Effects of Mineral Salts on Short-term Incorporation of Carbon Dioxide inChlorella

Abstract

The effects of various mineral salts have been studied, both singly and in combination, on the uptake and distribution of photosynthetically incorporated carbon-14 in Chlorella. When magnesium sulphate, potassium nitrate, and potassium phosphate were combined in the same concentrations as are found in the normal nutrient solution, the uptake of carbon-14 was increased and more radioactivity was incorporated into the amino-acids, with a decrease in the percentage of radioactivity in the sugar phosphates when compared to the controls in distilled water. The most striking effect of the addition of just one salt was obtained with salts containing nitrogen, particularly ammonium chloride, which in one experiment increased the radioactivity found in the amino-acids from 9.9 per cent. (expressed as percentage of the total soluble radioactivity found in this group of compounds) in the controls to 57 per cent., while the radioactivity in the sugar phosphates fell from 64 to 7 per cent., correspondingly. The total uptake of carbon dioxide by the cells supplied with ammonium chloride was three times as great as that in the controls in distilled water. The relevance of these findings to the methodology involved in experiments dealing with the path of carbon in photosynthesis is discussed, with particular emphasis upon the concept of a ‘steady state’ and how it is thought this may best be achieved.