Intracellular localization of capsaicin and its analogues, capsaicinoid, in Capsicum fruit 1. Microscopic investigation of the structure of the placenta of Capsicum annuum var. annuum cv. Karayatsubusa1

Transverse sections of the placenta of hot pepper, Capsicum annuum var. annuum cv. Karayatsubusa, at different stages after flowering were examined microscopically. Examination of the cellular structure of the placenta using a light microscope revealed that some morphological changes took place mainly in the epidermal tissue of the placenta during maturation. Elongation of the epidermal cells and many osmiophilic granules were recognized in the epidermal cells of the placenta in which capsaicinoid was being formed and actively accumulated. Moreover, a granule-like structure having an absorption at 280 nm was also recognized by ultraviolet microscopy around the same region where the osmiophilic granules were observed. By electron microscopy, many electron-dense granules stained with glutaraldehyde and osmium tetroxide were observed both in the small vesicles and vacuoles of epidermal cells of the placenta. The electron-dense granules varied in size from smaller than 1 μm to larger than 2 μm in diameter. They were thought to be capsaicinoid and were observed only in the epidermal cells. Therefore, the epidermal tissue appeared to be the site of capsaicinoid accumulation.