. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. TOTAL Cpm 200r "0 12 24 30 Time after feeding radioactive brine shrimp (hours). "0 12 24 30 Time after feeding radioactive brine shrimp (hours) FIGURE 4. Tritiated uridine uptake and incorporation into RN A of animal and algal fractions from light-grown (left) and dark-grown (right) hydras. Each point is mean from four independent experiments, each using 60 hydras. similar to that of cells of their hosts. The doubling time of green hydras is days (Cook and Rupright, 1980). There was no statistically significant
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. TOTAL Cpm 200r "0 12 24 30 Time after feeding radioactive brine shrimp (hours). "0 12 24 30 Time after feeding radioactive brine shrimp (hours) FIGURE 4. Tritiated uridine uptake and incorporation into RN A of animal and algal fractions from light-grown (left) and dark-grown (right) hydras. Each point is mean from four independent experiments, each using 60 hydras. similar to that of cells of their hosts. The doubling time of green hydras is days (Cook and Rupright, 1980). There was no statistically significant difference be- tween the amounts of label incorporated into algae from light-grown and dark- grown hydras. With prolonged exposure, the quantity of labeled DNA decreased because of cell division. According to Wanka et al. (1970), chlorellae lack the enzyme thymidine kinase. They take up, but degrade, the deoxynucleoside, and do not incorporate thymidine into DNA. In fact chlorellae utilize exogenous uridine more readily than thymidine as a precursor for DNA synthesis. They probably synthesize DNA by means of thymidylate synthetase. The symbiotic algal incorporation of thymidine into DNA seems to imply that the host kinases provide triphosphates which can then be utilized as well by the endosymbiotic chlorellae. Incorporation of thymidine into symbiotic algae DNA may be as indicated in this scheme: l*hymidine exogenous thymidine i dTMP ATP v dTDP AJ_P_ -)dTTP .DNA ^ MEDIUM —^ HOST ALGAE Radioautography Figure 7 shows a representative radioautograph, of algae isolated from light- grown hydras after 24 h in 3H-leucine. The label was distributed over the isolated algae and the animal tissue. Treatment of the cells with deoxyribonuclease and ribonuclease before auto- radiography significantly decreased the amount of label, indicating that the labeling was due to incorporation into DNA or RNA respectively. DISCUSSION Cook (1972) suggested hydra "back transfer" of photosy
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
