Photosynthetic Efficiency and Antioxidant Defense Potential are Key Players in Inducing Drought Tolerance in Transgenic Tobacco Plants Over-Expressing AVP1

Plants have developed a number of physiological, biochemical, and molecular strategies to overcome water deficit conditions. Arabidopsis vacuolar pyrophosphatase 1 (AVP1) can enhance stress tolerance in plants through ion homeostasis, redox balance, and photosynthetic activity. In the present study, three transgenic tobacco lines overexpressing AVP1 gene were compared with a wild type (WT) line to assess the role of AVP1 in inducing drought tolerance. For this purpose, four-week old tobacco plants were subjected to cyclic drought for three weeks and were evaluated for different physio-biochemical parameters. Drought stress reduced shoot and root dry mass (85% and 73%), relative water content (55%), K+ accumulation (42%), and Photosystem-II (PSII) efficiency (27%), but this effect was less on transgenic tobacco lines of AVP1 (L2, L3). Drought stress decreased performance index (PIABS) by 48% in WT plants, which is linked with substantial increase in specific energy fluxes through PSII per active reaction center (ABS/RC, TR0/RC) and cause a decrease in electron transport (ET0/RC) by 47%, that resulted in damage of donor end of PSII. However, AVP1 transgenic line L3 showed minimum decrease in quantum efficiency of PSII (3%) and PIABS (12%) due to lesser drought-induced oxidative damage and having higher catalase activity (96%). As compared to control plants, drought-stressed WT plants significantly enhanced hydrogen peroxide and malondialdehyde production by 101% and 98%, respectively. However, transgenic lines particularly L2 and L3 had lower levels of H2O2 (26% and 14%) and MDA (56% and 16%), which were positively associated with higher activities of catalase. In conclusion, AVP1 gene helped to maintain water and K+ homeostasis, which in turn affected the redox balance and PSII structural and functional stability.