Showing papers on "Photosynthesis published in 1983"

Adaptation of unicellular algae to irradiance: an analysis of strategies

Abstract: SUMMARY 157INTRODUCTION 158AN.^LYTICAL METHODS 159LIGHT HARVESTING BY MICROALGAE 160RANGE OF PHOTON FLUX DENSITIES ALLOWING GROWTH AND PHOTOSYNTHESIS INPHOTOTHOPHIC MICROALGAE (GENOTYPIC ADAPTATION) 163 Growth 163Photosynthesis 165Photoinhibition 165 PHENOTYPIC ADAPTATION 168 Changes in amounts of pigments 168Interpretation of the effects of pigment changes: models 169Observed changes in P vs I curves 170 ENERGETIC CONSIDERATIONS 174 General 174Reduction of capital costs 175Reduction of maintenance costs 175Energetic costs of changing the photosyothetic apparatus 177S2-S3 decay 177Proton leakage due to passive uniport 178 PHYLOGENETIC ASPECTS OF DIFFERENCES IN LIGHT RESPONSES OF MICROALGALPHOTOSYNTHESIS AND PHOTOLITHOTROPHIC GROWTH 178 Phylogenetic diflerences in photosynthetic structures 178Comparison of tbe photosynthetic characteristics of green algae and otherpbototrophs 180 ECOLOGICAL CONSIDERATIONS 182ACKNOWLEDGEMENTS 185REFERENCES 185 SUMMARY Analysis of data in the literature relating to micrcalgal adaptations to different photon fluxdensities indicates that different algal classes have significantly different ligbt requirennents forgrowth and photosynthesis. Although there is some variability within each class, dinoflagellatesand blue-green algae generally photosynthesize and grow best at low photon flux densities.Diatoms also tend to be able to grow at very low photon flux densities (growth for some specieshas been reported at less than 1 fi.E m"' s~'). Comparison of the photon flux densities at whichphotoinhibition occurs in dinoflagellates and diatoms suggests that the former often experiencephotoinhibition at comparatively low irradiances. In contrast, diatoms often can toleraterelatively high light environments. This tolerance of a large absolute range of photon fluxdensities may, in part, explain why diatoms are often associated with spring blooms. Green algae* New address; Department of Botany, La Trobe University, Bundoora, Victoria, 3083 Australia.0028-646X/83/020157 + 35 S03.00/0 © 1983 The New Phytologist

Microelectrode studies of the photosynthesis and O2, H2S, and pH profiles of a microbial mat1

Abstract: The profiles of O,, H,S, and pH within a microbial mat of the hypcrsaline pond Solar Lake, Sinai, were measured by 2-208pm-thick microelectrodes during diurnal and artificial light cycles. The oxygen concentration in the photic layer varied from a maximum of 1,400 PM during the day to 0 during the night. The pH in the same layer varied between 9.6 in the early afternoon and 7.7 in the early morning. Sulfide was not present in the photic zone during the day, but built up to about 50 /IM during the night. The diffusion gradients of sulfide and oxygen were very steep and the two compounds coexisted in a layer only 0.25 mm thick during the day. Diffusion flux calculations showed that the average turnover time of sulfide within this layer was 21 s. The rapid turnover indicated that the oxidation of sulfide must be biologically mediated. Oxygenic photosynthesis was measured by a new oxygen microprofile method which accurately determines the vertical distribution of photosynthetic activity. There was no difference in the efficiency of photosynthesis between morning and afternoon. The photosynthetic efficiency of the whole mat was about fourfold higher at low light intensities, ~120 PEinst. m-z.s-1, than at high light intensities, 120-1,600 pEinst*m-“es-‘. Anoxygenic photosynthesis within the mat was not quantitatively important.

Compromises between water-use efficiency and nitrogen-use efficiency in five species of California evergreens

Abstract: In five California evergreen trees and shrubs cooccurring in this study but most common in habitats of different moisture availability, leaf nitrogen was a major determinant of photosynthetic capacity. Within each species, stomatal conductance was highly correlated with photosynthetic capacity, resulting in little variation in the concentration of CO2 in the intercellular spaces. Among species, intercellular CO2 concentrations varied significantly. Under controlled conditions, the leaves that realized the highest photosynthesis per unit of leaf nitrogen tended to realize the lowest photosynthesis per unit of water transpired. The ratio of photosynthesis to transpiration, an instantaneous measure of intrinsic water-use efficiency, was highest in the species commonly found in the direst habitats and lowest in the species most common in the wettes habitats.

