Ryosuke Mochioka

Adverse effects of high temperature on the development of reproductive organs in ‘Hakuho’ peach trees

Summary To examine the effect of the temperature on the development of reproductive organs, potted plants of five year old ‘Hakuho’ peach were exposed to constant temperatures of 15°C, 20°C, 25°C, 30°C, and natural conditions. The rate of flower and leaf bud burst, and flowering were recorded every day. The characteristics of reproductive organs in each treatment were examined by measuring flower size, pollen germinabitily, pollen tube elongation, development of embryo sacs, and fruit set. Percentage of flower bud bursting at 30°C was about 80% within 3 d after the onset of the treatment, while it took 18 d to reach the same percentage in the control. Flower bud break preceded leaf bud break in all treatments. Flowering was earliest at 30°C, and the period from bud burst to flowering was as short as 3–4 d. Flower sizes were significantly decreased with increasing temperature. The pollen germination was negatively affected by higher temperature, but the pollen tube elongation in the pistils was faster at higher temperatures. On the other hand, the development of the embryo sac at high temperature was considerably less satisfactory than that at lower temperature and under field conditions. High temperatures also significantly reduced the percentages of fruit set. The results suggested that the high temperature above 25°C interferes with the normal development of reproductive organs especially embryo sac, and causes poor fruit set in ‘Hakuho’ peach.

Expression analysis of UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene in an interspecific hybrid grape between Vitis ficifolia var. ganebu and Vitis vinifera cv. Muscat of Alexandria

Kadainou R-1, an interspecific hybrid grape derived from red (Vitis ficifolia var. ganebu) and white (V. vinifera cv. Muscat of Alexandria) grapes, accumulates high concentrations of anthocyanin in the berry skin. Hence, the expression of uridine 5′-diphosphate (UDP)-glucose:flavonoid 3-O-glucosyltransferase (UFGT), the key enzyme of the anthocyanin pathway, was examined in the berry skin of Kadainou R-1. As information on gene sequences of V. ficifolia var. ganebu and other wild grape species was unavailable, we performed GeneChip hybridization using biotin-labeled genomic deoxyribonucleic acid (DNA) to investigate how the genomic sequences of V. vinifera varieties and that of V. ficifolia var. ganebu differ. The study showed a lower correlation coefficient between V. vinifera cultivars and V. ficifolia var. ganebu than that among V. vinifera cultivars. The sequences of the UFGT gene derived from both parents of the red and white cultivars were sequenced in Kadainou R1 and revealed that both were expressed irrespective of the fact that it was not expressed in the white grape (male parent).

The Role of Glutathione on the Onset of Endodormancy of Grape Buds

The role of glutathione, which maintains protein thiol groups in the reduced state in living cells, on the onset of endodormancy (rest) of grape buds was investigated. When potted grapevines were exposed to 30°C/25°C (high), day/night, or 20°C/15°C (low), day/night, before the onset of bud dormancy, buds administered low temperature became dormant, but those treated with high temperature did not. On shoots treated with low temperature, endogeneous ABA levels increased soon after treatment, whereas ABA levels in shoots treated with high temperature remained low. Reduced glutathione (GSH) content in the shoots treated with high temperature increased, whereas in shoots treated with low temperature, it decreased gradually. Oxidized glutathione (GSSG) content in the shoots treated with high temperature remained almost constant during the experimental period, whereas under the low temperature treatment it increased. GSSG content increased in shoots induced to dormancy by the ABA treatment. Furthermore, exogenous treatment with GSSG inhibited budbreak. Therefore, we conclude that glutathione is one of the potent factors in controlling grape bud dormancy.