INFLUENCE OF AGE, PHYSIOLOGICAL-STATE AND LIGHT LEVEL ON THE SENSITIVITY OF SYNECHOCOCCUS-LIVIDUS TO HYDROGEN-PEROXIDE

The effects of various factors that influenced the sensitivity of Synechococcus lividus to H2O2 have been investigated: these included (1) the growth phase in which inoculum cells were selected, (2) the physiological state of the latter, and (3) the lighting conditions. Cultures inoculated with transient cells were less inhibited by H2O2 than cultures inoculated with exponential or stationary cells. These results are related to an increase in activities of an enzyme which protects against peroxides induced in this period corresponding to a decrease in the growth rate. Responses to H2O2 also depended upon the physiological state of cells; photo-oxidative stressed cells, with high glucose-6-P-dehydrogenase and glutathione reductase activities, were stimulated after addition of 10-6 M and 10-7 M H2O2, but photosynthetic cells were inhibited by the same H2O2 concentrations. Addition of 10-5 M to 105 M to 10-7 M H2O2 in dimly illuminated cultures exhibiting high glucose-6-P-dehydrogenase activity resulted in growth stimulation. Glucose-6-P-dehydrogenase and glutathione reductase activities were increased, 1.5 and 2.5 times respectively, by 10-6 M H2O2. The similarity of these results to those previously described factors influencing sensitivity to low doses of gamma rays are discussed.