Abstract: Investigations were carried out on the role of ABA in the regulation of photosynthetic characteristics, sugar metabolism in rice leaves and grain filling processes in water-stressed rice plants (O. sativa cv. Shanyou 63). Half-dried treatment had little influence on leaf water potential and relative water content but endogenous ABA content of leaves and grains significantly increased. Following drought treatment, leaf water potential and relative water content declined substantially and again bulk leaf ABA and grain ABA concentrations increased markedly. Photosynthesis rate and Rubisco (RuBPcarboxylase /oxyge nase) activity of leaves were reduced significantly by half-dried and drought treatment. The accumulation and metabolism of sucrose and starch in leaves had a close relation to the endogenous ABA level, lower ABA concentration and high leaf water potential and relative water content were parallel to the enhanced accumulation of sucrose and increased sucrose phosphate synthase activity, but as the ABA concentration increased. the accumulation of sucrose and the activity of sucrose phosphate synthase were inhibited even in high leaf water potential. Higher leaf ABA concentration and lower leaf water potential had little influence on the activities of α- and β-amylases. The inhibition of grain growth by ABA was at least in part, related to its inhibition on sucrose synthase which was a key enzyme in catalyzing sucrose metabolism and starch accumulation in rice grains. In addition, the inhibitions of photosynthetic rate and accumulation of sucrose and starch by drought treatment were much more significant than those by halfdried treatment, indicating that drought had a direct effect on these processes. It was suggested that ABA plays important regulating roles in photosynthesis, sugar metabolism and grain development of water-stressed rice plants. The possible mechanism of ABA on these physiological processes were also discussed.

Key words: abscisic acid, grain filling, photosynthetic characteristics, split-root system

摘要： 利用水平分根系统研究了水稻抽穗后水分胁迫条件下ABA对水稻品种汕优63叶片光合特性、糖代谢和籽粒灌浆过程的调节。当一半根系受干旱胁迫时，叶片的水势和相对含量变化很小，但叶片和籽粒内ABA的含量显著增加。整个根系受干旱胁迫时，叶片的水势和相对含水量随着胁迫的增加而显著地降低，ABA含量则显著增加。半干和全干处理的水稻叶片的光合速率和RuBP羧化酶／氧化酶（Rubisco）的活性显著下降。叶片内蔗糖和淀粉的积累和代谢与叶片内ABA的含量和水分状况存在密切的关系，低浓度的ABA和高的叶水势与高的蔗糖积累和蔗糖磷酸合成酶活性相一致，但当叶片ABA的浓度增加时，即使叶片的水势与对照相似，叶片的蔗糖和淀粉积累以及蔗糖磷酸合成酶的活性则显著地下降，叶片的α－和β－淀粉酶活性似与ABA和水分状况关系不密切。ABA对籽粒灌浆有显著的抑制作用，ABA对籽粒灌浆的抑制作用至少部分与其对催化水稻籽粒内蔗糖代谢和淀粉积累的关键酶蔗糖合成酶的抑制有关。另外，干旱处理对叶片光合速率和蔗糖与淀粉积累的抑制程度显著高于半干旱处理，说明干旱本身也对这些过程有直接的效应。根据这些结果，作者认为，当水稻遇到干旱胁迫时，ABA对其光合作用、糖代谢以及籽粒的发育过程都有极其显著的调节作用。还就ABA对这些生理过程调节的可能性进行了讨论

关键词: 分根系统, 脱落酸（ABA）, 光合特性, 糖代谢, 籽粒灌浆