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At least 19 recordsLinked to original sources
PubMed1977

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum.

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.

Journal Article↗
PubMed1992

Degree of C(4) Photosynthesis in C(4) and C(3)-C(4)Flaveria Species and Their Hybrids : II. Inhibition of Apparent Photosynthesis by a Phosphoenolpyruvate Carboxylase Inhibitor.

Hybrids have been made between species of Flaveria exhibiting varying levels of C(4) photosynthesis. The degree of C(4) photosynthesis expressed in four interspecific hybrids (Flaveria trinervia [C(4)] x F. linearis [C(3)-C(4)], F. brownii [C(4)-like] x F. linearis, and two three-species hybrids from F. trinervia x [F. brownii x F. linearis]) was estimated by inhibiting phosphoenolpyruvate carboxylase in vivo with 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP). The inhibitor was fed to detached leaves at a concentration of 4 mm, and apparent photosynthesis was measured at atmospheric levels of CO(2) and at 20 and 210 mL L(-1) of O(2). Photosynthesis at 210 mL L(-1) of O(2) was inhibited 32% by DCDP in F. linearis, by 60% in F. brownii, and by 87% in F. trinervia. Inhibition in the hybrids ranged from 38 to 52%. The inhibition of photosynthesis by 210 mL L(-1) of O(2) was increased when DCDP was used, except in the C(4) species, F. trinervia, in which photosynthesis was insensitive to O(2). Except for F. trinervia, control plants with less O(2) sensitivity (more C(4)-like) exhibited a progressively greater change in O(2) inhibition of photosynthesis when treated with DCDP. This increased O(2) inhibition probably resulted from decreased CO(2) concentrations in bundle sheath cells due to inhibition of phosphoenolpyruvate carboxylase. The inhibition of photosynthesis by DCDP is concluded to underestimate the degree of C(4) photosynthesis in the interspecific hybrids because increased direct assimilation of atmospheric CO(2) by ribulose bisphosphate carboxylase may compensate for inhibition of phosphoenolpyruvate carboxylase.

Journal Article↗
PubMed1971

The Rate of Photorespiration during Photosynthesis and the Relationship of the Substrate of Light Respiration to the Products of Photosynthesis in Sunflower Leaves.

Single attached leaves of sunflower (Helianthus annus L. "Mennonite") were supplied (14)CO(2) of constant specific radioactivity in gas mixtures containing various CO(2) and O(2) concentrations. The (14)CO(2) and CO(2) fluxes were measured concurrently in an open system using an ionization chamber and infrared gas analyzer.The rate of photorespiration (5.7 +/- 0.3 mg CO(2).dm(-2).(-1)) during photosynthesis in 21% O(2) at 25 C and 3,500 footcandles was over three times the rate of dark respiration and was independent of CO(2) concentrations from 0 to 300 mul/l. The steady rate of CO(2) evolution into CO(2)-free air was about 30% lower. Low oxygen (1%) inhibited both (14)CO(2) and CO(2) evolution, both during photosynthesis and in CO(2)-free air in the light.At 300 mul/l CO(2) apparent photosynthesis was inhibited 41% by 21% O(2). Two-thirds of the inhibition was due to the inhibition of true photosynthesis by oxygen and one-third due to the stimulation of photorespiration. At 50 mul/l CO(2), where the percentage inhibition of apparent photosynthesis by 21% oxygen was 92%, photorespiration accounted for two-thirds of the total inhibition.The rate of (14)CO(2) uptake by the leaf decreased about 30 seconds after the introduction of (14)CO(2), indicating that (14)CO(2) was rapidly evolved from the leaf. The rate of (14)CO(2) evolution increased rapidly with time, the kinetics depending on the CO(2) concentration. The high specific radioactivity of the (14)CO(2) evolved during photosynthesis or in the early period of flushing in CO(2)-free air showed that the substrate for light respiration was an early product of photosynthesis. From the measurement of (14)CO(2) and CO(2) evolution into CO(2)-free air over a longer time period it was apparent that at least three compounds, each of decreased (14)C content, could supply the substrate for light respiration.Based on a consideration of the specific radioactivity of (14)CO(2) evolved under a variety of conditions, it is suggested that total CO(2) evolution in the light or photorespiration is composed of two processes, dark respiration and light respiration. Light respiration is a process that only occurs in the light, persists for some time on darkening, and metabolizes substrates that are quite different from those of dark respiration.

