No abstract

No abstract

No abstract

Various studies have shown that water-stressed plants are more tolerant of ozone exposures than are unstressed plants. Two (19). The plant root-mass was enclosed in a semipermeable membrane system (Spectrapor 1; exclusion limit, 6,000-8,000 D; Spectrum Medical Industries, Los Angeles, CA) and placed in either a nutrient solution (-35 kPa) or a nutrient solution to which polyethylene glycol (20 M) (mol wt distribution, 14,000-16,000 D) was added to create an osmotic potential of -80 kPa. Although a solution osmotic potential of -80 kPa does not appear to be a large stress, a previous study (21) showed that this level of osmotic stress in the solution caused significant changes in plant indicators of water stress. Over a 3-day period leaf conductance decreased 60%; leaf water potential and top dry weight of bean plants were reduced 13% and 34%, respectively, over a 7-d period. The osmotic potentials of the solutions were controlled at the root-water interface within the semipermeable membrane and thereby controlled plant water potential ( 19).After the plants had been maintained in -35 or -80 kPa for 4 day, 12 of the 28 plants in each replicate were sprayed with FC2 solutions (10, 15, or 20 Mm) until run-off. Previous studies showed that FC induced stomatal opening in both light and dark (4,22). The FC was dissolved in 0.1 ml ethanol and brought to volume with distilled H20. On the morning of day 5, 12 additional plants were sprayed with ABA solutions (100, 250, or 500 Mm, four plants per concentration level) and the leaves were allowed to dry (about 1 h). The ABA was dissolved in 0.1 ml of saturated Na2CO3 and diluted with a few milliliters of distilled H20 (pH 7.0). The solutions were brought to volume with 67 mm phosphate buffer (pH 7.0). Two to three drops of Triton X-100 per 50 ml of solution were added as a surfactant to each solution. The