Changes in the structure of apical buds and distribution of starch grains in wax apple during flower formation

Abstract:【Objective】To study the changes in the distribution of starch grains in cells and the structure of wax apple buds during flower bud induction and differentiation induced by shading and chlorpyrifos treatment.【Methods】‘Heizhenzhu'[Syzygium samarangense (BI.) Merr. et Perry.] wax apple trees were selected for the study at the stage when the leaves of the new shoots were turning green. Trees were shaded with 90% shading nets for 64 days to control the vegetative growth. After the shading net was removed, solution of 48% chlorpyrifos diluted by 300 times was sprayed to all the trees to promote flower bud initiation. After shaded for 0, 45, 64 d and removing the shading nets for 4, 11, 22 days, apical buds of all the trees were collected for paraffin sections to study the structure and the distribution of starch grains in cells of the apical buds.【Results】All the trees were at the stage of turning green prior to the treatment. After 64 d of shading treatment, apical buds in the treated trees were in a dormant state.Then the shading nets were removed from the trees and the trees were sprayed with diluted chlorpyrifos to promote flower initiation. Starch grain could be found before shading and they could be still seen during the shading treatment. They were concentrated in the axis of the treated apical buds. However, the starch grains in the control trees disappeared with the growing of the new shoots, and no starch grains in the cells of the control buds were found. These results suggested that the growth of the new flushes repressed starch accumulation in cells of buds whereas shading could maintain starch by suppressing the vegetative growth. Twenty two days after removing the shading nets from the trees, flower buds could be observed. The results also showed that starch grains could be found in the pedicel, receptacle, corolla, calyx and epidermis at corolla differentiation stage.【Conclusion】Shading can induce bud dormancyin wax apple and inhibit vegetative growth. Growth of new flushes represses starch accumulation in cells of buds whereas shading maintains starch accumulation by suppressing vegetative growth.