1994 Volume 63 Issue 2 Pages 313-321
To elucidate the mechanism of flower differentiation, a study was conducted on the morphological and cytological changes in apical meristem of Japanese pear (Pyrus pyrifolia Nakai cv. Shinsui) during flower differentiation comparing buds on spurs and vegetative buds on elongating shoots. Emphasis is put on the stages until sepal differentiation.
1. First sign of morphological flower differentiation became evident on June 26. The bud scales loosened and the apical meristem began to enlarge. Primordia of lateral flower buds appeared on July 3. In apical meristem sepal primordia differentiated on July 10, followed by the petal primordia on July 17, and stamen primordia on July 30. The pistil primordia appeared between September 2030.
2. Apical meristem was divided into the following 4 zones by the arrangement, shape, and cytology of the cells: tunica, corpus, quiescent zone and pith. Tunica and corpus were the main dividing tissues in which the cells contained small vacuoles and few starch grains, whereas cells of quiescent zone and pith contained larger vacuoles and many starch grains.
3. When the apical meristem began to enlarge, an indication of flower differentiation, the following was observed: 1) starch grains started to accumulate in the cells of quiescent zone, 2) the activity of corpus cells was enhanced, 3) shape of the cells of corpus and quiescent zone changed, and 4) the number of tunica cell layers decreased while the number of corpus cell layers increased.
4. The cells in queiscent zone and pith of apical meristem of the buds on spurs contained a large amount of starch grains which markedly increased particularly in the cells of quiescent zone during the enlargement of apical meristem. Contrarily, no accumulation of starch grains was observed in the cells of vegetative buds on the elongating shoots. In the apical meristem of the flower buds, starch grain temporarily appeared in the corpus cells but soon disappeared. After the sepal differentiation began, starch grains nearly disappeared in all parts of the apical meristem.
5. Role of quiescent zone in flower differentiation is discussed in relation to starch metabolism in these cells.