The relationship between leaf growth and ABA accumulation in the grass leaf elongation zone

Detached barley (Hordeum vulgare L.) shoots, maintained at different air temperatures and VPDs, were fed ABA via the sub-crown internode in a leaf elongation assay. Analysis of variance of leaf elongation rate (LER) showed significant effects of temperature (T), fed ABA] and the interaction T × ABA]. However, the interaction became non-significant when LER was modelled against the ABA] of the elongation zone, EZ-ABA] When detached barley shoots were fed sap from droughted maize (Zea mays L.) plants, sap ABA] could not explain the growth inhibitory activity. Measurement of EZ-ABA] accounted for this ‘unexplained’ growth inhibition. The detached shoot experiments indicated that EZ-ABA], and not xylem sap ABA], was an appropriate explanatory variable to measure in droughted plants. However, ABA accumulation in the elongation zone could not explain a 35% growth reduction in intact droughted plants; thus we considered an interaction of water status and ABA. Using a coleoptile growth assay, we applied mild osmotic stresses (ψ=0 to ?0.06 MPa) and 10^?4 mol m^?3 ABA. Individually, these treatments did not inhibit growth. However, osmotic stress and ABA applied together significantly reduced growth. This interaction may be an important mechanism in explaining leaf growth inhibition of droughted plants.