Chromoplast Ultrastructure in Fruit of Solanum pseudocapsicum and Fruit and Sepals of Physalis alkekengi

Abstract

The chromoplasts of ripe fruit of Solanum pseudocapsicum contain mostly β-carotene, with lesser amounts of lutein, antheraxanthin, zeaxanthin, mutatochrome and violaxanthin. The ultrastructure of these plastids reveals that the carotenoids appear to crystallize out from the plastoglobules into many small slabs. In addition, fibrils are also present and develop from plastoglobules. In fruit from wild plants, they consist of a single microfibril with a diameter of 21.3 ± 1.4 nm ( ± SD), while those from an ornamental cultivar, Solanum Christmas Cherry Jubilee, contain fibrils consisting of several small microfibrils, with an average centre-to-centre distance of 4.9 ± 0.5 nm (±SD). The chromoplasts of ripe fruit of Physalis alkekengi are remarkably similar to those of S. pseudocapsicum with respect to their ultrastructure, although they contain mainly zeaxanthin dipalmitate and β-carotene. Fruit from one plant contain the electron-transparent crystalloids described for S. pseudocapsicum, as well as fibrils consisting of one or more large microfibrils. Fruit from a second plant contain crystalloids and the short, small fibrils composed of several microfibrils with a centre- to-centre distance of 4.1 ± 0.2 nm (± SD ) . Treatment of mature green fruit of S. pseudocapsicum with CPTA, which inhibits β-carotene accumulation, prevents the formation of crystalloids and both types of fibrils. It is suggested that the crystalloids are the site of β-carotene deposition in S. pseudocapsicum, and of zeaxanthin di- palmitate in P. alkekengi. Furthermore, it is postulated that there are different types of plasto- globules, one type generating crystalloids and the other fibrils.