and of gymnosperms as reported in the literature.
307 citations
TL;DR: Shooting bud development within p-calli was controlled by a number of factors including light, temperature, basic medium composition, nature and source of phytohormones, the continued presence of an osmoticum, low concentrations of a utilizable carbohydrate, and the developmental stage of the p- callus.
Abstract: Mesophyll cell protoplasts were isolated from potato (Solanum tuberosum L. cv. Russet Burbank) leaves and induced to proliferate in culture. Protoplast division was observed only among preparations isolated from plants previously conditioned under short periods of low intensity illumination. Sustained growth and development of protoplast-derived calli (p-calli) occurred when they were maintained on defined media at 24 C under 500 lux lighting. Shoot bud development within p-calli was controlled by a number of factors including light, temperature, basic medium composition, nature and source of phytohormones, the continued presence of an osmoticum, low concentrations of a utilizable carbohydrate, and the developmental stage of the p-callus.
266 citations
TL;DR: The results suggest that only a small fraction of the total K absorbed by the roots can be translocated downward from the leaves to the roots in the phloem sap, and the possible extent of K recirculation is thus low.
Abstract: Tomato plants ( Lycopersicon esculentum L. var. Ailsa Craig) were grown in water culture in nutrient solution in a series of 10 increasing levels of nitrate nutrition. Using whole plant data derived from analytical and yield data of individual plant parts, the fate of anion charge arising from increased NO 3 assimilation was followed in its distribution between organic anion accumulation in the plant and OH − efflux into the nutrient solution as calculated by excess anion over cation uptake. With increasing NO 3 nutrition the bulk of the anion charge appeared as organic anion accumulation in the plants. OH − efflux at a maximum accounted for only 20% of the anion charge shift. The major organic anion accumulated in response to nitrate assimilation was malate. The increase in organic anion accumulation was paralleled by an increase in cation concentration (K + , Ca 2+ , Mg 2+ , Na + ). Total inorganic anion levels (NO 3 − , SO 4 2− , H 2 PO 4 − , Cl − ) were relatively constant. The effect of increasing NO 3 nutrition in stimulating organic anion accumulation was much more pronounced in the tops than in the roots. It is suggested that increasing the level of NO 3 nutrition to tomato plants stimulates cation uptake and translocation as counter-ions are required to accompany NO 3 − ions to the upper plant parts, the major site of NO 3 reduction. On NO 3 reduction, the resulting stoichiometric accumulation of organic anions is balanced by the cations originally accompanying NO 3 − ions. Organic anions and cations are largely retained in the upper plant parts. The results suggest that only a small fraction of the total K absorbed by the roots can be translocated downward from the leaves to the roots in the phloem sap. The possible extent of K recirculation is thus low.
TL;DR: All plant tissues examined contained most of their IAA as derivatives, either esterified or as a peptide; the cereal grains examined contained mainly ester IAA; and the legume seeds examined contain mainly peptidyl IAA.
Abstract: Seeds of oat, coconut, soybean, sunflower, rice, millet, kidney bean, buckwheat, wheat, and corn and vegetative tissue of oat, pea, and corn were assayed for free indole-3-acetic acid (IAA), esterified IAA, and peptidyl IAA. Three conclusions were drawn: (a) all plant tissues examined contained most of their IAA as derivatives, either esterified or as a peptide; (b) the cereal grains examined contained mainly ester IAA; (c) the legume seeds examined contained mainly peptidyl IAA. Errors in analysis of free and bound IAA are discussed.
TL;DR: The unique segregation of the two oxidative steps in the pentose phosphate pathway may be required to meet the metabolic needs of these fat-storing seeds.
Abstract: Two isoenzymes each of hexose-P isomerase, aldolase and 6-P-gluconate dehydrogenase have been found in the endosperm of developing castor beans (Ricinus communis L.). One isoenzyme for each activity is present in the proplastid fraction. Only one form of glucose-6-P dehydrogenase was found. It is suggested that the partition of an enzyme activity between cytosol and plastid is regulated by the synthesis of isoenzymes which are subcellular site specific. In addition, this report describes the use of diethylaminoethyl-Sephadex A-25 sievorptive chromatography for the preparation of plant enzymes.
