Botanisches Institut der Universität München, Menzinger Straße 67, D-8000, München 19, Federal Republic of Germany.
Planta. 1977 Jan;134(1):77-81. doi: 10.1007/BF00390098.
Epidermal strips with closed stomata were exposed to malic acid labelled with (14)C either uniformly or in 4-C only. During incubation with [U-(14)C]malate, radioactivity appeared in products of the tricarboxylic-acid cycle and in transamination products within 10 min, in sugars after 2 h. Hardly any radioactivity was found in sugars if [4-(14)C]malate had been offered. This difference in the degree of labelling of sugars indicates that gluconeogenesis can occur in epidermal tissue, involving the decarboxylation of malate. Epidermis incubated with labelled malate was hydrolyzed after extraction with aqueous ethanol. The hydrolysate contained glucose as the only radioactive product, indicating that starch had been formed from malate. Microautoradiograms were black above stomatal complexes, showing that the latter were sites of starch formation. In order to follow the fate of malate during stomatal closure, malate was labelled in guard cells by exposing epidermes with open stomata to (14)CO2 and then initiating stomatal closure. Of the radioactive fixation products of CO2 only malate was released into the water on which the epidermal samples floated; the epidermal strips retained some of the malate and all of its metabolites. In the case of rapid stomatal closure initiated by abscisic acid and completed within 5 min, 63% of the radioactivity was in the malate released, 22% in the malate retained, the remainder in aspartate, glutamate, and citrate. We conclude that during stomatal closing guard cells can dispose of malate by release, gluconeogenesis, and consumption in the tricarboxylic-acid cycle.
将具有闭合气孔的表皮条暴露于用 [(14)C]标记的苹果酸，无论是均匀标记还是仅在 4-C 处标记。在 [(U-(14)C)]苹果酸盐孵育期间，放射性出现在三羧酸循环的产物和转氨基产物中，在 2 小时后出现在糖中。如果提供了 [(4-(14)C)]苹果酸，则几乎没有放射性出现在糖中。糖的标记程度的这种差异表明，糖异生可以在表皮组织中发生，涉及苹果酸的脱羧。用标记的苹果酸孵育的表皮在用含水乙醇提取后进行水解。水解产物仅含有葡萄糖作为放射性产物，表明淀粉是由苹果酸形成的。微放射性自显影在气孔复合体上方为黑色，表明后者是淀粉形成的部位。为了在气孔关闭过程中跟踪苹果酸的命运，通过将具有开放气孔的表皮暴露于 [(14)CO2]并随后启动气孔关闭，在保卫细胞中标记苹果酸。在 CO2 的放射性固定产物中，只有苹果酸被释放到表皮样品漂浮的水中；表皮条保留了一些苹果酸及其所有代谢物。在由脱落酸引发的快速气孔关闭的情况下，在 5 分钟内完成，释放的苹果酸中的 63%、保留的苹果酸中的 22%、剩余的苹果酸中的天冬氨酸、谷氨酸和柠檬酸中的剩余的 63%、保留的苹果酸中的 22%。我们得出结论，在气孔关闭期间，保卫细胞可以通过释放、糖异生和三羧酸循环中的消耗来处理苹果酸。
