Chlorophyllase versus pheophytinase as candidates for chlorophyll dephytilation during senescence of broccoli

Correlation of leaf senescence and gene expression/activities of chlorophyll degradation enzymes in harvested Chinese flowering cabbage (Brassica rapa var. parachinensis)

“…These results support the finding that a newly identified enzyme, pheophytinase (PPH), a chloroplast-located and senescence-induced hydrolase, may function in the dephytylation of Mg-free chlorophyll pigment, and the sequence of early chlorophyll catabolic reactions may be revised (Schelbert et al, 2009). Büchert et al (2011) also found that BoPPH gene expression presented closer correlation to the visual manifestation of postharvest treatments than that of BoCLHs during senescence of broccoli (B. oleracea), suggesting that this enzyme is responsible for the dephytilation step in broccoli flower degreening.…”

Update on the biochemistry of chlorophyll breakdown

“…Contradictory results were also obtained in experiments with de-regulated CLH expression; absence of AtCLH1 and/or AtCLH2 in respective mutants ) as well as silencing of AtCLH1 (Kariola et al 2005) or AtCLH2 ) had little effect on senescence-related Chl breakdown, while antisense-suppression of broccoli CLH delayed rates of postharvest broccoli head yellowing . Furthermore, expression patterns of neither AtCLHs nor CLHs of broccoli or Chinese flowering cabbage correlate with Chl breakdown Zimmermann et al 2004;Büchert et al 2011;Zhang et al 2011). By contrast, CLH was convincingly shown to participate in Chl breakdown during fruit ripening of Citrus species (Azoulay Shemer et al 2008;Harpaz-Saad et al 2007).…”

The Pathway of Chlorophyll Degradation: Catabolites, Enzymes and Pathway Regulation

“…In addition, PPH / NYC3 mRNA increases with senescence, thus exhibiting high level of co-expression with other Chl catabolic genes such as PAO and NYE1 / SGR (Ren et al 2010 ) . Similarly, PPH expression correlated with yellowing of broccoli heads, indicating that also during postharvest PPH but not CLH is active (Büchert et al 2011 ) .…”

“…For example in broccoli, antisense-suppression of CLH delayed rates of postharvest head yellowing ) . Yet in the same tissue, expression of CLH genes does not correlate with progression of Chl breakdown (Büchert et al 2011 ) . During fruit ripening in Citrus species, CLH was convincingly shown to participate in Chl breakdown and also to promote Chl breakdown when expressed in squash ( Cucurbita pepo ) leaves or tobacco protoplasts (Harpaz-Saad et al 2007 ;Azoulay Shemer et al 2008 ) .…”