`Early Girl' tomato plants (Lycopersicon esculentum Mill.) were grown in a medium containing peatmoss and perlite (60%:40% by volume). The medium was drenched with 0% or 5% GLK-8924 antitranspirant. Half of the plants were flushed daily with 250 mL water (leaching), and the other half were subirrigated by capillarity. The solution osmotic potential of the medium was reduced significantly by 5% GLK 8924 treatment, then recovered gradually to the control level after 3 days with leaching or 10 days without leaching. Leaf stomatal conductance, transpiration rate, and plant growth were depressed by the antitranspirant application, and the depression was alleviated by leaching. Neither antitranspirant GLK-8924 treatment nor leaching influenced leaf abscisic acid (ABA) content. The effect of the antitranspirant on leaf gas exchange and plant growth was highly related to the reduction in the solution osmotic potential of the medium, but not to leaf ABA content. Younger leaves had higher stomatal conductance and transpiration rate but lower ABA content than older leaves in general.
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