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At least 793 records · Page 44Linked to original sources
PubMed1972

Temperature dependence of photosynthesis in cotton.

Cotton plants (Gossypium hirsutum L., var. Deltapine Smooth Leaf) were grown under controlled environmental conditions over a range of day/night temperatures from 20/15 to 40/35 C. Their photosynthetic characteristics were then measured over a comparable temperature range. Net photosynthesis tended stongly to be greatest, and intracellular resistance to CO(2) transport to be lowest, when the measurement temperature corresponded to the daytime growth temperature, suggesting pronounced acclimation of the plants to the growth temperature. The preferred growth temperature was close to the 25/20 C regime, since net photosynthesis of these plants, regardless of measurement temperature, was higher and intracellular resistance lower, than in plants from any other regime.Ribulose diphosphate carboxylase activity per unit leaf area was highest in plants grown at 25/20 C, but did not show pronounced changes with growth temperature. Glycolate oxidase activity decreased and NADH-malate dehydrogenase activity tended to increase with increasing growth temperature. In contrast, changes in carbonic anhydrase activity with growth temperature showed a general similarity to changes in photosynthetic rate. This may suggest that the "chemical resistance" component of the intracellular resistance bears a relationship to the amount of carbonic anhydrase in the leaf.

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PubMed1973

The interaction of respiration and photosynthesis in induction of nitrate reductase activity.

The respiration and photosynthesis requirement for induction and maintenance of nitrate reductase activity was determined on leaves of Hordeum vulgare L. In this induction, glucose substituted for light in both dark-grown and carbohydrate-depleted green leaves. Oxygen appeared to be required for induction in all cases studied. In light and under N(2), 3-(3,4-dichlorophenyl)-1,1-dimethylurea completely inhibited induction, presumably by inhibiting the production of O(2), Hence, under N(2) the leaves appeared to utilize both the O(2) produced by photosynthesis and the CO(2) produced by respiration. CO(2) fixation can then produce both photosynthate to drive the induction and terminal electron acceptors to allow photosynthetic electron flow. This possibility was further suggested by the observation that CO(2) was an absolute requirement for induction in carbohydrate-depleted barley leaves. Results obtained with respiratory inhibitors also indicated that respiration drove the induction of nitrate reductase.Exogenously supplied glucose also substantially slowed the loss of nitrate reductase that occurred when barley leaves were placed in darkness. It is presumed that glucose allowed the synthetic or activation phase of the induction to proceed more rapidly. Our results support the hypothesis that one of the main effects of light may be to supply photosynthate to support respiration, which then drives the induction process.

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PubMed1973

Zinc deficiency, carbonic anhydrase, and photosynthesis in leaves of spinach.

A shortage in the zinc supply to spinach (Spinacia oleracea L.) drastically reduced carbonic anhydrase levels with little effect on net CO(2) uptake per unit leaf area, except with the most severe zinc stresses. Under these conditions, carbonic anhydrase was below 10% and photosynthesis 60 to 70% of the control levels. When photosynthesis was measured at a range of CO(2) supply levels, zinc-deficient leaves were less efficient at 300 to 350 microliters per liter CO(2) and above, but the same as controls at lower CO(2) levels. This suggests that carbonic anhydrase does not affect the diffusion of CO(2), and that the effect of zinc deficiency was on the photosynthetic process itself. Our evidence does not support the hypothesis that carbonic anhydrase has some role in facilitating the supply of CO(2) to the sites of carboxylation within the chloroplast.

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PubMed1975

C(4) Photosynthesis: Light-dependent CO(2) Fixation by Mesophyll Cells, Protoplasts, and Protoplast Extracts of Digitaria sanguinalis.

