Expression of a gene for plastid ω-3 fatty acid desaturase and changes in lipid and fatty acid compositions in light- and dark- grown wheat leaves |
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Authors: | Gorou Horiguchi Hirotaka Iwakawa Hiroaki Kodama Naoto Kawakami Mitsuo Nishimura Koh Iba |
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Institution: | Dept of Biology, Fac, of Science, Kyushu Univ. 33, Hakozaki, Higashi-ku, Fukuoka 812–81, Japan;Kihara Inst. for Biological Research, Yokohama City Univ., Yokohama 244, Japan. |
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Abstract: | The leaves of monocotyledonous plants create a developmental sequence of cells and plastids from the base to the apical portion. We investigated fatty-acid and lipid compositions in successive leaf sections of light- and dark-grown wheat (Triticum aestivum L. cv. Chihoku) seedlings. The most notable change in the fatty acid composition was the increase of linolenic acid (18:3) with maturation of leaf cells, which occurred both in light- and dark-grown leaf tissues. In light-grown leaves, the increase of 18:3 with maturation was mainly attributed to the increase of monogalactosyldiacylglycerol (MGD) and also to the increase of the 18:3 level of MGD. In dark-grown leaves, the increase of 18:3 in the leaf apex was caused by the increase of the levels of MGD and digalactosyldiacylglycerol (DGD) and also by the increase of the 18:3 levels of within these two lipids. Since MGD and DGD are mainly found in plastid membranes, these findings indicate that both the synthesis of galactolipids and the formation of 18:3 these lipids take place during plastid development. The plastid ω-3 fatty acid desaturase is responsible for the formation of 18:3 in plastid membrane lipids. To investigate the regulation of desaturation, we isolated a gene for wheat plastid ω-3 fatty acid desaturase (TaFAD7). The mRNA level of TaFAD7 in light-grown leaves was much higher than that in dark-grown leaves. During the greening of etiolated leaves the level of TaFAD7 mRNA increased significantly, accompanied by an increase of the 18:3 level of total fatty acids. On the other hand, the levels of TaFAD7 mRNA were almost the same in all the leaf sections of both light- and dark-grown leaf tissues. These results suggest that the effect of the expression of the TaFAD7 gene on the increase of the 18:3 level is different between the leaf development under continuous light- or dark-conditions and the light-induced greening process of etiolated leaves. The increase of 18:3 content of MGD (or MGD and DGD) with maturation is apparently regulated not solely by the level of TaFAD7 mRNA. |
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Keywords: | Greening leaf cell maturity linolenic acid lipid plastid ω-3 fatty acid desaturase Triticum aestivum wheat |
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