Plant hormones regulate the growth and development of plants
under various environmental conditions related to changes in
their qualities and quantities. There are numerous reports on the
close relationships between leaf senescence and endogenous levels
of abscisic acid (ABA). ABA content increases during senescence
(Gepstein and Thimann, 1980; Dong et al., 2008) or N deficiency
(Zdunek and Lips, 2001; Schraut et al., 2005). Although there are
also numerous reports concerning the relationship between the
level of ABA and chlorophyll degradation in leaves, as described
above, we propose a new role for ABA in the accumulation of chlorophyll
in cucumber (Cucumis sativus) leaves grown under low-N
conditions. We recently found that the endogenous levels of ABA
increased in cucumber plants grown under low-N conditions, and
exogenously applied ABA resulted in the inhibition of the senescence
of leaves in these plants. In this study, we report the effects
of ABA on the biosynthesis and degradation of chlorophyll, and senescence in cucumber plants grown under low-N conditions in
the presence of ABA.