Cell Proliferation as an Index of Growth in Corals; Incorporation of ^3h-Thymidine

Abstract

Preliminary experiments are described which are designed to quantify the rates of DNA synthesis in corals. Whole colonies or small sections of Pocillopora damicornis and other corals were incubated in up to 1 ,uCi 3 H-thymidine/ml sea water under field and laboratory conditions. The tissue was extracted with hot 2N NaOH and solubilized, and the 3 H-DNA activity was measured with a liquid scintillation spectrometer. Activity was expressed as CPM/mg dry or wet weight or CPM/calice. Specificity and site of the label was confirmed and studied with autoradiography and DNAse extraction. The label was primarily concentrated in the epidermis with maximum activity in the polyp columns and coenosarc. Labeling indices in the tentacles appeared to increase 5 to 7 days after 3 H-thymidine incorporation and this increase was probably due to migration of labeled cells from the polyp column. No 3 H-thymidine uptake occurred in zooxanthellae and very little was taken up by planulae.Labeling between different calices of the coral species was uniform; however, decreasing rates of 3 H-thymidine incorporation were seen from apical polyps to basal branches in ramose forms. DNA synthesis in P. damicornis is markedly influenced by minor variations in incubation temperature.Optimum labeling occurred at an acclimation temperature of 31 oc with a rapid decline in rate on both sides. Indirect evidence demonstrates that the temperature optimum for the incorporation of 3 Hthymidine increases in parallel with the temperature of the habitat.

SPATIAL AND TEMPORAL PATTERNS OF MITOSIS IN THE CELLS OF THE AXIAL POLYP OF THE REEF CORAL ACROPORA CERVICORNIS

“…However Hale (1964), described cell division primarily among the ectodermal cells in the stolons of another hydroid, Clytia. Cheney (1973) used tritiated thymidine to label proliferating cells and found labeled cells primarily among cells of the column epidermis (ectoderm) and of the polyps and coenosarc of the reef coral Pocillopora damicornis. The internal tissues incorporated little, if any, label.…”

“…Site and frequency of cell division have been investigated in other cnidarians, e.g.. Hydra spp. (David and Campbell, 1972;Neckelmann, 1982); colonial hydroids (Hale, 1964;Campbell, 1968); anemones (Singer, 1971;Minasian 1980); and scleractinian corals (Cheney 1973). Some authors reported that cell proliferation occurs only or at least primarily in the ectoderm (Hale, 1964;Singer, 1971;Cheney, 1973) while others stated that cell division occurs in both the endoderm and the ectoderm (Campbell, 1968;David and Campbell, 1972;Minasian, 1980).…”

“…(David and Campbell, 1972;Neckelmann, 1982); colonial hydroids (Hale, 1964;Campbell, 1968); anemones (Singer, 1971;Minasian 1980); and scleractinian corals (Cheney 1973). Some authors reported that cell proliferation occurs only or at least primarily in the ectoderm (Hale, 1964;Singer, 1971;Cheney, 1973) while others stated that cell division occurs in both the endoderm and the ectoderm (Campbell, 1968;David and Campbell, 1972;Minasian, 1980). Whether this discrepancy in the site of cell proliferation is due to species specific differences or to incorrect interpretation of data has not yet been resolved (Davis, 1971).…”