Effect of lithium ions on the growth of wheat roots and the role of phosphoinositide cycle in growth regulation]

The influence of lithium ions (LiCl in concentrations of 0.5, 1.0, and 5.0 mM) on the growth processes of roots of 2-5-day old wheat seedlings was studied. It was shown that the inhibition of the root growth increased with the increase of LiCl concentration and seedling age. The membrane potential of root cells was lower and the loss of K+ by cells was greater when roots were treated with 5 mM LiCl, compared with the control. The growth inhibition by lithium was decreased by univalent ions, partially by potassium at the beginning of growth and completely by sodium throughout the experimental period. The divalent ions calcium and barium decreased the Li(+)-induced inhibition of root growth by reducing the rate of lithium uptake by cells. Myoinositol, controlled by Li-sensitive inositolmonophosphatase, reversed the Li-induced root growth inhibition in 2-day old seedlings, but did not prevent the inhibition during subsequent elongation. It can be concluded that lithium effects on wheat root growth are mediated by a partial blockage of signal transduction for proliferation (via the phosphoinositide cycle), because of calcium deficiency and caused by modification of ion transporting systems of the plasmalemma, and by disturbance of ion gradients, primarily H+ and K+.