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Long- and short-term response of leaf carbohydrate levels and photosynthesis to decreased sink demand in soybean
- Morcuende, R., Perez, P., Martinez-Carrasco, R., Martin del Molino, I., Sanchez de la Puente, L.
- Plant, cell and environment 1996 v.19 no.8 pp. 976-982
- source-sink relationships, ribulose-bisphosphate carboxylase, carbon dioxide, Glycine max, buds, sugar phosphates, photosynthates, cutting, leaf conductance, chemical constituents of plants, enzyme activity, chlorophyll, cold, shoots
- 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 degrees C. Also, in intact and trimmed shoots, the CO2 level was increased to 660 micromole mol-1 and temperature was lowered to 5 degrees 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 (GOP) 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-1,5-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 micromole mol-1 CO2; growth temperature or a short-term change to 5 degrees 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.