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Influence of Soil Moisture Stress and Abscisic Acid Pretreatment in Modifying SO2 Sensitivity in Poinsettia


Soil moisture stress (SMS) and abscisic acid (ABA) pretreatment had a marked effect in modifying SO2 sensitivity in 2 cultivars of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch.) ‘Ruff and Reddy’ and ‘Rudolph’. Plants grown in 10-cm plastic pots in the greenhouse and exposed to SMS by withholding water for 2.5 days prior to SO2 fumigation in the growth chamber (4 hr at 3 μ1·liter−1) showed greatly reduced SO2 injury; both cultivars were protected similarly. SMS treatment also greatly decreased stomatal conductance and transpiration rate of the leaves. ‘Ruff and Reddy’ plants pretreated with ABA (200 mg·liter−1 of the racemic mixture) 4 hr prior to SO2 fumigation were injured less by SO2 than ‘Rudolph’ and had correspondingly lower stomatal conductance and transpiration rate. ‘Rudolph’ plants pretreated with ABA did not show significantly less SO2 injury, even though stomatal conductance and transpiration rate were lower than controls after ABA pretreatment. These findings demonstrate the importance of moisture stress preconditioning in modifying sensitivity of poinsettia plants to SO2 and suggest a protective role for ABA in certain cultivars.