The nitrate reductase activity distribution and response of two nodulated species of Phaseolus (Phaseolus vulgaris-common bean, and Phaseolus lunatus-lima bean) to different exogenous nitrate levels were studied during the vegetative period. These Phaseolus species showed to be very contrasting in respect to the pattern of nitrate reductase (NR) activity distribution thought the plant. The highest level of NR activity in P. vulgaris was clearly shown to occur in leaves in contrast with the lowest one detected in roots and nodules as widely seen for other tropical species of the Phaseoleae tribe. Conversely, P. lunatus had higher NR activity in the nodules, whereas its leaves exhibited a steadily decrease during the plant development. Indeed, at 32 days after emergence (pre-flowering stage), the nodulated P. vulgaris had approximately 95% of the total NR activity localized in its leaves, whereas in P. lunatus it was equally distributed in the nodules and in the leaves. Under long-term exposure to increasing exogenous level of nitrate, the leaf-NR activity of nodulated P. vulgaris presented a positive response, whereas the enzyme activity was very low and unresponsive in P. lunatus. In contrast, the nodule-NR activity showed a reverse response to the increasing NO(3)(-) level. The nodule-NR activity of P. lunatus significantly increased whereas in the P. vulgaris nodules it was very low and unresponsive. This present study suggests that P. lunatus inoculated with Rhizobium tropici presents a singular pattern of nitrate reduction distribution among leaves and nodules during the vegetative development. It is speculated that the nodulated Phaseolus lunatus may have different NR isoforms in their leaves (at least a constitutive type) and an inducible form in their nodules, responsive to long-term exposure to nitrate.

中文翻译：

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接种根瘤菌属的两种不同菜豆属植物中硝酸盐还原酶的活性、分布和对硝酸盐的反应。

研究了两种菜豆（菜豆-普通豆和菜豆）在营养期对不同外源硝酸盐水平的硝酸还原酶活性分布和响应。这些菜豆物种在植物的硝酸还原酶 (NR) 活性分布模式方面表现出非常鲜明的对比。P. vulgaris 中最高水平的 NR 活性清楚地显示发生在叶子中，而在根和根瘤中检测到的最低水平则广泛见于菜豆部落的其他热带物种。相反，P. lunatus 在根瘤中具有较高的 NR 活性，而其叶子在植物发育过程中表现出稳步下降。事实上，在出苗后 32 天（开花前阶段），有瘤的 P. vulgaris 的总 NR 活性的大约 95% 位于其叶子中，而在 P. lunatus 中，它在根瘤和叶子中平均分布。在长期暴露于外源硝酸盐浓度不断增加的条件下，有节病的P. vulgaris的叶片NR活性呈阳性反应，而P. lunatus的酶活性很低且无反应。相比之下，结节 NR 活动表现出对增加 NO(3)(-) 水平的反向反应。P. lunatus 的结节-NR 活性显着增加，而在 P. vulgaris 结节中，它非常低且无反应。本研究表明，接种热带根瘤菌的 P. lunatus 在营养发育过程中呈现出叶片和根瘤中硝酸盐还原分布的奇异模式。