DEVELOPMENT OF DESICCATION TOLERANCE DURING EMBRYOGENESIS IN RICE (ORYZA-SATIVA) AND WILD-RICE (ZIZANIA-PALUSTRIS) - DEHYDRIN EXPRESSION, ABSCISIC-ACID CONTENT, AND SUCROSE ACCUMULATION

The ability of seeds to withstand desiccation develops during embryoge nesis and differs considerably among species. Paddy rice (Oryza sativa L.) grains readily survive dehydration to as low as 2% water content, whereas North American wild rice (Zizania palustris var inferior [Fas set] Dore) grains are not tolerant of water contents below 6% and are sensitive to drying and imbibition conditions. During embryogenesis, d ehydrin proteins, abscisic acid (ABA), and saccharides are synthesized , and all have been implicated in the development of desiccation toler ance. We examined the accumulation patterns of dehydrin protein, ABA, and soluble saccharides (sucrose and oligosaccharides) of rice embryos and wild rice axes in relation to the development of desiccation tole rance during embryogenesis. Dehydrin protein was detected immunologica lly with an antibody raised against a conserved dehydrin amino acid se quence. Both rice and wild rice embryos accumulated a 21-kD dehydrin p rotein during development, and an immunologically related 38-kD protei n accumulated similarly in rice. Dehydrin protein synthesis was detect ed before desiccation tolerance had developed in both rice embryos and wild rice axes. However, the major accumulation of dehydrin occurred after most seeds of both species had become desiccation tolerant. ABA accumulated in wild rice axes to about twice the amount present in ric e embryos. There were no obvious relationships between ABA and the tem poral expression patterns of dehydrin protein in either rice or wild r ice. Wild rice axes accumulated about twice as much sucrose as rice em bryos. Oligosaccharides were present at only about one-tenth of the ma ximum sucrose concentrations in both rice and wild rice. We conclude t hat the desiccation sensitivity displayed by wild rice grains is not d ue to an inability to synthesize dehydrin proteins, ABA, or soluble ca rbohydrates.