HIGHER ANTIOXIDANT CAPACITY PROTECTS PHOTOSYNTHETIC ACTIVITIES AS REVEALED BY CHL A FLUORESCENCE IN DROUGHT TOLERANT TOMATO GENOTYPES

Drought is the most important factor limiting growth and yield of tomato. Genetic improvement in tomato for water stress tolerance is of prime importance for economically and efficient utilization of arid area land resources. Since photosynthetic efficiency and antioxidant capacity are associated with degree of water stress tolerance in tomato genotypes, experiment was conducted to assess relationship between plant antioxidant capacity and activity of photosynthetic apparatus. Fifteen tomato genotypes differing in their drought tolerance were subjected to different levels of PEG(8000) (Control, 5%, 10% & 15%) at the seedling stage. It was concluded that water stress tolerant tomato genotypes (CLN-1767 and Lyallpur-1) also maintain relatively higher photosynthetic efficiency as assessed through A/Ci curve or PSII efficiency. Chlorophyll fluorescence measurements revealed that NPQ increased whereas the electron transport rate decreased under waters stress. Water stress tolerant tomato genotypes down regulate ETR with increase in NPQ to avoid photoinhibition and photodamge. Protection of photosynthetic machinery in water stress tolerant genotypes might have been due to higher antioxidant capacity. Water stress tolerant cultivars exhibited much lower lipid peroxidation, and showed increased activities of the enzymes involved in the ROS scavenging system. Up-regulation of the antioxidant system plays a role in water stress tolerance of tomato.