Effect of organ excision and kinetin treatment on chlorophyll content and DCPIP photoreduction activity of chloroplasts of pumpkin cotyledons

Abstract

Summary Pumpkin cotyledons show three distinct phases of development such as growth, steady state and senescence. The onset of steady state in the cotyledons is characterised by a relatively high and constant level of chlorophyll (Chl) and senescence by loss of the pigments. In seedlings from which one cotyledon is excised, steady state in the intact cotyledon starts from the 4th day of germination, while in the debudded, derooted and derooted plus kinetin-treated and control seedlings, it starts from the 6th day. The onset of the senescence phase in the different types of seedlings is significantly different from that of the control. The onset of a high 2,6-dichlorophenol indophenol (DCPIP) Hill reaction by chloroplasts coincides with the maximal level of Chl in all types of seedlings. However, except in the seedlings with one cotyledon and those without root (derooted), the decline in photochemical activity starts significantly earlier than the decline in Chl level. Although the maximal Chl level is prolonged by the excision of bud and root, and treatment of the derooted seedlings with kinetin, the loss of Hill activity starts almost at the same time as for the control, which indicates that Chl accumulation and Hill activity in the cotyledons have different temporal patterns of development in these seedlings.