title: High light inhibits chlorophyll biosynthesis at the level of 5-aminolevulinate synthesis during de-etiolation in cucumber (Cucumis sativus) cotyledons.
abstract: Using the vascular plant Cucumis sativus (cucumber) as a model, we studied the effects of high (intense and excess) light upon chlorophyll biosynthesis during de-etiolation. When illuminated with high light (1500-1600 microE/m2/s), etiolated cucumber cotyledons failed to synthesize chlorophyll entirely. However, upon transfer to low light conditions (40-45 microE/m2/s), chlorophyll biosynthesis and subsequent accumulation resumed following an initial 2-12 h delay. Duration of high light treatment negatively correlated with chlorophyll biosynthetic activity. Specifically, we found that high light severely inhibited 5-aminolevulinic acid (ALA) synthesis. This effect partly could be because of the decrease in protein level of glutamyl-tRNA reductase (GluTR) observed. Protein level of glutamate-1-semialdehyde (GSA-AT) remained unchanged. It was also found that high light did not suppress HEMA 1 expression. Therefore, we speculated that this significant inhibition of ALA synthesis might have occurred mainly because of concomitant inactivation of GluTR and/or inhibition of complex formation between GluTR and GSA-AT. Our further observation that both methyl viologen and rose bengal similarly inhibit ALA synthesis under low light conditions suggested that reactive oxygen species (ROS) could be responsible for the inhibition of ALA synthesis in cotyledons exposed to high light conditions.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Aarti
authors.forename: R
authors.initials: R
authors.lastname: Tanaka
authors.forename: H
authors.initials: H
authors.lastname: Ito
authors.forename: A
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D000622:Aminolevulinic Acid / Q000378:metabolism*; D001483:Base Sequence; D015152:Blotting, Northern; D002734:Chlorophyll / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D018553:Cucumis sativus / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology / Q000528:radiation effects*; D019751:Intramolecular Transferases / Q000378:metabolism; D007700:Kinetics; D008027:Light; D055537:Light Signal Transduction; D018384:Oxidative Stress / Q000502:physiology; D010269:Paraquat; D017382:Reactive Oxygen Species / Q000378:metabolism; D012395:Rose Bengal
chemical_list: D017382:Reactive Oxygen Species; D002734:Chlorophyll; D012395:Rose Bengal; D000622:Aminolevulinic Acid; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase; D019751:Intramolecular Transferases; C061049:glutamate-1-semialdehyde 2,1-aminomutase; D010269:Paraquat