Leaf age and seasonal effects on light, water, and nitrogen use efficiency in a California shrub.

Abstract: Photosynthetic capacity, leaf nitrogen content, and stomatal conductance decreased with increasing leaf age in the chaparral shrub, Lepechinia calycina, growing in its natural habitat Efficiency of resource use for three resources that potentially limit photosynthesis did not, however, decrease with increasing leaf age Light-use efficiency, given by the quantum yield of photosynthesis at low light intensities, was unaffected by leaf aging but decreased slightly through the winter and spring growing season Water-use efficiency, the ratio of photosynthesis to transpiration at light saturation and with a constant water vapor concentration gradient, was not affected by leaf aging or seasonal change Nitrogen-use efficiency, the ratio of photosynthesis at light saturation to leaf nitrogen content did not change with leaf age but was lower in the leaves with the highest specific weights This ensemble of leaf-age effects is consistent with the hypothesis that aging represents resource redistribution and not uncontrolled deterioration

Relationship between Photosynthesis and Respiration: The Effect of Carbohydrate Status on the Rate of CO2 Production by Respiration in Darkened and Illuminated Wheat Leaves

Abstract: The rate of dark CO(2) efflux from mature wheat (Triticum aestivum cv Gabo) leaves at the end of the night is less than that found after a period of photosynthesis. After photosynthesis, the dark CO(2) efflux shows complex dependence on time and temperature. For about 30 minutes after darkening, CO(2) efflux includes a large component which can be abolished by transferring illuminated leaves to 3% O(2) and 330 microbar CO(2) before darkening. After 30 minutes of darkness, a relatively steady rate of CO(2) efflux was obtained. The temperature dependence of steady-state dark CO(2) efflux at the end of the night differs from that after a period of photosynthesis. The higher rate of dark CO(2) efflux following photosynthesis is correlated with accumulated net CO(2) assimilation and with an increase in several carbohydrate fractions in the leaf. It is also correlated with an increase in the CO(2) compensation point in 21% O(2), and an increase in the light compensation point. The interactions between CO(2) efflux from carbohydrate oxidation and photorespiration are discussed. It is concluded that the rate of CO(2) efflux by respiration is comparable in darkened and illuminated wheat leaves.

Photosynthesis and structure of benthic microbial mats: Microelectrode and SEM studies of four cyanobacterial communities1

Abstract: The microzonation of photosynthetic organisms in four cyanobacterial mats of Solar Lake, Sinai, was studied by light and scanning electron microscopy. The zonation was compared to the distribution of photosynthesis and of O/sub 2/, H/sub 2/S, and pH. Microelectrodes were used to measure the chemical gradients as well as the photosynthetic rates by a newly developed technique which allows a spatial resolution of 100 ..mu..m. Two-dimensional maps of oxygen and photosynthesis distribution at the mat surface demonstrated a strong heterogeneity with rapid oxygen production within dense diatom tufts of 0.2-0.5-mm diameter overgrowing the cyanobacteria. Gas bubbles within the mat served as dynamic reservoirs for oxygen during light-dark cycles and buffered against extreme diurnal variations between oxygen and sulfide.

Photosynthesis and ion content of leaves and isolated chloroplasts of salt-stressed spinach.

