Galactosyl Cyclitols and Raffinose Family Oligosaccharides in Relation to Desiccation Tolerance of Pea and Soyabean Seedlings

Abstract

The loss of desiccation tolerance of pea and soyabean seedlings and associated changes in their soluble carbohydrates were studied. For the desiccation tolerance test, intact seedlings were dried rapidly at 12% relative humidity, or slowly in a series of decreasing relative humidities, followed by rehydration. Soluble carbohydrates were assayed before and after drying. Survival and regrowth of shoot, hypocotyl and root tissues were recorded. Soyabean hypocotyl and root tissues los t desiccation tolerance within 36 h during germination in association with the loss of raffinose, stachyose, galactopinitol A, galactopinitol B, ciceritol, and fagopyritol B1. In contrast, fructose, glucose and sorbitol accumulated. Sucrose levels increased during desiccation, but there was no effect of drying on changes of other soluble carbohydrates. Pea root tissues lost desiccation tolerance during the first 36 h of germination. Unlike roots, 80% of pea epicotyls survived the slow drying treatment and 40% survived the fast drying treatment of seedlings at up to 96 h after imbibition. Sucrose levels increased 5 to 10 fold in root and hypocotyl tissues and even more in epicotyls during desiccation. Glucose and fructose increased during germination and remained elevated after drying. The data indicate that monosaccharides may induce desiccation damage whereas oligosaccharides are not a prerequisite for desiccation tolerance of pea seedling epicotyls.