TL;DR: Results indicate that growth responses due to temperature shifts were more sensitive to changes in leaf area partitioning or relative leaf area expansion rates than to net assimilation rates.
Abstract: Despite continuing efforts to correlate unit area rates of photosynthesis of crop varieties with growth rates, there has been little or no success. It is reasonable to assume that partitioning of photosynthate into new leaf area is an important component of growth. Accordingly, an expression was developed to measure leaf area partitioning. Using growth analysis techniques, relative growth rates were compared to net assimilation rates, partitioning of daily weight gain into new leaf area, and partitioning of daily weight gain into new leaf weight of nine species grown in growth chambers under three temperature regimes. Day/night temperatures of 21/10, 32/21, and 38/27 C caused large differences in relative growth rates. Relative growth rates were closely correlated with leaf area partitioning in seven of the nine species, but were inversely correlated with leaf weight partitioning for six of the nine species. Relative growth rates were poorly correlated with net assimilation rates for five of the nine species. The product of net assimilation rate times leaf area partitioning is shown to be equal to the relative leaf area expansion rate. These results indicate that growth responses due to temperature shifts were more sensitive to changes in leaf area partitioning or relative leaf area expansion rates than to net assimilation rates. Because changes in leaf area partitioning or relative leaf area expansion rates can have an effect on relative growth rates that overshadow changes in net assimilation rates, and because net assimilation rates are largely a function of unit area rates of photosynthesis, the correlation of unit area rates of photosynthesis with growth should include consideration of leaf area partitioning or relative leaf area expansion rates.
TL;DR: The results raise the possibility that primary auxin action occurs at ER membranes and could represent facilitation of the transfer of hydrogen ions and nascent secretory protein into the ER lumen followed by secretory transport of these products to the cell exterior via the Golgi system.
Abstract: Sites in maize (Zea mays L.) coleoptile homogenates that reversibly bind naphthalene-1-acetic acid with high affinity and may represent receptor sites for auxins are located primarily on cellular membranes that show the enzymic and buoyant density characteristics of membranes of the rough endoplasmic reticulum. The sites remain attached to the endoplasmic reticulum (ER) membranes after the ribosomes have been stripped off them. Binding sites for naphthylphthalamic acid, an inhibitor of auxin transport, are located on membranes different from those that carry the naphthalene-1-acetic-acid (NAA)-binding sites, and which are probably plasma membrane. The two kinds of binding sites can be largely separated by appropriate density gradient centrifugation. The results raise the possibility that primary auxin action occurs at ER membranes and could represent facilitation of the transfer of hydrogen ions and nascent secretory protein into the ER lumen followed by secretory transport of these products to the cell exterior via the Golgi system.
TL;DR: Observations suggest that the conversion of methionine into MTA and MTR is closely related to ethylene biosynthesis and provide indirect evidence that SAM may be an intermediate in the Conversion of Methionine to Ethylene.
