Cap-morphogenesis in a Giant Unicellular Alga, Acetabularia caliculus

Abstract

Morphological transition of cap differentiation at the stalk-apex of a giant unicellular alga, Acetabularia caliculus, was observed with a scanning electron microscope. Beginning with a ring-shaped arrangement of primary protuberances, cap-rays were differentiated after the successive development of primary, secondary and tertiary protuberances. The insides of these protuberances were separated into cavities by septa, however these cavities were continuous with each other due to perforation of the septa. Through the pores on the septa, protoplasmic streaming and central vacuole were continuous in all of the cavities and they were also continuous in a whole cell. Based on these structures, the homology and synchrony in the cap-morphogenesis were discussed, concerning turgor pressure.