水稻根尖边缘细胞对铁毒的形态生理响应

以水稻(Oryza sativa L.)品种Azucena（铁耐性）和IR64（铁敏感）为材料，研究了Fe2+毒胁迫下附着于根尖边缘细胞(即原位边缘细胞)的数目、存活率，根尖细胞形态结构、根尖保护酶活性的变化。结果显示，Fe2+ 毒对根边缘细胞的产生有抑制作用。相对于敏感性品种而言，一定浓度Fe2+(100~200 μmol/L)有利于耐性品种边缘细胞的产生；Fe2+ 毒对边缘细胞有致死效应，随Fe2+浓度的提升，边缘细胞的存活率呈下降趋势，根尖外围细胞壁增厚，并出现细胞程序性死亡特征(敏感性品种)。同时，Fe2+ 毒对根尖保护酶活性有一定的影响，200~400 μmol/L Fe2+处理下，耐性品种POD、CAT、SOD活性都超过对照；敏感品种只有SOD活性超过对照。说明Fe2+毒胁迫下，水稻根尖通过增加边缘细胞数目、提高细胞拒铁作用，维持较高水平的POD、CAT和SOD活性来对抗Fe2+毒，缓解铁毒害。

Morphological and physiological response of the root tip border cells to Fe2+ toxicity in rice

Toxicity of Fe2+ is one of the major constraints for lowland rice production in tropical and subtropical areas. However the mechanism of Fe-induced inhibition of root growth and the reasons for the spatial variations in Fe2+sensitivi-ty among the apical root zones are still poorly understood. The root tip is a primary site of Fe2+ toxicity in rice. The root border cells (BC), which originate from the root cap meristem by mitosis, can separately carry out metabolism and resist adverse stress through a series of distinct responses. In this study, the response mechanism of the root tip cells to Fe2+ toxicity were tested by comparing response of rice varieties Azucena (Fe-tolerance) and IR64 (Fe-sensitive) known to vary in Fe2+resistance at a whole-root level. Results showed that Fe2+ toxicity inhibited the development of BC. Howev-er, compared to IR64, Fe2+ at 100 - 200μmol/L was propitious to the development of BC in Azucena. With increase of Fe2+ concentration, the viability of the rice BC became lower, the cell wall of root tip outermost cells became thicker, and some characteristics of programmed cell death were observed in the ceils (Fe-sensitive variety). Meanwhile, Fe2+ concentration affected the activities of poroxidase (POD), catalase (CAT), and superoxide dismutase (SOD). Higher enzyme activities were found in Fe-tolerance variety under high concentration Fe2+ ( ≥ 200 μmol/L) compared to control. These results indicated that, under the Fe2+ toxicity, root tip could resist Fe2+ toxicity by increasing BC, thickening cell wall, maintaining high POD, CAT and SOD activities.