Mesophyll cells, protoplasts, and protoplast extracts of Digitaria sanguinalis were used for comparative studies of light-dependent CO(2) fixation. CO(2) fixation was low without the addition of organic substrates. Pyruvate, oxaloacetate, and 3-phosphoglycerate induced relatively low rates (10 to 90 mumoles/mg chlorophyll.hr) of CO(2) fixation when added separately. However, a highly synergistic relationship was found between pyruvate + oxaloacetate and pyruvate + 3-phosphoglycerate for inducing light-dependent CO(2) fixation in the mesophyll preparations. Highest rates of CO(2) fixation were obtained with protoplast extracts. Pyruvate, in combination with oxaloacetate or 3-phosphoglycerate induced light-dependent rates from 150 to 380 mumoles of CO(2) fixed/mg chlorophyll.hr which are equivalent to or exceed reported rates of whole leaf photosynthesis in C(4) species. Concentrations of various substrates required to give half-maximum velocities of CO(2) fixation were determined, with the protoplast extracts generally saturating at the lowest substrate concentrations. Chloroplasts separated from protoplast extracts showed little capacity for CO(2) fixation. The results suggest that CO(2) fixation in C(4) mesophyll cells is dependent on chloroplasts and extrachloroplastic phosphoenolpyruvate carboxylase.The stimulation of pyruvate-induced CO(2) fixation by oxaloacetate and 3-phosphoglycerate is thought to be due to induction of noncyclic electron transport which generates ATP for the conversion of pyruvate to phosphoenolpyruvate by pyruvate Pi dikinase. The primary products of the substrate-induced CO(2) fixation were oxaloacetate and malate, which provides further evidence for carbon fixation through the beta-carboxylation pathway. High rates of light-dependent CO(2) fixation with a significant percentage of (14)C fixed into malate suggest an efficient operation of both photosystems I and II.The substrate inductions are discussed with respect to the proposed role of the mesophyll cell in C(4) photosynthesis, and schemes suggesting the stoichiometry of energy requirements for photosynthetic carbon metabolism in C(4) mesophyll cells are presented.

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PubMed1975

C(4) photosynthesis in tree form euphorbia species from hawaiian rainforest sites.

The (13)C (12)C isotope ratios and the leaf anatomy of 18 species and varieties of Euphorbia native to the Hawaian Islands indicated that all possess C(4) photosynthesis. These species range from small prostrate coastal strand shrubs to shrubs and trees in rainforest and bog habitats. The results show that C(4) photosynthesis occurs in plants from a much wider range of habitats and life-forms than has been previously reported.

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PubMed1975

Sulfur dioxide inhibition of photosynthesis in isolated spinach chloroplasts.

Photosynthetic oxygen evolution by isolated spinach (Spinacia oleracea L.) chloroplasts approached complete inhibition in the presence of a 5 mm concentration of sulfur dioxide. A similar inhibition was observed in the presence of equimolar concentrations of bisulfite ions, suggesting a parallel mode of action. In contrast, an equimolar concentration of sulfite ions was markedly less inhibitory and sulfate ions caused negligible inhibition of apparent photosynthesis. The mode of action of sulfur dioxide and related sulfur anions in inhibiting photosynthesis was found to be essentially independent of direct hydrogen-ion effects. Supplements of inorganic pyrophosphate lessened the inhibition of oxygen evolution caused by sulfur dioxide and the sulfur anions.Sulfur dioxide and the sulfur anions were almost equally effective in inhibiting cyclic and noncyclic photophosphorylation in chloroplast suspensions. However, the extent of the inhibition of these photosynthetic reactions does not appear sufficient to account for the inhibition of photosynthetic oxygen evolution by sulfur dioxide.

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PubMed1976

Differential Oxygen Response of Photosynthesis in Soybean and Panicum milioides.

The carbon dioxide compensation concentration of Panicum milioides was less than that of soybean over the range of 15 to 35 C. In soybean (Glycine max [L.] Merr. cv. Wayne), the compensation concentration was directly proportional to O(2) concentration. In P. milioides, the compensation concentration was near zero up to 10% O(2) and then increased linearly with higher O(2), although the slope of the response was less than that in soybean. Leaf extracts of P. milioides contained 3-fold higher phosphoenolpyruvate carboxylase activity than soybean leaf extracts. Oxygen inhibition of photosynthesis and carboxy-lation efficiency was less in P. milioides than that observed in soybean. The affinity of P. millioides ribulose-1,5-di-P carboxylase for CO(2) appeared to be slightly greater than that of soybean. The affinity of both enzymes for O(2) was similar. The reduced response of the compensation concentration and photosynthesis to O(2) in P. milioides may be explained by photosynthetic phosphoenolpyruvate carboxylase fixation and by an apparent increased affinity of ribulose-1,5-di-P carboxylase for CO(2).

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PubMed1977

C(4) Pathway Photosynthesis at Low Temperature in Cold-tolerant Atriplex Species.

