In laboratory hydroponic experiments with spring barley genotypes the juvenile plants with 5 leaves were
tested for their physiological responses to osmotic stress evoked by blocking the water uptake in roots by
polyethylenglycol (PEG-6000) and to exogenous abscisic acid (ABA) applied in the nutrient solution which
inhibits the stomata opening. Results from the measurements of leaf diffusion resistance, relative water
content, transpiration and leaf elongation rates show dominant role of chemical signalization drought from
root environment and of stomata in the regulation of water loss as well as sensitiveness of leaf elongation to
lowered water availability. Maintenance of water content and turgor in the leaf tissues resulted from
expression of morphological and physiological mechanisms of resistance and tolerance to drought different
from that in mature plants which might be useful in the screening genotypes with different level of drought
tolerance.
