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 tolerance ofhydrated crop seeds (tomato, okra, snow pea, mung bean, and cucumber) wasevaluated by imbibing seeds with or without ABA, followed by dehydrationand germination. During the process of hydration, but before the seeds lostdesiccation tolerance, monosaccharide content increased only slightly,sucrose increased in snow peas, mung bean and cucumber, but maintained itsoriginal level in other species and the oligosaccharides declineddramatically. At the time of losing desiccation tolerance, the sucrosecontent of imbibed seeds was 2-3 times higher than the original level inmost species. Positive significant correlation coefficients(r) were found in many, but not all crop seeds betweendesiccation tolerance and the oligosaccharide mass, or oligo/sucrose ratio.The ratio of oligo/sucrose in intact seeds at the time of losingdesiccation tolerance, however, was not a fixed value and varied amongspecies. Oligosaccharides declined significantly in different seed parts ofimbibed cucumber seeds while sucrose increased to a higher level in theradicle than in the hypocotyl. Radicles were far more sensitive todesiccation than hypocotyls. The same observation was found for cucumberseeds imbibed in 100 M ABA, yet desiccationtolerance was largely maintained in hypocotyls and cotyledons. It isconcluded that sucrose and oligosaccharides are not the determinants of theloss of desiccation tolerance in hydrated seeds.Imbibed seeds did not showany differences between seed parts in their ability to resynthesize sugarsduring the process of slow dehydration. Differences in sensitivity todesiccation among seed parts were not due to differences in the initialwater content or to the rate of water content increase among seed parts.Physiological regulation of the loss of desiccation tolerance in crop seedsduring hydration is discussed.