Effect of Sulfur Deficiency on Protein Synthesis and Amino Acid Accumulation in Cell Suspension Cultures of Nicotiana tabacum

Abstract

Summary Sulfur starvation in photoheterotrophic and heterotrophic cell suspension cultures of Nicotiana tabacum var. Samsun affects growth, protein synthesis and the accumulation of soluble nitrogen compounds. After depletion of the sulfate supply in the medium no further net-protein synthesis was observed and large amounts of soluble nitrogen accumulated. In photohete-rotrophically grown cells this accumulation was mainly due to an intense increase in arginine and glutamine which accounted for 70–85 % of the free amino acid nitrogen. In heterotrophically grown cells only a small amount of arginine was formed and glutamine was the predominant soluble nitrogen compound accumulated. In contrast to the changes in the free amino acid fraction, the protein content of the cultures remained constant during the early period of sulfur deficiency and the amino acid composition of the bulk protein did not change appreciably. Therefore it appears that the amino acids accumulating during sulfur deficiency have been produced by de novo synthesis. Under sulfur starvation conditions photoheterotrophically grown cells contained citrulline and ornithine which were not present in detectable amounts in suspensions grown on sulfur-rich media. The observed twofold increase in arginine production under sulfur starvation also indicates a stimulation of arginine synthesis by these conditions.