Abstract:

【Objective】 The objective of the current study was to investigate the effects of different-stage shading after anthesis on grain weight and quality of maize at cytology level. 【Method】 The shading experiment was conducted in the field from 2005 to 2006, with a common maize cultivar (TY2) as the experimental material. Plants were stressed using horizontal shading net and the light intensity reduced by 55%. Field-grown maize plants were shaded at 1-14 d (S1), 15-28 d (S2) and 29-42 d (S3) after pollination respectively. Control plants (S0) were grown under natural light. Grain weight, quality, endosperm cell proliferation, cob sugar content and grain pedicel vascular bundle cross section area were measured. The ultrastructural changes of endosperm cells and endosperm transfer cells were observed after pollination. 【Result】 The result indicated that the grain weight, starch content, endosperm cell number and volume were declined after shading. On the contrary, embryo/endosperm ratio, protein content and fat content in grain increased. Shading treatments significantly delayed the development of the starch granules, also remarkably reduced the endosperm filling status. Among the three treatments, the number of the grain endosperm was the least under shading stress at 1-14 d after pollination. However, the volume of starch granules and the substantiation of endosperm under shading treatment at 15-28 d after pollination were the worst. Compared with the control (natural sunlight without shading), the soluble sugar of maize cob increased significantly, while there was no obvious change in vascular structure of small cluster stalk. The number of protein body in maize endosperm was influenced markedly by low light at different stages after pollination. Low light decreased the volume of the grain endosperm transfer, and the cell wall extensions of the basal transfer cells became thinner and shorter under shading treatment than those of the control, furthermore, the degree of connect extent and the capacity of the nutrient transport were decreased, and the mitochondrion number of the transfer cell was reduced after shading. 【Conclusion】 The change of grain quality after shading caused by the increase of embryo/endosperm ratio and the variety of the endosperm inclusion percentage cell. The morphology and functions in endosperm transfer cell and the shortage of energy restricted the nutrient transport greatly with shading at different stages, suggesting that an impeded flux may be one of the important reasons for kernel weight decrease of maize grain at later growth stage under low light condition.

Key words: common maize (Zea mays L.), kernel weight, endosperm cell, transfer cell, shading