Modulation of Dehydration Tolerance in Soybean Seedlings (Dehydrin Mat1 Is Induced by Dehydration but Not by Abscisic Acid).

Germinated soybean (Glycine max L. cv Williams 82) seedlings subjected to rapid dehydration begin to lose the ability to recover when the relative water content of the plant decreases below 60%. The expanded cells of the hypocotyl appear more susceptible to dehydration-induced damage than do cells in the hypocotyl zone of cell growth. Pretreatment of seedlings prior to rapid dehydration with nonlethal water deficit or exogenous abscisic acid (ABA) shifts this viability threshold to progressively lower relative water contents, indicating the acquisition of increased dehydration tolerance. Increased tolerance is associated with osmotic adjustment in the hypocotyl zone of cell growth and with increases in soybean dehydrin Mat1 mRNA levels. The accumulation of Mat1 mRNA is dehydration dependent but insensitive to ABA. Induction of Mat1 mRNA accumulation by dehydration but not by ABA makes it an unusual member of the dehydrin family.