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  • Author or Editor: Hiroshi Gemma x
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A water stress treatment was imposed on peach trees [Prunus persica (L.) Batsch `Kansuke Hakuto' (Peach Group)] to elucidate the relationship among sugar accumulation, sugar metabolism, and abscisic acid (ABA) in fruit under water stress. Treatment was carried out on peach trees grown in containers from 8 July 1996 [80 days after full bloom (DAFB)] for 16 days, to achieve a predawn water potential of -0.8 to -1.1 MPa compared to that of -0.4 to -0.6 MPa in control trees. Levels of sorbitol, sucrose, and total sugars, as well as the activity of sorbitol oxidase increased in fruit of water stressed trees under moderate water stress (-0.8 MPa), whereas under severe water stress (-1.1 MPa), no difference between the waterstressed trees and the controls was observed. Water stress also induced an increase in ABA in the fruit. These initial results indicated that water-stress-induced ABA accelerated sugar accumulation in peaches by activating sorbitol metabolism.

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Effects of n-propyl dihydrojasmonate (PDJ) treatment on flowers of Japanese pear 'Kousui' (Pyrus pyrifolia Nakai cv. Kousui) during spring frost were investigated to study mechanisms for avoiding spring frost injury. PDJ applied during the flowering period resulted in a lower injury index for the ovules and pistils after freezing tests. Average ion leakage in control flowers was 37.9% during the balloon stage at -5 °C, while the flowers treated with PDJ displayed a 16.6% ion leakage. Similarly, at the full bloom stage, PDJ treatment reduced ion leakage at -5 °C from 73.1% to 47.8% in the control. The organs of the flower more sensitive to low temperature stress were the ovule, pistil, and ovary; stamens were more resistant. Sugar content in the flower at the balloon stage was increased by PDJ when treated at the pink stage. Moreover, free amino acids, especially proline, increased similarly with PDJ treatment. These results show that PDJ affects supercooling capacity of a flower by changing solute content and protects organs from freezing.

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