Effects of water deficiency on the activities of key enzymes involved in the starch synthesis and the accumulation of starch for the transgenic rice plants carrying antisense Wx gene during grain filling

chinois. 以反义Wx基因转化系水稻及其受体亲本武运粳7号（9522）为材料，研究了结实期水层灌溉和水分亏缺条件下籽粒淀粉合成关键酶活性、淀粉及直支链淀粉含量的变化。结果表明，以水层灌溉为对照，结实初期（花后5～10d）的水分亏缺利于籽粒中腺苷二磷酸葡萄糖焦磷酸化酶（ADPGPase）和颗粒淀粉合成酶（GBSS）活性的提高，但随着水分亏缺时间的延长，到灌浆后期2种酶活性降低的速度快于对照。水分亏缺显著降低了可溶性淀粉合成酶（SSS）的峰值。Q酶活性于水分胁迫下显著受到抑制，花后20d到成熟期酶活性降低的幅度较大。而2类去分支酶（异淀粉酶和普鲁兰酶）于水分亏缺下活性显著升高，在灌浆后期花后25～30d普鲁兰酶仍保持着较高的活性。与水层灌溉相比，水分亏缺下籽粒中总淀粉的积累和支链淀粉含量明显降低。GBSS最大活性与直链淀粉含量关系最为密切，呈极显著正相关（r=0.981. ___SSS、Q酶和DBE最大酶活性分别与淀粉和支链淀粉含量不显著相关性。由此推测土壤水分对支链淀粉合成和积累的影响并不是由某一种酶调节的，而是由SSS、Q酶和DBE以及其他一些酶共同催化完成的。

anglais. Soil drought is one of the most important factors limiting rice production in China. Recently, more attention for the inferior quality of rice caused by water stress has been paid in agricultural production. The previous study showed that the indices of quality, such as chalkiness, gel consistency and RVA profile were changed by soil drought. It is considered that rice quality is related to the process of starch accumulation. Therefore, all changes of rice quality under water deficit conditions are responsible for physiological metabolism of starch accumulation during grain filling. In present study, the pot experiments were conducted at Yangzhou University. Three transgenic rice plants CA1, CA2 and CA3 carrying antisense Wx gene and a wild type （cv. Wuyunjing 7 ）were grown under water deficiency at flowering stage. In order to assess the implication of physiological metabolism of starch accumulation to water deficiency, as the indictors of rice quality, the contents of soluble sugar, starch,amylose and amylopectin were measured. The starch accumulation capacity was determined by measuring adenosine diphosphoglucose pyrophosphorylase（ADPGPase）, soluble starch synthase（SSS）, granule-bounding starch synthase（GBSS）, starch branching enzyme（Q-enzyme） and two debranching enzymes（ Isoamylase and Pullulanase） in rice grain during filling period. The results showed that the activities of ADPGPase and GBSS were significantly enhanced at initial filling stage（5-10 d）, and then declined rapidly from 20 days after anthesis（DAA） to ripening（ Fig. 1 ） by drought stress. The maximum activity of SSS significantly decreased, but less affected by water deficiency at the later stage of starch accumulation. Q enzyme catalyzed the formation of a-1,6 indican bond involved in the synthesis of amylopoctin was most sensitive to water in that it responded earlier, and to a greater extent, than the other enzymes. The significant decrease in activity of Q enzyme was observed under water-deficit conditions, especially in later grain-filling stage（ Fig.2）. However, under such drought conditions, leading to decrease of starch accumulation, the decline in Q enzyme activity was more than that in ADPGPase and SSS. The activities of two debranching enzymes（ DBE, Isoamylase and Pullulanase） were elevated significantly, and the high activity of Pullulanase was substantially observed at 20-30 DAA under water deficiency（ Fig. 3）. The total accumulation of starch and the content of amylopoctin were reduced under water deficiency compared to wellwatered treatments（ Fig.4, Fig. 5）. A positive correlation between the maximal activity of GBSS and the content of amylose was observed（ r = 0. 981. __）. However, there were no clear correlations between the maximal activities of SSS, Q enzyme, DBE and starch content or amylopoctin content. The results suggested that the influences of soil water potential on starch accumulation and the synthesis of the amylopoctin were attributed to changes of activities in SSS, Q-enzyme, DBE and other enzymes, and not regulated by only one of them.