Conversion of chlorophyll b to chlorophyll a precedes magnesium dechelation for protection against necrosis in Arabidopsis.

Abstract

Chlorophyll is a deleterious molecule that generates reactive oxygen species and must be converted to nontoxic molecules during plant senescence. The degradation pathway of chlorophyll a has been determined; however, that of chlorophyll b is poorly understood, and multiple pathways of chlorophyll b degradation have been proposed. In this study, we found that chlorophyll b is degraded by a single pathway, and elucidated the importance of this pathway in avoiding cell death. In order to determine the chlorophyll degradation pathway, we first examined the substrate specificity of 7-hydroxymethyl chlorophyll a reductase. 7-hydroxymethyl chlorophyll a reductase reduces 7-hydroxymethyl chlorophyll a but not 7-hydroxymethyl pheophytin a or 7-hydroxymethyl pheophorbide a. These results indicate that the first step of chlorophyll b degradation is its conversion to 7-hydroxymethyl chlorophyll a by chlorophyll b reductase, although chlorophyll b reductase has broad substrate specificity. In vitro experiments showed that chlorophyll b reductase converted all of the chlorophyll b in the light-harvesting chlorophyll a/b protein complex to 7-hydroxymethyl chlorophyll a, but did not completely convert chlorophyll b in the core antenna complexes. When plants whose core antennae contained chlorophyll b were incubated in the dark, chlorophyll b was not properly degraded, and the accumulation of 7-hydroxymethyl pheophorbide a and pheophorbide b resulted in cell death. This result indicates that chlorophyll b is not properly degraded when it exists in core antenna complexes. Based on these results, we discuss the importance of the proper degradation of chlorophyll b.

• Authors: Yousuke Shimoda, Hisashi Ito, Ayumi Tanaka
• Journal: The Plant journal : for cell and molecular biology (Plant J) Vol. 72 Issue 3 Pg. 501-11 (Nov 2012) ISSN: 1365-313X [Electronic] England
• PMID: 22762131 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.

Chemical References

• 7-hydroxymethyl chlorophyll
• Arabidopsis Proteins
• Light-Harvesting Protein Complexes
• Photosystem I Protein Complex
• Chlorophyll
• chlorophyll b
• Alcohol Oxidoreductases
• chlorophyll b reductase
• Magnesium
• Chlorophyll A

Topics

• Alcohol Oxidoreductases (genetics, metabolism)
• Arabidopsis (genetics, metabolism)
• Arabidopsis Proteins (genetics, metabolism)
• Cell Death
• Chlorophyll (analogs & derivatives, metabolism)
• Chlorophyll A
• Light-Harvesting Protein Complexes (metabolism)
• Magnesium (metabolism)
• Phenotype
• Photosystem I Protein Complex (metabolism)
• Substrate Specificity