Effects of low light and darkness on structural transformations in plastids of the Rhodophyta

Abstract

Four. natural populations of Batrachospermum moniliforme Kylin, growing at different light intensities, were examined ultrastructurally. It was observed that only one population, namely that growing at the lowest relative light intensity (6% of full sunlight), exhibited fragmentation and dilation of thylakoids to form tubular units. These structures were prevalent only in plastids of the inner cells, indicating a further reduction of light by self-shading from outer lateral branch cells. Plastids from laboratory-incubated populations of the same species also exhibited a number of structural transformations in response to dark incubation. These alterations included rearrangement of thylakoids into hexagonally-shaped units, production of thylakoidal tubes and formation of large, granular units, somewhat reminiscent of the prolamellar body of higher plant etioplasts.A survey of the effects of dark incubation upon plastid organization of fourteen species from five orders of red algae revealed some interesting trends. All members of the Bangiophyceae examined possessed plastids that underwent dark-induced structural transformations. In the Florideophyceae, plastids undergoing alterations were observed only in species belonging to the order Nemaliales. In addition, pyrenoid-containing rhodophycean plastids were more subject to structural rearrangements than were plastids without pyrenoids.