Two species of Atriplex were grown under low temperature (8 C day/6 C night) and high temperature (28 C day/20 C night) regimes. The photosynthetic capacity of these plants was studied as a function of temperature in a leaf gas exchange cuvette. Both species showed substantial photosynthetic capacity between 4 and 10 C and this was not enhanced by growth at low temperatures but rather, was somewhat greater in plants grown at higher temperature. Photosynthetic capacity of low temperature-grown plants at high temperature was greater in Atriplex confertifolia (Torr. and Frem.) S. Watts., a native of cool deserts, than in Atriplex vesicaria (Hew. ex. Benth.) from warmer desert areas. Leaves of both species were also subjected to (14)CO(2) pulse-chase and steady-state feeding experiments under controlled temperature conditions. These experiments revealed that the kinetics of carbon assimilation through the intermediates of the C(4) pathway is not substantially disrupted at low temperature in either species. There was, however, a substantial interchange of label between aspartate and malate at low temperature which was not evident at high temperature. There was also an increase in the pool sizes of the C(4) acids involved in photosynthesis of A. confertifolia. Speculation as to the explanation of these changes and their possible significance in promoting low temperature C(4) photosynthesis in these plants is presented.

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PubMed1977

Oxygen Concentration in Isolated Chloroplasts during Photosynthesis.

The O(2) concentration in intact and osmotically disrupted isolated spinach (Spinacia oleracea, L.) chloroplasts during photosynthesis was estimated. The chloroplasts were allowed to reduce 3-phosphoglycerate, CO(2), or ferricyanide in light until the rate of O(2) production was linear. When the light was turned off O(2) evolution from the chloroplasts continued for a few seconds. This prolonged O(2) evolution is due to an O(2) surplus inside the chloroplasts which equilibrates with that in the medium. From this surplus the O(2) concentration inside the chloroplasts at the moment when the light had been switched off was calculated. In all experiments the O(2) concentration inside the photosynthesizing chloroplasts was higher than that outside, but was dependent upon the O(2) concentration of the chloroplast medium. At low external O(2) concentration (30 mum) the ratio of the internal to the external O(2) concentration was about 5, whereas at concentrations corresponding to those in airsaturated water this ratio was close to 1. With osmotically broken chloroplasts this ratio was 1.2 at 30 mum O(2) and almost 1 from 150 mum onward. When the O(2) surplus found in broken chloroplasts during photosynthesis was related to the volume of the thylakoids, a ratio of about 2.3 was observed.

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PubMed1978

Effects of inhibitors of catalase on photosynthesis and on catalase activity in unwashed preparations of intact chloroplasts.

The catalase activity of unwashed preparations containing intact spinach (Spinacia oleracea L.) chloroplasts is inhibited both by cyanide and by azide at concentrations which also cause inhibition of photosynthetic CO(2)- dependent O(2) evolution.Aminotriazole can also be used to inhibit this contaminant catalase, and in this case inhibition of catalase can be achieved at aminotriazole concentrations which have little effect on the rate of photosynthetic CO(2) fixation. Aminotriazole may be used as a specific inhibitor of catalase in order to demonstrate inhibition of photosynthesis by added H(2)O(2).It is therefore concluded that inhibition of photosynthesis by cyanide and azide does not necessarily result from inhibition of catalase in the chloroplast preparation, and that intact chloroplasts do not produce inhibitory concentrations of H(2)O(2) under the best experimental conditions for CO(2) fixation.

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PubMed1978

Photolability of Photosynthesis in Two Separate Mutants of Scenedesmus obliquus: Preferential Inactivation of Photosystem I.

Two separate mutants of the green alga, Scenedesmus obliquus, are described in which photosynthesis is sensitive to moderate intensities of white light (100 mw cm(-2)). Heterotrophic cultures of both mutants lose photosynthetic activity when exposed to white light; the site of at least the initial phase of this inactivation is within photosystem I. Although all whole cell and cell-free reactions typical of photosystem I examined are inhibited by irradiation, the principal component of photosystem I affected is P-700. In light-sensitive-4 the inactivation of P-700 activity is restored during the subsequent dark period. This recovery is prevented by various antibiotics and by anaerobic conditions. In light-sensitive-41 P-700 activity is recovered only after a complete cell division and new growth. Irradiation periods which inhibit photosynthesis in both mutants are without effects upon the activity or presence of ferredoxin, ferredoxin-NADP(+) oxidoreductase, plastocyanin, cytochrome f(552), cytochrome b-562 or cytochrome b-559.Prolonged irradiation of cells of light-sensitive-41 causes the disappearance of photosystem II activity, alpha-tocopherol, and plastoquinone. Some decrease of both the chlorophylls and carotenoids occurs but there is no preferential deletion of any particular carotenoid.

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PubMed1979

Photosynthesis in Grass Species Differing in Carbon Dioxide Fixation Pathways: II. A Search for Species with Intermediate Gas Exchange and Anatomical Characteristics.

