Showing papers in "Plant Cell and Environment in 1989"
TL;DR: The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the Rhizosphere leading to intensive chemical extraction of a limited soil volume.
Abstract: . White lupin (Lupinus albus L.) was grown for 13 weeks in a phosphorus (P) deficient calcareous soil (20% CaCO3, pH(H2O)7.5) which had been sterilized prior to planting and fertilized with nitrate as source of nitrogen. In response to P deficiency, proteoid roots developed which accounted for about 50% of the root dry weight. In the rhizosphere soil of the proteoid root zones, the pH dropped to 4.8 and abundant white precipitates became visible. X-ray spectroscopy and chemical analysis showed that these precipitates consisted of calcium citrate. The amount of citrate released as root exudate by 13-week-old plants was about 1 g plant−1, representing about 23% of the total plant dry weight at harvest. In the rhizosphere soil of the proteoid root zones the concentrations of available P decreased and of available Fe, Mn and Zn increased. The strong acidification of the rhizosphere and the cation/anion uptake ratio of the plants strongly suggests that proteoid roots of white lupin excrete citric acid, rather than citrate, into the rhizosphere leading to intensive chemical extraction of a limited soil volume. In a calcareous soil, citric acid excretion leads to dissolution of CaCO3 and precipitation of calcium citrate in the zone of proteoid roots.
680 citations
TL;DR: A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride as mentioned in this paper, but much of this variation is in response to differences in environmental conditions both prior to and during fumigation.
Abstract: . Important physiological processes, photosynthesis, respiration, carbon allocation and stomatal function are known to be affected by air pollutants. A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride. Some of this variation is clearly due to genetic factors, but much is in response to differences in environmental conditions both prior to and during fumigation. Exposure of plants to mixtures of pollutants generally reduced the threshold at which effects were first detected and increased the level of inhibitory responses. In the majority of studies on stomatal responses to air pollutants, opening occurs at low concentrations, below the threshold for effects on photosynthesis, and closure occurs at injurious concentrations; this latter response often following the inhibition of photosynthesis. Effects on carbon allocation have been reported in response to air pollutants. Changes usually favour leaf development over root growth, which can compensate for a decline in net assimilation rate up to a certain point but may limit water uptake from soils with low moisture content. Future research into physiological effects of air pollutants should incorporate an integrated approach in which both key physiological parameters and growth parameters are measured together with estimates of the effective dose of pollutant. In this way, the underlying mechanisms to changes in growth and development will be more fully understood.
560 citations
TL;DR: It is suggested that ABA produced by dehydrating roots and which was subsequently transported to the shoots provided a sensitive indication of the degree of soil drying, which resulted in a substantial increase in the ABA content of roots.
Abstract: . Maize plants were grown in 1-m-long tubes of John Innes No. 2 potting compost. From the start of the experimental period, half of the plants were unwatered. Stomatal conductance of these plants was restricted 6 d after last watering and continued to decline thereafter. This was despite the fact that as a result of solute accumulation, unwatered plants showed consistently higher leaf turgors than well-watered plants. Leaf water potentials of unwatered plants were not significantly lower than those of plants that were watered well. Main seminal and nodal roots showed solute regulation in drying soil and continued to grow even in the driest soil, and plants growing in drying soil showed consistently higher root dry weights than did well-watered plants, water potentials and turgors of the tips of fine roots in the upper part of the column decreased as the soil dried. Soil drying below a water content of around 0–25 g cm−3 (a bulk soil water potential of between -0.2 and -0.3 MPa) resulted in a substantial increase in the ABA content of roots. As soil columns dried progressively from the top, ABA content increased in roots deeper and deeper in the soil. These responses suggest that ABA produced by dehydrating roots and which was subsequently transported to the shoots provided a sensitive indication of the degree of soil drying.
389 citations
TL;DR: A negative correlation between water-use efficiency and carbon isotope discrimination was established for barley in pot experiments using 12 cultivars as discussed by the authors, and the mean k for these barley cultivars was similar to that calculated by others for grasses.
