Factors for the formation of deep-root-system that improves the drought resistance in the view of cell elongation and cell-wall expansibility

在本研究中，我们首先建立了以玉米为研究对象，研究不同水分条件下种子根伸长与细胞伸长和细胞分裂之间关系的方法。利用高压灭菌蛭石对苗木进行了真实干旱胁迫，而不是低渗透势的伪干旱胁迫。用冷冻微银器制作精根顶端切面，用荧光显微镜观察，以测定皮层细胞的细胞长度。用该方法测定了不同抗旱性水稻品种种子根顶端5cm处皮层细胞的细胞长度。抗旱品种在低含水量培养基下，根伸长区细胞长度显著增加，表明根伸长区细胞伸长模式与品种间根伸长差异及根系对干旱的响应密切相关。抗旱品种根系（尤其是内胚层）的细胞壁厚度较大。不同品种间的最终细胞长度没有差异，说明根尖的细胞分裂和根生长角对根的垂直分布有很大的影响。对玉米植株根冠的观察表明，随着小柱组织的纵向发育和淀粉体的增大，根的生长角度逐渐向垂直方向靠拢。还研究了不同品种根内胚层细胞壁硅积累量的差异与抗旱性的关系。

In this study, we first established the method using maize plants to investigate the relationships between the elongation of seminal roots and cell elongation and cell division under different water conditions. Not the low osmotic potential as pseudo-drought stress but the real drought stress using autoclaved vermiculite was treated on seedlings. Closs sections of the apical part of the seminal roots were made by a freezing microsilcer and observed by a fluorescent microscope to measure the cell length of the cortex cells. The cell length of cortex cells in the apical 5cm of seminal roots in rice cultivars with different drought resistance was measured with this method. The drought resistant varieties showed remarkable increase of cell length in the root elongation zone under low water content of the medium, suggesting the close relation of the cell elongation pattern in the elongation zone to the varietal differences in root elongation and the root response to the drought. The cell wall thickness in roots (in particular, in endodermis) was large in drought resistant varieties. The final cell length, however, did not showed difference among the varieties, suggesting the large contribution of the cell division in root apex and the root growth angle in the determination of the vertical distribution of roots. The observation of the root caps of maize plants indicated that the root growth angle gets closer to vertical with the longitudinal development of columella tissue and the enlargement of amyloplasts. Varietal difference in the accumulation of silicon on the cell wall of the root endodermis was also investigated in relation to the drought resistance.