Effect of cytokinin application on lateral bud growth and endogenous auxin concentration under control and B deficiency conditions

摘要

The release of lateral bud growth from apical dominance is a typical symptom of boron (B) deficiency. In various experiments with exogenous application of synthetic cytokinin (CPPU) to pea (Pisum sativum L.) seedlings, the possible regulatory mechanism of phytohormone in apical dominance was studied under control and B-deficient conditions. In detail, lateral bud growth and IAA concentration in different plant positions, as well as IAA export from shoot apex, were analyzed. Under control conditions, exogenous cytokinin (CPPU) application to the 2nd node of pea plants continuously stimulated lateral bud growth, manifested by increasing the number, length and weight. This treatment also increased endogenous IAA concentration at the application site, while at the same time reduced its concentration in the dominant branch. Compared with control, CPPU application reduced the IAA export from dominant apex. Under B-deficient conditions, CPPU application to the 2nd node transiently increased lateral bud growth but later this effect disappeared. In addition, CPPU application to B deficient plants did not stimulate IAA concentration at the application site and had no effect on IAA concentration and export from dominant branch. These results confirmed the idea that polar auxin transport played an important role in apical dominance and the decrease in IAA export induced by B deficiency caused the release of lateral bud growth. Moreover, cytokinin could stimulate auxin concentration in the application site under control conditions, which resulted in breaking apical dominance and releasing lateral bud growth. In contrast to control, the inability of CPPU in B-deficient plants to influence IAA concentration and release of apical dominance indicated that B might also beinvolved in the IAA biosynthesis or metabolism.