Effect of osmotic stress on abscisic acid efflux and compartmentation in the roots of two maize lines differing in drought susceptibility

Roots of two Zea mays L. lines (drought-resistant Polj 17, and drought-susc eptible F-2) were exposed to osmotic stress induced by sorbitol (osmotic po tential -1.0 MPa). The following parameters were determined in cortex cells : membrane permeability for abscisic acid (ABA), ABA fluxes across membrane s, pH values and ABA content in cytoplasm and vacuole. Osmotic stress induc ed different distribution of ABA within cell compartments in the investigat ed lines. ABA transport in the F-2 line occurred according to the intracell ular pH gradient and the anion trap concept. In Polj 17, however, osmotic s tress did not cause any significant effect on pH gradient and compartmental ABA content, but had a stimulating effect on ABA efflux from cytoplasm to apoplast and than via xylem to the leaf. These findings indicate different mechanisms of ABA transport between the investigated lines in response to o smotic stress.