Abstract:

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, CA3 carrying antisense Wx gene and a wild type (cv. Wuyunjing7) 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 was significantly decreased, but less affected by water deficiency at the later stage of starch accumulation. Q enzyme catalyzed the formation of α-1, 6 indican bond involved in the synthesis of amylopectin 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 20-30DAA under water deficiency (Fig.3). The total accumulation of starch and the content of amylopectin were reduced under water deficiency compared to well-watered 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 amylopectin content. The results suggested that the influences of soil water potential on starch accumulation and the synthesis of the amylopectin were attributed to changes of activities in SSS, Q-enzyme, DBE and other enzymes, and not regulated by only one of them.

Key words: Rice, Water deficiency, Q enzyme, Debranching enzyme, Amylose content, Grain-filling period