LIGHT CONTROL OF THE RESPIRATION OF EXOGENOUS GLYCEROL IN THE RED MACROALGA GRATELOUPIA-DORYPHORA

Heterotrophic activity in macroalgae has been little studied, but the red macroalga Grateloupia doryphora is known to grow in light at a hig her rate in a glycerol-containing medium than in seawater. The effects of 0.1 IM exogenous glycerol in seawater (SW90-gly) on the respiratio n rate of G. doryphora and the role played by light were investigated The algae pretreated for 2h in the light and in SW90-gly evolved oxyge n and fixed carbon dioxide ((HCO3-)-C-14), but also evolved radioactiv e (CO2)-C-14 from [C-14]glycerol. The rate of oxygen evolution was low er than that of samples in seawater, due to a high respiration rate an d/or a partial inhibition of photosynthesis induced by glycerol. In co ntrast, the rate of inorganic carbon fixation was higher in SW90-gly t han in control samples in seawater, suggesting that non-photosynthetic patterns were operating. In darkness, after pretreatment in the light in SW90-gly, samples showed a high oxygen uptake rate just after the light was turned off. Twenty minutes of darkness were enough to decrea se this high respiration rate to that of samples in seawater. The oxyg en uptake observed in all experiments with glycerol was mitochondrial as it was inhibited by potassium cyanide and salicylhydroxamic acid (S HAM). Pretreatment of samples in the light in SW90-gly with the photos ynthetic inhibitor DCMU did not inhibit ensuing dark respiration, thus providing evidence for a non-photosynthetic effect of the light. The highest dark respiration rate was observed after the samples were pret reated in monochromatic blue light in glycerol-containing media.