Abstract: A negative correlation between water-use efficiency (W), defined as the ratio of moles of carbon in the plant to moles of water transpired, and carbon isotope discrimination (Δ) was established for barley in pot experiments using 12 cultivars. The correlation was strong in two independent experiments in four different controlled environment where ambient temperature and vapour pressure deficit were varied and plants were either well-watered or given limited amounts of water. Variation among cultivars was found in both Δ and W and rankings of both parameters, according to cultivar, were similar in different environments. Limiting water usually increased water-use efficiency of plants. Total dry matter can be substituted for moles of carbon when calculating water-use efficiency but the correlation between W and Δ were calculated using the carbon content of dry matter. There were differences varied significantly among cultivars. Despite these differences, correlations were also large between whole plant W and Δ of any of the plant parts. The amount of dry matter partitioned into reproductive growth varied genetically, as did the effect of stress on the partitioning. Growth, W and Δ of barley were compared with theory derived from gas exchange properties and with other literature. The effect on W of variation in vapour pressure deficit in these experiments was removed by multiplying W by vapour pressure deficit to derive the parameter, k(Pa mol C/mol H2O). This allowed comparisons among experiments with different vapour pressure deficits. The mean k for these barley cultivars was similar to that calculated by others for grasses. However, variation was found, and, in contrast with previous work which treats k as a species constant, we conclude that there is promise in selecting for increased k.
222 citations
TL;DR: The red: far-red ratio provides a reliable signal of plant density, even before shading by neighbours occurs, and it is concluded that plants are able to perceive and respond to these signals, and that possible ambiguities due to low red:Far-red at low solar angles may be avoided by modulation of the perception process by fluence-rate dependent mechanisms.
Abstract: . It has previously been proposed that the fundamental function of phytochrome in the natural environment is the perception of the relative proportions of red and far-red light, i.e. the red: far-red ratio. This paper re-evaluates this hypothesis, for vegetative green plants, in the light of recent findings. Essentially, three issues are considered: (a) the modulation of the response to red: far-red by fluence rate: (b) the anticipation of competition for light by perception of changes in red: far-red that precede actual shading: and (c) characteristics of phytochrome that may be important in the mechanism of photoperception (i.e. the accumulation of photoconversion intermediates, and the stability of Pfr). We conclude: (a) the red: far-red ratio provides a reliable signal of plant density, even before shading by neighbours occurs: (b) plants are able to perceive and respond to these signals, and that possible ambiguities due to low red: far-red at low solar angles may be avoided by modulation of the perception process by fluence-rate dependent mechanisms; (c) although direct experimental evidence does not yet exist, circumstantial evidence suggests that the perception of red: far-red may confer positive adaptive advantage; and (d) plants of certain species perceive and respond to fluence rate changes, mediated perhaps by a blue-light absorbing photoreceptor or by phytochrome, but that these responses do not necessarily lead to shade avoidance reactions and their ecological relevance is not fully understood.
198 citations
TL;DR: Comparisons between measured and calculated rates of transport indicate that 22Na transport may underestimate transport to the shoot because of dilution of the tracer in the root cytoplasm, and that Na transport and tissue concentrations were markedly inhibited by salinity.
Abstract: Salt-stressed plants often show Ca deficiency symptoms. The effects of NaCl salinity (1 to 150 mol m-3) and supplemental Ca (10 mol m-3) on Na and Ca transport in barley (Hordeum vulgare L.) and their relationship to growth were investigated. The adjustment of Na and Ca transport was investigated by examining young seedlings exposed to short-term (immediate) and long-term (7 d) exposure to salinity. When the plants were exposed to long-term treatments of salinity, the rate of sodium accumulation in roots was approximately 10 to 15% of short-term treatments. No significant adjustment in the transport to the shoot was observed. Rates of tracer (22Na) transport were compared to calculated rates based on relative growth rates and tissue element concentrations. Comparisons between measured tracer and calculated rates of transport indicate that 22Na transport may underestimate transport to the shoot because of dilution of the tracer in the root cytoplasm. Calcium uptake showed only minor adjustment with time. Measured rates of tracer transport to the shoot correlated well with calculated values. The transport and tissue concentrations of Na were significantly affected by supplemental Ca. Calcium transport and tissue concentrations were markedly inhibited by salinity. Supplemental Ca increased Ca transport and accumulation at all NaCl treatments above that of control plants without supplemental Ca. Salinity inhibited plant growth at 150 mol m -3NaCl, but not at 75 mol m-3.
