Abstract
Plants are continuously challenged by abiotic stresses like drought leading to changes in physiological,
biochemical and molecular processes. Exogenous application of protectants is one of the important
options for modulating antioxidant defense and the glyoxalase system, which reduces drought-induced
oxidative damage in plants. The present study investigated the physiological and biochemical alterations
conferring drought tolerance in sesame in presence of exogenous protectants. Forty sesame genotypes
were screened against drought stress in a pot experiment at the Poly House of Seed Technology Division
of BARI, Gazipur during 2015-16. The sesame genotypes were grown under control (90-95% FC) and
drought (40-45% FC) stress. Drought stress was imposed at thirty days after sowing and maintained up to
maturity. The drought stress had a significant effect on various yield and yield parameters and also the
drought tolerance indices. Based on the study's results, a second screening experiment was carried out to
determine the drought-related biochemical alterations of 10 selected sesame genotypes. A significant
difference was also recorded among biochemical characteristics (viz. chlorophyll, proline, O2, H2O2,
MDA and MG content) in all sesame genotypes against drought. Considering the biochemical alterations
BD 6971 and BD 6964 appeared as relatively tolerant genotypes whereas, BD 6982 and BD 6980 were as
relatively susceptible genotypes. In third experiment, these four genotypes were evaluated under drought
stress for exerting their drought tolerance in presence of exogenous protectants proline (15 mM) and
trehelose (10 mM). Significant decrease in respect to plant height, number of pods plant¹, leaf area, RWC,
TDM, CGR, RGR and seed yield plant¹ were observed in all the genotypes due to drought. However,
growth and yield performance of all sesame genotypes were regained when the plants were treated with
either proline or trehelose. Genotype BD 6971 showed the best performance whereas BD 6980 showed the
least one. Fourth and fifth experiments were conducted using a relatively drought tolerant BD 6971 and a
drought sensitive BD 6980 to evaluate the protective roles of protectants on the antioxidant defense and
glyoxalase systems for alleviating the effect of drought in sesame. Drought stress caused a significant
decrease in chlorophyll pigments (Chl a and Chl b), carotenoid (Car) and increase in endogenous proline
of both sesame genotypes. However, this trend was more prominent in BD 6980 genotype compared with
BD 6971. Protectants (Pro and Tre) treated seedlings of both genotypes maintained higher chlorophyll and
Car contents, compared with drought treated seedlings without the protectants. The tolerant genotype BD
6971 exhibited lower accumulation of MDA, LOX, ROS (H2O2 and O2*) and MG than that of BD 6980
genotype under drought condition. In contrast, drought increased SOD, POD, APX, GPX, GST, and
DHAR activities in both the genotypes. The activities of CAT and MDHAR decreased in both genotypes,
but these antioxidants activities were higher in tolerant genotype BD 6971 at both under control and
drought stress conditions than sensitive genotype BD 6980. In addition, GR activities and toxic MG
production were recorded which were possibly detoxified by glyoxalase enzymes (Gly-I, and Gly-II)
activities. Application of exogenous proline and trehelose under drought stress improved physiological
parameters and minimized oxidative damage in both the genotypes, where BD 6971 was significantly
superior to BD 6980. The results suggest that exogenous application of proline and trehelose in sesame
increased drought tolerance in the crop by alleviating drought-induced oxidative damage through
upregulation of antioxidant defense and glyoxalase system.