Thirty-three grass species were examined in two experiments in an attempt to locate plants with photosynthetic responses to O(2), CO(2) compensation concentrations, and leaf anatomy intermediate to those of C(3) and C(4) species. Species examined included seven from the Laxa group in the Panicum genus, one of which, P. milioides Nees ex Trin., has been reported earlier to have intermediate characteristics. The species with O(2)-sensitive photosynthesis typical of C(3) plants showed more than 37% increase in apparent photosynthesis at 2% O(2) compared to 21% O(2) at 25 C and 335 microliters per liter CO(2), whereas in Panicum milioides, P. schenckii Hack., and P. decipiens Nees ex Trin., members of the Laxa group of Panicum, increases ranged from 25 to 30%. The remainder of the species did not respond to O(2). Species with O(2) responses characteristic of C(3) plants exhibited CO(2) compensation concentrations of 44 microliters per liter or higher at 21% O(2) and 25 to 27.5 C and species characterized as O(2)-insensitive had values of microliters per liter or less. The CO(2) compensation concentration (capital GHE, Cyrillic) values of P. milioides, P. schenckii, and P. decipiens ranged from 10.3 to 23.3 microliters per liter. Other species of the Laxa group of Panicum exhibited O(2) response and capital GHE, Cyrillic values of either C(3) (P. laxum Sw., P. hylaeicum Mez., and P. rivulare Trin.) or C(4) (P. prionitis Griseb.) plants. Leaves of species with O(2) response and CO(2) compensation values typical of C(3) plants had poorly developed or nearly empty bundle sheath cells, and much larger distances and mesophyll cell numbers between veins than did the O(2)-insensitive ones. Vein spacings in P. milioides, P. schenckii, and P. decipiens ranged from 0.18 to 0.28 millimeter and mesophyll cell number between veins from 5.2 to 7.8. While these vein spacings are closer than those of most C(3) grasses, two O(2)-sensitive species of Dactylis had vein spacings similar to these Panicums and veins in Glyceria striata, another O(2)-sensitive plant, were separated by only four mesophyll cells and 0.12 millimeter. Bundle sheath cells of the three intermediate Panicums contained greater quantities of organelles than are typical for C(3) grasses.

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PubMed1979

Photosynthesis and ribulose 1,5-bisphosphate levels in intact chloroplasts.

The response of ribulose 1,5-bisphosphate levels and CO(2) fixation rates in isolated, intact spinach chloroplasts to pyrophosphate, triose phosphates, dl-glyceraldehyde, O(2), catalase, and irradiance during photosynthesis has been studied. Within 1 minute in the light, a rapid accumulation of ribulose bisphosphate was measured in most preparations of intact chloroplasts, and this subsequently dropped as CO(2) fixation increased. Pyrophosphate, triose phosphates, and catalase increased CO(2) fixation and also the levels of ribulose bisphosphate. CO(2) fixation was inhibited by dl-glyceraldehyde and O(2) with corresponding decreases in ribulose bisphosphate. When the rate of photosynthesis decreased at limiting irradiances (low light), the level of ribulose bisphosphate in the chloroplast did not always decrease, suggesting that ribulose bisphosphate was not limiting CO(2) fixation under these conditions. When triose phosphates (fructose bisphosphate plus aldolase) were added to suspensions of chloroplasts at low irradiances, ribulose bisphosphate increased while CO(2) fixation decreased. These observations provide considerable evidence that high ribulose bisphosphate levels clearly are not solely sufficient to permit rapid rates of CO(2) fixation, but that factors other than ribulose bisphosphate concentration are overriding the control of photosynthesis.Isolated chloroplasts are capable of using carbon reserves to produce considerable ribulose bisphosphate. Upon illumination in the absence of CO(2) and O(2), intact chloroplasts produced up to 13 millimolar ribulose bisphosphate.

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PubMed1980

The effect of glyoxylate on photosynthesis and photorespiration by isolated soybean mesophyll cells.

Incubating isolated soybean leaf mesophyll cells with glyoxylate increased the rates of CO(2) fixation by as much as 150%. In order to cause this stimulation, the glyoxylate must be presented to the cells before the NaHCO(3). Significant stimulation was observed 15 seconds after beginning the glyoxylate treatment. The glyoxylate-dependent stimulation was increased by high O(2) concentrations and decreased by high CO(2) concentrations. Glyoxylate treatment resulted in a 71% inhibition in the rate of CO(2) incorporation into glycolate and glycine. Glyoxylate may be stimulating net photosynthesis solely by decreasing photorespiration or it may be increasing the amount of CO(2) fixed by both decreasing photorespiration and increasing gross photosynthesis. Ribulose bisphosphate carboxylase, when preactivated and assayed in situ, was unaffected by the glyoxylate treatment.

