20. hmg1変異体が示すトリテルペンの新しい機能

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Plants produce a wide variety of triterpenes (compounds derived from squalene). However, the physiological role of each compound has not yet been well understood except for brassinosteroid. Squalene is an uncyclic triterpene, biosynthesized via the mevalonate (MVA) pathway in the cytoplasm, and is metabolized to two kinds of cyclic tritertpenes; one is steroid (sterol and brrasinosteroid) and the other is triterpenoid. To understand the physiological roles of various triterpenes, we have characterized Arabidopsis T-DNA insertion mutants for HMG1 and HMG2, that encode HMG-CoA reductase. The previous work of hmg1 suggests that triterpenes are involved in cell elongation, senescence and fertility (Suzuki et al. 2004). The analyses of the expression of the marker gene of the wild-type (WT) plant treated with various inhibitors of the MVA pathway suggest that squalene is involved in the inhibition of senescence progression, and 24-acylated sterols are involved in cell elongation. These findings correspond to the gene expression analyses in the various mutants downstream of hmg1 in the MVA pathway. Squalene may contribute the inhibition of senescence by the prevention of lipid peroxidation. 24-Acylated sterols may contribute the cell elongation as components of the plasma-membrane. The sterility of hmg1 is caused by the loss of ability of the pollen germination. The expression of the HMG1 in WT flowers by in situ hybridization revealed that the strong signals was mainly detected in the tapetum. We observed the structures in hmg1 tapetam by transmission electron microscopy. Lipid-rich organelles, tapetosomes and elaioplasts, in the tapetum of hmg1 were stunted. Esterified sterols may contribute the normal pollen development by the transfer to pollen coats from the tapetum.
植物化学調節学会の論文
2004-10-13

20. hmg1変異体が示すトリテルペンの新しい機能

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