Abstract: If S-adenosylmethionine (SAM) is the direct precursor of ethylene as previously proposed, it is expected that 5'-S-methyl-5'-thioadenosine (MTA) would be the fragment nucleoside. When [Me-(14)C] or [(35)S]methionine was fed to climacteric apple (Malus sylvestris Mill) tissue, radioactive 5-S-methyl-5-thioribose (MTR) was identified as the predominant product and MTA as a minor one. When the conversion of methionine into ethylene was inhibited by (l)-2-amino-4-(2'-aminoethoxy)-trans-3-butenoic acid, the conversion of [(35)S] or [Me(14)C]methionine into MTR was similarly inhibited. Furthermore, the formation of MTA and MTR from [(35)S]methionine was observed only in climacteric tissue which produced ethylene and actively converted methionine to ethylene but not in preclimacteric tissue which did not produce ethylene or convert methionine to ethylene. These observations suggest that the conversion of methionine into MTA and MTR is closely related to ethylene biosynthesis and provide indirect evidence that SAM may be an intermediate in the conversion of methionine to ethylene.When [(35)S]MTA was fed to climacteric or preclimacteric apple tissue, radioactivity was efficiently incorporated into MTR and methionine. However, when [(35)S]MTR was administered, radioactivity was efficiently incorporated into methionine but not MTA. This suggests that the sulfur of MTA is incorporated into methionine via MTR. A dual label experiment with [(35)S, Me-(3)H]MTA indicates that the CH(3)S group of MTA was transferred as a unit to form methionine.A scheme is presented for the production of ethylene from methionine, the first step being the activation of methionine by ATP to give SAM. SAM is fragmented to give ethylene, MTA, and other products. MTA is then hydrolyzed to MTR which donates its methylthio group to a four-carbon acceptor to reform methionine.
TL;DR: The increased cell injury and infiltration in the -11 C treatment were paralleled by increases in conductivity, K(+) content, sugar content, and pH of the effusate, which may indicate that freezing or thawing involves a disruption of the active transport system before the cells reveal any injury microscopically.
Abstract: Onion ( Allium cepa L.) bulbs were frozen to −4 and −11 C and kept frozen for up to 12 days. After slow thawing, a 2.5-cm square from a bulb scale was transferred to 25 ml deionized H 2 O. After shaking for standard times, measurements were made on the effusate and on the effused cells. The results obtained were as follows. Even when the scale tissue was completely infiltrated, and when up to 85% of the ions had diffused out, all of the cells were still alive, as revealed by cytoplasmic streaming and ability to plasmolyze. The osmotic concentration of the cell sap, as measured plasmolytically, decreased in parallel to the rise in conductivity of the effusate. The K + content of the effusate, plus its assumed counterion, accounted for only 20% of the total solutes, but for 100% of the conductivity. A large part of the nonelectrolytes in the remaining 80% of the solutes was sugars. The increased cell injury and infiltration in the −11 C treatment, relative to the −4 C and control (unfrozen) treatments, were paralleled by increases in conductivity, K + content, sugar content, and pH of the effusate. In spite of the 100% infiltration of the tissue and the large increase in conductivity of the effusate following freezing, no increase in permeability of the cells to water could be detected. The above observations may indicate that freezing or thawing involves a disruption of the active transport system before the cells reveal any injury microscopically.
TL;DR: Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO(2) diffusion into the leaf, and the ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with Photosystem II than with photosystem I.
Abstract: Pisum sativum L. was exposed to ultraviolet-B (UV-B) radiation (280-315 nm) in greenhouse and controlled environment chambers to examine the effect of this radiation on photosynthetic processes. Net photosynthetic rates of intact leaves were reduced by UV-B irradiation. Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO2 diffusion into the leaf. Dark respiration rates were increased by previous exposure to this radiation. Electron transport capacity as indicated by methylviologen reduction was also sensitive to UV-B irradiation. The ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with photosystem II than with photosystem I. Electron micrographs indicated structural damage to chloroplasts as well as other organelles. Plant tissue irradiated for only 15 minutes exhibited dilation of thylakoid membranes of the chloroplast in some cells. Some reduction in Hill reaction activity was also evidenced in these plant materials which had been irradiated for periods as short as 15 minutes.
TL;DR: Protoplasts isolated from Avena sativa L. leaves undergo progressive senescence when incubated aseptically in 0.6 m mannitol with or without added nutrients, and the presence in the incubation medium of l-arginine, l-lysine, certain polyamines related to these amino acids, or streptomycin stabilizes the protoplasts.
