Hormonal Control of Assimilate Movement and Compartmentation

Abstract

Correlated growth and development of plant organs is generally regarded as being controlled by a balance of endogenous hormones and/or responsiveness of the tissues to the hormones present. For many years, several approaches haven been followed to investigate the possibility that hormones may be involved in the production and movement of assimilates to developing organs. These approaches include the collation of correlative evidence, pharmacological studies, manipulation of endogenous hormones by environment or genotype and hormone replacement studies following sink excision [68]. All these approaches have yielded information tending to support the concept of hormonal control of assimilate partitioning, but the general conclusion seems to be that the major rate-limiting steps arise from or occur in the sink tissues themselves. This idea is supported in that sink tissues, particularly fruits and seeds, are often the richest sources of plant hormones as demonstrated by the use of modern hormone analytical procedures [38]. However, detailed knowledge of the distribution of hormones in various tissues and their fluxes within the plant are still required before the exact role of hormones in assimilate synthesis and partitioning can be elucidated. Since the topic of assimilate control has received considerable attention recently this brief review will attempt to highlight some of the current evidence in favour of hormonal control, particularly in relation to sink activity.