Journal Article↗
PubMed2005

Is C4 photosynthesis less phenotypically plastic than C3 photosynthesis?

C4 photosynthesis is a complex specialization that enhances carbon gain in hot, often arid habitats where photorespiration rates can be high. Certain features unique to C4 photosynthesis may reduce the potential for phenotypic plasticity and photosynthetic acclimation to environmental change relative to what is possible with C3 photosynthesis. During acclimation, the structural and physiological integrity of the mesophyll-bundle sheath (M-BS) complex has to be maintained if C4 photosynthesis is to function efficiently in the new environment. Disruption of the M-BS structure could interfere with metabolic co-ordination between the C3 and C4 cycles, decrease metabolite flow rate between the tissues, increase CO2 leakage from the bundle sheath, and slow enzyme activity. C4 plants have substantial acclimation potential, but in most cases lag behind the acclimation responses in C3 plants. For example, some C4 species are unable to maintain high quantum yields when grown in low-light conditions. Others fail to reduce carboxylase content in shade, leaving substantial over-capacity of Rubisco and PEP carboxylase in place. Shade-tolerant C4 grasses lack the capacity for maintaining a high state of photosynthetic induction following sunflecks, and thus may be poorly suited to exploit subsequent sunflecks compared with C3 species. In total, the evidence indicates that C4 photosynthesis is less phenotypically plastic than C3 photosynthesis, and this may contribute to the more restricted ecological and geographical distribution of C4 plants across the Earth.

Acclimatization↗
PubMed2004

A list of photosynthesis conferences and of edited books in photosynthesis.

This paper is a general appendix to the three parts of 'Celebrating the millennium - historical highlights of photosynthesis research' (Photosynthesis Research, Vols~73(2002), 76(2003), 80(2004)). The major part of this paper includes a comprehensive list of most of the edited volumes on research in the area of photosynthesis. However, I begin this paper by describing selected conferences, related to photosynthesis, held in USA, during 1935-1965, followed by the 1963 International Colloquim held in Gif-sur-Yvette, France (René Wurmser (1890-1993), President); and the 2nd Western European Congress (1965), held in the Netherlands, under the leadership of Jan B. Thomas (1907-1991), both these European conferences being the precursors of the first International Congress on Photosynthesis (1968), organized by Helmut Metzner (1925-1999) at Freudenstadt, Germany. A list of the subsequent international photosynthesis congresses is available in Govindjee and David Krogmann (this issue).

Journal Article↗
PubMed2004

Inhibition of photosynthesis by heat stress: the activation state of Rubisco as a limiting factor in photosynthesis.

Although the catalytic activity of Rubisco increases with temperature, the low affinity of the enzyme for CO(2) and its dual nature as an oxygenase limit the possible increase in net photosynthesis with temperature. For cotton, comparisons of measured rates of net photosynthesis with predicted rates that take into account limitations imposed by the kinetic properties of Rubisco indicate that direct inhibition of photosynthesis occurs at temperatures higher than about 30 degrees C. Inhibition of photosynthesis by moderate heat stress (i.e. 30-42 degrees C) is generally attributed to reduced rates of RuBP regeneration caused by disruption of electron transport activity, and specifically inactivation of the oxygen evolving enzymes of photosystem II. However, measurements of chlorophyll fluorescence and metabolite levels at air-levels of CO(2) indicate that electron transport activity is not limiting at temperatures that inhibit CO(2) fixation. Instead, recent evidence shows that inhibition of net photosynthesis correlates with a decrease in the activation state of Rubisco in both C(3) and C(4) plants and that this decrease in the amount of active Rubisco can fully account for the temperature response of net photosynthesis. Biochemically, the decrease in Rubisco activation can be attributed to: (1) more rapid de-activation of Rubisco caused by a faster rate of dead-end product formation; and (2) slower re-activation of Rubisco by activase. The net result is that as temperature increases activase becomes less effective in keeping Rubisco catalytically competent. In this opinionated review, we discuss how these processes limit photosynthetic performance under moderate heat stress.

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PubMed2002

Instantaneous canopy photosynthesis: analytical expressions for sun and shade leaves based on exponential light decay down the canopy and an acclimated non-rectangular hyperbola for leaf photosynthesis.

