DISAPPEARANCE OF DESICCATION TOLERANCE OF IMBIBED CROP SEEDS IS NOT ASSOCIATED WITH THE DECLINE OF OLIGOSACCHARIDES

The relationship between sugar content and loss of desiccation toleran ce of hydrated crop seeds (tomato, okra, snow pea, mung bean, and cucu mber) was evaluated by imbibing seeds with or without ABA, followed by dehydration and germination. During the process of hydration, but bef ore the seeds lost desiccation tolerance, monosaccharide content incre ased only slightly, sucrose increased in snow pea, mung bean and cucum ber, but maintained its original level in other species and the oligos accharides declined dramatically. At the time of losing desiccation to lerance, the sucrose content of imbibed seeds was 2-3 times higher tha n the original level in most species. Positive significant correlation coefficients (r) were found in many, but not all crop seeds between d esiccation tolerance and the oligosaccharide mass, or oligo/sucrose ra tio. The ratio of oligo/sucrose in intact seeds at the time of losing desiccation tolerance, however, was not a fixed value and varied among species. Oligosaccharides declined significantly in different seed pa rts of imbibed cucumber seeds while sucrose increased to a higher leve l in the radicle than in the hypocotyl. Radicles were far more sensiti ve to desiccation than hypocotyls, The same observation was found for cucumber seeds imbibed in 100 mu M ABA, yet desiccation tolerance was largely maintained in hypocotyls and cotyledons, It is concluded that sucrose and oligosaccharides are not the determinants of the loss of d esiccation tolerance in hydrated seeds. Imbibed seeds did not show any differences between seed parts in their ability to resynthesize sugar s during the process of slow dehydration. Differences in sensitivity t o desiccation among seed parts were not due to differences in the init ial water content or to the rate of water content increase among seed parts. Physiological regulation of the loss of desiccation tolerance i n crop seeds during hydration is discussed.