The occurrence of chloroplast peripheral reticulum in grasses: A matter of phylogeny or a matter of function?

Abstract

The chloroplast peripheral reticulum (PR) is a structure of unknown function. Some authors postulated that it is a characteristic feature of C4 plants, although it was reported from C3 species as well. It is unknown whether the occurrence of PR follows a phylogenetic (it is found in clades containing C4 species, regardless of the photosynthetic type) or functional (photosynthetic pathway dependent) pattern. Here, we present a phylogenetically controlled analysis of the occurrence, form and functional aspects of PR in grasses. The occurrence of the PR follows a functional and not a phylogenetic pattern. Its most elaborated form (PR type I) is a unique feature of C4 species. Although PR was found in some of the studied C3 grasses, it was always less developed than PR in the chloroplasts of Kranz mesophyll cells of C4 species. The size of PR in C4 plants was found to increase when the plants were grown under low light intensity. Additional observations, such as a negative correlation between PR size and chloroplast surface and PR occurrence in vicinity of mitochondria or plasmodesmata, suggest that PR may play some role in C4 metabolism. © 2014 The Author(s).