Abstract: Spinach (Spinacia oleracea) plants were subjected to salt stress by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar. Plants were harvested 3 weeks after starting NaCl treatment. Fresh and dry weight of both shoots and roots was decreased more than 50% compared to control plants but the salt-stressed plants appeared healthy and were still actively growing. The salt-stressed plants had much thicker leaves. The salt-treated plants osmotically adjusted to maintain leaf turgor. Leaf K(+) was decreased but Na(+) and Cl(-) were greatly increased.The potential photosynthetic capacity of the leaves was measured at saturating CO(2) to overcome any stomatal limitation. Photosynthesis of salt-stressed plants varied only by about 10% from the controls when expressed on a leaf area or chlorophyll basis. The yield of variable chlorophyll a fluorescence from leaves was not affected by salt stress. Stomatal conductance decreased 70% in response to salt treatment.Uncoupled rates of electron transport by isolated intact chloroplasts and by thylakoids were only 10 to 20% below those for control plants. CO(2)-dependent O(2) evolution was decreased by 20% in chloroplasts isolated from salt-stressed plants. The concentration of K(+) in the chloroplast decreased by 50% in the salt-stressed plants, Na(+) increased by 70%, and Cl(-) increased by less than 20% despite large increases in leaf Na(+) and Cl(-).It is concluded that, for spinach, salt stress does not result in any major decrease in the photosynthetic potential of the leaf. Actual photosynthesis by the plant may be reduced by other factors such as decreased stomatal conductance and decreased leaf area. Effective compartmentation of ions within the cell may prevent the accumulation of inhibitory levels of Na(+) and Cl(-) in the chloroplast.

Effect of Photosynthesis and Carbohydrate Status on Respiratory Rates and the Involvement of the Alternative Pathway in Leaf Respiration

Abstract: In spinach ( Spinacia oleracea Hybrid 102 [New World seeds]) and wheat ( Triticum aestivum L cv Gabo) leaves, O 2 uptake rates in the dark were faster after the plants had been allowed to photosynthesize for a period of several hours Alternative path activity also increased following a period of photosynthesis in these leaves No such effects were observed with isolated mitochondria In spinach and wheat leaves, the level of fructose plus glucose decreased during a period of darkness In pea ( Pisum sativum cv Alaska) leaves, the level of these sugars did not vary significantly during the day, and respiratory rates were also constant In slices cut from wheat leaves harvested at the end of the night, addition of sugars increased the rate of respiration and engaged the previously latent alternative oxidase In pea leaves, O 2 uptake in the first few minutes following illumination was faster than that observed before illumination, but declined during the next 15 to 20 minutes Adding the alternative oxidase inhibitor salicylhydroxamic acid, or imposing high bicarbonate concentrations during the period of photosynthesis, prevented the rise in O 2 uptake rate during the immediate post illumination period We conclude that the level of respiratory substrate in leaves determines their rate of O 2 uptake, and the degree to which the alternative path contributes to that O 2 uptake

Effects of Low Concentrations of O3 on Net Photosynthesis, Dark Respiration, and Chlorophyll Contents in Aging Hybrid Poplar Leaves

Abstract: Chronic exposure of hybrid poplar (Populus deltoides × trichocarpa) plants to low concentrations of ozone had negative impact upon net photosynthetic capacity, dark respiration, and leaf chlorophyll contents. Exposure to as much as 0.20 microliters per liter O3 had no immediate effect on net photosynthesis (Pn), but chronic exposure to 0.125 or 0.085 microliters per liter had a number of gradual effects on CO2 exchange. These included increased dark respiration and consequently increased light compensation points in very young leaves (4-6 days old); and decreased Pn, leaf chlorophyll a and b contents, light saturation points, and apparent quantum yields in leaves 10 to 70 days old. Decreased Pn was partially due to accelerated aging in leaves exposed to O3, and lightsaturated Pn was linearly related to chlorophyll a + b contents. Differences in light-saturated Pn between control and O3-treated leaves of the same age were mostly due to photosaturation in O3-treated leaves and to a much lesser extent to lowered apparent quantum yields. Also, since Pn and dark respiration were most affected by O3 at different leaf ages, distinct modes of action are suggested. The effects of leaf aging on CO2 exchange were considerable, but typical of other species. However, careful monitoring of the interacting effects of leaf age and pollutant exposure was needed in order to characterize the impact of chronic O3 exposure upon CO2 exchange.

Photosynthesis and Ribulose 1,5-Bisphosphate Carboxylase in Rice Leaves: Changes in Photosynthesis and Enzymes Involved in Carbon Assimilation from Leaf Development through Senescence

