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  • 1
    Electronic Resource
    Electronic Resource
    Long- and short-term responses of leaf carbohydrate levels and photosynthesis to decreased sink demand in soybean (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Axillary buds and the apical portion of shoots of soybean [Glycine max (L.) Merr. cultivar Turchina] plants were trimmed to investigate long-term regulation of photosynthesis by sink demand at ambient CO2 and 22 °C. Also, in intact and trimmed shoots, the CO2 level was increased to 660 μmol mol−1 and temperature was lowered to 5°C to examine the superimposed short-term responses of photosynthesis to low sink demand. Under growth conditions, trimming the shoots increased leaf photosynthesis and the levels of sucrose, glucose-6-phosphate (G6P) and 3-phosphoglycerate (PGA), as well as the G6P/fructose-6-phosphate (F6P) and sucrose/starch ratios, while it decreased the level of starch and the triose-phosphate (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, TP)/PGA ratio. Photosynthesis enhancement was accompanied by increased chlorophyll contents and ribulose-l,5-bisphosphate carboxylase oxygenase (Rubisco) activity. Sink removal consistently increased photosynthesis measured under a variety of conditions (growth CO2 or a short-term change to 660 μmol mol-1 CO2; growth temperature or a short-term change to 5 °C), except when low temperature was combined with ambient CO2; the increase in photosynthesis was higher under short-term elevated CO2 than at ambient CO2. In contrast with its effect at ambient CO2, shoot trimming increased the levels of TP and ribulose-1,5-bisphosphate (RuBP) and the TP/PGA ratio under high-CO2 conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00462.x
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  • 2
    Electronic Resource
    Electronic Resource
    Long- and short-term effects of decreased sink demand on carbohydrate levels and photosynthesis in wheat leaves (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Wheat (Triticum aestivum L.) ears were removed to investigate long-term regulation of photosynthesis by sink demand at ambient CO2 and 22 °C. The CO2 level was also increased to 660 μmol mol−1 and temperature was lowered to 5 °C to examine short-term responses of photosynthesis to low sink demand. Sink removal inhibited photosynthesis and increased leaf levels of glucose, fructose and ribulose-1, 5-bisphosphate (RuBP), and the glucose-6-phosphate (G6P)/fructose-6-phosphate (F6P) and RuBP/3-phosphoglycerate (PGA) ratios under growth conditions, but had no effect on the activity and activation state of ribulose-1, 5-bisphosphate carboxylase oxygenase (Rubisco) either under growth or short-term conditions, suggesting an inhibition of photosynthesis by decreased in vivo catalysis of Rubisco. Photosynthesis increased similarly in eared and earless shoots after a rise in CO2 concentration, and the ratio of triose-phosphates (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, TP) to PGA was similar or higher for removed than intact ears, suggesting that feedback inhibition of photosynthesis was not caused by a limitation of ATP synthesis in chloroplasts. Under short-term conditions (660 μmol mol−1 CO2, 5 °C), TP and RuBP levels and the TP/PGA and TP/RuBP ratios were increased by sink removal, indicating an additional limitation of photosynthesis by the rate of RuBP regeneration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00436.x
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  • 3
    Electronic Resource
    Electronic Resource
    Regulation of nitrate reductase expression in leaves by nitrate and nitrogen metabolism is completely overridden when sugars fall below a critical level (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: These experiments use Nia30(145), a tobacco nia1nia2 double null mutant transformed with a NIA2 construct, to define when sugar supply plays the dominating role in the regulation of nitrate reductase (NIA) expression. The null alleles of Nia30(145) are transcribed and translated to produce non-functional NIA transcript and NIA protein, providing an endogenous reporter system to track NIA expression at the transcript and protein level. The re-introduced NIA2 construct is expressed at low efficiency, providing a background in which the response to changes in sugar status is not complicated by simultaneous changes in the rate of nitrate assimilation and the levels of nitrate and glutamine. In an alternating light–dark regime, Nia30(145) contained high levels of nitrate and low levels of glutamine and other amino acids. This drives constitutive overexpression of NIA. After transfer of Nia30(145) to continuous darkness, nitrate remains high and glutamine low, but the NIA transcript level and NIA protein decreased significantly within 24 h and were undetectable from 48 h onwards. The decrease of the NIA transcript level was fully reversed and the decrease of NIA protein was partly reversed when leaves were detached from the pre-darkened plants and supplied with sucrose in the dark. The decrease was not reversed by nitrate or cytokinin. The NIA transcript disappeared when the leaf sugar content fell below 4 μmol hexose equivalents g−1 FW, and recovered when sugars rose above 8 μmol hexose equivalents g−1 FW. It is concluded that low sugar represses NIA, completely overriding signals derived from nitrate and nitrogen metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00593.x
