Effects of Age and Water Stress on Endogenous Levels of Plant Growth Regulators inEuphorbia lathyrusL.

Abstract

The effect of droughting and waterlogging on changes in endogenous levels of hormones have been studied in Euphorbia lathyrus L. with particular reference to plant age and leaf age. Younger tissues (i.e. immature leaves and young plants) synthesized significantly greater amounts of ABA per unit fresh weight than did corresponding older tissue. The increased ABA levels correlated well with corresponding increases in water saturation deficit (WSD) and stomatal resistance in a given treatment but the relationship between the absolute values of these three parameters varied greatly between seedlings of different ages. Endogenous ethylene levels in leaves and stems were unaffected by droughting irrespective of age. Imposition of waterlogging led to marked increases in ABA levels in young plants though this was not strictly related to changes in WSD or stomatal resistance. Endogenous levels of ethylene increased in response to waterlogging, this being marked in the older seedlings which also had a higher incidence of senescence and abscission. The more complex effects of waterlogging, the significance of age of tissue on hormonal responses to stress, and the adaptive value of such responses to younger tissues are discussed.