XANTHINE ACCUMULATION AND VACUOLIZATION IN CHLAMYDOMONAS REINHARDTII CELLS

摘要

Utilization of xanthine as the sole nitrogen source for growth by Chlamydomonas reinhardtii cells involved the formation of a transient, intracellular pool of xanthine. Up to 20% of the total xanthine supplied to the medium was nor assimilated after uptake but stored in the cells at concentrations that exceeded xanthine solubility in water. At the subcellular level, a massive accumulation of starch grains in the chloroplast and the appearance of many vacuoles in the cytoplasm distinguished xanthine-grown from ammonium-grown cells. Starch accumulation, but not development of vacuoles, was also observed in N-starved cells. Uptake experiments with radiolabelled xanthine showed that this accumulates only in the cytoplasm, most probably inside vacuoles. The electron-dense material observed in vacuoles of xanthine-grown cells suggests that the intracellular xanthine is in part solid xanthine. [References: 24]