42 植物における微量トレハロースの存在意義 : イネの低温応答への関与
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The disaccharide trahalose (α-D-glucopyranosyl-l, l-α-D-glucopyranoside) is synthesized from UDP-glucose and glucose-6-phosphate in a two step process, analogous to sucrose synthesis, by trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP). Trehalose is present in a variety of microorganisms and invertebrate animals where it appears to serve as a reserve carbohydrate and as a stress protectant, especially during heat, freezing and desiccation stress. In contrast, occurrence of endogenous trehalose in higher plants is ambiguous until recently when Arabidopsis genes for trehalose biosynthesis were cloned and characterized. Following researches have demonstrated that endogenously formed trehalose may act as a signal molecule in the regulation of plant metabolism and development. It was also suggested that the precursor of trehalose, trehalose-6-phosphate, may play a role in the regulation of carbohydrate metabolism and of sugar sensing in plants. In this study, cDNA microarrray (provided by Rice Genome Project) was utilized to screen for cDNA clones that are induced by chilling stress in rice roots. Among the clones that are induced at 12℃ for 2h, two cDNAs involved in trehalose biosynthesis, TPS and TPP, were identified. Using corresponding EST sequences, full-length cDNA clones (OsTPS1 and OsTPP1,respectively) were isolated after library screening. Southern blot analysis indicates that OsTPP1 is a single copy gene while OsTPS1 may have similar genes in the rice genome. Northern blotting with the total RNA extracted from roots and shoots of rice seedlings grown hydroponically at 12℃ for 1,2,4,6,10,24 and 48 hours showed that both OsTPP1 and OsTPS1 were a strongly induced even within 1 hour of chilling stress. The induction was transient and signals disappeared after 6 to 10 hours of the chilling stress. Determination of soluble sugars in chilling-treated rice roots using Dionex HPLC revealed that fructose and glucose levels initiated to increase after 5h of chilling treatment and constantly increased thereafter. Trehalose levels were fairly low but increased rapidly and transiently. Sucrose levels were increased consistently during 24h of chilling treatment. Increase in trehalose levels occurs apparently faster and earlier than the other sugars, and followed the pattern of mRNA. Collectively, these data suggested that trehalose biosynthesis is induced transiently during the course of chilling stress, which may be involved in the regulation of sugar accumulation in chilling stressed root tissue.
- 植物化学調節学会の論文
- 2002-10-31
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