Effects of ADP-Glucose Pyrophosphorylase Activity on Sterility and Develop-ment of Grain in K, V, and T-Cytoplasmic Male

Abstract

Cytoplasmic male-sterile (CMS) lines, especially K (Aegilops kotchyi), V (Aegilops ventricosa), and T (Triticum timopheevi) types of cytoplasms, are of high value in heterosis utilization in wheat (Triticum aestivum L.). The sterile mechanisms of these CMS types have been focused in hybrid wheat research. As a key and rate-limiting starch biosynthetic enzyme, ADP-glucose pyrophosphorylase (AGPase) is considered to play an important role in the sterility of CMS lines. For gaining an insight into the physiological basis of the sterility in CMS lines of wheat, the activities of AGPase in leaves, young spikes, and grains were measured in K, V, and T types of isogenic CMS lines (Ji 5418 background) at different growth stages, and compared with those of their maintainer line. The dynamic accumulations of starch, amylose, and amylopectin were also investigated in both superior (the first and the second grains in a spikelet) and inferior (grains except for the first and the second grains in a spikelet) grains. In young spikes, the AGPase activities of the three CMS lines were significantly higher (F=133.81, P＜0.0001) with the differences of 9.33-27.94 μmol g^(-1) FW h^(-1) at floret primordium stage, and significantly lower (F=13.97-75.20, P＜0.0001) by 4.27-7.44 μmol g^(-1) FW h^(-1) at tetrad stage as compared with the maintainer line. From floret primordium to tetrad stage, the CMS lines had continuously higher level of AGPase activities in leaves than the maintainer line, with the differences ranged from 7.39 to 80.77 μmol g^(-1) FW h^(-1) (F=135.76-5454.28, P＜0.0001). Compared with the maintainer line, the three CMS lines all presented lower accumulations (P＜0.05) of starch, amylose and amylopectin in grain. The starch content and AGPase activity in superior grains were significantly higher than those in inferior grains for CMS lines. The dynamic accumulations of starch in superior and inferior grains fitted Logistic equations, and positively correlated with the starch accumulation rate (r=0.4460-0.7150, P=0.0004-0.0487). The AGPase activity in leaves had an insignificantly negative correlation with net photosynthetic rate. In conclusion, the male sterility is probably in relation to the insufficiency of energy in leaves and young pikes at floret primordium stage resulting from the high AGPase activity, and the low accumulation of starch in pollens at tetrad stage caused by low AGPase activity in young spikes. The sterile cytoplasm has a negative effect on AGPase activity, resulting in decreases of ADPG level and starch accumulation in grains. Besides, the negative effect of AGPase activity on net photosynthetic rate in flag leaves may result in unfilled grains in CMS lines.