Supplemental Ca significantly improved root length but not fresh weight after 7d of salinity, although differences in fresh weight were detected after 9d. There were significant Na-Ca interactions with ion transport, ion accumulation, and growth. The effects of salinity on Na and Ca transport to the shoot do not appear to play a major role in shoot growth of barley.
151 citations
TL;DR: The authors conclude that survival of dehydration is correlated with the presence of sucrose, a key factor in preserving membranes in dry pollen.
Abstract: . Two pollen species from the Gramineae family were investigated as to their differential sensitivity to desiccation. Germination in vivo ceased to occur after previous drying to 7–8% moisture content in Zea mays and 3% in Pennisetum typhoides. The reduced vitality coincided with extensive membrane damage, as evidenced by the considerable leakage of fluorescein and K+ from the prehumidified grains into liquid media. Further experiments were undertaken to investigate the basis for this interspecific difference: (1) phospholipid analyses revealed little difference in composition and content both before and after drying; (2) free fatty acid contents increased in both species upon drying but levels were generally low; and (3) sucrose was the sole soluble carbohydrate found in both species. Fresh maize pollen contained 5% sucrose, as compared to 14% in Pennisetum pollen. During slow drying (8h) this level went up to 12% and 17%, respectively. Drying corn pollen in the cold (2°C), or at high rate, limited sucrose levels and affected the resistance to drying. The authors conclude that survival of dehydration is correlated with the presence of sucrose. Finally, they tested the ability of sucrose to preserve dry liposomes prepared from phospholipids purified from the two species. When liposomes were dried in the presence of sucrose, fusion and leakage could largely be prevented at mass ratio's of sugar to lipid of > 4. Trehalose was also effective but myo-inositol was not. No species differences were observed. The authors suggest that the presence of sucrose is a key factor in preserving membranes in dry pollen.
130 citations
127 citations
TL;DR: The ethylene-air mixture experiments, the effect of AgNO3 and observed increase of the endogenous ethylene concentration during submergence suggest that ethylene plays a regulatory role in the growth responses of these Rumex species under submerged conditions.
Abstract: . Submergence stimulates growth of the petioles of Rumex palustris and Rumex crispus under field, greenhouse and laboratory conditions. Growth of Rumex acetosa petioles was hardly influenced by submergence. These growth responses under flooded conditions can be partially mimicked by exposing non-submerged Rumex plants to ethylene-air mixtures. Submergence of intact plants in a solution of AgNO3 inhibited the elongation of all petioles of R. palustris and the youngest petiole of R. crispus and stimulated growth of the youngest petiole of R. acetosa, The ethylene-air mixture experiments, the effect of AgNO3 and observed increase of the endogenous ethylene concentration during submergence suggest that ethylene plays a regulatory role in the growth responses of these Rumex species under submerged conditions. The three Rumex species showed a gradient in elongation responses to submergence, which correlates with the field distribution of the three species in a flooding gradient.
126 citations
TL;DR: In this paper, the half time of the reduction of photochemically oxidized P-700 has been measured in vivo using absorbance changes around 820 nm, and the results showed that t1/2 is independent of irradiance and decreases as photosynthetic induction progresses.
Abstract: . The half time (t1/2) of the reduction of P-700+ in the millisecond time frame is known to be limited by the reaction between plastoquinol and the cytochrome cytb6f complex. This is considered to be the rate limiting reaction of thylakoid electron transport and measurements of it provide a means of analysing how thylakoid election transport is regulated in vivo. The half time for the reduction of photochemically oxidized P-700 has been measured in vivo using absorbance changes around 820 nm. The results showed that t1/2 is independent of irradiance and decreases as photosynthetic induction progresses. Even with a constant t1/2 the quantum efficiency of PSI declined as irradiance increased. The significance of the concept of photosynthetic control of electron transport is discussed in the light of these observations.
114 citations
TL;DR: During the initial stages of C4-evolution it is proposed that improvements in photorespiratory CO2-loss and their influence on increasing the rate of net CO2 assimilation per unit leaf area represented the evolutionary ‘driving-force’.