Analytical expressions for the contributions of sun and shade leaves to instantaneous canopy photosynthesis are derived. The analysis is based on four assumptions. First, that the canopy is closed in the sense that it is horizontally uniform. Secondly, that there is an exponential profile of light down the canopy with the same decay constant for light from different parts of the sky. Thirdly, that the leaf photosynthetic response to incident irradiance can be described by a three-parameter non-rectangular hyperbola (NRH). And lastly, that light acclimation at the leaf level occurs in only one parameter of the NRH, that describing the light-saturated photosynthetic rate, which is assumed to be proportional to the local averaged leaf irradiance. These assumptions have been extensively researched empirically and theoretically and their limitations are quite well understood. They have been widely used when appropriate. Combining these four assumptions permits the derivation of algebraic expressions for instantaneous canopy photosynthesis which are computationally efficient because they avoid the necessity for numerical integration down the canopy. These are valuable for modelling plant and crop ecosystems, for which canopy photosynthesis is the primary driver. Ignoring the sun/shade dichotomy can result in overestimates of canopy photosynthesis of up to 20 %, but using a rectangular hyperbola instead of a non-rectangular hyperbola to estimate canopy photosynthesis taking account of sun and shade leaves can lead to a similarly sized underestimate.

Acclimatization↗
PubMed1999

The use of the ratio between the photosynthesis parameters p(ml)and v(cmax)for scaling up photosynthesis of C(3)Plants from leaves to canopies: A critical examination of different modelling approaches

Recent models of photosynthesis have adopted the close correlation between the main photosynthetic component processes, the maximum rate of carboxylation and the potential rate of RuBP (ribulose-1, 5-bisphosphate) regeneration, at a reference temperature of 20 degrees C. When using the ratio between these two processes in models of photosynthesis, assumptions though have to be made about the temperature response of the potential rate of RuBP regeneration, which varies with growth conditions and among species. In order to assess the effects of deviations from the real temperature response of the potential rate of RuBP regeneration on photosynthesis, a sensitivity analysis, scaling up photosynthesis from the leaf to the canopy level, is applied in the present paper. No changes are predicted to occur for sunlit leaves, which receive both direct and diffuse radiation, as long as incident radiation does not cause carboxylation to shift from RuBP saturation to RuBP limitation, which, depending on incident radiation and canopy structure, might occur deeper down in the canopy. Carboxylation of shaded leaves, which receive solely diffuse radiation, is generally limited by the regeneration of RuBP, and is thus prone to be affected by changes in the temperature response of the potential rate of RuBP regeneration. Due to the saturation type response of the RuBP-limited rate of carboxylation to temperature at light intensities below saturation, the impact of deviations from the real temperature response is negligible at high leaf temperatures, but may become significant when leaf temperatures are low and photosynthetically active radiation incident on shaded leaves is comparably high, as in the upper canopy layers. The largest effects on whole canopy photosynthesis will therefore occur under cool conditions and a completely overcast sky, when all leaves receive diffuse radiation only. Copyright 1999 Academic Press.

Journal Article↗
PubMed1983

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

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 degrees 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 degrees 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.

Journal Article↗
PubMed1989

Effects of the Phosphoenolpyruvate Carboxylase Inhibitor 3,3-Dichloro-2-(Dihydroxyphosphinoylmethyl)propenoate on Photosynthesis: C(4) Selectivity and Studies on C(4) Photosynthesis.

The effect of 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)-propenoate (DCDP), an analog of phosphoenolpyruvate (PEP), on PEP carboxylase activity in crude leaf extracts and on photosynthesis of excised leaves was examined. DCDP is an effective inhibitor of PEP carboxylase from Zea mays or Panicum miliaceum; 50% inhibition was obtained at 70 or 350 micromolar, respectively, in the presence of 1 millimolar PEP and 1 millimolar HCO(3) (-). When fed to leaf sections via the transpiration stream, DCDP at 1 millimolar strongly inhibited photosynthesis in C(4) species (79-98% inhibition for a range of seven C(4) species), but only moderately in C(3) species (12-46% for four C(3) species), suggesting different mechanisms of inhibition for each photosynthetic type. The response of P. miliaceum (C(4)) net photosynthesis to intercellular pCO(2) showed that carboxylation efficiency, as well as the CO(2) saturated rate, are lowered in the presence of DCDP and supported the view that carboxylation efficiency in C(4) species is directly related to PEP carboxylase activity. A fivefold increase in intercellular pCO(2) over that occurring in P. miliaceum under normal photosynthesis conditions only increased net photosynthesis rate in the presence of 1 millimolar DCDP from zero to about 5% of the maximal uninhibited rate. Therefore, it seems unlikely that direct fixation of atmospheric CO(2) by the bundle sheath cells makes any significant contribution to photosynthetic CO(2) assimilation in C(4) species. The results support the concept that C(4)-selective herbicides may be developed based on inhibitors of C(4) pathway reactions.

