Prior to the extraction of xylem sap, absorbent cotton wassoaked in distilled water and air-dried three times to reducecontamination in the ABA and ZR measurements. A comparisonbetween the ABA and ZR concentrations in xylem sap collected byabsorbent cotton and by vacuum extraction revealed no significantdifference (P < 0.05). Thus, the use of absorbent cotton exerted littleeffect on the ABA and ZR measurements. In vacuum extraction, a sil-icon tube was tightly attached to the cut portion of corn seedlings,which was then squeezed to vent air and tied with string at theother end. After 12 h, the solution in the silicon tube was collected.Values in the graphs represent averages and were analysed withSAS (version 6.12). Analysis of variance (ANOVA) was performedby using the least significant ranges test for multiple comparisonsamong treatment groups at P = 0.05.