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  • 1
    ISSN: 1432-2048
    Keywords: Carbon dioxide assimilation ; Light and carbon assimilation ; Spinacia (photosynthesis) ; Sucrose synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When leaves of Spinacia oleracea L. were subjected to a decrease from a saturating to a limiting irradiance, photosynthetic carbon assimilation exhibited a pronounced lag. This comprised a postlower-illumination CO2 burst (Vines et al. 1982, Plant Physiol. 70, 629–631) and a slow increase in the rate of carbon assimilation to the new lower steady-state rate. The latter phenomenon was distinguishable from the former because it was present in leaves when photorespiration was inhibited by high concentrations of CO2 or by 2% O2. A lag which followed a decrease in irradiance was also evident in leaves of Zea mays in air or in isolated spinach protoplasts photosynthesising in high CO2. The lag was not stomatal in origin. The origin of the lag which followed the decrease in irradiance was investigated. Measurements of total 14CO2 fixation and 14C incorporated into sucrose during the transition in irradiance showed that sucrose synthesis displayed an overshoot during the transient which accounted for all of the carbon fixed during the first 90 s of the transition period. The behaviour of hexose phosphates in the intact leaf and in the cytosol was inconsistent with their supporting sucrose synthesis during the transient. It is concluded that the overshoot in sucrose synthesis imposes a drain on chloroplast intermediates which contributes to the temporary lag in the rate of carbon assimilation.
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  • 2
    ISSN: 1432-2048
    Keywords: Benson-Calvin cycle ; Phosphate and photosynthesis ; Photosynthesis ; Photorespiration ; Spinacia (photosynthesis)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of phosphate feeding on the influence of low (2%) oxygen on photosynthetic carbon assimilation has been investigated in leaf discs of spinach (Spinacia oleracea L.) at 12°C. The following observations were made. First, after the transition from 20% O2 to 2% O2, the rate of CO2 uptake was inhibited at CO2 concentrations between about 250 and about 800 μl CO2·l-1. Second, phosphate feeding stimulated the rate of CO2 uptake in 20% O2 at higher concentrations of CO2 (500–900 μl·l-1). Third, phosphate feeding stimulated the rate of CO2 uptake in 2% O2 at all but the highest (900 μl·l-1) and lowest 74 (μl·l-1) concentrations of CO2 employed. Phosphate thereby restored the stimulation of photosynthesis by 2% O2 and it did so over a wide range of lower temperatures. Fourth, oscillatory behaviour, however generated, was dampened by phosphate feeding, even at very low concentrations of CO2. Contents of leaf metabolites were measured during the transition to 2% O2 in control and phosphate-fed leaf discs. During this period the ratio glycerate-3-phosphate/triose phosphate rose steeply, but fell again only in the phosphate-treated leaf discs. These data, taken together with measured ATP/ADP ratios, showed that assimilatory power, the ratio [ATP]·[NAD(P)H]/[ADP]·[Pi]·[NAD(P)], decreased when leaves were exposed to 2% O2, but that this decrease was minimised by previous feeding of phosphate. The mechanism of phosphate limitation is discussed in the light of the results.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Planta 140 (1978), S. 275-282 
    ISSN: 1432-2048
    Keywords: Cotyledons ; CO2 dark fixation ; Cucurbita ; Gluconeogenesis ; RUDP carboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We did this work to discover the pathway of CO2 fixation into sugars in the dark during gluconeogenesis by the cotyledons of 5-day-old seedlings of Cucurbita pepo L. We paid particular attention to the possibility of a contribution from ribulosebisphosphate carboxylase. The detailed distribution of 14C after exposure of excised cotyledons to 14CO2 in the dark was determined in a series of pulse and chase experiments. After 4s in 14CO2, 89% of the 14C fixed was in malate and aspartate. In longer exposures, and in chases in 12CO2, label appeared in alanine, phosphoenolpyruvate, 3-phosphoglycerate and sugar phosphates, and accumulated in sugars. The transfer of label from C-4 acids to sugars was restricted by inhibition of phosphoenolpyruvate carboxykinase in vivo by 3-mercaptopicolinic acid. We conclude as follows. Initial fixation of CO2 in the dark is almost entirely into phosphoenolpyruvate, probably via phosphoenolpyruvate carboxylase (EC 4.1.1.31) which we showed to be present in appreciable amounts. Incorporation into sugars occurs chiefly, if not completely, as a result of randomization of the carboxyl groups of the C-4 acids and subsequent conversion of the oxaloacetate to sugars via the accepted sequence for gluconeogenesis. Ribulosebisphosphate carboxylase appears to make very little contribution to sugar synthesis from fat.
