The effect of seed conditioning, short-term heat shock and salicylic, jasmonic acid or brasinolide on sunflower (Helianthus annuus L.) chilling resistance and polysome formation

The aim of this study was to develop the method for increasing resistance of sunflower seedlings 'Wielkopolski' to chilling. Seeds were conditioned at 25 A degrees C for 2 days in water to 15, 20 and 25 % moisture content or in salicylic or jasmonic acid in concentration of 10(-2); 10(-3) and 10(-4) M or brassinolide in concentration of 10(-6); 10(-8) and 10(-10)-15 % moisture content. After 2 days of incubation the conditioned seeds were heat shocked at 45 A degrees C for 0, 30, 60, 120 and 240 min and 5 mm seedlings were exposed to chilling at 0 A degrees C for 21 days. The effectiveness of the methods was assessed by evaluation of roots growth in Phytotoxkit Microbiotest, changes in the activity of dehydrogenases, the integrity of the cytoplasmic membrane and formation of polysomes after seedling were returned to 25 A degrees C for 72 h. Seeds were conditioned at 25 A degrees C for 2 days in water to 15 % moisture content and then heat shocked at 45 A degrees C for 2 h decreased chilling injury of seedlings expressed by subsequent growth of the roots, electrolyte leakage, dehydrogenases activity and polysomes formation. Application of heat shock of 45 A degrees C for 2 h during seed conditioning additionally provided seedling protection against subsequent chilling conditions. Brasinolide, salicylic acid or jasmonic acid applied during seeds conditioning exhibited further beneficial effect on seedling resistance to chilling. The most pronounced effect was obtained due to seed conditioning to 15 % moisture content in solutions of brassinolide in concentration of 10(-8) M. After 2 days of imbibition treated in this way seeds were exposed to heat shock at 45 A degrees C for 2 h. The role of physiological events in improvement of sunflower chilling tolerance are discussed.