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PubMed1980

Distribution of Metabolites between Chloroplast and Cytoplasm during the Induction Phase of Photosynthesis in Leaf Protoplasts.

A method for rapid separation of the chloroplast and cytoplasmic fractions from isolated leaf protoplasts of wheat and spinach has been used to determine the distribution of (14)C-labeled products during photosynthesis. In the dark, CO(2) fixation was only 1 to 2% of that in the light and the products were mainly in the cytoplasmic fraction suggesting fixation by phosphoenolpyruvate carboxylase. Label appeared rapidly in the chloroplast fraction following illumination but the amount leveled off after 4 to 5 minutes reflecting the buildup of intermediates to steady state levels. There was only a slight lag before label appeared in the cytoplasmic fraction and it continued to increase at a constant rate reflecting synthesis of neutral products. In the light, the percentage of label in the chloroplast fraction decreased rapidly in the first minute of illumination and was only 10 to 20% in the steady-state. It is suggested that the chloroplast phosphate transporter promotes a rapid transfer of sugar phosphates from the chloroplast to the cytoplasm, even during the induction phase of photosynthesis.

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PubMed1980

Effects of Boron Deficiency on Rubidium Uptake and Photosynthesis in the Diatom Cylindrotheca fusiformis.

Culturing the diatom Cylindrotheca fusiformis under boron-deficient conditions leads to changes in (86)Rb uptake and photosynthesis prior to any effect on the rate of cell division. The influx rate of (86)Rb into boron-deficient cells was 79% of the control rate after 5 to 5.5 hours culture. Despite lowered (86)Rb influx, however, boron-deficient diatoms accumulated more (86)Rb than did control cells; this was due to the deficient cells' lower efflux rate. After 24 hours culture, boron-deficient cells had accumulated 30% more (86)Rb than had control cells, while releasing (86)Rb at only one-half the control rate. Increased photosynthetic rates were another effect of boron deficiency during this early stage of culture. Prior to 20 hours boron-deficient culture, diatoms had photosynthetic rates 37% greater than those of control cells. Corresponding to the increase in photosynthesis, boron-deficient diatoms had 12% more carbohydrate than control cells after 16 hours culture.

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PubMed1981

Abscisic Acid and photosynthesis in isolated leaf mesophyll cell.

Abscisic acid (AbA) treatments of concentrations of up to 135 micromolar did not inhibit photosynthesis in enzymatically isolated leaf mesophyll cells of Phaseolus vulgaris, Nicotiana tabacum, and Lycopersicum esculentum over periods of up to 5 hours. Thin slices of leaves preincubated in hypertonic solutions identical to those used to isolate cells were shown to synthesize AbA rapidly, although accumulation of AbA in the cells was low due to extensive release of the newly synthesized AbA into the medium. The levels of endogenously made AbA in leaf cells of Phaseolus vulgaris rose from a low of 0.27 micromolar to a high of 6.74 micromolar during 2 hours preincubation. Exogenously applied AbA can be taken up by the cells as was demonstrated using (14)[C]AbA. Thus, AbA applied at concentrations 19 times higher than endogenous levels does not change the rate of photosynthesis.

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PubMed1981

Osmoregulation in Cotton in Response to Water Stress : I. ALTERATIONS IN PHOTOSYNTHESIS, LEAF CONDUCTANCE, TRANSLOCATION, AND ULTRASTRUCTURE.

Cotton plants subjected to a series of water deficits exhibited stress adaptation in the form of osmoregulation when plants were subjected to a subsequent drying cycle. After adaptation, the leaf water potential coinciding with zero turgor was considerably lower than in plants that had never experienced a water stress. The relationship between leaf turgor and leaf water potential depended on leaf age.Nonstomatal factors severely limited photosynthesis in adapted plants at high leaf water potential. Nonetheless, adapted plants maintained photosynthesis to a much lower leaf water potential than did control plants, in part because of increased stomatal conductance at low leaf water potentials. Furthermore, adapted plants continued to translocate recently derived photosynthate to lower leaf water potentials, compared with control plants.Stress preconditioning modified cellular ultrastructure. Chloroplasts of fully turgid adapted leaves contained extremely large starch granules, seemed swollen, and had some breakdown of thylakoid membrane structure. In addition, cells of adapted leaves appeared to have smaller vacuoles and greater nonosmotic cell volume than did control plants.

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