Chlorophyll: a symptom and a regulator of plastid development

Abstract

SUMMARY The metabolism of chlorophylls and related tetrapyrroles directly influences, and is influenced by, the proteins and cell structures with which they are associated. During net accumulation, de‐greening and at the steady state chlorophyll and its derivatives are important elements in the post‐translational regulation of the expression of genes for chloroplast proteins. At the same time, they represent potential photodynamic hazards against which green cells need to have protective mechanisms. This review deals with genetic, chemical and environmental perturbations of chlorophyll biosynthesis that impact on protein stability, membrane organization and susceptibility to photodamage. NADPH‐protochlorophyllide oxidoreductase is considered in detail as a pigment– protein regulating, and regulated by, chlorophyll metabolism. The question of the extent and significance of chlorophyll turnover at the steady state is addressed, with particular emphasis on the dynamics of the photosystem II reaction centre. The pathway of chlorophyll catabolism is described, along with its interrelationship with protein mobilization in chloroplast senescence. Finally, the structural basis of pigment‐protein interaction and stability is examined, and the discussion ends by expressing some general thoughts about the control of protein lifetimes in the living cell.

The GATA-type transcription factors GNC and GNL/CGA1 repress gibberellin signaling downstream from DELLA proteins and PHYTOCHROME-INTERACTING FACTORS

“…3B; Thomas 1997). We hypothesized that a reduction of POR levels may be the molecular cause for the greening defect of gnc and gnl mutants.…”

Ozone and water deficit reduced growth of Aleppo pine seedlings

“…Such a change was not observed in the present study, as chl b concentrations were also reduced by O 3 . Indeed, marked changes in the chl b concentration may be expected especially in the needles showing visible O 3 damage, as chl b is broken down in senescence [36] and O 3 injury seems to be among the factors affecting needle retention in mature Aleppo pines in the field [33]. The differences in the chl a, chl a + b and car concentrations in the c + 1 needles between the WW and DS NF + O 3 seedlings in May 1999 also suggest that the WW NF + O 3 seedlings had not (yet) been able to compensate for the O 3 -induced chlorophyll loss [31].…”

Stay-green protein, defective in Mendel’s green cotyledon mutant, acts independent and upstream of pheophorbide a oxygenase in the chlorophyll catabolic pathway

“…Introgression of the sid locus into different Lolium species allowed the molecular 4 tagging of the gene (Thomas, 1997). By exploiting the high micro synteny between Lolium-Festuca and rice, it was possible to identify the candidate locus in a Lolium stay-green mapping population that corresponded to a stay-green locus (SGR) in rice (Armstead et al, 2006).…”

“…Thus, the mutants consistently accumulated 5 chlorophyllide (chlide) and pheide a during senescence and they exhibited reduced PAO activities. It was argued that pheide a accumulation would feed back inhibit chl breakdown, in order to prevent further chl intermediate accumulation, thereby minimizing the phototoxic potential of these pigments (Thomas, 1997;Matile et al, 1999;Hörtensteiner, 2006). Along with the retention of chl, chl-binding proteins were shown to be retained in the mutants (Hilditch et al, 1989;Jiang et al, 2007;Park et al, 2007;Sato et al, 2007).…”