Morpho-physiological studies on gas exclusion system of a crop root relating to salt and drought tolerances

据报道，空化现象，即木质部溶液中由负压产生的气泡，阻止水分吸收，并且只发生在遭受严重干旱胁迫的植物中。这表明在植物根系吸水过程中存在排除溶解气体的可能性。研究了几种气体的排气机理、结构特征和排气比。以水稻和大麦根为材料，比较了木质部汁液与根培养液中溶解气体的含量。在0.3或0.5 MPa的液压压力下，将切除的根近端暴露于空气或氮气饱和的蒸馏水中，从木质部的柱状结构中取样。因此，根在吸水过程中具有排除培养液中溶解气体的功能。研究了不同干旱胁迫条件下水稻根系的排气率（1-Gr/Gc、根木质部溶出气体含量、培养液溶出气体含量）。在严重干旱胁迫条件下生长的根系排气率较高。采用小檗碱-苯胺蓝荧光染色法，在这些根的皮层厚壁组织和内胚层中诱导了强烈的荧光。这表明气体排出率与根的成分有关。研究了水稻根系在饱和氧气或氮气蒸馏水中的排气率。氧气气体排出率较高。这表明，在植物根系中，培养液中的每种气体都是单独排除的。

It is reported that cavitation, i.e.bubbles in xylem solution produced by negative pessure, prevents water absorption and occurs only in plants which suffer severe drought stress. This suggests a possibility of dissolved-gas exclusion in the process of water absorption in plant roots. In this research, a mechanism of gas exclusion, structural characteristics and gas exclusion ratio in several gases were studied.Dissolved-gas content in xylem sap was compared with that in root culture solution by using rice and barley roots. Xylem sap was sampled from the stele of proximal end of a excised root exposed to air- or nitrogen gas-saturated distillled water with 0.3 or 0.5 MPa of hydraulic pressure. As a result, a root has a function to exclude dissolved gas from culture solution in the process of water uptake.The gas exclusion rate (1-Gr/Gc, Gr : dissolved-gas content in root xylem, Gc : dissolved-gas content in culture solution) of rice roots which grown under different drought stress conditions was investigated. The gas exclusion rate of a root grown under severe drought stress condition was higher. In those roots, the intense fluorescence in cortical sclerenchyma and endodermis was induced by using a berberine-aniline blue fluorescent staining procedure. This suggest that the gas exclusion rate relate to the component of the root.The gas exclusion rate of rice roots exposed oxygen or nitrogen gas-saturated distillled water were investigated. The gas exclusion rate of oxygen gas was higher. This suggest that each gases in culture solution are excluded separately in plant root.