Submergence-induced leaf senescence may alter chlorophyll metabolism. The objective of this study was to characterize chlorophyll biosynthesis and degradation in contrasting perennial ryegrass (Lolium perenne ) in response to submergence stress and recovery. The light-green and fast-growing accession PI238938 and the darker-green and slow-growing cultivar BrightStar SLT were exposed to 0, 6 h, 1-, 3-, and 7-d of submergence stress and 1- and 5-d of de-submergence, respectively. Plant growth of PI238938 were more severely inhibited by sub-mergence stress and recovery. Both accessions showed increased leaf malondialdehyde under stress and re-covery, but reduced chlorophyll (Chl) concentrations were observed at 3- and 7-d of stress and at recovery. The reduction in Chl was more severe in BrightStar SLT at 7 d of stress. The concentration of 5-aminolevulenic acid was unaffected by stress but increased at 1d of recovery. Activities of 5-aminolevulinic acid dehydratase (ALAD) involved in Chl biosynthesis remained unchanged under stress and recovery, while the activities of Chl de-grading enzymes chlorophyllase (CHL) and pheophytinase (PPH) increased at 3 d or 7 d of stress, and returned to the control level after recovery in both accessions. The downregulation of Chl-biosynthetic genes CHLI , POR , and CHLP and the upregulation of Chl-degrading genes CLH, PPH , and SGR were observed in both accessions under most of the stress periods. BrightStar SLT exhibited much lower expressions of the Chl-biosynthetic genes PBGD , CHS , and CHID under stress, while PI238938 had remarkably higher expressions of genes involved in Chl breakdown including CLH, PPH , PAO , RCCR , and SGR , and the expressions of these genes remained at a higher level at 1 d of recovery. The results indicated that submergence-induced leaf senescence and declines in Chl were associated with downregulation of more Chl-biosynthetic genes in slow-growing genotype and upregulation of more Chl-degrading genes in fast-growing genotype of perennial ryegrass.