duced by the plants known as plant hormones. The plant hormones
are organic substances, which in very low concentrations have
influence on growth, differentiation and development of plants
[1]. Plant hormones play a crucial role in the regulation and coordination
of plant growth, morphogenesis, metabolism and role in
biosynthesis of secondary metabolites [2]. The naturally occurring
plant growth substances as well as synthetic substances like
auxins, gibberellins, cytokinins, abscisic acid, ethylene, cytokinin,
brassinosteroids, terpenoids, aliphatic alcohols and polyamines
have growth regulating properties in various plants [3]. Plant
growth retardants are widely used to modify canopy structure,
yield and stress tolerance in many crop plants [4].
Abscisic acid (ABA) is a plant growth regulator that has been
identified as a messenger in stress–perception–response pathways
such as drought, high temperature, low temperature and salinity
stress. Many studies have shown that ABA can enhance the tolerance
of plants to environmental stresses. ABA is involved in many
physiological processes [