PHYSIOLOGICAL AND BIOCHEMICAL-CHANGES INDUCED IN SUNFLOWER SEEDS BY OSMOPRIMING AND SUBSEQUENT DRYING, STORAGE AND AGING

Sunflower (Helianthus annuus L.) seeds show more germination at high t emperatures (25-30 degrees C) than at temperatures below 20 degrees C. Osmopriming with polyethylene glycol-6000 for 3-5 days at 15 degrees C strongly increases germination at suboptimal temperatures. This stim ulatory effect of priming persists after seed redrying and during subs equent storage at 20 degrees C (55% RH) for at least 14 weeks. However , primed seeds deteriorate faster than untreated seeds during accelera ted aging (45 degrees C, 100% RH). The longer the priming treatment. t he higher is the amount of germination but at the same time the higher is the sensitivity of seeds to accelerated aging. Priming enhances th e respiratory activity of seeds transferred onto water and their abili ty to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. These effects remain after drying the seeds and are maintained in par t during dry storage, whereas they disappear during accelerated aging. These results suggest that ACC-dependent ethylene production might be a good indicator of seed vigour; it increases with duration of primin g and decreases very early during aging, well before significant loss of seed viability. Decrease in ACC conversion to ethylene indicates th at aging is probably associated with membrane deterioration since in v ivo ACC oxidase activity depends on membrane properties. However, no i ncrease in electrolyte leakage is observed during aging.