Effects of Far-red Light on the Hormonal Control of Side Shoot Growth in the Tomato

Abstract

Side shoot growth in young tomato plants was almost completely suppressed by a 5 min period of far-red light immediately following a 16 h photoperiod from fluorescent tubes, whereas plants given an identical photoperiod but lacking the far-red treatment branched profusely. The influence of far-red light on the degree of side shoot suppression and the correlated changes in the levels of auxins, gibberellins, cytokinins and abscisic acid is presented and discussed in relation to current hypotheses of correlative inhibition. It is suggested that far-red light causes increased auxin synthesis in the apex and young leaves, which in turn induces the formation of abscisic acid in or near the axillary buds, and it is this hormone which inhibits bud outgrowth. The role of cytokinins and gibberellins remains uncertain but they probably act in a sequential manner, the gibberellins promoting bud growth following cytokinin-mediated release from apical dominance.