Abstract:

【Objective】 The objective of this study was to determine the distribution of ATPase in phloem cells and to analyze the relationships between the ATPase active products in phloem cells and the accumulation of photo-assimilates in grain during grain filling. 【Method】 During grain filling of wheat (Triticum aestivum L.), different photo-assimilates in grain were determined by Anthrone’s method, the positions of polysaccharide in phloem and endosperm of caryopsis were located by microscopic cyto-chemical technology and the ATPase activity in phloem were located by ultracytochemical technology. Meanwhile, correlation analysis and linear regression analysis were done between ATPase active products in phloem cells and accumulation of photo-assimilates in grain. 【Result】 At early stage of grain filling, the photo-assimilates of grain were mainly soluble sugar. At around 14 d after flowering, the contents of soluble sugar and starch of grain were basically equal and then starch became the main form of photo-assimilates. During the whole filling stage, the changes of soluble sugar and starch showed mutual growth and decline, but the total sugar of grain showed a "S"-type growth. The cell wall of SE and the starch granules in endosperm were dyed bright red by PAS reaction during gradual increasing period and fast increasing period, but they showed light red during slight increasing period. In the SE, IC, CC and PPC, ATPase active products mainly distributed on the plasma membrane, the cell wall and the vesicles around plasma membrane. The P-type plastids, double-layer membrane of mitochondria in SE and the branches of the plasmodesmata between SE and IC also had a strong ATPase activity. The ATPase activity in SE was higher than that in IC during gradual increasing period and fast increasing period, but the ATPase activity in IC was higher than that in SE during slight increasing period. There was a significant negative correlation between the soluble sugar contents of grain and the ATPase active products of the SE, a very significant positive correlation between the starch contents and the ATPase active products and a significant positive correlation between the total sugar contents and the ATPase active products. Otherwise, there was a clear linear relationship between the ATPase active products and the photo-assimilates contents. The soluble sugar contents of grain and the ATPase active products of the IC also had a highly significant positive correlation. 【Conclusion】 In the grain filling process, the changes of grain soluble sugar and starch showed mutual growth and decline, but the total sugar content was still increased. The contents of different photo-assimilates of grain and the ATPase active products of SE and IC had significant or very significant correlations. The distribution of ATPase active in phloem showed a dynamic changes in time and space. The SE played a leading role at the first and second filling stages, but IC played a leading role at the third filling stages. This result has provided a cytological basis for the physiological study of wheat grain filling

Key words: wheat (Triticum aestivum L.)')">wheat (Triticum aestivum L.), grain filling, photo-assimilates, phloem, ATPase localization