Journal Article↗
PubMed1998

Tracking molecular evolution of photosynthesis by characterization of a major photosynthesis gene cluster from Heliobacillus mobilis.

A DNA sequence has been obtained for a 35.6-kb genomic segment from Heliobacillus mobilis that contains a major cluster of photosynthesis genes. A total of 30 ORFs were identified, 20 of which encode enzymes for bacteriochlorophyll and carotenoid biosynthesis, reaction-center (RC) apoprotein, and cytochromes for cyclic electron transport. Donor side electron-transfer components to the RC include a putative RC-associated cytochrome c553 and a unique four-large-subunit cytochrome bc complex consisting of Rieske Fe-S protein (encoded by petC), cytochrome b6 (petB), subunit IV (petD), and a diheme cytochrome c (petX). Phylogenetic analysis of various photosynthesis gene products indicates a consistent grouping of oxygenic lineages that are distinct and descendent from anoxygenic lineages. In addition, H. mobilis was placed as the closest relative to cyanobacteria, which form a monophyletic origin to chloroplast-based photosynthetic lineages. The consensus of the photosynthesis gene trees also indicates that purple bacteria are the earliest emerging photosynthetic lineage. Our analysis also indicates that an ancient gene-duplication event giving rise to the paralogous bchI and bchD genes predates the divergence of all photosynthetic groups. In addition, our analysis of gene duplication of the photosystem I and photosystem II core polypeptides supports a "heterologous fusion model" for the origin and evolution of oxygenic photosynthesis.

Bacteria↗
PubMed1992

Photosynthesis of a Scots pine shoot: a comparison of two models of shoot photosynthesis in direct and diffuse radiation fields.

Two models of shoot photosynthesis, the needle surface element model (SEM) and needle volume element model (VEM), were tested against empirical data obtained from measurements of the photosynthetic response of twelve Scots pine (Pinus sylvestris L.) shoots in direct and diffuse radiation. The models assume that shoot photosynthesis is obtained as the integrated response of either all needle surface area elements (SEM) or all needle volume elements (VEM) of the shoot. The models differ in that needles are treated as optically black in SEM, whereas in VEM radiation penetrates into the needle. The photosynthetic response of a surface/volume element was described as a Blackman-type curve and the distributions of irradiance on the elements were derived by computer simulation, based on a model of shoot geometry. The parameters (initial slope and maximum rate) of the Blackman-curve of an element were estimated iteratively by the method of least squares, i.e., by minimizing the residual sum of squares of simulated and measured rates of shoot photosynthesis. The parameter estimation was done separately for direct and diffuse radiation, and the models were evaluated based on the notion that, for the "ideal" model, the estimated parameter values should be the same in direct and diffuse radiation. Both models produced shoot photosynthesis curves that agreed well with measurements, but there was a discrepancy in the estimated parameter values, indicating that differences in the photosynthetic response of shoots in direct and diffuse radiation could not be explained solely on the basis of the simulated irradiance distributions. The agreement was, however, much better for the volume element model, which accounts for penetration of radiation into the needles.

Journal Article↗
PubMed1977

Inhibition of photosynthesis by azide and cyanide and the role of oxygen in photosynthesis.

Cyanide and azide inhibit photosynthesis and catalase activity of isolated, intact spinach (Spinacia oleracea) chloroplasts. When chloroplasts are illuminated in the presence of CN(-) or N(3) (-), accumulation of H(2)O(2) is observed, parallel to inhibition of photosynthesis. Photosynthetic O(2) evolution is inhibited to the same extent, under saturating light, whether CO(2) or phosphoglycerate is present as electron acceptor.The illumination of chloroplasts with CN(-) or N(3) (-) inactivates the NADPH- and ATP-dependent phosphoglycerate reduction. This enzyme system can be reactivated by dithiothreitol. In reconstituted, envelope-less chloroplasts, the phosphoglycerate-dependent and the ribose 5-phosphate-dependent O(2) evolution are inhibited to the same extent, while electron transport to NADP is unaffected.It is concluded that the inhibition of photosynthesis by CN(-) and N(3) (-) is due to H(2)O(2) accumulation, which is a consequence of catalase inhibition.The inhibition of phosphoglycerate reduction, but not of CO(2) reduction, is abolished under conditions where ATP is available in excess of NADPH (low light, supply of ATP). This is taken as an indication that electron flow from photosystem I is diverted to O(2) (Mehler reaction, which produces H(2)O(2)) when the unavailability of ATP is limiting the rate of reoxidation of NADPH. The Mehler reaction is considered a physiological process supplying ATP for photosynthesis.

