Photoregulation of growth and branching of plum shoots: Physiological action of two photosystems

Plum shoot proliferation was investigated in terms of two distinct processe s: axillary bud differentiation and axillary shoot development. Results sho wed that light quality influenced bud differentiation and interacted with a pical dominance in determining shoot outgrowth, resulting in a differentiat ed structure of shoot clusters and type of branching. Results suggested tha t blue light, acting through its photoreceptor, increased the number of axi llary buds differentiated from apical meristem, but did not remove the apic al dominance. Red light removed apical dominance, while reducing the format ion of axillary buds; both events appeared to be dependent on the putative amount of phytochrome active form, and independent of light photon fluence rate. On the contrary, blue light action appeared to be dependent on photon fluence rate. In addition, apparent blue-red interactions related to photo morphogenic events fit an antagonistic model for branching regulated by lig ht via cryptochrome and phytochrome, photoreceptors. Our results show that the dynamics of shoot cluster development is the product of two events: the formation of new axillary buds and their release from apical dominance.