Control of photosynthetic sucrose synthesis by fructose-2,6-bisphosphate
Control of photosynthetic sucrose synthesis by fructose-2,6-bisphosphate
复制标题
2,6-二磷酸果糖控制光合蔗糖合成
作者：
M. Stitt;H. Heldt
玉米叶肉组织中代谢物的含量。已经与来自叶肉的胞质果糖-1，6-二磷酸酶的调节特性进行了比较，以显示用于蔗糖合成的磷酸丙糖的提取如何与允许光合作用期间碳的细胞间扩散所需的高浓度磷酸丙糖的产生相协调。i）提出了一种用于测量玉米中代谢物的细胞间分布的新技术。在液氮下，通过差速均质化和尼龙网过滤，将叶鞘和叶肉组织部分分离。ii）在叶肉和维管束鞘之间存在3-磷酸甘油酸、磷酸丙糖、苹果酸和磷酸烯醇丙酮酸的相当大的梯度，这将允许细胞间穿梭由扩散驱动。这些梯度可能是由玉米叶片电子传递的分布和卡尔文循环所引起的。iii）因此，叶肉含有高浓度的磷酸丙糖和1，6-二磷酸果糖。iv）大多数调节代谢物果糖-2，6-二磷酸存在于叶肉中。v）细胞溶质果糖-1，6-二磷酸酶具有比来自C3物种的酶所发现的更低的底物亲和力，特别是在存在抑制剂如果糖-2，6-二磷酸的情况下。vi）对底物的这种降低的亲和力使得可以将磷酸丙糖用于蔗糖合成与维持该物种中光合作用操作所需的叶肉中的磷酸丙糖的高浓度相协调。
The metabolite levels in the mesophyll of leaves of Zea mays L. have been compared with the regulatory properties of the cytosolic fructose-1,6-bisphosphatase from the mesophyll to show how withdrawal of triose phosphate for sucrose synthesis is reconciled with generation of the high concentrations of triose phosphate which are needed to allow intercellular diffusion of carbon during photosynthesis. i) A new technique is presented for measuring the intercellular distribution of metabolites in maize. The bundle-sheath and mesophyll tissues are partially separated by differential homogenization and filtration through nylon nets under liquid nitrogen. ii) considerable gradients of 3-phosphoglycerate, triose phosphate, malate and phosphoenolpyruvate exist between the mesophyll and bundle sheath which would allow intercellular shuttles to be driven by diffusion. These gradients could result from the distribution of electron transport and the Calvin cycle in maize leaves. iii) consequently, the mesophyll contains high concentrations of triose phosphate and fructose-1,6-bisphosphate. iv) Most of the regulator metabolite fructose-2,6-bisphosphate, is present in the mesophyll. v) The cytosolic fructose-1,6-bisphosphatase has a lower substrate affinity than that found for the enzyme from C3 species, especially in the presence of inhibitors like fructose-2,6-bisphosphate. vi) This lowered affinity for substrate makes it possible to reconcile use of triose phosphate for sucrose synthesis with the maintenance of the high concentration of triose phosphate in the mesophyll needed for operation of photosynthesis in this species.