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

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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.