1981 Volume 50 Issue 3 Pages 287-296
The purpose of our investigation is to clarify the development of apple fruit in the early stages of its growth. Tukey (22, 23) observed that early fruit development was stimulated by high night temperatures. This observation suggested that night heating treatment would be a useful means for our purpose. Therefore, the effect of heating on fruit development, elongation and division of cells and development of seed and embryo were investigated. Eight-year-old ′Spartan′ trees were covered with plastic films and heated with oil heaters for 30 days beginnirg on the 7th day after full bloom. Night temperatures in night-heating treatment and day- and night-heating treatment were regulated at 23°C, and the day temperature in day-and night-heating treatment was kept 4°C higher than outdoor temperature. Under these conditions, the developments of fruit and seed were histologically investigated.
1. Little difference between night-heating and day-and night-heating treatments was recognized in the development of fruit.
2. Increase of diameter and weight of fruit was enhanced by heating, and the differences between control and heating were seen at their maxima 19 days afterfull bloom. However, no difference was recognized 35 days after full bloom and the size of fruit in heating was almost the same as in control.
3. Changes of cell diameter of fruit flesh in heating were similar to those in diameter and weight of fruit. In other words, the difference of these values between heating and control was at its maximum 19 days after full bloom but it became smaller with time and finally disappeared.
4. Cell division of fruit flesh was stimulated by heating. It ceased 40 days after full bloom in control while 10 days earlier in heating.
5. The development of seeds in fruit in heating showed a tendency to correspond to the increase in number of cell layers of fruit flesh. The seed in heating developed rapidly unitl the 30th day after full bloom, and ceased to develop thereafter. The seed development in control, however, continued unitl the 40th day after full bloom.
6. The development of embryos was stimulated by heating. The embryo in heating reached the spindle type stage ten days earlier than in control. However, the difference in embryo development between heating and control reached its maximum on the 30th to 40th days after full bloom.
As described above, the development of fruit was stimulated by heating, and that was due to the enhanced cell enlargement and division of fruit flesh. In addition, a close relation was observed between the developments of fruit and seeds. However, it seems that the embryo has hardly any effect on the development of fruit. Therefore, it is surmised that the endosperm may be related to the development of fruit.