SITE OF BETA-CHITIN FIBRIL FORMATION IN CENTRIC DIATOMS .1. PORES AND FIBRIL FORMATION

The silica valve structures related to β-chitin fibril formation were investigated in the centric diatom algae Cyclotella cryptica, Cyclotella nana, Cyclotella meneghiniana, and Thalassiosira fluviatilis with transmission and scanning electron microscopy. The results for T. fluviatilis are given in detail: The silica valves are characterized by a marginal ring of up to 86 pores and a central, less regular set of pores. The pores are surrounded by a system of chambers and supporting structures. The β-chitin fibrils originate from these pore apparatuses. All pores may function in fibril formation. Normally one, but sometimes two, fibril is seen to be attached in a pore. Each pore may be the source of numerous, sequentially formed fibrils, as judged from the huge number of chitin fibrils, relative to the number of cells, when the fibrils are continually detached from the cells by aerating the cultures. In the investigated Cyclotella species, the situation is very similar with respect to pores and chitin fibrils, with species-specific variations in the architecture of the pore apparatus and the valves. It is concluded that the pores of the investigated centric diatoms are structures specialized for the formation of β-chitin fibrils. © 1979 Academic Press, Inc.