The relationship between chlorophyllase activity and chlorophyll degradation during the course of leaf senescence in various plant species

In the present study we compared the changes in chlorophyllase (Chlase) activity and chlorophyll content during leaf senescence in eleven plant species, using an improved Chlase activity assay. Parsley (Petroselinum sativum L.), vinca (Vinca rosea L.), squash (Cucurbita pepo L.), tomato (Lycopersicon esculentum L.), canola (Brassica napus L.), tobacco (Nicotiana glutinosa L.), wheat (Triticum aestivum vulgare L.), and sunflower (Helianthus annuus L.) revealed a decline in Chlase activity corresponding to the descent in chlorophyll concentration. Melia (Melia azedarach L.) and nasturtium (Tropaeolum majus L.), on the other hand, retained high Chlase activity throughout senescence, even when most of the chlorophyll had disappeared. Barley (Hordeum vulgare L.) showed an increase in Chlase activity upon senescence of young seedling leaves, but when leaves of older plants were senesced, Chlase activity declined in correlation with the disappearance of chlorophyll. High levels of chlorophyll were retained in detached parsley leaves treated with N₆ benzyladenine (BA) or gibberellin A₃ (GA) and correspondingly, these leaves maintained high Chlase activity. Contrary to expectation, Chlase activity does not increase during leaf senescence, but rather declines in most plant species examined.