Ritte G, Rosenfeld J, Rohrig K, Raschke K
Albrecht-von-Haller-Institut fur Pflanzenwissenschaften, Universitat Gottingen, Untere Karspule 2, 37073 Gottingen, Germany.
Plant Physiol. 1999 Oct;121(2):647-56. doi: 10.1104/pp.121.2.647.
We wished to determine whether the capacity of the sugar uptake mechanisms of guard cells of the Argenteum mutant of pea (Pisum sativum L.) sufficed to support a concurrent stomatal opening movement. Sugar uptake by guard cell protoplasts was determined by silicone-oil-filtering centrifugation. The protoplasts took up [(14)C]glucose, [(14)C]fructose, and [(14)C]sucrose (Suc), apparently in symport with protons. Mannose, galactose, and fructose competed with Glc for transport by a presumed hexose carrier. The uptake of Glc saturated with a K(m) of 0.12 mM and a V(max) of 19 fmol cell(-1) h(-1). At external concentrations <1 mM, the uptake of Suc was slower than that of Glc. It exhibited a saturating component with a K(m) varying between 0.25 and 0.8 mM and a V(max) between 1 and 10 fmol cell(-1) h(-1), and at external concentrations >1 mM, a non-saturating component. At apoplastic sugar concentrations below 4 mM, sugar import was estimated to be mainly in the form of hexoses and too slow to support a simultaneous stomatal opening movement. If, however, during times of high photosynthesis and transpiration, the apoplastic Suc concentration rose and entered the range of non-saturating import, absorbed Suc could replace potassium malate as the osmoticum for the maintenance of stomatal opening.
我们希望确定豌豆（Pisum sativum L.）银叶突变体保卫细胞的糖分吸收机制能力是否足以支持同时发生的气孔开放运动。通过硅油过滤离心法测定保卫细胞原生质体对糖分的吸收。原生质体吸收[（14）C]葡萄糖、[（14）C]果糖和[（14）C]蔗糖（Suc），显然是与质子协同运输。甘露糖、半乳糖和果糖与葡萄糖竞争通过一种假定的己糖载体进行运输。葡萄糖的吸收在K（m）为0.12 mM和V（max）为19 fmol细胞（-1）h（-1）时达到饱和。在外部浓度<1 mM时，蔗糖的吸收比葡萄糖慢。它表现出一个饱和成分，K（m）在0.25至0.8 mM之间变化，V（max）在1至10 fmol细胞（-1）h（-1）之间，并且在外部浓度>1 mM时，表现出一个非饱和成分。在质外体糖分浓度低于4 mM时，糖分输入估计主要以己糖形式存在，且速度太慢，无法支持同时发生的气孔开放运动。然而，如果在光合作用和蒸腾作用强烈的时期，质外体蔗糖浓度升高并进入非饱和输入范围，吸收的蔗糖可以替代苹果酸钾作为维持气孔开放的渗透剂。
