Abstract
Drought is a very common environmental stress affecting crop production significantly worldwide. Exogenous application of protectants is one of the important options to modulate antioxidant defence and the glyoxalase system that reduces drought-induced oxidative damage in plants. But drought with exogenous application of protectants for improving the capacity of drought tolerance has not been examined in Bangladeshi wheat genotypes. The present study investigated the physiological and biochemical mechanisms of drought tolerance in wheat in presence of protectants. Forty wheat genotypes were screened against drought stress in a pot experiment at the greenhouse of BARI, Gazipur during 2012- 13. The wheat genotypes were grown under 90-100% and 40-45% FC that were imposed after CRI stage. The water regimes had a significant effect on various yield and yield parameters and also the drought tolerance and susceptibility indices. Based on these findings of the study another screening experiment
was conducted in laboratory conditions using ten wheat genotypes against four concentrations of PEG- 6000 (0, 10, 15 and 20%). The seedling traits showed a decreasing trend in response to increased PEG concentrations. A significant difference was also recorded among genotypic and PEG levels treatment
means regarding all the traits. On the basis of seedling traits and drought tolerance indices against PEG induced drought, CSISA DR-30 genotype performed the best. In third experiment, four genotypes were evaluated for growth and yield performance under three water regimes. Results showed that, decreased FC reduced the grain yield. Genotype CSISA DR-30 showed the best performance in respect of plant height, leaf area, RWC and grain yield under moderate (55-60% FC) and severe stress (35-40% FC) conditions while the susceptible genotype BAW-1163 exhibited poor performance. Drought tolerant genotype also maintained a higher rate of CGR and RGR which contributed towards higher TDM plant1 under drought stress compared with susceptible genotype. Fourth and fifth experiments were conducted to appraise the roles of protectants on the antioxidant defense and glyoxalase systems for alleviating the effect of drought in wheat. Two contrasting wheat genotypes, a relatively drought tolerant CSISA DR-30 and a drought sensitive BAW 1163 were used in the study. Eight-day old seedlings of approximately equal sizes of two wheat genotypes were subjected to drought stress induced by 12% PEG with or without 15 mM proline, 15 mM betine, 10 mM trehelose, 1 mM ascorbate, 1 mM glutathione and 1 mM salicylic acid as a rooting medium for 2, 4 and 6 day, respectively. Drought stress caused a significant decrease in chlorophyll pigments (Chla and Chlb), carotenoid (Car) and RWC and increased endogenous proline of both wheat genotypes. However, this trend was more severe in seedlings of BAW-1163 genotype compared with CSISA DR-30. Protectants treated seedlings of both genotypes maintained higher chlorophyll contents, Car, RWC and growth compared with without protectants-treated seedlings. The
MG
tolerant genotype CSISA DR-30 exhibited lower accumulation of MDA, LOX, ROS (H2O2 and O2*-) and than that of BAW-1163 genotype under drought condition. Drought stress increased SOD, POD, APХ, GPX, GST, DHAR, DHA and GSSG activities in both seedlings. However, CAT, MDHAR, ASA, ASA redox, GSH and GSH redox activities were decreased in both genotypes, but these antioxidants activities
were higher in tolerant genotype at both under control and drought stress conditions than sensitive wheat seedling. The activities of GR, Gly-I, and Gly-II were reduced in sensitive genotype and these were increased in tolerant genotype by drought stress. Exogenous Pro, GB, Tre, ASA, GSH and SA application with PEG-induced drought stress improved physiological parameters and reduced oxidative damage in both
exogenous
genotypes where CSISA DR-30 wheat seedlings showed better tolerance. The result suggest that application of Pro, GB, Tre, ASA, GSH and SA increased wheat seedlings' tolerance to drought- induced oxidative damage by upregulating their antioxidant defense and glyoxalase system where these protectants rendered better performance with CSISA DR-30 and Pro appeared as the best protectant.This genotype should be utilized as parent materials in breeding program to develop drought tolerant wheat variety in Bangladesh.