Ultrastructure of tetrasporogenesis in the red alga Rhodymenia californica var. attenuata (Rhodymeniaceae, Rhodymeniales, Rhodophyta)

Tetrasporogenesis in Rhodymenia californica var. attenuata is accomplished in four developmental stages. The first stage is represented by a uninucleate tetraspore mother cell sourrounded by an electron transparent cell wall. Dictyosome activity and endoplasmic reticulum are not evident at this stage and starch formation does not occur. Thylakoids are formed from unraveling concentric lamellar bodies. Multiplication of plastids results from fission of the existing organelles. The tetraspore mother cell increases in size and undergoes decussate cruciate division by cleavage infurrowing, resulting in the formation of four tetraspores which represents the second stage of tetraspore development. Also, granular vesicles are formed from the endoplasmic reticulum. The third stage is characterized by the formation of fibrous vacuoles from the fibrous vacuole associated organelles. The fourth developmental stage is represented by maturation of tetraspores and is signaled by the massive production of cored vesicles from hypertrophied dictyosomes and the presence of abundant starch granules. Mature tetraspores are surrounded by a bilayered wall and the tetrasporangial wall, while unbranched, tubular structures run parallel to the plasmalemma.