Abstract: Evidence is drawn from previous studies to argue that C3—C4 intermediate plants are evolutionary intermediates, evolving from fully-expressed C3 plants towards fully-expressed C4 plants. On the basis of this conclusion, C3—C4 intermediates are examined to elucidate possible patterns that have been followed during the evolution of C4 photosynthesis. An hypothesis is proposed that the initial step in C4-evolution was the development of bundle-sheath metabolism that reduced apparent photorespiration by an efficient recycling of CO2 using RuBP carboxylase. The CO2-recycling mechanism appears to involve the differential compartmentation of glycine decarboxylase between mesophyll and bundle-sheath cells, such that most of the activity is in the bundlesheath cells. Subsequently, elevated phosphoenolpyruvate (PEP) carboxylase activities are proposed to have evolved as a means of enhancing the recycling of photorespired CO2. As the activity of PEP carboxylase increased to higher values, other enzymes in the C4-pathway are proposed to have increased in activity to facilitate the processing of the products of C4-assimilation and provide PEP substrate to PEP carboxylase with greater efficiency. Initially, such a ‘C4-cycle’ would not have been differentially compartmentalized between mesophyll and bundlesheath cells as is typical of fully-expressed C4 plants. Such metabolism would have limited benefit in terms of concentrating CO2 at RuBP carboxylase and, therefore, also be of little benefit for improving water- and nitrogen-use efficiencies. However, the development of such a limited C4-cycle would have represented a preadaptation capable of evolving into the leaf biochemistry typical of fully-expressed C4 plants. Thus, during the initial stages of C4-evolution it is proposed that improvements in photorespiratory CO2-loss and their influence on increasing the rate of net CO2 assimilation per unit leaf area represented the evolutionary ‘driving-force’. Improved resourceuse efficiency resulting from an efficient CO2-concentrating mechanism is proposed as the driving force during the later stages.
TL;DR: The model comprises three submodels, which together give an integrated picture of nitrogen pools and fluxes in grassland under grazing or cutting.
Abstract: The model comprises three submodels, which together give an integrated picture of nitrogen pools and fluxes in grassland under grazing or cutting
TL;DR: In this paper, it is proposed that these transient rapid cooling-induced responses, sometimes elicited by temperature drops of only a few degrees centigrade, are manifestations of temperature sensing.
Abstract: . The different effects which fast versus slow cooling have on such fundamental plant processes as ion transport, protoplasmic streaming, phloem translocation, growth, cell motility, water absorption and membrane potential are reviewed. When plant cells are rapidly cooled to non-injurious temperatures, many of the physiological ramifications of rapid-cooling stimulation are only transiently observed. It is proposed that these transient rapid-cooling-induced responses, sometimes elicited by temperature drops of only a few degrees centigrade, are manifestations of temperature sensing. The hypothesis is advanced that graded potentials, produced in response to rapidly falling temperature, are associated with graded increases in cytosolic free calcium. These transient increases in cytosolic free calcium give rise to many of the physiological effects elicited by rapid cooling. Other effects, however, such as those associated with alterations in membrane composition, gene expression and post-translational modifications of proteins, may persist longer. The questions of the possible physiological advantage of temperature sensing, and its implications for the study of chilling injury, are discussed.
TL;DR: Growth and gas exchange measurements are used to formulate a carbon balance model to describe the sorghum-Striga hermonthica host-Parasite association, which reduces the growth and radically alters the architecture of infected Sorghum plants.
Abstract: . Growth and gas exchange measurements are used to formulate a carbon balance model to describe the sorghum-Striga hermonthica host-Parasite association. S. hermonthica reduces the growth and radically alters the architecture of infected sorghum plants. Grain and stem weight are reduced, whilst leaf and root biomass are maintained. Losses in host productivity result from two processes: export of carbon to the parasite and Parasite-induced reductions in host photosynthesis. The latter occurs before the emergence of the Parasite above ground and accounts for 80% of the Predicted loss in production over the lifecycle of the association. S. hermonthica is dependent on carbon exported from the host, since the plant has low rates of photosynthesis coupled with high rates of respiration. Host-derived carbon accounts for approximately one-third of the total parasite carbon requirement.
TL;DR: In this paper, the effect of soil drought on water-use efficiency and water relations was examined for potted Artemisia tridentata Nutt and Pinus ponderosa Laws., a dominant Great Basin desert shrub and a Sierran montane tree, respectively.
