Comparative studies of senescence-related enzymes in the cotyledon of chlorophyll b-deficient mutant and its wild type oilseed rape during senescence

Abstract

The change patterns of senescence-related enzymes during cotyledon senescence were studied in a chlorophyll (Chl) b-deficient mutant type (MT, Cr3529) and its wild type (WT) of Brassica napus L. seedlings. The fresh weight on the basis of cotyledon number initially increased till 20 days after planting (DAP) and then kept relative constant. The protein content decreased sharply since 20 DAP and Chl content reduced since 10 DAP in both types; however the rate of degradation in protein and Chl in the MT was slower than that in the WT since 20 DAP. Superoxide dismutase (SOD; E.C.1.15.1.1) activity declined in the WT but increased in the MT since 20 DAP. Activity of peroxidase (POD; E.C.1.11.1.7) increased markedly after 20 DAP in both types. Esterase (EST; E.C.3.1.1.1) activity increased in both types since 10 DAP, whereas at 40 DAP it was much lower in the MT than that in the WT. In addition, bands patterns of SOD, POD and EST isozymes were changed during cotyledon development in both types, but some differences were observed. Cu/ZnSODs activities were higher in the MT at 40 DAP as compared with the WT. These results showed that day 20 was the turning point during the cotyledon development and the senescence in the MT cotyledon was slower than that in the WT.