Effect of the Form of Mineral Nitrogen on the Growth and Heterotrophic Fixation of ¹⁴С-Bicarbonate in Chlamydomonas reinhardtii

Abstract

The earlier-detected effect of the mineral nitrogen form in the nutrient medium (ammonium or nitrate) on the quantity of ribosomes in the cells of chlamydomonas and the callus of soybean requires experimental corroboration of the proposed interpretation of the discovered phenomenon. In order to elucidate the mechanism of ammonium’s action on the formation of protein-producing structures (ribosomes) in the cells of green alga chlamydomonas (Chlamydomonas reinhardtii, strain gr 21), we compared the effect of the form of mineral nitrogen (nitrate and ammonium) on the growth and heterotrophic fixation of ¹⁴С-bicarbonate. Our experiments have shown that the process of cell division (mitosis) was hampered at the beginning of the growing cycle (on days 1–3) when the cells were cultured on nitrate medium. By the end of the growing cycle (days 7–10), the number of cells and the content of dry matter in the cells equalized. It was found that the cells grown on TAP medium with ammonium fixed Н¹⁴С${\text{O}}_{3}^{ - }$ at a higher rate than the cells cultured on TAP medium with nitrate. The obtained results have shown that the rate of dark fixation of Н¹⁴С${\text{O}}_{3}^{ - }$ in the cells grown in the medium with ammonium was higher than in the cells on nitrate medium irrespective of the mode of calculation: on the number of cells or per dry weight unit. An assumption that ammonium present in the nutrient medium can activate synthesis of extra amino acids participating in the formation of protein components of ribosomes in the alga chlamydomonas is discussed.