Journal Article↗
PubMed1991

On the Role of Mitochondrial Oxidative Phosphorylation in Photosynthesis Metabolism as Studied by the Effect of Oligomycin on Photosynthesis in Protoplasts and Leaves of Barley (Hordeum vulgare).

Low concentrations of oligomycin, which strongly inhibit mitochondrial oxidative phosphorylation but do not affect chloroplast photophosphorylation, caused an inhibition of photosynthesis by 30 to 40% in barley (Hordeum vulgare L.) leaf protoplasts. This inhibition is reversed and the full rate of photosynthesis is regained when the protoplasts are ruptured so as to leave the chloroplasts intact. Oligomycin fed into barley leaves by the transpiration stream inhibited photosynthesis in these leaves by up to 60%. The measurement of metabolites in protoplast and leaf extracts showed that oligomycin caused a decrease in the ATP/ADP ratio and an increase in the content of glucose- and fructose 6-phosphate. Subcellular analysis of protoplasts revealed that the decrease in ATP/ADP ratio in the cytosol was larger than in the stroma and that the increase in hexose monophosphates was restricted to the cytosol, whereas the stromal hexosemonophosphates decreased upon the addition of oligomycin. Moreover, oligomycin caused an increase in the triosephosphate-3-phosphoglycerate ratio. It is concluded from these results that during photosynthesis of a plant leaf cell mitochondrial oxidative phosphorylation contributes to the ATP supply of the cell and prevents overreduction of the chloroplast redox carriers by oxidizing reductive equivalents generated by photosynthetic electron transport.

Journal Article↗
PubMed2000

Acclimation of photosynthesis to temperature in eight cool and warm climate herbaceous C(3) species: Temperature dependence of parameters of a biochemical photosynthesis model.

To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, eight cool and warm climate herbaceous crop and weed species were grown at 15 and 25 degrees C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 - 35 degrees C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substomatal carbon dioxide concentration (C(i)), A at high C(i), and stomatal conductance. The first two measurements allow calculation of V(Cmax), the maximum rate of carboxylation of ribulose bisphosphate carboxylase and J(max), the maximum rate of photosynthetic electron transport, of Farquhar-type photosynthesis models. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 - 35 degrees C, even when A decreased at high measurement temperature. There were larger increases in conductance over this temperature range in the warm climate species (4.3 x) than in the cool climate species (2.5 x). The initial slope of A vs. C(i) exhibited an optimum temperature which ranged from 20 to 30 degrees C. There was a larger increase in the optimum temperature of the initial slope at the warmer growth temperature in the cool climate species than in the warm climate species. The optimum temperature for A at high C(i) ranged from 25 to 30 degrees C among species, but changed little with growth temperature. The absolute values of both the initial slope of A vs. C(i) and A at high C(i) were increased about 10% by growth at the warmer temperature in the warm climate species, and decreased about 20% in the cool climate species. The ratio of J(max) - V(Cmax) normalized to 20 degrees C varied by more than a factor of 2 across species and growth temperatures, but differences in the temperature response of photosynthesis were more related to variation in the temperature dependencies of J(max) and V(Cmax) than to the ratio of their normalized values.

Journal Article↗
PubMed1981

Photosynthesis in Polyploid Tall Fescue : II. PHOTOSYNTHESIS AND RIBULOSE-1, 5-BISPHOSPHATE CARBOXYLASE OF POLYPLOID TALL FESCUE.

