SummaryThe changes of the activity of growth inhibitors in the latter half of the development of strawberry fruits and the interaction of cytokinin and growth inhibitors on fruit development were investigated.1. Fruits grown at day/night temperature of 30°C/25°C matured earlier than those at 20°C/17°C. The activity of growth inhibitors in the fruits increased with their maturing, and inhibitor activity in the fruits grown at high temperature appeared earlier than that at low temperature.In chromatography of inhibitors on a Sephadex column, peak of inhibitory activity in a bioassay using rice seedling was found in fractions 5 and 6 corresponding with those of authentic ABA.2. Number of days to maturity of fruits in vitro decreased as the concentration of ABA increased in the medium. Number of days to maturity was definitely affected by the concentration of ABA independently of BA concentration when fruits were cultured on the medium with BA and ABA. Fruit maturing was suppressed and inhibitor activity in them decreased when fruits were cultured on the medium with BA.Based on these results, following conclusion can be induced. In the latter half of the development of strawberry fruits, ABA synthesized actively owing to lowering of cytokinin activity in fruits promotes fruit maturing.

To investigate the relationship between cell size and sugar accumulation, fruit of the melon was heated during the early stage of the growing period. The minimum air temperature in the heating apparatus was ≈10 °C higher than the ambient air temperature, and the weight of the heated fruit was greater than that of the control fruit. The number of rectangular parallelepiped (7-mm-long sample serially collected beginning at one end of the 10-mm-wide strip removed from the 10-mm-thick disk at the maximum transverse diameter of the fruit to the opposite end) with cells larger than 200 μm in the heated fruit at 17 days after anthesis (DAA, the end of heating treatment) was much larger that of the control fruit. The mean cell size in the heated fruit at 17 DAA was larger than that of the control fruit. Mean sucrose content of the heated fruit on 40 DAA was larger than the level in the control fruit. Higher fruit temperatures in melons covered with heating apparatus results in the predominance of larger cells and increased accumulation of sucrose in the fruit.

Hollowing (formation of a central cavity) in watermelons plagues the growers by reducing their market values. This paper reports the relationship between the occurrence of this disorder and fruit weight, cell size and number, and the volume of the intercellualr air spaces as by a) nodal position of the fruit, b) NAA application, and c) partial defoliation of the bearing. Fruits borne on the lower, basal nodes (Treatment L) were lighter at harvest than those borne on higher, distal nodes (Treatment H) but the former trended to develop hollowing, whereas the latter did not exhibit this physiological disorder. The basal fruits had fewer but larger cells through the transverse diameter than those of distal fruits ; they also had larger intercellular air spaces than the distal melons did. Fruits painted with NAA (Treatment N) and those on partially defoliated shoots (Treatment D) produced smaller melons having a small or no hollowing. Compared to the basal melons, the NAAtreated ones and those on defoliated shoots had proportionately less large cells and smaller intercellular air spaces. From these results, the following assumptions are drawn. The growth of cells in the inner region of basal fruits with its lower cell density cannot keep pace with the growth of the peripheral cells and of the rind having higher cell density. This differential growth causes cleavage to arise in the inner part of the fruit which gradually develops into a hollowing. When the growth of the fruit is suppressed by NAA or by defoliation, the cells in the inner region are able to grow as fast as those in and near the rind so that no stress is generated within the fruit. Conversely, when the number of cells per fruit is large, as it is in fruits on distal nodes, the growth of cells of the inner region keeps pace with that of the rind. Consequently, no internal strain ensues and no cavitation occurs.

No abstract

Earl's Knight Natsukei No. 2 melons (Cucumis melo L.) were grown in a plastic film greenhouse after seeds were sown on June 25 (early sowing) or on July 15 (late sowing) , 2002. Melons grown early tended to be higher in weight than those grown late. The average temperature throughout the growth period after the early sowing date was much higher than that after the late sowing date. In both rectangular parallelepipeds (7-mm long samples serially collected beginning at one end of the 10-mm wide strip removed from the 10-mm thick disk at the maximum transverse diameter of the fruit to the opposite end) and fruit, the cell size of melons grown early was greater at every stage of fruit development than that of melons grown late. Sucrose content on 30 and 50 DAA (days after anthesis) was greater after the early sowing than the late sowing .These results show that an increasing number of larger cells during early fruit development after early sowing brings active sucrose accumulation, resulting in high sucrose content in the fruit due to high temperature.