大豆(Glycinemax L.)边缘细胞对铝毒的生理生态响应

Physiological and ecological response of the root border cells to aluminum toxicity in soybean

以大豆浙春2号(铝耐性)和华春18号(铝敏感)为材料,研究了铝胁迫下附着于根尖边缘细胞(即原位边缘细胞)的存活率、根伸长抑制率和PME活性变化以及Al3+对离体后边缘细胞存活率、黏液层厚度的影响。结果表明:铝胁迫下附着于根尖的边缘细胞比离体边缘细胞有更高的活性,前者Al3+处理24h后,其成活率仍能达到74%以上,而后者Al3+处理12h,浙春2号和华春18号边缘细胞的活性在400μmol/L时分别只有44.58%和26.16%;前后两者细胞活性都有随着Al3+浓度升高和处理时间的延长,边缘细胞活性呈越来越低的变化趋势,而离体边缘细胞Al3+处理6h时,相对于敏感性品种而言,高浓度Al3+(≥200μmol/L)有利于铝耐性品种的边缘细胞存活。随Al3+浓度的提升,果胶甲基酯酶(PME)活性增加,根伸长受抑加剧,敏感品种PME活性及铝造成的根伸长抑制均高于耐性品种;同时,Al3+对黏液的产生有一定的影响,黏液层的厚度随Al3+浓度成正向变化趋势。不同Al3+浓度及处理时间下,耐性品种都比敏感品种边缘细胞有较高的活性、分泌较多的黏液。以上结果说明Al3+对边缘细胞具有一定的毒害效应,果胶甲基酯化程度、根伸长受抑及边缘细胞黏液的分泌是根冠对Al毒胁迫反应的结果。

Aluminum （Al） toxicity is an important factor in determining the distribution of plant species and ecotypes in the natural habit at crop productivity in the acid soils. However, the mechanism of Alinduced inhibition of root growth and the reasons for the spatial variations in Al sensitivity among the apical root zones are still poorly understood. The root tip is a primary site of Al toxicity in senior plants. The root border cells, which originate from the root cap meristem by mitosis, can separately carry out metabolism and resist adverse stress through a series of distinct responses after being detached from the root tips. Furthermore, the root border cells also play many crucial roles in protecting the root tip from the abiotic stress, which especially can participate in detection and tolerance of aluminum （Al） toxicity. The toxin effects of Al^3＋ on the border cells and response mechanism of the root border cells to Al^3＋ toxicity were tested by comparing response of soybean varieties Zhechun No. 2 （Al-tolerance） and Huachun No. 18 （Al-sensitive） known to vary in Al resistance at a whole-root level. The response of the root border cells to Al toxicity and its mechanism of resisting Al toxicity clearly were further investigated. The study shows that the higher viability was found in the root border cells clinging to the root tip than the detached border cells under Al^3＋ stress. After being exposed to Al^3＋ for 24 h, the border cells clinging to the root tip from two varieties significantly reached more than 74% viability, and that of the detached border cells was lower when exposed to Al^3＋ for 12 h. The viability of Zhechun No. 2 and Huachun No. 18 was just 44.58% and 26.16% respectively at 400 μmol/L Al^3＋. No matter clinging to the root tip or detached, the viability of the soybean border cell became lower and lower with increase of Al^3＋ concentration and treatment time. However, the viability of the detached border cells in Al- tolerance variety had an inflexion at 200 μmol/L Al^3＋treated for 6 h, i. e. , higher concentration Al^3＋ （ ≥200 μmol/L） was propitious to the border cells viability. With increase of Al^3＋concentration, both the PME activity and relative root elongation inhibit rates increased, and those of the Al-sensitive variety were higher than Al-tolerance. At the same time, Al^3＋ concentration was influential on secretion of mucilage and the mucilage layer became much thicker with increase of Al^3＋ concentration. Under different Al^3＋ concentration and treatment time, these results indicated that Al can speed up death of the border cells. The higher penetrative was propitious to the viability of the border cells and the exfoliate cell mortality was correlated with production of mucilage under greater Al^3＋ concentration. Al binding to the cell walls, root elongation inhibited and secretion of mucilage represented an important pathway in the response of the soybean root cap to Al toxicity. Results also suggest that the Al-resistance mechanisms in the border cells levels were consistent with those of the soybean whole plant levels.