Chemical regulation of plastid development III. Effect of light and CPTA on chromoplast ultrastructure and carotenoids of Capsicum annum

Abstract

Fibrils are shown to form in Capsicum annuum fruit chromoplasts that develop from plastids which normally contain little chlorophyll, as in the cultivar ‹Fiesta›, and from leucoplasts, as in Long Red Cayenne fruit that have been grown in the dark to prevent chlorophyll synthesis. It is concluded that the assembly and disintegration of photosynthetic lamellae are not necessary for the formation of fibrils in chromoplasts, although light seems to promote optimal fibril size and numbers, and maximum carotenoid content. The effect of 2-(4-chlorophenylthio)ethyldiethylammonium chloride (CPTA) is most pronounced in tissue in which chromoplasts develop from leucoplasts. The formation of β-carotene and its derivatives is greatly inhibited, and the major carotenoid is lycopene. The total level of carotenoids is reduced significantly in both Fiesta fruit and dark-grown Long Red Cayenne fruit treated with CPTA, and in the latter fruit, the size of mature chromoplasts is also reduced. The points at which CPTA is thought to regulate carotenoid biosynthesis are shown, and used to explain the varying carotenoid patterns at different levels of CPTA inhibition. It is suggested that CPTA may regulate the synthesis of cyclopentyl ketocarotenoids in a manner similar to the y allele of Capsicum .