Abstract: . The effect of soil drought on water-use efficiency (WUE) and water relations was examined for potted Artemisia tridentata Nutt. and Pinus ponderosa Laws., a dominant Great Basin desert shrub and a Sierran montane tree, respectively. Before the onset of drought, A. tridentata had slightly higher photosynthetic rates than P. ponderosa and A. tridentata maintained positive photosynthetic rates at substantially lower water potentials (Ψ). Complete stomatal closure and cessation of photosynthesis occurred at a Ψ of ca. −2.5 MPa for P. ponderosa and less than −5.0 MPa for A. tridentata. Repeated drought cycles caused a small increase in bulk modulus of elasticity for A. tridentata and neither species exhibited significant osmotic adjustment. WUE was similar at Ψ≥−1.0 MPa but as Ψ decreased P. ponderosa consistently maintained higher WUE than A. tridentata. The primary factor contributing to higher WUE for P. ponderosa was the rapid decrease in stomatal conductance with decreasing Ψ. Comparatively low WUE for A. tridentata, a drought tolerant species, suggests that efficient use of water is a conservative ecophysiological ‘strategy’ that can be detrimental in a competitive water-limited environment. The combination of profligate use of water and a high degree of drought tolerance may be a more successful combination of physiological characteristics in certain dry habitats.
TL;DR: The authors conclude that both temperature and photoperiod are determinants of leaf appearance rate, and suggest that the slow rate for late sowings may be caused by a non-linear response to the higher temperatures experienced by the plant during that part of the year.
Abstract: . Analysis is made of leaf numbers observed in the field for several wheat genotypes over a wide range of sowing dates. Within any treatment, leaf number was a linear function of thermal time from seedling emergence (°C.d, the mean daily temperatures summed above a base temperature of 0°C) but the slope of the relation depended on sowing date. Leaf appearance rate doubled from October to February sowings, for which it was maximum, and usually decreased for later sowings. However, when expressed on the basis of photothermal time (°C.dl, temperatures accumulated during the light time period only), much of the sowing date effect was removed, except for the latest spring sowings. For these late sowings, leaf appearance rate was usually slower than expected. The authors conclude that both temperature and photoperiod are determinants of leaf appearance rate, and suggest that the slow rate for late sowings may be caused by a non-linear response to the higher temperatures experienced by the plant during that part of the year. The genotypic differences indicate that it may also be associated with a lack of vernalization. The use of photothermal time rather than thermal time significantly improves prediction of leaf number. However, it still provides only an empirical description of the dependence of leaf number on time and climate.
TL;DR: This unusual pattern of growth and carbon allocation of the CO2 treated Chestnut trees emphasizes the concept of a response specificity within trees to an increase of atmospheric CO2.
Abstract: . Two-year-old potted sweet chestnut seedlings were grown at 350 ppm CO2 and 700 ppm, day and night in constantly ventilated tunnels during two full growing seasons, near Paris, France (48° N, 2° E). Enrichment with CO2 caused an unusual shoot growth response. After the end of July, stem elongation ceased in 62% of the CO2 enriched plants as compared with 37% in the control. The leaves of CO2-enriched seedlings showed early senescence, indicated by premature yellowing and a decrease in chlorophyll content. This was associated with nutrient dilution brought about by the rapid growth of these trees. The increase in total dry weight of the CO2-enriched seedlings was essentially the result of increase in the root dry weight (69%). Shoot weight decreased by 22% relative to the control. Total leaf area per enriched plant was 25% smaller than the control. This unusual pattern of growth and carbon allocation of the CO2 treated Chestnut trees emphasizes the concept of a response specificity within trees to an increase of atmospheric CO2.
TL;DR: In this paper, the physics of ultrasonic acoustic emissions (AEs) were investigated for AE transmission through w o o o d and transducers and the physical properties measured were velocity, attenuation and frequeney composition of AEs produced by two sources: cavitation events in xylem and peticil lead breaks.