Abstract: Changes in photosynthesis and the ribulose 1,5-bisphosphate (RuBP) carboxylase level were examined in the 12th leaf blades of rice ( Oryza sativa L.) grown under different N levels. Photosynthesis was determined using an open infrared gas analysis system. The level of RuBP carboxylase was measured by rocket immunoelectrophoresis. These changes were followed with respect to changes in the activities of RuBP carboxylase, ribulose 5-phosphate kinase, NADP-glyceraldehyde 3-phosphate dehydrogenase, and 3-phosphoglyceric acid kinase. RuBP carboxylase activity was highly correlated with the net rate of photosynthesis ( r = 0.968). Although high correlations between the activities of other enzymes and photosynthesis were also found, the activity per leaf of RuBP carboxylase was much lower than those of other enzymes throughout the leaf life. The specific activity of RuBP carboxylase on a milligram of the enzyme protein basis remained fairly constant (1.16 ± 0.07 micromoles of CO 2 per minute per milligram at 25°C) throughout the experimental period. Kinetic parameters related to CO 2 fixation were examined using the purified carboxylase. The K m (CO 2 ) and V max values were 12 micromolar and 1.45 micromoles of CO 2 per minute per milligram, respectively (pH 8.2 and 25°C). The in vitro specific activity calculated at the atomospheric CO 2 level from the parameters was comparable to the in situ true photosynthetic rate per milligram of the carboxylase throughout the leaf life. The results indicated that the level of RuBP carboxylase protein can be a limiting factor in photosynthesis throughout the life span of the leaf.

Action of UV‐B radiation on photosynthetic primary reactions in spinach chloroplasts

Abstract: Spinach (Spinacia oleracea L. cv. Matador) chloroplasts were irradiated with several levels of UV-B radiation. Measurements which reflect characteristic steps of photosynthetic electron transport were made to localize the site of impairment of photosynthesis by UV-B radiation. Variable fluorescence, the μs-kinetics of the 320 nm absorption changes and also oxygen evolution were substantially reduced in chloroplasts irradiated with UV-B. It was not possible to restore the amplitude of the 320 nm absorption changes nor the signal of the transmembrane electric field measured at 520 nm by adding the photo-system II donor couple hydroquinone/ascorbate to UV-B treated chloroplast samples. This indicates that impairment of photosystem II activity is not caused by selective inhibition of the water-splitting enzyme system Y, but rather is due to blockage of photosystem II reaction centers. Photosystem 1 is inferred to be highly resistant to UV-B radiation. These results suggest that the reaction centers of photosystem II are transformed into dissipative sinks for excitation energy by action of UV-B radiation.

Carotenoid enhancement and its role in maintaining blue-green algal (Microcystis aeruginosa) surface blooms1

Abstract: Ah tract Photosynthetic pigment alteration by Microcystis aeruginosa in surface blooms was related to persistence and dominance by this blue-green alga. The progression of summer blooms coincided with rising carotenoid : chlorophyll a ratios. When analyzed by high performance liqllid chromatography (HPLC), carotenoids exhibited strong in vitro absorbance in the UV and near-UV regions. Increased cellular carotenoid content was accompanied by increased sulfate photosynthesis as well as increased photosynthetic efficiencies in surface Microcystis populations. These data indicate that radiant energy is most effectively utilized as a source of photoreducing power in the presence of elevated cellular carotenoid : chlorophyll a ratios of surface populations. It is concluded that enhanced cellular carotenoid synthesis increases light utilization in the low and middle regions of the photosynthetically active radiation (PAR) spectrum and provides protection from UV damage. This is shown to have a positive effect on photosynthetic CO, fixation and bloom persistence in surface waters.

Photosynthesis, photorespiration and nitrogen metabolism

Abstract: . The ATP and reduced ferredoxin generated in photosynthetic reactions in the chloroplast are utilized for a large number of reactions other than CO2-fixation. Quantitatively the most important reaction is the reassimilation of ammonia liberated during photorespiration in C3 plants via the glutamate synthase cycle. Chloroplasts are also able to reduce nitrite to ammonia, sulphate to sulphide, and synthesize a number of amino acids. The amino acids essential for human nutrition are all synthesized in the chloroplast and evidence is presented to suggest that they may be the sole site of such biosynthetic reactions.