Abstract: Protoplasts isolated from Avena sativa L. leaves undergo progressive senescence when incubated aseptically in 0.6 m mannitol with or without added nutrients. This senescence is manifested by morphological deterioration and ultimate lysis of protoplasts, by a decrease in incorporation of [ 3 H]uridine and [ 3 H]leucine into macromolecules, and by a sharp increase in ribonuclease activity. The presence in the incubation medium of l-arginine, l-lysine, certain polyamines related to these amino acids (cadaverine, putrescine, spermidine), Ca 2+ , or streptomycin stabilizes the protoplasts. Protoplasts incubated with 10 mml-arginine or l-lysine show an initial inhibition of [ 3 H]uridine incorporation, but with time, incorporation is restored to levels greater than in control protoplasts. The rise in ribonuclease activity of protoplasts is completely inhibited if the protoplasts are incubated with 10 mml-arginine. Greater incorporation of [ 3 H]uridine into RNA of aging protoplasts is also maintained by appropriate concentration of cadaverine, putrescine, spermidine, Ca 2+ , or streptomycin in the incubation medium; the same concentrations of these substances stabilize the protoplasts against additional lysis.
TL;DR: The results suggest that the in (P) and in (V) characteristics of all plant cells are similar, and the significance of the pressure and volume effects for the water relations and growth processes of plant cells is discussed briefly.
Abstract: Direct measurements of the volumetric elastic modulus, ∈, of cells of a higher plant were performed on the epidermal bladder cells of Mesembryanthemum crystallinum using a pressure probe technique. Measurements on giant algal cells (Valonia, Nitellopsis) are given for comparison. Giant celled algae and M. crystallinum bladders have elastic moduli, ∈, which depend strongly on turgor pressure, P, and on cell volume, V. The ∈ values of Mesembryanthemum bladders range between 5 bar at zero pressure and 100 bar at full turgor pressure (3-4 bar). ∈ increased with cell size (volume) at a given turgor pressure, and this volume dependence was pronounced more in the high pressure range. From the ∈ (P) characteristics, complete volume-pressure curves were obtained for Mesembryanthemum bladders and giant algal cells. The results suggest that the ∈ (P) and ∈ (V) characteristics of all plant cells are similar. The significance of the pressure and volume effects for the water relations and growth processes of plant cells is discussed briefly.
TL;DR: Individual leaves of potato (Solanum tuberosum L. W729R), a C(3) plant, were subjected to various irradiances, CO(2) levels, and temperatures in a controlled-environment chamber and found that water use efficiency, when considered at a constant vapor pressure gradient, increased with increasing irradiance, CO (2) concentration, and temperature.
Abstract: Individual leaves of potato (Solanum tuberosum L. W729R), a C(3) plant, were subjected to various irradiances (400-700 nm), CO(2) levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins.cm(-2).sec(-1) (about (1/2) of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins.cm(-2).sec(-1). These results contrast with many C(3) plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.Inhibition of photosynthesis by 21% O(2) was nearly overcome by a 2-fold increase in atmospheric levels of CO(2) (about 1,200 ng.cm(-3)). Photosynthesis at 25 C, high irradiance, 2.5% O(2) and atmospheric levels of CO(2) was about 80% of the CO(2)-saturated rate, suggesting that CO(2) can be rate-limiting even without O(2) inhibition of photosynthesis. With increasing CO(2) concentration, mesophyll resistance decreased slightly while stomatal resistance increased markedly above 550 ng.cm(-3) which resulted in a significant reduction in transpiration.Although potato is a very productive C(3) crop, there is substantial O(2) inhibition of photosynthesis. The level of O(2) inhibition was maximum around 25 C but the percentage inhibition of photosynthesis by O(2) increased steadily from 38% at 16 C to 56% at 36 C. Photosynthesis and transpiration showed broad temperature optima (16-25 C). At higher temperatures, both the increased percentage inhibition of photosynthesis by O(2) and the increased stomatal resistance limit photosynthesis, while increased stomatal resistance limits transpiration. Water use efficiency, when considered at a constant vapor pressure gradient, increased with increasing irradiance, CO(2) concentration, and temperature.
