Role of polyamines and ethylene as modulators of plant senescence

Under optimal conditions of growth, senescence, a terminal phase of develop ment, sets in after a certain physiological age. It is a dynamic and closel y regulated developmental process which involves an array of changes at bot h physiological and biochemical levels including gene expression. A large n umber of biotic and abiotic factors accelerate the process. Convincing evid ence suggests the involvement of polyamines (PAs) and ethylene in this proc ess. Although the biosynthetic pathways of both PAs and ethylene are interr elated, S-adenosylmethionine (SAM) being a common precursor, their physiolo gical functions are distinct and at times antagonistic, particularly during leaf and flower senescence and also during fruit ripening. This provides a n effective means for regulation of their biosynthesis and also to understa nd the mechanism by which the balance between the two can be established fo r manipulating the senescence process. The present article deals with curre nt advances in the knowledge of the interrelationship between ethylene and PAs during senescence which may open up new vistas of investigation for the future.