水分和氧气对毛萼田菁茎瘤固氮作用的影响

水分剥夺引起毛萼田菁（Ｓｅｓｂａｎｉａｒｏｓｔｒａｔａ）茎瘤固氮活性的下降；水分剥夺还导致茎瘤类菌体固氮的最适Ｏ２分压（ｐＯ２）和呼吸强度的下降及茎瘤豆血红蛋白和细胞质可溶性蛋白含量的下降。测定水分剥夺的茎瘤在不同ｐＯ２下的固氮活性和茎瘤组织切片的显微观察，支持水分胁迫可使Ｏ２扩散阻力增大这一观点。测定不同ｐＯ２下离体茎瘤固氮活性以ｐＯ２为６０％最高；当把茎瘤切碎后，茎瘤皮层的扩散屏障作用降低或失去，最适ｐＯ２降至４０％，说明Ｏ２是茎瘤固氮作用的限制因子。

EFFECTS OF WATER AND O_2 ON NITROGEN FIXATION OF SESBANIA ROSTRATA STEM NODULE

The nitrogenase activity of Sesbania rostrata stem nodule was decreased when the plant was under stress of water deprivation. The optimal pO2 of nitrogen fixation,respiration rate of stem nodule bacteroids, nodule leghemoglobin and cytosol soluble protein were reduced by water deprivation.The results of the nitrogenase activity of water deprived stem nodule under different pO2 and its micrographic observation supported that the oxygen diffusion resistance increased in response to water stress. The nitrogenase activity of the detached stem nodule was measured under different pO2 and the highest was obtained at 60%.When the stem nodule was sliced, the optimal pO2 of nitrogen fixation was at 40% due to the loss of diffusion barrier.This indicated that there is an oxygen diffusion barrier in the nodule cortex and oxygen is a restrictive factor in nitrogen fixation.