Abstract: The physics of ultrasonic acoustic emissions ( A E s ) was investigated for AE transmission through w o o d and transducers. The physical properties measured were velocity, attenuation and frequeney composition ol\" AEs produced by two sources: cavitation events in xylem and peticil lead breaks. T h e authors also measured the relative sensitivity of var ious combinations of ultrasound transducets and ampliflers to aid in the selection of a measuring system optitnized for cavitation detection iti woody plan ts . Some of the authois' conclusions are; (1) Softwoods {Thuja, Pinus) attenuate AEs more rapidly t h a n hardwoods (maple, birch), (2) The velocity of A E s in wood exceeds that tneasured by others in w a t e r so the main medium of AE transmission tnust be the cellulose, (3) The strongest frequencies of AEs are in the range of 100-300 kHz, (4) Cavitationinduced AEs tend to shift to higher frequency as w o o d dehydration progtesses. (5) One cannot determine the locus of origin of AEs from its frequency cotnposition, (6) The frequency composition of the acoustic emissions probably canno t be determined at all with the sensors used because of their tendency to 'ring'. The data collected in this paper were used to aid in the design of an improved AE counter having a seven-fold increase in signal to noise ratio compared to counters previously used in our laboratory. The improved counter, tnodel 4615 Drought Stress Monitot, is now cotntnetcially available frotn Physical Acoustics Corp,, Princeton, N J , U,S,A, Key-words: acoustic emission; xylem cavitation; .icer saeehaiimi: Thuja oecidentalis: Pitius strobus.
TL;DR: In green and etiolated leaves of rye (Secale cereale L. ev. "Halo" as mentioned in this paper ) exposed to strong light at low temperature (0.4°C) catalase was inactivated.
Abstract: In green as well as in etiolated leaves of rye (Secale cereale L. ev. ‘Halo’), exposed to strong light at low temperature (0.4°C) catalase was inactivated. Other heme-containing enzymes (peroxidases) and various enzymes of photosynthetic, photorespiratory or peroxide metabolism were not photoinactivated. After returning plants from a low to a physiological temperature (22°C), catalase activity recovered within 12 h through new synthesis. The leaf contents of H2O2 and organic peroxides were not affected by the photoinactivation of catalse. The content of malondialdehyde generally increased after exposure to a higher light intensity. High-light-induced increases of ascorbate, and particularly of glutathione, were more marked in catalase-deficient than in normal leaves. Photoinactivation of catalase was accompanied by severe inhibition of photosynthesis. Photoinhibition of photosynthesis was not related to the lack of catalase because photosynthesis was not impaired when catalase activity was kept low by growing the plants under non-photorespiratory conditions. Photoinhibition appeared to result from photodamage in primary photochemistry of photosystem II, as indicated by a decrease of the maximal variable fluorescence. Photoinhibition of photosynthesis and of catalase have in common that in both instances proteins are involved that are continuously inactivated in light and, therefore, particularly sensitive to stress conditions that prevent their replacement by repair synthesis.
TL;DR: In this article, the relationship between nitrogen uptake, transpiration, and carbon assimilation was investigated in plants growing on nutrient solution in a growth chamber, where temperature, photon flux density, vapour saturation deficit and CO2 concentration were controlled.
Abstract: . The present study investigates the relationships between nitrogen uptake, transpiration, and carbon assimilation. Plants growing on nutrient solution were enclosed for 10–16 d in a growth chamber, where temperature, photon flux density, vapour saturation deficit and CO2 concentration were controlled. One of these factors was modified every 4 to 5 d. Shoot photosynthesis and root and shoot respiration were recorded every half-hour. Nitrogen uptake from the root medium and plant transpiration were measured daily. In most cases, an increase in photon flux density led to increases in transpiration, net daily carbon assimilation, and nitrogen uptake. By modifying transpiration rate without changing photosynthesis (varying vapour saturation deficit), or by modifying transpiration and carbon assimilation in opposite ways (varying CO2 air concentration), it was shown that nitrogen uptake does not follow transpiration, but is linked to the carbon uptake of the plant. When light was increased from low to intermediate levels, the N uptake/C assimilation ratio remained constant. At higher photon flux density, this ratio declined markedly. It is proposed that in the first case, growth is limited by carbohydrate availability, thus any increase in carbon assimilation leads to a proportional increase in nitrogen uptake, in contrast to the second situation where carbohydrates may accumulate in the plant without further nitrogen requirement.
TL;DR: Little consistency was seen in the iso-aperture patterns among sampling times, although the stomata were always relatively closed at the leaf tip and base, and gradients of mean stomatal aperture were as high as 1 μm mm−1.
