Morphological, physiological, and biochemical plant
responses were studied in unstressed and stressed seedlings
of
indica rice (
Oryza sativa
L.) genotypes. The effect of NB
medium supplemented with a 100 mM mannitol treatment,
which induced drought stress conditions, was measured for
relative growth rate, cell membrane stability, antioxidant
enzyme activity (superoxide dismutase [SOD], catalase [CAT],
and peroxidase [POD]), and total antioxidant capacity by
DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2′-azinobis[
3-ethylbenzothiazoline-6-sulfonic acid] diammonium salt)
assays. Results of morphological and physiological factors
showed two contrasting rice groups, drought-sensitive and
drought-tolerant genotypes. After drought stress, the increased
rate of SOD activity was lower in drought-tolerant than in
drought-sensitive genotypes, but the increased rate of CAT
and POD activity and total antioxidant capacity was higher
in drought-tolerant than in drought-sensitive genotypes.
Increasing changes in activity levels of antioxidant enzymes
and total antioxidant capacity indicated more rapid free
radical scavenging compared with relative growth and cell
membrane stability in drought-tolerant genotypes under shortterm
treatment. The trend toward change in CAT and POD
antioxidant enzyme activity and total antioxidant capacity of
stressed seedlings, as well as the correlation between these
changes, and the morphological and physiological responses
(0.96 correlation coefficient [R
2] between relative growth
rate and CAT; 0.93 R
2 between relative growth rate and POD
enzyme activity; 0.96 R
2 between relative growth rate and
Trolox equivalent antioxidant capacity values) coincided with
the degree of drought tolerance.
