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Articles

Amino Acid Transport into Cultured Tobacco Cells

II. EFFECT OF CALCIUM ¹

The University of Tennessee/United States Department of Energy, Comparative Animal Research Laboratory, Oak Ridge, Tennessee 37830

The effects of calcium ions on lysine transport into cultured Wisconsin-38 tobacco cells were examined. In the presence of calcium, lysine was transported at a relatively low rate for 30 to 40 minutes followed by a period of increasing rates and subsequent stabilization at a higher rate after 2 to 3 hours. In the absence of calcium, transport was uniformly low.

Time-dependent stimulation of lysine transport rate was observed after the cells had been preincubated in calcium-containing media. Similar treatments also resulted in the stimulated uptake of a variety of other amino acids, organic compounds, and sulfate. The stimulation of lysine uptake was apparently not due to nutrient starvation.

Lysine transport was not stimulated in a time-dependent fashion by K⁺, La³⁺, Mg²⁺, or Mn²⁺. Cells with stimulated transport rates continued to exhibit high rates when washed with calcium-containing media followed by transport in calcium-containing media. All other cation wash treatments were inhibitory, although magnesium treatments resulted in partial preservation of stimulated transport rates. Cycloheximide inhibited the calcium/time-dependent stimulation of lysine transport and caused the stimulated rate to decay.

The initial experimental treatments or the culture conditions may represent some form of shock that alters the membrane transport mechanism, thus reducing transport. The observed calcium/time-dependent stimulation may require protein synthesis and represents damage repair.

³ To whom reprint requests should be addressed.

¹ This work was supported by The University of Tennessee Agricultural Experiment Station and by United States Department of Energy Contract DE-AC05-760R00242 with The University of Tennessee. A portion of this work has been presented in abbreviated form (7).