Ecophysiology of Amaranthus palmeri, a sonoran desert summer annual

Abstract: Basic photosynthetic and water relations characteristics in relation to soil water availability were investigated in Amaranthus palmeri, a common C4 summer annual of the Sonoran Desert Under conditions of high soil water availability, photosynthetic capacity exceeded 70 μmol CO2 m-2 s-1 at a leaf temperature optimum of 42°C, and photosynthesis was not light saturated at an irradiance of 20 mmol m-2 s-1 (400–700 nm) Leaves of A palmeri exhibited diaheliotropic movements, allowing them to take advantage of their high photosynthetic capacity In response to a long term drought cycle, both photosynthetic rate and leaf conductance to water vapor decreased, reaching minima at an approximate leaf water potential of-29 MPa Active leaf osmotic adjustment appeared to play an important role in allowing leaves to maintain gas exchange activities down to these low leaf water potentials The photosynthetic rate became light saturated at the lower leaf water potentials Although the two parameters decreased in concert, the decreased photosynthetic rate was not due to increased stomatal diffusion limitations, since intercellular CO2 concentrations remained constant over the range of leaf water potentials Instead it appeared that during the drought cycle, both intrinsic photosynthetic capacity and leaf protein content decreased as well These results suggested a coordination of gas exchange parameters during long term drought such that the intercellular CO2 concentration remained constant

Mechanisms of photoadaptation in three strains of the symbiotic dinoflagellate Symbiodinium microadriaticum

Abstract: Mechanisms of photoadaptation of photosynthesis have been studied in three strains of the symbiotic dinoflagellate Symbiodinium microadriaticum. Algal strains isolated from the clam Tridacna maxima, the sea anemone Aiptasia pulchella, and the scleractinian coral Montipora verrucosa were maintained in the defined medium ASP-8A, and were grown at irradiances ranging from 22 to 248 μE m-2 s-1 on a 14 h:10 h (light:dark) photoperiod at 26°C. All algal cultures were analysed during log-phase of growth. At all light levels, rates of cell division and photosynthesis were determined, as were cell volumes, pigmentation (including chlorophyll a, chlorophyll c 2, peridinin, β-carotene and xanthophylls), and carbon and nitrogen content. Low light-induced changes in pigmentation were evident to varying degrees in all three algal strains, although alterations in the photosynthesis-irradiance relations were distinctly different in each strain. The algae from T. maxima show the least photoadaptive capability, and seem to photoadapt by changing photosynthetic unit (PSU) size. Algae from A. pulchella appear to adapt by changing PSU number, while algae from M. verrucosa appear to photoadapt by changes in the activities of CO2-fixing enzymes or electron transport systems. These are the first observations that demonstrate functional differences in different strains of S. microadriaticum. The adaptive capabilities of the algae appear to correlate well with the ecological distribution of their respective hosts. The study was made from July 1981 through December 1982.

Breakdown of photosynthetic pigments and lipids in spinach leaves with ozone fumigation: role of active oxygens

Abstract: In spinach (Spinacia oleracea L. cv. New Asia) plants fumigated with ozone in light, destruction of chlorophylls and carotenoids and formation of malondialdehyde (MDA), an indicator of lipid peroxidation, were observed. Chlorophyll a and carotenoids in leaves started to be broken down 6–8 h after the commencement of 0.5 ppm ozone fumigation, whereas MDA formation in leaves increased linearly for the initial 8 h of fumigation followed by a more rapid increase. In leaf discs excised from 6-h fumigated plants, destruction of chlorophyll a and carotenoids and MDA formation proceeded in the light but were almost completely suppressed under an anaerobic condition. Effects of exogenously applied scavengers of active oxygen species suggest that active oxygens, especially superoxide radical (O2-), participated in both the destruction of chlorophyll a and carotenoids and the formation of MDA. Ozone fumigation reduced the levels of endogenous scavengers of O2-, superoxide dismutase (SOD) and L-ascorbate, in leaves to one-half the initial levels each by 3.5 and 8 h fumigation, respectively. The results indicate that the photosynthetic pigments and lipids were broken down by active oxygens accumulated in leaves as a result of the ozone-induced destruction of physiological defense against oxygen toxicity. Activity of polyphenol oxidase in chloroplast membranes of 4-h fumigated leaves increased to 240% of the initial level, suggesting that the thylakoid membranes had been affected severely before the pigment destruction. The relations between the pigment destruction and the disintegration of thylakoids are discussed.

