Short-term water stress leads to a stimulation of sucrose synthesis by activating sucrose-phosphate synthase

摘要: The aim of this work was to identify which aspects photosynthetic metabolism respond most sensitively leaf water deficit. Spinach (Spinacia oleracea L.) discs were floated on sorbitol concentrations increasing molarity and changes the protoplast volume estimated using [(14)C]sorbitol (3)H2O penetration. Detached leaves also wilted until 10% their fresh weight lost. Photosynthesis studied at very high external CO2 concentrations, eliminate effect closing stomata. There no large inhibition fixation after wilting leaves, or deficit greater than-1.2 MPa. However, partitioning changed markedly these moderate deficits: more sucrose less starch made. When an CO2-saturated photosynthesis did appear a of-2.0 MPa above, measurements chlorophyll-fluorescence quenching metabolite levels showed thylakoid reactions not especially susceptible short-term stress. accompanied by small increase triose phosphate: ribulose-1,5-bisphosphate ratio, showing regeneration affected. there general metabolites, indicating that is specific site for photosynthesis. Increasing led fructose-2,6-bisphosphate. This explained in terms simultaneous fructose-6-phosphate inorganic phosphate as cell shrinks. fructose-2,6-bisphosphate accumulation phosphates, potential significance protection against photoinhibition discussed. extractable activity sucrose-phosphate synthase. only detected when enzyme assayed conditions distinguish between different kinetic forms have previously been identified spinach leaves. It proposed activation synthase one first sites rising could be importance osmoregulation.