PLASTID ONTOGENY DURING PETAL DEVELOPMENT IN ARABIDOPSIS

Imaging of chlorophyll autofluorescence by confocal microscopy in inta ct whole petals of Arabidopsis thaliana has been used to analyze chlor oplast development and redifferentiation during petal development. You ng petals dissected from unopened buds contained green chloroplasts th roughout their structure, but as the upper part of the petal lamina de veloped and expanded, plastids lost their chlorophyll and redifferenti ated into leukoplasts, resulting in a white petal blade. Normal green chloroplasts remained in the stalk of the mature petal. In epidermal c ells the chloroplasts were normal and green, in stark contrast with le af epidermal cell plastids. In addition, the majority of these chlorop lasts had dumbbell shapes, typical of dividing chloroplasts, and we su ggest that the rapid expansion of petal epidermal cells may be a trigg er for the initiation of chloroplast division. In petals of the Arabid opsis plastid division mutant arc6, the conversion of chloroplasts int o leukoplasts was unaffected in spite of the greatly enlarged size and reduced number of arc6 chloroplasts in cells in the petal base, resul ting in few enlarged leukoplasts in cells from the white lamina of arc 6 petals.