Development of Desiccation Tolerance during Embryogenesis in Rice (Oryza sativa) and Wild Rice (Zizania palustris) (Dehydrin Expression, Abscisic Acid Content, and Sucrose Accumulation)

Abstract

The ability of seeds to withstand desiccation develops during embryogenesis and differs considerably among species. Paddy rice (Oryza sativa 1.) grains readily survive dehydration to as low as 2% water content, whereas North American wild rice (Zizania palusfris var inferior [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 tolerante during embryogenesis. Dehydrin protein was deteded 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 deteded 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.Most seeds enter a period of desiccation and physiological quiescence during the last phase of development. However, there are considerable differences among species in their ability to survive desiccation. Orthodox seeds such as paddy rice (Oryza sativa L.) caryopses readily tolerate desiccation to <5% water content, and their longevity in storage increases as temperature and water content decrease (Roberts, 1973 for example, are tolerant of desiccation only under restricted dehydration and rehydration conditions. Wild rice is an aquatic grass whose seeds (caryopses) normally abscise at a relatively high moisture content, fall into the water, remain dormant through the winter, and genninate the following spring. Wild rice seeds were thought to be intolerant of dehydration <30% moisture content (Probert and Brierly, 1989; Probert and Longley, 1989), but the seeds can survive dehydration to as low as 6% moisture content if dehydration and rehydration occur at 15 to 25OC and imbibitional damage is avoided (Kovach and Bradford,

Proteomic analysis of stress-related proteins in rice seeds during the desiccation phase of grain filling

“…The glass structure assures cell stability at the time of dehydration, since the high viscosity of glass can prevent the crystallization of chemical compounds, membrane fusion, and conformational changes of proteins (Hoekstra et al 2001). Still et al (1994) reported that in developing embryos of rice seeds, sucrose is accumulated linearly from 10 to 40 DAF and this accumulation pattern paralleled the increase we observed in LEA proteins ( Figure 5). Using synthetic models, Shimizu et al (2009) reported that LEA proteins are intrinsically disordered in solution but fold into α-helices during drying, and these proteins play a role in reinforcing the glassy matrix of oligosaccharides.…”

Expression of a Late Embryogenesis Abundant Protein Gene, HVA1, from Barley Confers Tolerance to Water Deficit and Salt Stress in Transgenic Rice

“…On the other hand, the presence of other LEA proteins is not always correlated with stress tolerance. For example, comparative studies of wild rice and paddy rice showed that the intolerance of wild rice seeds to dehydration at low temperature is not due to an absence of, or an inability to synthesize, group 2 LEA/dehydrin proteins, ABA, or soluble carbohydrates (Bradford and Chandler, 1992;Still et al, 1994). Overproduction of a group 2 LEA protein from the resurrection plant Craterostigma in tobacco did not confer tolerance to osmotic stress (Iturriaga et al, 1992).…”

Importance of cytomatrix-bound polysomes to synthesis of lysine-containing proteins in triticale germs under ABA treatment

“…Along with other regulators of plant growth and development, ABA plays a major role in the control of embryo maturation and seed formation via regulation of storage reserve deposition, acquisition of desiccation tolerance as well as induction of primary dormancy and suppression of precocious germination (Still et al 1994;Bartels et al 1988;Gerjets et al 2010). Although more research dealing with mechanisms of ABA action has been conducted, many questions remain unanswered.…”

“…Although more research dealing with mechanisms of ABA action has been conducted, many questions remain unanswered. It is well known that ABA affects the induction of genes for some specific proteins (Still et al 1994;Mukherjee et al 2006;Cao et al 2007;Xiang et al 2008) and the inhibition of certain reserve mobilizing enzymes (Robertson et al 1989;Gómez-Cadenas et al 1999, 2001Bethke et al 2006). Some studies show that ABA also has the ability to modify the orientation of microtubules, a cytoskeletal element directing mRNA transport and localization, which may lead to the alteration of targeted synthesis of proteins within the cell (Shibaoka 1994;Klyachko 2003).…”