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of nitrogen supply and sink strength on changes in leaf nitrogen compounds during senescence in two wheat cultivars (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 95 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Changes in various nitrogen compounds during senescence of the fourth leaf were studied in two cultivars of spring wheat (Triticum aestivum L.). One of the cultivars (Yecora) was supplied with two N levels; the other (Tauro) was grown with the high N level and pruned above the fourth leaf, whereas the control was left intact. In both cultivars grown with high N supply, net nitrogen export from the fourth leaf did not occur until 35 days after sowing (DAS). Loss of leaf soluble proteins started earlier than that of chlorophylis, and coincided initially with an increase in insoluble protein. In N deficient plants the level of total N, soluble protein, and the activity of nitrate reductase (NRA. EC 1.6.6.1) started to decrease about 5 days earlier, and along with chlorophyll, continued to decrease at a faster rate, than in high N plants. Also, with low N supply, the large subunit (LSU, 58 kDa) of ribulose-1.5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) decreased in greater proportion than other soluble proteins, while with high N supply the decrease in Rubisco LSU was similar to that of other soluble proteins. Nitrogen deficiency caused a greater decrease in soluble proteins than in insoluble proteins, and NRA relative to soluble proteins. The faster senescing Tauro cultivar had lower levels of most parameters, especially NRA, soluble protein and, after 35 DAS. Rubisco LSU as a proportion of soluble protein. The decrease in sink strength due to shoot pruning did generally not affect the level of the various nitrogenous compounds until 35 DAS; thereafter the levels of most parameters, especially soluble protein, Rubisco LSU and, at late stages of senescence, insoluble protein, were higher in pruned than in control shoots. Thus, shoot pruning slows down senescence. The 56- and 78-kDa polypeptides increased, rather than decreased, with leaf age; the level of these two polypeptides showed a negative relationship with Rubisco LSU (r = -0.933 and r = -0.758, respectively).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00807.x
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 89 (1993), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Photosynthesis and carbohydrate content of flag leaves were measured during the post-anthesis period of three spring wheat (Triticum aestivum L.) varieties grown with two levels of nitrogen supply, with ears either left intact or with the upper halves removed at anthesis. With low nitrogen supply, removing the upper half of the ear increased photosynthesis in the varieties Shasta and Anza, but not in Yecora. With high nitrogen, removing half ears inhibited photosynthesis in Yecora but had no effect on the other two varieties. Early in grain growth, halving ears decreased the contents of glucose, fructose (hexose), fructans and starch in leaves of Shasta and Anza, and increased those of Yecora, grown with low nitrogen level. The treatment of the ear increased hexose content of leaves of the three varieties supplied with high nitrogen level but had no effect on fructan and starch contents. Neither with high nor with low nitrogen level was leaf sucrose content affected by the treatment of the ear. There were significant correlations among levels of carbohydrates, the level of hexoses being most closely related to that of fructans. The rate of photosynthesis showed a significant negative regression over hexose levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb05198.x
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  • 6
    Electronic Resource
    Electronic Resource
    Short-term feedback inhibition of photosynthesis in wheat leaves supplied with sucrose and glycerol at two temperatures (1997)
    Springer
    Photosynthetica 33 (1997), S. 179-188 
    Details
    ISSN: 1573-9058
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The inhibition of photosynthesis by reduced sink demand or low rates of end product synthesis was investigated by supplying detached wheat (Triticum aestivum L. cv. Tauro) leaves with 50 mM sucrose, 50 mM glycerol or water through the transpiration stream for 2 h, either at 23 or 12 °C. Lowering the temperature and sucrose and glycerol feeding decreased photosynthetic oxygen evolution at high irradiance and saturating CO2. The decrease in temperature reduced the pools of sucrose and starch, and the ratio glucose 6-phosphate (G6P)/fructose 6-phosphate (F6P), while it increased the concentrations of G6P and F6P (hexose phosphates). Sucrose feeding, in contrast to glycerol feeding, increased sucrose, glucose and fructose contents and the G6P/F6P ratio. Sucrose and glycerol incubations at 23 °C, as well as decreasing the temperature in leaves incubated in water, increased the concentration of triose-phosphates (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, TP) and decreased the glycerate 3-phosphate (PGA) content, thus increasing the TP/PGA ratio; they also tended to increase the ribulose 1,5-bisphosphate (RuBP) content and the RuBP/PGA ratio. Sucrose and glycerol feeding at 12 °C and the decrease in temperature of leaves incubated in these solutions decreased TP and RuBP contents and the TP/PGA and RuBP/PGA ratios. The results suggest that the phosphate limitation caused by accumulation of end products, restriction of their synthesis and sequestration of cytosolic phosphate can inhibit photosynthesis through decreased carboxylation of RuBP or, with increased phosphate limitation, through lowered supply of ATP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022199927264
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