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

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Abstract
Four natural populations of Batrachospermum moniliforme Kylin, growing at different light intensities, were examined ultrastructurally. Only 1 population, 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 14 spp. from 5 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. Pyrenoid-containing rhodophycean plastids were more subject to structural rearrangements than were plastids without pyrenoids.

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