| Chile peppers (Capsicum spp.) are members of a plant clade that contain unique, interesting, and useful characteristics. Chile peppers are utilized in traditional cuisines, dying / coloring agents, decoration, and even medicinal products. The genus Capsicum produces unique plant metabolites that make it a desirable target for modern research. Two of the major secondary products formed with Capsicum fruit during the metabolic process include capsaicinoids and carotenoids. Capsaicinoids are compounds that account for the pungency (heat) of a pepper fruit while carotenoids function as nutrient precursors and as pigments. The total carotenoid accumulation and specific carotenoid composition in many Capsicum cultivars have been described as well as the biosynthetic pathways of these compounds, However. there has been little research done on the sites of carotenoid accumulation, the chromoplast, and whether there are ultrastructural differences in chromoplasts from fruit with different carotenoid composition.;Increased accumulation of specific carotenoids in plastids through either plant breeding or genetic engineering requires an understanding of the limitations that storage sites for these compounds may impose. Here using Capsicum annuum L. fruit, I demonstrate directly the unique sub-organellar accumulation sites of specific carotenoids using live cell hyperspectral confocal Raman microscopy. Further, chromoplasts from specific cultivars vary in shape and size; again these structural variations are associated with carotenoid compositional differences. Live cell imaging utilizing laser scanning confocal (LSCM) and confocal Raman microscopy as well as fixed tissue imaging with scanning and transmission electron microscopy (SEM and TEM), all demonstrated morphological differences with high concordance for the measurements of chromoplast volume and aspect ratio across multiple imaging modalities.;No correlation was found between transcript levels of fibrillin, a gene associated with increased carotenoid accumulation, and Capsicum carotenoid accumulation or chromoplast shape in two lines, Costello Amarillo Orange and Costello Amarillo Red. F1 progeny between varieties with distinct chromoplast shapes, had intermediate chromoplast shapes, but inherited the dominant red terminal fruit color. These results reveal additional opportunities for genetic controls on fruit color and carotenoid based phenotypes. |