Abstract: . The silicone rubber impression technique was used to measure stomatal apertures in 9 mm2 sampling areas covering the entire lower surface of leaves of Commelina communis L. The data were analysed using a computer program which produced ‘iso-aperture' contours illustrating local differences in mean stomatal aperture. Little consistency was seen in the iso-aperture patterns among sampling times, although the stomata were always relatively closed at the leaf tip and base. When stomata in the middle of the lamina were open, those near to the leaf margin tended to be relatively closed. In places, gradients of mean stomatal aperture were as high as 1 μm mm−1. Measurements along a transect across the lower epidermis revealed no correlation of stomatal aperture with the presence of major veins in the mesophyll tissue. Variation in guard-cell size and stomatal frequency on the lower leaf surface was also analysed. The guard cells were smallest and the stomata more frequent near to the leaf margins. The significance of the results is discussed in relation to measurements of leaf conductance and models of stomatal function.
TL;DR: In this paper, a comparison of hexaploid wheat (Triticum aestivum cvs. Chinese Spring or PI 178704) and derivatives containing chromosomes from both a cultivar and a wild, salt-tolerant species (Lophopyrum elongatum or L. ponticum) were compared to determine differences in growth, ion transport and ion accumulation under salt-stress.
Abstract: . Cultivars of hexaploid wheat (Triticum aestivum cvs. Chinese Spring or PI 178704) and derivatives containing chromosomes from both a cultivar and a wild, salt-tolerant species (Lophopyrum elongatum or L. ponticum) were compared to determine differences in growth, ion transport and ion accumulation under salt-stress. Two experiments were conducted in which plants were grown under saline and non-saline conditions and harvested at various lime intervals throughout ontogeny. Under salt-stress the growth rate of the cultivars, as compared to the growth rate of the derivatives, decreased more rapidly later in development. Transport rates from root to shoot of Na+ and Cl− reached higher levels in the cultivars. The cultivars accumulated more Na+ and Cl− and relatively less K+ in the shoot. The K+/Na+ ratio was higher in the derivatives than in the cultivars from which they were derived. The addition of chromosomes from Lophopyrum species into wheat altered ion accumulation, growth rates, and ion transport rates from root to shoot.
TL;DR: The salt resistance of Protador relative to LGH (salt-sensitive) appears to be related to higher K+ fluxes and cytoplasmic concentrations, and lower Na+ and Cl fluxes, when grown in NaCl.
Abstract: Cytoplasmic concentrations, fluxes of K+, Na+ and Cl and microsomal membrane lipids were investigated in a salt-sensitive and salt-resistant variety of Zea mays. The salt resistance of Protador relative to LGH (salt-sensitive) appears to be related to higher K+ fluxes and cytoplasmic concentrations, and lower Na+ and Cl fluxes and cytoplasmic concentrations, when grown in NaCl. There were no apparent differences in the simple chemical composition of root microsomal membrane lipids between the two varicties, neither were these affected by salt.
TL;DR: A novel technique to record the variability of stomatal aperture over the leaf surface using low-temperature scanning electron microscopy (LTSEM), with digital image analysis to produce the most accurate aperture measurements obtained to date is described.
Abstract: . A novel technique to record the variability of stomatal aperture over the leaf surface is described. This combines observations of leaf surfaces using low-temperature scanning electron microscopy (LTSEM), with digital image analysis to produce the most accurate aperture measurements obtained to date. Leaf samples are rapidly immobilized by cryo-fixation in liquid nitrogen and stored in a purpose-built cryo-storage system. Specimens can be collected in the field, remote from the cryopreparation system, and stored for up to several weeks before being examined on the LTSEM. The advantages of this method are that the time frame of the measurements is accurately known, and is identical for all stomatal apertures in a sample, and the precision of the measurements is not limited by the resolving power of the microscope. Measurements of stomatal aperture were obtained from leaves of field grown Avena fatua using the above procedure. Leaf surface conductance (gsur) was determined by porometry immediately before cryo-fixation of the same region of the leaf. Measurements of aperture size showed a high degree of variability within each specimen, with coefficients of variation similar to those found in previous studies. Stomatal conductance (gs) was calculated from stomatal dimensions using formulae derived elsewhere. A linear regression between the computed values of gs and porometric estimates of gsur showed good agreement with the regression line passing through the origin with a slope of 1.0 (R2=0.96). Applications of the experimental system are discussed.
TL;DR: In this article, a modification to the pressure probe is described which allows very rapid extraction of sap samples from single higher plant cells, and the performance of this rapid sampling probe was assessed and compared with the unmodified probe for cells of both wheat and Tradescantia.
