| Research Abstract |
In the experiments of effects of temperature and nitrogenous fertilizer, and comparison between bitter line and non-bitterline or bitter fruit and non-bitter fruit, a high occurrence of bitter fruit was observed in plants with leaves which contained high total-N, arnino acid-N, protein contents, or bitterness developed well in fruits with high total-N, amino acid-N and protein contents in the peels. These results suggest that active nitrogen metabolism occurs entirely in plants with high occurrence of bitter fruits or in bitter fruits, and finally results in high protein content in plants with high occurrence of bitter fruits or in bitter fruits, Cucurbitacin C, bitter principle, is synthesized from mevalonic acid via 3-hydroxy-3-methyl-glutaiyl-CoA and acetyl-CoA, and a lot of enzymes are related to the pathway of cucurbitacin C synthesis. On the pathway to mevalonic acid from 3-hydroxy-3-methyl-glutaryl-CoA, HMG-CoA reductase works and the reductase is a rate limiting enzyme of the synthesis. A high occurrence of batter fruit was observed in the plants with leaves in which HMG-CoA reductase activity was high, or bitterness developed well in the fruit with high HMG-CoA reductase activity. Putting togather these reports, it can be pointed out that active protein synthesis induces high HMG-CoA reductase activity.
From these results the following asuumption can be made. In plants having high occurrence of bitter fruit or in bitter fruits, protein is wholly actively synthesized The active protein synthesis causes a high activity of HMG-CoA reductase which provokes an active synthesis of cucurbitacin C, which leads to a high occurrence of bitter fruit Therefore, it can be considered that the occurrence of bitter fruit in cv. Kagafutokyuri is regulated by maintaining protein synthesis in plants relatively low.
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