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  • 4
    ISSN: 1432-2048
    Keywords: Nicotiana (photosynthesis) ; Nitrogen ; Photosynthesis (control analysis) ; Ribulose-1,5-bisphosphate carboxylase-oxygenase ; Transgenic plant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of nitrogen supply during growth on the contribution of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) to the control of photosynthesis was examined in tobacco (Nicotiana tabacum L.). Transgenic plants transformed with antisense rbcS to produce a series of plants with a progressive decrease in the amount of Rubisco were used to allow the calculation of the flux-control coefficient of Rubisco for photosynthesis (CR). Several points emerged from the data: (i) The strength of Rubisco control of photosynthesis, as measured by CR, was altered by changes in the short-term environmental conditions. Generally, CR was increased in conditions of increased irradiance or decreased CO2. (ii) The amount of Rubisco in wild-type plants was reduced as the nitrogen supply during growth was reduced and this was associated with an increase in CR. This implied that there was a specific reduction in the amount of Rubisco compared with other components of the photosynthetic machinery. (iii) Plants grown with low nitrogen and which had genetically reduced levels of Rubisco had a higher chlorophyll content and a lower chlorophyll a/b ratio than wild-type plants. This indicated that the nitrogen made available by genetically reducing the amount of Rubisco had been re-allocated to other cellular components including light-harvesting and electron-transport proteins. It is argued that there is a “luxury” additional investment of nitrogen into Rubisco in tobacco plants grown in high nitrogen, and that Rubisco can also be considered a nitrogen-store, all be it one where the opportunity cost of the nitrogen storage is higher than in a non-functional storage protein (i.e. it allows for a slightly higher water-use efficiency and for photosynthesis to respond to temporarily high irradiance).
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  • 5
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  • 7
    Publication Date: 1981-02-01
    Print ISSN: 0140-7791
    Electronic ISSN: 1365-3040
    Topics: Biology
    Published by Wiley
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  • 8
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 
 C i, intercellular CO2 concentration
Fv/Fm, quantum efficiency of excitation capture by open photosystem II centres
FBPase, fructose-1,6-bisphosphatase
GAPDH, glyceraldehyde-3-phosphate dehydrogenase
GDC, glycine decarboxylase
GS-2, chloroplastic glutamine synthetase
HPR, hydroxypyruvate reductase
PFD, photon flux density
ΦCO2, quantum efficiency of CO2 assimilation
ΦPSII, quantum efficiency of photosystem II electron transport
ψ, water potential
qN, non-photochemical chlorophyll a fluorescence quenching
qP, photochemical chlorophyll a fluorescence quenching
RuBP, ribulose-1,5-bisphosphate
Rubisco, ribulose-1,5-bisphosphate carboxylase-oxygenase
SBPase, sedoheptulose-1,7-bisphosphatase
SGAT, serine : glyoxylate aminotransferase

The significance of photorespiration in drought-stressed plants was studied by withholding water from wild-type barley (Hordeum vulgare L.) and from heterozygous mutants with reduced activities of chloroplastic glutamine synthetase (GS-2), glycine decarboxylase (GDC) or serine : glyoxylate aminotransferase (SGAT). Well-watered plants of all four genotypes had identical rates of photosynthesis. Under moderate drought stress (leaf water potentials between –1 and –2 MPa), photosynthesis was lower in the mutants than in the wild type, indicating that photorespiration was increased under these conditions. Analysis of chlorophyll a fluorescence revealed that, in the GDC and SGAT mutants, the lower rates of photosynthesis coincided with a decreased quantum efficiency of photosystem II and increased non-photochemical dissipation of excitation energy. Correspondingly, the de-epoxidation state of xanthophyll-cycle carotenoids was increased several-fold in the drought-stressed GDC and SGAT mutants compared with the wild type. Accumulation of glycine in the GDC mutant was further evidence for increased photorespiration in drought-stressed barley. The effect of drought on the photorespiratory enzymes was determined by immunological detection of protein abundance. While the contents of GS-2 and P- and H-protein of the GDC complex remained unchanged as drought stress developed, the content of NADH-dependent hydroxypyruvate reductase increased. Enzymes of the Benson–Calvin cycle, on the other hand, were either not affected (ribulose-1,5-bisphosphate carboxylase-oxygenase and plastidic fructose-1,6-bisphosphatase) or declined (sedoheptulose- 1,7-bisphosphatase and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase). These data demonstrate that photorespiration was enhanced during drought stress in barley and that the control exerted by photorespiratory enzymes on the rate of photosynthetic electron transport and CO2 fixation was increased.