Photosynthetic Unit Organization in a Red Alga: Relationships between Light-Harvesting Pigments and Reaction Centers

Abstract: The relative concentration of biliproteins, phycobilisomes, chlorophyll a, and reaction centers I and II are reported for Neoagardhiella bailyei, a macrophytic red alga collected in the field and compared with Anacystis nidulans, a cyanobacterium cultured in the laboratory. The ratios of chlorophyll to reaction center I, of chlorophyll to reaction center II, and the mass of phycobiliprotein per reaction center II are quite similar in Neoagardhiella and Anacystis, supporting the concept that the red algal chloroplast is derived from a cyanobacterial progenitor. The ratios of reaction center I to reaction center II are about 2.3 in both species. The Anacystis phycobilisome has about 40% of the mass of the Neoagardhiella phycobilisome, 4.9 and 14.9 × 106 daltons, respectively. The reaction center II/phycobilisome ratio is about 1.7 in Anacystis and 4.1 in Neoagardhiella. Phycobilisome size and physical restrictions on phycobilisome packing may be a major constraint on the reaction center II-phycobilisome association and the assembly of the photosynthetic membrane in both the red algae and cyanobacteria.

INFLUENCE OF PHOTON FLUX DENSITY IN THE 400–700 nm WAVEBAND ON INHIBITION OF PHOTOSYNTHESIS BY UV‐B (280–320 nm) IRRADIATION IN SOYBEAN LEAVES: SEPARATION OF INDIRECT AND IMMEDIATE EFFECTS

Abstract: — Visible radiation can substantially influence the degree to which plant photosynthesis is inhibited by UV-B radiation. This study was designed to separate the immediate effects of visible radiation on UV-B photosynthetic inhibition from the indirect influence of visible irradiation on morphological and physiological properties of leaves during leaf development. Soybean plants were pretreated in growth chambers with either high or low visible irradiance (750 and 70 μmol m-2s-1 quantum flux in the 400–700 nm waveband, respectively) during the development of leaves used subsequently for UV irradiation. Test leaves still attached to the plant were exposed to 5 h of polychromatic UV-B irradiation and the photosynthetic capacity (net CO2 exchange) was determined before and after the UV irradiation. During the UV irradiation, plants from both pretreatment groups received either high or low visible flux. Development of leaves in the high visible flux pretreatment conditions resulted in thicker leaves, higher chlorophyll a/b ratios, more UV-absorbing pigments, and reduced sensitivity to the UV-B irradiation. However, higher visible flux during the UV-B irradiation resulted in greater depression of photosynthesis by the UV-B irradiation. The relative magnitude of photosynthetic depression under these treatment combinations was the same when photosynthesis was measured under either light-limited or light-saturated conditions.

Phosphofructokinase activities in photosynthetic organisms : the occurrence of pyrophosphate-dependent 6-phosphofructokinase in plants and algae.

Abstract: A pyrophosphate-dependent phosphofructokinase (PPi-PFK) activity is detectable in extracts of a wide variety of primitive and advanced plants, the Charalean algae, and in the photosynthetic bacterium, Rhodospirillum rubrum. Angiosperms with extractable PPi-PFK activities 4- to 70-fold higher than the respective ATP-PFK activities tend to be succulent and to exhibit CAM. Even though PPi-PFK activity is not detected in crude extracts of some well known CAM plants, e.g. plants in the Crassulaceae, gel filtration of the extract and/or inclusion of the PPi-PFK activator, fructose 2,6-bisphosphate, in the assay reveals that a PPi-PFK activity is present in these species. Fructose 2,6-bisphosphate likewise activates PPi-PFK activities in extracts of C3 and C4 plants. C3 and C4 plant PPi-PFK activities are roughly equivalent to ATP-PFK activities in the same species. PPi-PFK activity is also detected in some bryophytes, lower vascular plants, ferns, and gymnosperms. The Charophytes, advanced algae presumed to be similar to species ancestral to vascular plants, exhibit at least 4-fold higher PPi-PFK than ATP-PFK activities. R. rubrum also exhibits a much higher PPi-PFK activity than ATP-PFK activity. These data indicate that PPi-PFK may serve as an alternate enzyme to ATP-PFK in glycolysis in a wide range of photosynthetic organisms.

