Ion Composition of Tobacco Cells Cultured under Sulfur Deficiency

In both photoheterotrophic and heterotrophic tobacco cells areduced supply of sulfate in the medium did not alter the ratebut the duration of exponential growth. The higher the sulfatesupply in the medium the longer exponential growth proceeded.However, the ion composition of photoheterotrophic and heterotrophiccells was affected by sulfur deficiency in completely differentways. The dynamics in the K⁺-, Na⁺-, Mg²*-, nitrate-, phosphate-,and malate-con-tents of photoheterotrophic cells during growthwere not at all, or only slightly changed, when the sulfatesupply in the medium was reduced from 1.8mM to 1.2 mM, 0.6 mM,or 0.3mM. In heterotrophic tobacco suspensions, however, severesulfur deficiency caused K⁺, Na⁺, Mg²⁺, and malate to accumulateand nitrate to begin to accumulate earlier inside the cells.Addition of sulfate after 4 days to heterotrophic suspensionsgrown under sulfur-limiting conditions prevented the accumulationof these cations and anions. During the initial period of growthalso phosphate accumulated inside heterotrophic tobacco cellsto amounts found to be the higher the smaller the sulfate-contentof the media. Apparently, in photoheterotrophic tobacco cellsthe ion composition can homeostatically be regulated independentfrom the cells' sulfate supply, whereas the ion compositionof heterotrophic tobacco cells appears to be highly dependenton the sulfate supply of the cells. ⁴Present address: Fraunhofer Institut für AtmosphärischeUmwéltforschung, Kreuzeckbahnstr. 19, D-8100 Garmisch-Partenkirchen, F.R.G. (Received August 30, 1988; Accepted January 18, 1989)