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  • 9
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Unlike wheat chloroplasts, wheat protoplasts showed a pronounced restoration of the induction phase after a short period of darkness. This difference was used to investigate the relative roles of light-induced reductive activation of enzymes and the auto-catalytic increase in the level of substrates in the control of the rate of photosynthesis during induction. Light activation and dark inactivation of ribulose 5-phosphate kinase, fructose 1,6-biphosphatase and NADP+-specific glyceraldehydephosphate dehydrogenase were measured. In this respect there was no appreciable difference between protoplasts and chloroplasts. In contrast, the level of photosynthetic intermediates remained constant in darkened isolated chloroplasts, but declined rapidly in chloroplasts isolated from darkened protoplasts. When fructose 1,6-bisphosphatase was pre-activated by treating protoplasts with dithiothreitol the lag was only slightly shortened. These results are discussed in terms of control of the rate of the photosynthesis during the lag by substrates rather than limitation imposed by activity of any of the enzymes measured.
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  • 10
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The effect of gradually-developing water-stress has been studied in Lupinus albus L., Helianthus annuus L., Vitis vinifera cv. Rosaki and Eucalyptus globulus Labill. Water was withheld and diurnal rhythms were investigated 4–8d later, when the predawn water deficit was more negative than in watered plants, and the stomata closed almost completely early during the photoperiod. The contribution of ‘stomatal’ and ‘non-stomatal’ components to the decrease of photosynthetic rate was investigated by (1) comparing the changes of the rate of photosynthesis in air with the changes of stomatal conductance and (2) measuring photosynthetic capacity in saturating irradiance and 15% CO2. Three species (lupin, eucalyptus and sunflower) showed larger changes of stomatal conductance than photosynthesis in air, and showed little or no decrease of photosynthetic capacity in saturating CO2. Photosynthesis in air also recovered fully overnight after watering the plants in the evening. In grapevines, stomatal conductance and photosynthesis in air changed in parallel, there was a marked decrease of photosynthetic capacity, and photosynthesis and stomatal conductance did not recover overnight after watering water-stressed plants. Relative water content remained above 90% in grapevine. We conclude that non-stomatal components do not play a significant role in lupins, sunflower or eucalyptus, but could in grapevine. The effect of water-stress on partitioning of photosynthate was investigated by measuring the amounts of sucrose and starch in leaves during a diurnal rhythm, and by measuring the partitioning of 14C-carbon dioxide between sucrose and starch. In all four species, starch was depleted in water-stressed leaves but sucrose was maintained at amounts similar to, or higher than, those in watered plants. Partitioning into sucrose was increased in lupins and eucalyptus, and remained unchanged in grapevine and sunflower. It is concluded that water-stressed leaves in all four species maintain high levels of soluble sugars in their leaves, despite having lower rates of field photosynthesis, decreased rates of export, and low amounts of starch in their leaves.
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