TL;DR: Results are consistent with the idea that proline accumulation results from inactivation by water stress of normal control mechanisms, and it seems likely that inhibition of proline oxidation is necessary in maintaining the high levels of prolines found in stressed barley leaves.
Abstract: The conversion of proline to glutamic acid and hence to other soluble compounds (proline oxidation) proceeds readily in turgid barley (Hordeum vulgare) leaves and is stimulated by higher concentrations of proline. This suggests that proline oxidation could function as a control mechanism for maintaining low cellular levels of proline in turgid tissue. In water-stressed tissue, however, proline oxidation is reduced to negligible rates. These results are consistent with the idea that proline accumulation results from inactivation by water stress of normal control mechanisms. It seems likely that inhibition of proline oxidation is necessary in maintaining the high levels of proline found in stressed barley leaves.
TL;DR: Changes in activities of several proteolytic enzymes and in concentrations of protein and chlorophyll as a function of intraleaf segments, leaf position, and leaf senescence during grain development and maturation were followed in crude leaf extracts.
Abstract: Some proteolytic enzymes occurring in the leaves of field-grown corn (Zea mays) (B73) were identified and partially characterized. Changes in activities of several proteolytic enzymes and in concentrations of protein and chlorophyll as a function of intraleaf segments (tip to base), leaf position, and leaf senescence during grain development and maturation were followed in crude leaf extracts.
The aminopeptidase (not affected by sulfhydryl or fluoride reagents) was most active at pH 7, while the carboxypeptidase(s) (sensitive to fluoride, but insensitive to sulfhydryl reagents) was most active in the acid range, pH 3 to 6. The presence of two or more endopeptidases is indicated. Endopeptidase (caseolytic) activity at pH 5.4 appeared to be stimulated by sulfhydryl groups or EDTA, while caseolytic activity at pH 7.5 was not.
Visually, individual leaf senescence starts at the leaf tip and the necrotic (brown) V-shaped area enlarges progressively toward the leaf base. Canopy senescence occurs in two phases. Foliar symptoms are first observed on the bottom leaf and then in sequential order up the plant. Subsequently, senescence occurs on the top leaf and moves downward. These foliar senescence symptoms are paralleled by decreases in exopeptidase activities, protein, and chlorophyll concentrations and by increases in endopeptidase activities.
During development and maturation of the grain, both aminopeptidase and carboxypeptidase activity of the middle half of the ear leaf increased (2- to 3-fold) during the onset of the visual reproductive phase (tassel and car emergence). However, during grain development and plant senescence, both activities decreased rapidly and concurrently with the loss of protein and chlorophyll from this leaf section. In contrast, caseolytic activity at both pH 5.4 and 7.5 increased gradually during the early reproductive phase and rapidly with leaf senescence. The fastest rate of increase in caseolytic activities was concurrent with the most rapid loss of protein from the leaves. The coincidence of these events suggests a major role for the caseolytic enzymes in initiating the rapid hydrolysis of leaf protein.
TL;DR: The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O(2) in the C(3) species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio in the leaf.
Abstract: The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O2 in the C3 species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of O2/CO2 in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of O2 and CO2 in the intercellular spaces of leaves as derived from whole leaf measurements of photosynthesis and transpiration. The solubility ratio of O2/CO2 can be increased by increased leaf temperature under constant atmospheric levels of O2 and CO2 (since O2 is relatively more soluble than CO2 with increasing temperature); by increasing the relative levels of O2/CO2 in the atmosphere at a given leaf temperature, or by increased stomatal resistance. If the solubility ratio of O2/CO2 is kept constant, as leaf temperature is increased, by varying the levels of O2 or CO2 in the atmosphere, then the percentage inhibition of photosynthesis by O2 is similar. The decreased solubility of CO2 relative to O2 (decreased CO2/O2 ratio) may be partly responsible for the increased percentage inhibition of photosynthesis by O2 under atmospheric conditions with increasing temperature.
