Research Progress in the Interconversion, Turnover and Degradation of Chlorophyll

Abstract

Chlorophylls (Chls, Chl a and Chl b) are tetrapyrrole molecules essential for photosynthetic light harvesting and energy transduction in plants. Once formed, Chls are noncovalently bound to photosynthetic proteins on the thylakoid membrane. In contrast, they are dismantled from photosystems in response to environmental changes or developmental processes; thus, they undergo interconversion, turnover, and degradation. In the last twenty years, fruitful research progress has been achieved on these Chl metabolic processes. The discovery of new metabolic pathways has been accompanied by the identification of enzymes associated with biochemical steps. This article reviews recent progress in the analysis of the Chl cycle, turnover and degradation pathways and the involved enzymes. In addition, open questions regarding these pathways that require further investigation are also suggested.

Keywords: chlorophyll cycle; chlorophyll degradation; chlorophyll turnover; enzymes; pathway.

Figure 1

Schemes of the enzymatic reactions in Chl cycle. Blue characters indicate the enzymes.

Figure 2

Schemes of the enzymatic reactions in Chl turnover. Blue characters indicate the enzymes.

Figure 3

Schemes of the enzymatic reactions in Chl degradation. Arrows show metabolic reactions; Dotted arrows indicate the proposed reactions that need further investigation; Blue characters indicate the enzymes.

Figure 4

Updated model of the Chl cycle, turnover and degradation pathways in plants. The model shows the subcellular localisation (bold black characters), representative intermediates (black characters) and enzymes (blue characters). Arrows show metabolic pathways; dotted arrows indicate the proposed pathways that need further investigation.