PLANT PHYSIOLOGY , Vol 104, Issue 2 431-438, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Development of Desiccation Tolerance during Embryogenesis in Rice (Oryza sativa) and Wild Rice (Zizania palustris) (Dehydrin Expression, Abscisic Acid Content, and Sucrose Accumulation)
D. W. Still, D. A. Kovach and K. J. Bradford
Department of Vegetable Crops, University of California, Davis, California 95616-8631
The ability of seeds to withstand desiccation develops during embryogenesis
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 interior [Fasset] Dore) grains
are not tolerant of water contents below 6% and are sensitive to drying and
imbibition conditions. During embryogenesis, dehydrin proteins, abscisic
acid (ABA), and saccharides are synthesized, and all have been implicated
in the development of desiccation tolerance. 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 tolerance during embryogenesis. Dehydrin protein
was detected immunologically with an antibody raised against a conserved
dehydrin amino acid sequence. Both rice and wild rice embryos accumulated a
21-kD dehydrin protein during development, and an immunologically related
38-kD protein accumulated similarly in rice. Dehydrin protein synthesis was
detected 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 rice
embryos. There were no obvious relationships between ABA and the temporal
expression patterns of dehydrin protein in either rice or wild rice. Wild
rice axes accumulated about twice as much sucrose as rice embryos.
Oligosaccharides were present at only about one-tenth of the maximum
sucrose concentrations in both rice and wild rice. We conclude that the
desiccation sensitivity displayed by wild rice grains is not due to an
inability to synthesize dehydrin proteins, ABA, or soluble carbohydrates.