TL;DR: Observations are inconsistent with the proposal that photorespiration exists in these algae.
Abstract: The CO2 exchange of several species of fresh water and marine algae was measured in the laboratory to determine whether photorespiration occurs in these organisms. The algae were positioned as thin layers on filter paper and the CO2 exchange determined in an open gas exchange system. In either 21 or 1% O2 there was little difference between 14CO2 and 12CO2 uptake. Apparent photosynthesis was the same in 2, 21, or 50% O2. The compensation points of all algae were less than 10 μl 1−1. CO2 or 14CO2 evolution into CO2-free air in the light was always less than the corresponding evolution in darkness. These observations are inconsistent with the proposal that photorespiration exists in these algae.
TL;DR: At high measurement temperatures, the improved net photosynthetic performance of the high temperature acclimated desert plants appeared to be due to a combination of decreased respiration rates, decreased temperature dependence of respiration, and an apparent increased thermal stability of Photosynthetic CO(2) exchange.
Abstract: Atriplex lentiformis plants collected from coastal and desert habitats exhibit marked differences in capacity to adjust photosynthetic response to changes in growth temperature. Plants from desert habitats grown at 43 C day/30 C night temperatures had higher CO 2 uptake rates at high temperatures but reduced rates at low temperatures as compared to plants grown at 23 C day/18 C night temperatures. In contrast, growth of the coastal plants at high temperatures resulted in markedly reduced photosynthetic rates at all measurement temperatures. Leaf conductances to CO 2 were not important in controlling either the differences in the temperature dependence of net CO 2 uptake or the differences in photosynthetic capacities at any measurement temperature. At low measurement temperatures, differences in photosynthetic capacities among plants acclimated to the contrasting growth regimes were correlated with differences in leaf ribulose diphophate carboxylase activities. At high measurement temperatures, the improved net photosynthetic performance of the high temperature acclimated desert plants appeared to be due to a combination of decreased respiration rates, decreased temperature dependence of respiration, and an apparent increased thermal stability of photosynthetic CO 2 exchange.
TL;DR: It is concluded that d-glucose and other hexoses are transported by carrier-mediated diffusion across the inner envelope membrane, similar to the transport of d- glucose into erythrocytes.
Abstract: The uptake of radioactively labeled hexoses and pentoses into the sorbitol-impermeable (3)H(2)O space (the space surrounded by the inner envelope membrane) of spinach (Spinacia oleracea L.) chloroplasts has been studied using silicone layer filtering centrifugation. Of the compounds tested, d-xylose, d-mannose, l-arabinose, and d-glucose are transported most rapidly, followed by d-fructose and l-arabinose. The rate of l-glucose uptake is only about 5% of that of d-glucose.The transport of d-glucose and d-fructose shows saturation characteristics, the K(m) for d-glucose was found to be about 20 mm. All sugars transport and phloretin inhibit d-glucose transport. The temperature dependency of d-glucose transport appears to have an activation energy of 17 kcal/mol.With low external concentrations of d-glucose the transport into the chloroplasts proceeds until nearly the external concentration is reached inside the chloroplasts.d-glucose transport is inhibited by high d-glucose concentrations in the medium. It is concluded that d-glucose and other hexoses are transported by carrier-mediated diffusion across the inner envelope membrane. This transport is similar to the transport of d-glucose into erythrocytes.
TL;DR: The affinity of the specific binding sites for auxins is modified by an unidentified dialyzable, heat-stable, apparently amphoteric, organic factor ("supernatant factor") found in maize tissue.
