Repression of AtCLH1 expression results in a decrease in the ratio of chlorophyll a/b but doesnot affect the rate of chlorophyll degradation during leaf senescence.

To explore the possible regulatory role of chlorophyllase (Chlase) in chlorophyll (Chl) degradation during leaf senescence, Arabidopsis (Arabidopsis thaliana) plants were constructed to repress the expressions of AtCLH1 and/or AtCLH2. Transcript levels of AtCLH1 and/or AtCLH2 were dramatically lowered and Chlase activity was correspondingly inhibited, but the Chl degradation kinetics was not affected in the duanyu1615 plants. Results of further analysis indicated that the Chl a/b ratio decreased in AtCLH1 duanyu1615 lines, in comparison with the increasing Chl a/b ratio in the wide type during leaf senescence. In addition, an induced Chlase activity was consistently detected at the initial stage of senescence in all the plants examined. In contrast, transcript levels of both AtCLH1 and AtCLH2 decreased dramatically upon the initiation of senescence in both the wide-type and the duanyu1615 plants. Interestingly, compared with the wide type, lower but still significant transcript levels of the duanyu1615 targeted Chlase gene(s) were sustained during the whole period of dark incubation in all the three duanyu1615 lines examined, indicating the functioning of some compensatively regulating mechanism. Based on these results, along with related reports, we conclude that Chlase might be required at the initial stage of leaf senescence, quite likely playing a role in converting Chl b to a.

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