Studies on the Assimilation of Nitrate-N and its Translocation within Plants, Fruit and Vegetables.

硝酸盐还原发生在植物的所有部位，但速率不同。已知硝酸盐- n在植物内部很难通过韧皮部进行再转运。因此，硝酸盐还原活性低的器官可能依赖于其他还原氮活性高的器官。本研究以黄瓜为材料，研究叶片、根系和果实对整株硝酸盐还原的相对贡献。根系的硝酸还原酶活性明显低于叶片。但根系对总硝态氮还原的相对贡献在白天和晚上是不同的，这主要是由于叶片中硝态氮还原酶活性的每日波动。白天和夜间，还原性氮从叶片向根系的再转运速率大致相同。当根中不含氮时，根系利用叶片提供的氮生长良好。然而，当培养基中有足够的N时，它的再易位量很小。结果表明，黄瓜根系通常通过自身的硝态氮还原来获取大部分被还原氮。黄瓜果实的硝酸还原酶活性低于叶片，果皮的硝酸还原酶活性高于叶片。因此，黄瓜果实能够减少硝酸盐氮，以供其生长使用。另一方面，冷却花梗和叶面喷施抑制谷氨酰胺合成活性的药剂大大降低了果实的生长和根系吸收氮的积累。这一结果表明，黄瓜果实的生长至少在一定程度上依赖于叶片对还原性氮的供应。如果是这样，那么黄瓜果实的生长可能受到叶片和果实之间的源库关系的影响。

Nitrate reduction takes place in all parts of plants but at different rates. It is known that nitrate-N hardly retranslocate within plants through phloem. Therefore, the organs low in nitrate reducive activity may depend on other organs high in the activity for reduced-N. This research work was conducted to see the relative contribution leaves, roots and fruits to the whole plant nitrate reduction, using cucumber as plant materials. The nitrate reductase activity of roots was much lower than that of leaves. But, the relative contribution of roots to the total nitrate reduction varied between the day and night, mainly due to the daily fluctuation of nitrate reductase activity in leaves.Retranslocation of reduced-N from leaves to roots took place at about the same rate in the day and night. When N was omitted in the rooting medium, roots grew well by utilizing N supplied from leaves. However, the amount of retranslocation of it was small when adequate N was present in the medium. It was concluded that cucumber roots normally acquire most of reduced-N by their own nitrate reduction.Nitrate reductase activity of cucumber fruits was low, compared with the activity in leaves, though peels of fruits possesed high activity comparable to the activity in leaves. Thus, cucumber fruits is able to reduce nitrate-N for their use in growth. On the other hand, it was found that cooling the peduncle and the foliar spray of agent which inhibits glutamine synthetese activity decreased greatly the fruit growth as well as the accumulation of N absorbed by the roots. This result indicates that growth of cucumber fruits depend, at least to some extent, on the supply of reduced-N by leaves. If this is the case, then growth of cucumber fruits can be influenced by the source-sink relationships to reduced-N between leaves and fruits.