Journal Article

Light and Cytokinin Play a Co-operative Role in MGDG Synthesis in Greening Cucumber Cotyledons

Yoshiki Yamaryo, Daisuke Kanai, Koichiro Awai, Mie Shimojima, Tatsuru Masuda, Hiroshi Shimada, Ken-ichiro Takamiya and Hiroyuki Ohta

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 8, pages 844-855
Published in print August 2003 | ISSN: 0032-0781
Published online August 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg110
Light and Cytokinin Play a Co-operative Role in MGDG Synthesis in Greening Cucumber Cotyledons

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The current research investigated the regulation of monogalactosyldiacylglycerol (MGDG) biosynthesis, catalyzed by MGDG synthase (MGD) (UDP-galactose:1,2-diacylglycerol 3-β-d-galactosyltransferase; EC 2.4.1.46), during chloroplast development in cucumbers (Cucumis sativus L. cv. Aonagajibai). In etiolated seedlings, white light induced a transient increase in MGD mRNA, followed by a subsequent increase in enzyme activity. MGDG, digalactosyldiacylglycerol (DGDG), and linolenic acid (18 : 3) of both MGDG and DGDG accumulated in a light-dependent manner. Early light-dependent induction of MGD protein was also identified in isolated chloroplasts. When cotyledons were detached from seedlings, these light-induced changes diminished. However, when a synthetic cytokinin, benzyladenine, was added to the detached cotyledons, a transient increase in MGD mRNA and a linear increase in the enzyme activity were induced even in the dark. Galactolipids subsequently accumulated to some extent and 18 : 3 content also increased. MGDG fully accumulated in detached cotyledons with co-treatment of light and a cytokinin. Red light (>600 nm) and far-red light (>700 nm) both induced an increase in MGD mRNA and enzyme activity but far-red light did not induce an accumulation of MGDG. These results suggest that (1) galactolipid biosynthesis is regulated by the cooperation of light and a cytokinin; (2) the accumulation of MGDG requires cytokinin in addition to light; (3) a red light (600–700 nm) dependent factor is necessary for the maximal galactolipid accumulation in addition to increase in MGD transcript and activity.

Keywords: Keywords: Chloroplast development — Cytokinin — Desaturase — Galactolipids — Light response — MGDG synthase.; Abbreviations: BA, benzyladenine; DG, diacylglycerol; DGDG, digalactosyldiacylglycerol; DTT, dithiothreitol; lh, long hypocotyl; MGD, UDP-galactose:1,2-diacylglycerol 3-β-d-galactosyltransferase; MGD, MGDG synthase gene; MGDG, monogalactosyldiacylglycerol; PhyB, phytochrome B; POR, NADPH–protochlorophyllide oxidoreductase; TLC, thin layer chromatography; 16 : 0, palmitic acid; 18 : 2, linoleic acid; 18 : 3, linolenic acid.

Journal Article.  7454 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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