Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, Universitätsstrasse 30, W-8580, Bayreuth, Germany.
Planta. 1991 Dec;183(1):40-50. doi: 10.1007/BF00197565.
Leaves on transgenic tobacco plants expressing yeast-derived invertase in the apoplast develop clearly demarcated green and bleached sectors when they mature. The green areas contain low levels of soluble sugars and starch which are turned over on a daily basis, and have high rates of photosynthesis and low rates of respiration. The pale areas accumulate carbohydrate, photosynthesis is inhibited, and respiration increases. This provides a model system to investigate the "sink" regulation of photosynthetic metabolism by accumulating carbohydrate. The inhibition of photosynthesis is accompanied by a decrease of ribulose-1,5-bisphosphate and glycerate-3-phosphate, and an increase of triosephosphate and fructose-1,6-bisphosphate. The extracted activities of ribulose-1,5-bisphosphate carboxylase, fructose-1, 6-bisphosphatase and NADP-glyeraldehyde-3-phosphate dehydrogenase decreased. The activity of sucrose-phosphate synthase remained high or increased, an increased portion of the photosynthate was partitioned into soluble sugars rather than starch, and the pale areas showed few or no oscillations during transitions between darkness and saturating light in saturating CO2. The increased rate of respiration was accompanied by an increased level of hexose-phosphates, triose-phosphates and fructose-1,6-bisphosphate while glycerate-3-phosphate and phosphoenolpyruvate decreased and pyruvate increased. The activities of pyruvate kinase, phosphofructokinase and pyrophosphate: fructose-6-phosphate phosphotransferase increased two- to four-fold. We conclude that an increased level of carbohydrate leads to a decreased level of Calvin-cycle enzymes and, thence, to an inhibition of photosynthesis. It also leads to an increased level of glycolytic enzymes and, thence, to a stimulation of respiration. These changes of enzymes are more important in middle- or long-term adjustments to high carbohydrate levels in the leaf than fine regulation due to depletion of inorganic phosphate or high levels of phosphorylated metabolites.
在质外体中表达酵母衍生的转化酶的转基因烟草植株的叶片在成熟时会明显出现绿色和白化区域的清晰划分。绿色区域含有低水平的可溶性糖和淀粉，这些物质每天都在周转，光合作用率高，呼吸作用率低。苍白区域积累碳水化合物，光合作用受到抑制，呼吸作用增加。这为研究通过积累碳水化合物对光合作用代谢的“汇”调节提供了一个模型系统。光合作用的抑制伴随着核酮糖-1,5-二磷酸和甘油酸-3-磷酸的减少，以及三磷酸和果糖-1,6-二磷酸的增加。提取的核酮糖-1,5-二磷酸羧化酶、果糖-1,6-二磷酸酶和 NADP-甘油醛-3-磷酸脱氢酶的活性降低。蔗糖磷酸合酶的活性保持较高或增加，一部分光合产物被分配到可溶性糖中而不是淀粉中，在饱和 CO2 下从黑暗到饱和光的转变过程中，苍白区域几乎没有或没有振荡。呼吸作用的增加伴随着己糖磷酸、三磷酸和果糖-1,6-二磷酸水平的增加，而甘油酸-3-磷酸和磷酸烯醇丙酮酸减少，丙酮酸增加。丙酮酸激酶、磷酸果糖激酶和焦磷酸：果糖-6-磷酸磷酸转移酶的活性增加了两到四倍。我们得出结论，碳水化合物水平的增加导致卡尔文循环酶水平降低，从而抑制光合作用。它还导致糖酵解酶水平增加，从而刺激呼吸作用。这些酶的变化在叶片中高碳水化合物水平的中长期调节中比由于无机磷耗尽或磷酸化代谢物水平高而导致的精细调节更为重要。
