Unknown Mechanism of Plants Response to Drought: Low Soil Moisture and Osmotic Stresses Induce Severe Decrease in CEC and Increase in Acidity of Barley Roots

Huge amount of papers describe plant response to drought, however information on reaction of plant roots cation exchange capacity and surface acidity on draught conditions is up to date lacking. These parameters are important for amount and ratio of cations uptake by plants. Since other stresses induce changes in roots cation exchange capacity and acidity, we hypothesized that draught does this also. In this paper we checked this hypothesis. Surface charge properties of roots of drought tolerant and draught resistant barley varieties taken from pot (soil draught at water potential pF=3.5) and hydroponic (osmotic stress induced by mannitol) experiments were determined using back-titration method. The stresses were applied at tillering stage. Soil draught and osmotic stress caused even fivefold decrease in cation exchange capacity and up to tenfold increase in acidity of roots of all barley varieties. Surface charge properties of nonstressed roots did not differentiate draught resistant and draught tolerant varieties, however the intensity of roots reaction on the stresses seemed to be higher for draught sensitive plants. This newly presented mechanism of plant reaction on drought indicates that nutrients uptake by plants can be severely limited and relative uptake of polyvalent cations (aluminum or heavy metals) may increase causing additional toxicity. This may serve as additional explanation of plant growth and yield limitation in dry environments.