Abstract
To establish a cultivation system for the production of high quality cucumbers (Cucumis sativus L. cv. Kagafutokyuri), differences in nitrogen levels in the leaves between a non-bitter line and a bitter line and in the leaves and fruits between the bitter ones and the non-bitter ones were compared. A percentage of bitter fruit was higher in the bitter line than in the non-bitter line. Stem length, leaf weight, and root weight per plant were larger in the former than in the latter. The total leaf nitrogen and amino acid-N levels were higher in the bitter line than in the non-bitter line, but the nitrate ion level was lower in the former than in the latter. On plants grafted on Cucurbita ficifolia Bouche, the leaves on the upper node were more bitter than those in the lower node. The degree of bitterness of the upper leaf or fruit corresponded to the total nitrogen and amino acid-N levels. We concluded from these results that high total nitrogen and amino acid-nitrogen 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.