Net photosynthesis on a leaf area and leaf weight basis increased significantly with ploidy in a 4X, 6X, 8X and 10X allopolyploid series of tail fescue (Festuca arundinacea Schreb.). Total protein did not increase significantly with ploidy. Rocket immunoelectrophoresis was used to quantitate ribulose-1, 5-bisphosphate carboxylase (RuBPCase) protein. RuBPCase content, expressed on both a concentration basis and as a percentage of total protein increased significantly with ploidy in both field and greenhouse experiments. The range of RuBPCase content was 16 to 73% of total protein and 2.8 and 6.5 mg/ml of extract. Specific activity of RuBPCase did not increase significantly with ploidy. Chlorophyll concentration increased as a quadratic function of ploidy, with the mean for 8X genotypes representing maximal chlorophyll content. Evidence is presented that increasing concentrations of RuBPCase are associated with higher net photosynthesis rates in tall fescue. This suggests that RuBPCase may represent a marker for increased net photosynthesis. RuBPCase was extracted in a partially active state or inhibited state and must be fully activated by Mg(2+) and HCO(3) (-) to measure maximal activities. Polyploidization appeared to increase selectively the allocation of total protein for synthesis of RuBPCase; however, there was also a range for carboxylase content among the genotypes within a given ploidy level.

Journal Article↗
PubMed1983

Photosynthesis in Tall Fescue : IV. Carbon Assimilation Pattern in two Genotypes of Tall Fescue Differing in Net Photosynthesis Rates.

We previously reported that the net photosynthetic rate of a decaploid genotype (I-16-2) of tall fescue (Festuca arundinacea Schreb.) was 32 to 41 versus 22 milligrams CO(2) per square decimeter per hour in a hexaploid genotype (V6-802) (Randall, Nelson, Asay Plant Physiol 59: 38-41). The high rate was later correlated with increases in total ribulose 1,5-bisphosphate carboxylase protein (17%) and activity (27%) (Joseph, Randall, Nelson Plant Physiol 68: 894-898). This report characterizes photosynthesis with respect to light saturation and early products of photosynthesis in an attempt to identify regulatory metabolic site(s) in these two genotypes. Analysis of the early products of photosynthesis indicated that both genotypes fixed CO(2) via the Calvin-Benson cycle with phosphoglyceric acid as the initial primary product. Both genotypes had similar (14)C-labeled intermediates. Sucrose was the primary sink of (14)CO(2) assimilation. After 10 min of (14)CO(2) assimilation with attached leaves, sucrose accounted for 89% (decaploid) and 81% (hexaploid) of the total (14)C incorporated. In 10 min, this amounted to 1.3 (decaploid) and 0.8 (hexaploid) mumol [(14)C]sucrose formed g fresh weight(-1) and reflected the observed differences in photosynthetic rates. There was limited labeling of starch (1%) and fructan (1%). Results of total nonstructural carbohydrates and P(i) analysis also demonstrated sucrose was the predominant carbohydrate in fescue leaves. Quantitative differences in sucrose and P(i) between the two genotypes may reflect changes in partitioning and this possibility is discussed.

Journal Article↗
PubMed1986

Limitation of Photosynthesis by Carbon Metabolism : I. Evidence for Excess Electron Transport Capacity in Leaves Carrying Out Photosynthesis in Saturating Light and CO(2).

It has been investigated how far electron transport or carbon metabolism limit the maximal rates of photosynthesis achieved by spinach leaves in saturating light and CO(2). Leaf discs were illuminated with high light until a steady state rate of O(2) evolution was attained, and then subjected to a 30 second interruption in low light, to generate an increased demand for the products of electron transport. Upon returning to high light there is a temporary enhancement of photosynthesis which lasts 15 to 30 seconds, and can be up to 50% above the steady state rate of O(2) evolution. This temporary enhancement is only found when saturating light intensities are used for the steady state illumination, is increased when low light rather than darkness is used during the interruption, and is maximal following a 30 to 60 seconds interruption in low light. Decreasing the temperature over the 10 to 30 degrees C range led to the transient enhancement becoming larger. The temporary enhancement is associated with an increased ATP/ADP ratio, a decreased level of 3-phosphoglycerate, and increased levels of triose phosphate and ribulose 1,5-bisphosphate. Since electron transport can occur at higher rates than in steady state conditions, and generate a higher energy status, it is concluded that leaves have a surplus electron transport capacity in saturating light and CO(2). From the alterations of metabolites, it can be calculated that the enhanced O(2) evolution must be accompanied by an increased rate of ribulose 1,5-bisphosphate regeneration and carboxylation. It is suggested that the capacity for sucrose synthesis ultimately limits the maximal rates of photosynthesis, by restricting the rate at which inorganic phosphate can be recycled to support electron transport and carbon fixation in the chloroplast.

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