Two castor bean cultivars were subjected to
water stress induced by polyethylene glycol 6000 (PEG)
under in vitro conditions. After 15 days, a reduced percentage
of surviving plants, leaf abscission and greater leaf
cuticular wax content were observed, accompanied by
reduced water loss through the leaves. PEG also caused a
decrease in soluble protein content and increases in the
levels of hydrogen peroxide (H2O2) and malondialdehyde,
as well as increases in the specific activities of superoxide
dismutase, ascorbate peroxidase and catalase enzymes.
These findings suggest that the mechanisms of tolerance of
these genotypes are associated with their ability to activate
key enzymes of the antioxidant defense system. However,
the adaptive responses induced in response to stress were
not sufficient to improve plant performance during the
acclimatization period, and their survival rate dropped
nearly 50 % relative to control treatment.