Exogenous gibberellin treatment can promote early growth of grape fruit, but the underlying regulatory mechanisms are not well understood. Here, we show that VvDELLA2 directly regulates the activity ...of the VvCEB1 transcription factor, a key regulator in the control of cell expansion in grape fruit. Our results show that VvCEB1 binds directly to the promoters of cell expansion-related genes in grape fruit and acts as a transcriptional activator, while VvDELLA2 blocks VvCEB1 function by binding to its activating structural domain. The exogenous gibberellin treatment relieved this inhibition by promoting the degradation of VvDELLA2 protein, thus, allowing VvCEB1 to transcriptionally activate the expression of cell expansion-related genes. In conclusion, we conclude that exogenous GA3 treatment regulates early fruit expansion by affecting the VvDELLA-VvCEB1 interaction in grape fruit development.
The roles of plant hormones in the early growth of pepper fruit (Capsicum annuum L.) were investigated. An exogenous hormone treatment study indicated that cytokinin (CK) was more effective at ...stimulating early fruit growth in two lines than auxin or gibberellin (GA). Endogenous levels of CKs, 3-indole-acetic acid (IAA), and GAs in young pollinated and unpollinated fruit of four lines (two with medium-sized and two with small fruit) were also investigated. In pollinated fruit, the level of trans-zeatin riboside (tZR) increased with fruit size. In unpollinated fruit, tZR did not increase in any lines. IAA levels decreased gradually after flowering and did not differ between pollinated and unpollinated fruit in any lines. Levels of GA1 in unpollinated fruit of the lines in which unpollinated fruit were relatively well enlarged were slightly higher. In the line in which unpollinated fruit could not enlarge, GA1 levels of all samples were lower than the others. These results indicate that tZR is important in the early enlargement of pollinated pepper fruit, and that GA1 is involved in early fruit enlargement, especially in unpollinated pepper.
We investigated the effects of the application of chemical flower and fruit thinners on the fruit thinning time and fruit weight in four major apple cultivars. The effects of chemical flower and ...fruit thinning varied among cultivars due to the differences in the fruit drop rate of apical buds and the fruit set rate of axillary buds. In ‘Tsugaru’ and ‘Jonagold’, the single application of the flower thinner did not result in a labor-saving effect because the fruit set rate of axillary buds was high. Considering fruit enlargement, the combined application of the flower thinner and fruit thinner was the most effective in these two cultivars. In ‘Shinano Sweet’, the application of the flower thinner had no labor-saving effect on fruit thinning, but promoted fruit enlargement. In ‘Fuji’, the combined application of the flower and fruit thinners after hand pollination was the most effective for both labor-saving and fruit enlargement. The single application of the flower thinner had a more labor-saving effect than the fruit thinner.
We studied the influence of a 2°C increase in air temperature on physiological fruit drop in Citrus using a growth chamber for two months after full bloom. One room of the growth chamber was ...maintained at the standard temperature (control), while the other was maintained at 2°C higher than the control (+2°C treatment). The average temperature was changed every ten days. In ‘Okitsu wase’, ‘Ishiji’, ‘Shirakawa’ Satsuma mandarin (Citrus unshiu Marcow.), and ‘Shiranui’ (Citrus unshiu Marcow. × C. sinensis Osbeck) × C. reticulate Blanco, physiological fruit drop occurred more intensively in +2°C treatment than in the control after 10–20 days of full bloom. At the end of the experimental period, the physiological fruit drop ratio in plants receiving +2°C treatment was higher (5%) than that in controls for ‘Okitsu wase’ and ‘Ishiji’. In ‘Miyagawa wase’ and ‘Sasebo unshiu’ Satsuma mandarin, in which number of fruit was controlled by artificial fruit thinning, physiological fruit drop also occurred more intensively in plants receiving +2°C treatment than in controls after 10–20 days of full bloom. Especially in ‘Sasebo unshiu’ at the end of the experimental period, the difference in the physiological fruit drop ratio between plants receiving +2°C treatment and controls was larger (26%) than that in ‘Miyagawa wase’. In ‘Miyagawa wase’ and ‘Sasebo unshiu’ fruit diameter of plants receiving +2°C treatment was larger than that of controls. These findings suggested that with acceleration of fruit enlargement, and physiolosical fruit drop were both promoted by a 2°C increase in air temperature after full bloom.
This study had been conducted to investigate the effect of some plant growth regulators inducing fruit enlargement and optimal harvest time in Sageretia thea. Two hundred fifty mg/l mepiquat chloride ...treatment, 1mg/l thidiazuron treatment on full bloom, and 200mg/l gibberellic acid treatment on 7 days before full bloom resulted in the increase of 21.7% in weight, and 200mg/l gibberellic acid treatment 7 days before full bloom, 10mg/l forchlorfenuron treatment 14 days after full bloom, and 1mg/l thidiazuron treatment on full bloom also brought about positive effects on the enlargement of the fruit, increasing 6.3%, 6.3% and 8.1% in its transverse diameter, respectively. Furthermore, the effects of the plant growth regulator treatments on the harvest time of Sageretia thea were determined as follows: the increase in the optimal harvest time of 57.2 - 75.4%, shorter maturation period, by the treatments with 500mg/l mepiquat chloride 7 days after full bloom, 100mg/l gibberellic acid treatment on full bloom, 2.5mg/l forchlorofenuron 7 days after full bloom and 2mg/l thidiazuron treatment 7 days before full bloom; and the greater effects of plant growth regulator treatments on the fruit maturation in the following order, gibberellic acid thidiazuron forchlorofenuron mepiquat chloride. The results of this study are expected to be used as a reference data to develop Sageretia thea as a new local specific crop for Jeju island.
The effects of timing of high temperature treatment around watermelon fruit during the fruit enlargement were investigated with respect to the sugar content and cell size in the central, intermediate ...(between the two placental sectors) and outer regions of fruit. Fruit growth was significantly accelerated during high temperature treatment regardless of its timing. Cells in the central region of fruit enlarged more actively from 10 to 20 days after anthesis (DAA) at higher temperatures, but high temperature treatment after 20 DAA resulted in cell enlargement in the intermediate and outer regions of fruit. With the exception of sucrose content in the central and intermediate regions of fruit, sugar contents at harvest time increased with high temperature treatment from 10 to 20 DAA, whereas high temperature treatment after 20 DAA reduced sugar levels throughout the fruit. These results suggest that active cell enlargement in the central region of fruit during the early stage of the fruit enlargement caused by high temperature promote sugar accumulation in fruit during maturation.
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