Effect of Pod Removal on Leaf Photosynthesis and Soluble Protein Composition of Field-Grown Soybeans

Abstract: Well nodulated, field-grown soybeans (Glycine max [L.] Merr. var Williams) were depodded just prior to seed development and near mid pod-fill. Both treatments caused a considerable increase in leaf dry weight, suggesting continued photosynthate production following pod removal. Moreover, depodding had a marked effect on leaf soluble protein without affecting total proteolytic activity. Early depodding caused a 50% increase in leaf protein, and both early and late depodding caused the retention of protein for several weeks following the decline in control leaves. But despite this retention of protein, leaves of depodded plants showed no difference in the onset of the irreversible decline in photosynthesis. Therefore, although depodding delayed the loss of leaf chlorophyll and protein, it did not delay the onset of functional leaf senescence and in fact, actually appeared to enhance the rate of decline in photosynthesis. There was a good correlation between the irreversible decline in ribulose bisphosphate carboxylase (activity and amount) and that of photosynthesis. In contrast, the correlation did not seem as good between stomatal closure and the onset of the irreversible decline in photosynthesis. The reason total soluble protein remained high following depodding while carboxylase, which normally comprised 40% of the soluble protein, declined was because several polypeptides increased in amounts sufficient to offset the loss of carboxylase. This change in leaf protein composition indicates a change in leaf function; this is discussed in terms of other recent findings.

Photosynthetic Characteristics of C3-C4 Intermediate Flaveria Species I. Leaf Anatomy, Photosynthetic Responses to O2 and CO2, and Activities of Key Enzymes in the C3 and C4 Pathways

Abstract: Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C(3)-C(4) plants based on leaf anatomy, photosynthetic CO(2) compensation point, O(2) inhibition of photosynthesis, and activities of C(4) enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C(4) species F. trinervia, while the other C(3)-C(4) intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO(2) compensation points of these intermediates at 30 degrees C were very low relative to those of C(3) plants, ranging from 7 to 14 microliters per liter. In contrast to C(3) plants, net photosynthesis by the intermediates was not sensitive to O(2) concentrations below 5% and decreased relatively slowly with increasing O(2) concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O(2) varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C(3) species. The inhibition of carboxylation efficiency by 21% O(2) varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C(4) (2% for F. trinervia) and C(3) (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C(4) enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C(4) photosynthesis. It appears that these Flaveria species may be true biochemical C(3)-C(4) intermediates.

Photosynthetic adaptation to temperature in four species from the Colorado shortgrass steppe: a physiological model for coexistence.

Abstract: Several aspects of photosynthetic adaptation to temperature were examined in four graminoid species from the Colorado shortgrass steppe. The experimental species were chosen to provide examples of a variety of in situ seasonal phenology patterns. The cool season grass, Agropyron smithii (C3), exhibited higher photosynthesis rates when grown in a cool temperature regime (20/15°C), and compared to warm grown plants (35/15°C). The warm season species, Bouteloua gracilis (C4) and Buchloe dactyloides (C4), exhibited higher photosynthetic capacities when grown in the warmer temperature regime. The sedge, Carex eleocharis (C3), which exhibits seasonal growth potential during the cool and warm portions of the growing season, exhibited a marked capacity for photosynthetic temperature acclimation. Differential effects of growth temperature on the intracellular conductance to CO2 appeared to have a greater regulatory role in these responses for the two C3 species, relative to stomatal conductance or photorespiration (O2 inhibition of photosynthesis). In the two C4 species decreases in the intracellular conductance in cool grown plants were correlated with the decreased photosynthetic capacity in normal air for B. gracilis, but not for B. dactyloides. Analysis of the Arrhenius relationship for CO2 saturated net photosynthesis at low leaf temperatures (4.5-17°C) indicated sharp breaks in the apparent energy of activation at 5.8-9.0°C in the warm season species B. gracilis and B. dactyloides. Leaves of A. smithii and C. eleocharis exhibited no significant low temperature limitations according to this analysis. The low temperature limitations in the warm season species were partially reflected in an inhibition of the quantum yield for CO2 uptake after 2 h at 5-6°C in the presence of high photon flux densities. Temperature dependent increases in the chlorophyll fluorescence yield at high temperatures revealed the lowest breakpoint values for A. smithii, and the highest values for B. gracilis. The differential patterns of temperature adaptation among the species further extend the proposal of Kemp and Williams (1980; Ecology 61:846-858) that seasonal temperature gradients in the shortgrass steppe have a regulatory role in maintaining offset patterns of resource utilization and decreasing interspecific competition.