Abstract: Characteristics of and optimum conditions for saturable (“specific”) binding of [14C]naphthaleneacetic acid to sites located on membranous particles from maize (Zea mays L.) coleoptiles are described. Most, if not all, of the specific binding appears to be due to a single kinetic class of binding sites having a KD of 5 to 7 × 10−7m for naphthalene-1-acetic acid (NAA). Binding of NAA is insensitive to high monovalent salt concentrations, indicating that binding is not primarily ionic. However, specific binding is inhibited by Mg2+ or Ca2+ above 5 mm. Specific binding is improved by organic acids, especially citrate. Binding is heat-labile and is sensitive to agents that act either on proteins or on lipids. Specific binding is reversibly inactivated by reducing agents such as dithioerythritol; a reducible group, possibly a disulfide group, may be located at the binding site and required for its function. The affinity of the specific binding sites for auxins is modified by an unidentified dialyzable, heat-stable, apparently amphoteric, organic factor (“supernatant factor”) found in maize tissue.
TL;DR: The lectin-binding properties of the SBL-positive R. japonicum strains were found to change substantially with culture age, and one strain had a distinctly different pattern.
Abstract: Highly purified soybean lectin (SBL) was labeled with fluorescein isothiocyanate (FITC-SBL) or tritium ( 3 H-SBL) and repurified by affinity chromatography. FITC-SBL was found to bind to living cells of 15 of the 22 Rhizobium japonicum strains tested. The lectin did not bind to cells of the other seven R. japonicum strains, or to cells of any of the nine Rhizobium strains tested which do not nodulate soybean. The binding of the lectin to the SBL-positive strains of R. japonicum was shown to be specific and reversible by hapten inhibition with d-galactose or N-acetyl-d-galactosamine. The lectin-binding properties of the SBL-positive R. japonicum strains were found to change substantially with culture age. The percentage of cells in a population exhibiting fluorescence after exposure to FITC-SBL varied between 0 and 70%. The average number of SBL molecules bound per cell varied between 0 and 2 × 10 6 . While most strains had their highest percentage of SBL-positive cells and maximum number of SBL-binding sites per cell in the early and midlog phases of growth, one strain had a distinctly different pattern. The SBL-negative strains did not bind lectin at any stage of growth. Quantitative binding studies with 3 H-SBL indicated that the affinity constant for binding of SBL to its receptor sites on R. japonicum is approximately 4 × 10 7 m −1 . Many of the binding curves were biphasic. An inhibitor of SBL binding was found to be present in R. japonicum culture filtrates.
TL;DR: The above results indicate that the semipermeable properties of the cell are uninjured but that the ion and sugar transport mechanism is damaged by freezing, and most likely the primary injury is to the active transport mechanism involved in their transport.
Abstract: Onion ( Allium cepa L.) bulbs were subjected for 12 days to either a moderate freeze (−4 C) or a severe freeze (−11 C). They were then thawed slowly over ice. During 7 to 12 days following the thaw, the injury progressed with time in the severely frozen bulbs, but appeared completely repaired in the moderately frozen bulbs. This was shown by the following post-thawing changes. Infiltration of the intercellular spaces increased from 80 to 90% to 100% after the severe freeze, and decreased from 30 to 50% to zero after the moderate freeze. All of the cells were alive immediately after thawing whether the freeze was moderate or severe. Corresponding to the infiltration results 7 to 12 days later, many to most were dead following the severe freeze, all were alive following the moderate freeze. The conductivity of the effusate from pieces of bulb tissue increased after the severe freezing, and decreased after the moderate freezing. The concentration of K + , total solutes, and sugars in the effusate paralleled the conductivity changes. Neither the pH of the effusate nor the permeability of the cells (as long as cells were living) to water was changed following either the severe or the moderate freezes. Some treatments of the thawed tissue following the severe freeze halted the progress of injury. The above results indicate that the semipermeable properties of the cell are uninjured but that the ion and sugar transport mechanism is damaged by freezing. Most likely the primary injury is to the active transport mechanism involved in their transport. It must be concluded that the final injury following freezing and thawing cannot be evaluated from the degree of infiltration or the conductivity of the effusate immediately after thawing, since injury may progress or recede following the thawing.