engleski

The effect of darkness on chromoplast differentiation in cucumber petals

Although, in most plants, light is indispensable for the development of chloroplast photosynthetic structures, it is believed that it is not necessary for morphogenesis of chromoplast substructures. However, some studies indicated the regulatory role of light in chromoplastogenesis. In this work, we studied the effect of darkness on the content of plastid pigments as well as on the differentiation of fibrillar type chromoplasts in the petals of cucumber (Cucumis sativus L. 'Vert Petit de Paris'). Experiments were performed on freshly collected green flower buds (6 mm in size) and yellow-green buds (8, 10 and 12 mm in size). Spectrophotometric and ultrastructural analyses were carried out after 2 and 4 days of bud growth on 150 mM sucrose solution. Analyses of plastid pigments showed that darkness increased carotenoid accumulation in green flower buds: after 2 days of treatment the content of carotenoids per corolla was 37% higher than in the control buds. In the petals of older buds, in which chromoplast differentiation had already started, darkness had no effect on carotenogenesis or was even inhibitory. Ultrastructural studies showed that the plastids in young green buds treated for 4 days contained considerably more plastoglobules and fibrils than control buds, while there were no differences in the level of chromoplast differentiation between control and treated buds, in older developmental stages. Our studies indicated that the effect of darkness on chromoplast differentiation depends on their developmental stage: darkness has a positive effect on chromoplast differentiation in very young buds, while in older buds it could even be inhibitory.

chromoplast differentiation; cucumber; petals

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