硝酸盐在两个小白菜品种体内的分布及调配

 硝酸盐在作物体内的分布及调配规律研究是降低蔬菜硝酸盐含量、提高植物体对硝态氮利用效率的基础理论问题。本试验采用水培和植物电生理方法测定了两个小白菜品种的不同器官组织硝酸盐含量和液泡中硝酸盐浓度（活度）；氮亏缺条件下叶片、叶柄和根系组织硝酸盐含量、叶片硝酸还原酶活性以及叶片、根系的液泡和细胞质中硝酸盐活度。结果表明，叶片、叶柄和根系液泡中硝酸盐活度分别是组织硝酸盐含量的4.6、2.0和7.4倍，液泡硝酸盐活度远高于细胞质硝酸盐活度；亮白叶1号叶片、叶柄和根系液泡硝酸盐活度分别是上海青的2.4、1.9和3.6倍；不同器官组织硝酸盐含量呈叶柄>叶片>根系，而各器官液泡硝酸盐活度不存在显著差异；小白菜组织及液泡硝酸盐含量随氮饥饿时间急剧下降，而细胞质硝酸盐活度及叶片硝酸还原酶活性则基本维持稳定。硝酸盐主要累积于液泡内且可以再利用；叶柄及根系组织硝酸盐在氮亏缺时均可被运至叶片，而液泡硝酸盐则被释放至细胞质中，维持了细胞质硝酸盐浓度的稳定，使叶片硝酸还原酶得以稳定。高硝酸盐累积品种亮白叶1号液泡硝酸盐活度高，氮亏缺时其组织硝酸盐下降速度较慢，这可能由其硝酸还原酶活性低引起的。

Distribution and Remobilization of Nitrate in Two Cultivars of Pakchoi Plant

Studies on the distribution and remobilization of nitrate in vegetable plants are important theoretical bases for decreasing nitrate content in vegetables and increasing nitrate use efficiency by plants.Hydroponic experiments and plant electro-physiological methods were used to determine tissue nitrate content and vacuolar nitrate activity of different organs of two pakchoi cultivars,which were significantly different in nitrate accumulation.Results obtained were as follows:Vacuolar nitrate activities of leaf blades,petioles and roots were 4.6,2.0 and 7.4 times of tissue nitrate content respectively,inferring that nitrate activity in vacuoles was much higher than in cytosol.Nitrate contents in leaf blades,petioles and roots of Liangbaiye 1 were 2.4,1.9 and 3.6 times of those of Shanghaiqing.Tissue nitrate contents in different organs of pakchoi were in the decreasing order of petiole > leaf blade > root,but no significant difference was found among these three organs.After pakchoi plants were transferred to the solution without nitrate,both the tissue nitrate contents and vacuolar nitrate activity significantly decreased,while cytosolic nitrate activity and NRA in leaf blades maintained relatively unchanged.Nitrate was predominantly stored in vacuole and could be reused by plants.Tissue nitrate stored in roots and petioles could be remobilized by leaf blades,and vacuolar nitrate could be released into cytosol to maintain a steady cytosolic nitrate concentration,and thus the nitrate reductase activity was kept in normal level.Liangbaiye 1,a high nitrate accumulating cultivar,had a high vacuolar nitrate activity,and its tissue nitrate contents decreased more slowly than Shanghaiqing after transferring to the solution without nitrogen,which probably was caused by its low NRA.