A model of seed dormancy

Abstract

Seed dormancy is considered as an aspect of growth cessation. It is characterized by partial metabolic arrest with its inception and termination under endogenous hormonal control. Although several distinct types of seed dormancy have been recognized traditionally, an examination of the experimental literature suggests that a common regulatory mechanism exists. Dormancy onset, control, and termination are apparently regulated by a balance of growth inhibitors and promotors. At the onset of dormancy this balance is shifted in favor of the inhibitor component; at its termination it is shifted back in favor of the promotor component. The experimental evidence indicates that the levels of growth-promoting hormones decrease markedly during seed maturation, imposing dormancy. A trigger mechanism stimulates hormone activation and/or synthesis, thus terminating dormancy and culminating in resumption of embryo growth (germination). A model is proposed that embodies a hormonal regulation of four phases of dormancy: an inductive mechanism, a maintenance mechanism, a trigger mechanism, and a germination mechanism. This hormonal regulation, in conjunction with specific metabolic inhibitors, is considered to mediate the activation and/or synthesis of hydrolytic enzymes. From this model the dormant seed is viewed as a cybernetic system. Particular emphasis is given to the regulatory role of gibberellins in seed dormancy and germination.