THE ULTRASTRUCTURE AND CYTOCHEMISTRY OF RESTING CELL FORMATION INAMPHORA COFFAEFORMIS(BACILLARIOPHYCEAE)1

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Abstract
SUMMARY: The ultrastructure of logarithmic‐growing cells and of resting cells in laboratory cultures ofAmphora coffaeformis(Ag.) Kütz. isolated from deep ocean water was examined using electron and light microscopy. The acid Phosphatase activity, chlorophyll a and lipid content were assessed at weekly intervals of resting cell formation during cold‐dark treatment, simulating deep ocean water. Approximately 4 wk are required to complete resting cell formation. During the first week, the cytoplasm undergoes extensive transformation and lysosomal activity is observed. Large vacules decrease in size and many small ones develop, the mitochondria become fewer and one or more massive mitochondria appear possibly by fusion of smaller ones; the cytoplasm becomes densely granular. During the second and third week, the cytoplasm continues to contract, lipid bodies begin to develop and the plastid becomes densely stained. At the fourth week, the mature resting cell is formed containing one or more massive mitochondria, a well‐formed plastid, and granular cytoplasm containing occasional lipid droplets. There is no change in frustule morphology and the cytoplasm does not produce a protective layer. The variation in chemical constituents correlates with microscopic structure of the cells. The fine structure of cells during growth resumption when exposed to light at 25 c is presented. Previous reports of viable, chlorophyll‐containing cells at great depths in the ocean may be explained by the results reported in this paper.