Magnesium chelatase involved in chlorophyll a degradation in the chlorophyll-protein complexes of photosystem I (PSI) and photosystem II (PSII) (PubMed:27604697). Contributes to the degradation of PSI and PSII in the thylakoid membranes (PubMed:27604697). Recombinant SGRL possesses high dechelating activity against chlorophyllide a, very low activity against chlorophyll a, and no activity against chlorophyll b (PubMed:27604697). Contributes to abiotic stress-induced chlorophyll degradation and leaf yellowing during vegetative plant growth (PubMed:25261252). chlorophyllide a + 2 H(+) = Mg(2+) + pheophorbide a Interacts with the light harvesting complex II (LHCII) (PubMed:25261252). Interacts with the chlorophyll catabolic enzymes (CCEs) NYC1, NOL, PAO and RCCR (PubMed:25261252). Expressed in cotyledons, pollen and young leaves. Down-regulated during natural and dark-induced leaf senescence. Belongs to the staygreen family.