Light and cytokinin play a co-operative role in MGDG synthesis in greening cucumber cotyledons

• Published in: Plant and cell physiology 2003-08, Vol.44 (8), p.844-855
• Main Authors: Yamaryo, Y. (Tokyo Inst. of Technology, Yokohama (Japan)), Kanai, D, Awai, K, Shimojima, M, Masuda, T, Shimada, H, Takamiya, K, Ohta, H
• Format: Article
• Language: English
• Subjects: 16 : 0; 18 : 2; 18 : 3; 2-diacylglycerol 3-β-d-galactosyltransferase; Adenine - analogs & derivatives; Adenine - pharmacology; Benzyl Compounds; benzyladenine; BIOSYNTHESIS; Chloroplasts - metabolism; Cotyledon - metabolism; COTYLEDONS; CUCUMIS SATIVUS; Cucumis sativus - drug effects; Cucumis sativus - genetics; Cucumis sativus - metabolism; CYTOKININS; Cytokinins - physiology; Darkness; DGDG; diacylglycerol; digalactosyldiacylglycerol; dithiothreitol; DTT; Galactolipids - biosynthesis; GALACTOSE; Galactosyltransferases - metabolism; Keywords: Chloroplast development — Cytokinin — Desaturase — Galactolipids — Light response — MGDG synthase; Kinetin; LIGHT; linoleic acid; linolenic acid; LIPIDS; long hypocotyl; MGD; MGDG; MGDG synthase gene; monogalactosyldiacylglycerol; Mutation; NADPH–protochlorophyllide oxidoreductase; palmitic acid; PhyB; phytochrome B; POR; Purines; Seedlings - physiology; thin layer chromatography; TLC; UDP-galactose:1
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcg110

The current research investigated the regulation of monogalactosyldiacylglycerol (MGDG) biosynthesis, catalyzed by MGDG synthase (MGD) (UDP-galactose:1,2diacylglycerol 3-??-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.