ACETYL SALICYLIC ACID AND 24-EPIBRASSINOLIDE ATTENUATE DECLINE IN PHOTOSYNTHESIS, CHLOROPHYLL CONTENTS AND MEMBRANE THERMO- STABILITY IN TOMATO (LYCOPERSICON ESCULENTUM MILL.) UNDER HEAT STRESS

Abstract

The effect of exogenous application of varying levels of 24-epibrassinolide (0.75, 1.5 and 3 µM) and acetyl salicylic acid (0.25, 0.75 and 1.25 mM) for induction of heat tolerance in terms of their effect on photosynthesis, chlorophyll content, membrane integrity and survival in four weeks old tomato (cultivar: Mei Jie Lo) seedlings under high temperature stress (46°C/4 h daily) for 21 days was investigated. The daily heat stress treatment had deleterious effects on seedlings but chemical treatments significantly reduced the magnitude of losses to different extents. 24-epibrassinolide (3 µM) was over all the best treatment to improve survival (86.11%), photosynthesis (39.4%) and chlorophyll contents (26.12%) accompanied with initiation of flower buds and improved vegetative growth. Whereas acetyl salicylic acid (1.25 mM) best improved photosynthetic activity (40.6%) as compared to the untreated heat stressed control seedlings. Moreover, 3 µM 24- epibrassinolide and 0.75 mM acetyl salicylic acid reduced cell membrane injury to 8.3 and 6.9% respectively as compared with 22.4% in heat stressed control seedlings. However lower doses of acetyl salicylic acid (0.25 and 0.75 mM) had slight (5.6 and 12.8%) inhibition effect on the photosynthesis than the heat stressed controls. Overall both acetyl salicylic acid and 24-epibrassinolide up regulated basal heat tolerance in tomato seedlings and studied concentrations demonstrated signature affect upon different parameters. Thus both chemical agents can be potential candidates for further investigations for exogenous application aiming at extension of tomato growth season in summer.