The role of chlorophyllase in degreening canola (Brassica napus) seeds and its activation by sublethal freezing

Chlorophyllase mediates dephytylation of chlorophylls and pheophytins during seed degreening in canola ( Brassica napus cv. Westar). Degreening can be correlated with chlorophyllase activity in vitro, but it is difficult to demonstrate in vivo activity because of low levels of the dephytylated breakdown products during rapid degreening. If, however, degreening is inhibited by sublethal freezing, chlorophyllide and pheophorbide accumulation can be related to the action of chlorophyllase. Changes in the rate of in vitro dephytylation during degreening and the dramatic increase following freezing may indicate enzyme activation and de novo enzyme synthesis. Evidence from Western blots is presented in support of de novo synthesis. It is concluded that failure of the seed to degreen following sublethal freezing does not result from a reduction in chlorophyllase activity.