Abstract: Abstract. A modification to the pressure probe is described which allows very rapid extraction of sap samples from single higher plant cells. The performance of this rapid-sampling probe was assessed and compared with the unmodified probe for cells of both wheat and Tradescantia. Under some conditions, the unmodified probe operated too slowly to avoid dilution of cell sap during the extraction process. This led to values for apparent sample osmotic pressures that were below the turgor pressures for the same cells. The problem was particularly acute in young wheatleaf epidermal cells which are small, elongate and have high turgor pressure. These exhibited rapid water influx when their turgor was depressed during the sampling of their contents (half-time for pressure recovery in wheat cells was less than 1 s while in Tradescantia cells it was 3–5 s). Dilution during sampling was apparently negligible when the rapid sampling probe was used. The study was complemented by a simple model of the way cells dilute during sampling. Quantitative predictions of the model were consistent with our observed findings. The model is used to assess the major factors which determine a cell's susceptibility to dilution during sampling.
TL;DR: In this paper, the isotopic composition of water of wheat leaves (Triticum aestivum L. var. Aroona) was examined at natural abundance levels, at the same time as transpiration rate.
Abstract: . The authors examine the isotopic composition of leaf water, at natural abundance levels, as influenced by transpiration rate. The isotopic composition of water of wheat leaves (Triticum aestivum L. var. Aroona) was followed while their transpiration rate adjusted to ‘steady-state’ environmental conditions. Leaf diffusive resistance was modified by short-term salt treatment and by plant culture in either nutrient solution, free-draining sand, or vermiculite. Resultant changes in 18O and 2H in leaf water are described and fitted to the model of Leaney et al. (1985). The treatments with lower transpiration rates were found to have a greater fraction of their leaf water equilibrated with water vapour in the atmosphere. Comparable results were obtained with both 18O and 2H, with some differences being interpreted in terms of turbulence in the vapour diffusion path. The fraction of the leaf water equilibrated with the atmosphere varied between leaves of different ages. However, this may have been due to their different positions in the canopy.
TL;DR: Results indicate the involvement of a plasma membrane-associated Ca2+ channel in the process of temperature sensing by plants, and Calmodulin antagonists prolong the repolarization phase of the electrical responses, suggesting a role for calmodulin in the recovery from stimulation.
Abstract: . Rapid-cooling pulses to non-stressful temperatures cause strong, transient depolarizations in cortical cells of cucumber roots. The amplitudes of these electrical responses are graded according to the rate and amplitude of the cooling pulse. Such graded potentials are typical of sensory processes and indicate that plants possess the ability to sense temperature change. La3+, a blocker of Ca2+ channels, and ethylene glycol bis-(β-aminoethyl ether) N,N,N′,N′-acetic acid (EGTA), a Ca2+ chelator, inhibit the electrical responses elicited by rapid-cooling pulses. High external [Ca2+] enhances them. These results indicate the involvement of a plasma membrane-associated Ca2+ channel in the process of temperature sensing by plants. Calmodulin antagonists prolong the repolarization phase of the electrical responses, suggesting a role for calmodulin in the recovery from stimulation.
TL;DR: In this paper, the effect of plant competition on spectral reflectance in the 400-2500 nm wavelength region was determined for 3-month-old and 15-monthold leaves of loblolly pine (Pinus taeda L.).
Abstract: . The effect of plant competition on spectral reflectance in the 400–2500 nm wavelength region was determined for 3-month-old and 15-month-old leaves of loblolly pine (Pinus taeda L.). Strong competition decreased water potentials and Mg concentrations, and increased K in young and old leaves. Also, competition decreased Ca and total chlorophyll in young leaves. As measured with a scanning radiometer, reflectance in young leaves at 551 nm decreased from 20 to 14% as water potentials increased from -2.2 to -0.9 MPa (r2= 0.82). For young and old leaves reflectance at 551 nm decreased from 20 to 10% with increasing total chlorophyll (r2= 0.64). Reflectance decreased slightly with increasing K in young leaves (401 nm, r2= 0.55), and with increasing Mg in old leaves (470 nm, r2= 0.57). Increased visible reflectance under strong competition may have resulted primarily from decreased water potentials. Reflectances were much greater in young versus old leaves in the 750–1300 nm range, and were greater in old rather than young leaves from 1400–2500 nm. Infrared reflectances were not, however, significantly affected by competition.