Physiological, biochemical, and molecular differences in chloroplast synthesis between leaf and corolla of cabbage (Brassica rapa L. var. chinensis) and rapeseed (Brassica napus L.)

Although much information regarding the chloroplast and chromoplast biosynthesis has been accumulated in recent years, details of the physiological, biochemical, and molecular differences between green tissues and colorful chromoplast tissues are still poorly understood. In this study, the pigment accumulation, plastid ultrastructure, and the expression of genes involved in chloroplast synthesis were analyzed between leaf and corolla in cabbage and rapeseed. The results showed that both petals contained less chlorophyll contents and a lower ratio of Chl a/b, but contained higher carotenoid contents compared with that of sepals and leaves. Accordingly, ultrastructural observations indicated that plastid development of petals was arrested or inhibited. In addition, data obtained from biochemical studies were correlated with those at the mRNA level, the transcripts of almost all the chlorophyll biosynthetic genes (especially the downstream genes) and plastid genes required for early chloroplast development and photosynthesis were higher in leaves than that in petals. Besides, the different pigment accumulation in corollas was also corroborated by the changes in the expression of selected genes associated with chlorophyll accumulation and/or chloroplast development. Collectively, the results contribute to better understand the molecular mechanisms underlying tissue-specific chloroplast development in plants.