Accessory structures of pyrenoid in secondary chloroplast

Abstract

Pyrenoid is a proteinaceous membraneless organelle, mainly composed of Rubisco. Many oxygenic photosynthetic organisms in aquatic environment possess the pyrenoids, which are responsible for the carbon concentrating mechanism. Pyrenoid is probably liquid-like structure, so that its morphology is simple and close to spherical. However, its accessory structure, a pyrenoid-penetrating thylakoid, a structure in pyrenoid periphery, and a membrane sac wrapping a pyrenoid, give rise to a variety of pyrenoid morphology, resulting in its usage as a taxonomic feature. The accessory structures seem to occur sporadically and evolve convergently, as well as pyrenoid itself. In this paper, the morphological aspect of pyrenoid in Heterokontophyta, which support primary production in the hydrosphere, has been reviewed to discuss the roles of pyrenoid accessory structures by summarizing the diversity and commonality of their morphological characteristics.