The occurrence of bitterness in cucumber (Cucumis sativus L. cv. Kagafutokyuri) in relation to nitrogen levels

摘要

For the production of high qyuality cucumber Cucumis sativus L. cv. Kagatutokyun, differences in nitrogen levels in the leaves between a non-bitter line and a bitter line, and in the leaf and fruit between the bitter ones and the non-bitter ones were Compared. The percentage of bitter fruit was higher in the bitter line than in the non-bitter line. Vegetative growth was more vigorous in the former than in the latter. The total leaf nitrogen and amino acid nitrogen levels were higher in the bitter line than in the non bitter line, but the nitrate ion level was lower in the former in the latter. The leaves on the upper nodal position were more bitter than those on the lower one. The degree of bitterness of the leaf or fruit corresponded to total-N and amino acid-N levels. We concluded from these results that high total-N and amino acid-N levels in the leaf induce bitterness in leaves and fruits by promoting nitrogen metabolism, which in turn favors the enzymatic synthesis of cucurbitacin C, the bitter factor.