INFLUENCE OF INVERSE DAY-NIGHT TEMPERATURE ON OZONE SENSITIVITY AND SELECTED MORPHOLOGICAL AND PHYSIOLOGICAL-RESPONSES OF CUCUMBER

Cucumis sativus L. (cvs. Poinsett and Ashley) plants were grown from seed in a growth chamber at a +10C (28/18) or a -10C (18/28) difference (DIF) between day temperature (DT) and night temperature (NT) on a 12-hour photoperiod for 24 days prior to ozone (O3) fumigation (3 hours at 0.5 mumol.mol-1). Negative DIF, compared to +DIF, reduced plant height, node count, fresh weight, dry weight, and leaf area in both cultivars. Photosynthetic rate (Pn), chlorophyll concentration, and variable chlorophyll fluorescence (F(v)) were lower and O3 injury and polyamine concentrations were higher at -DIF than at +DIF. Ozone fumigation generally increased leaf concentration of polyamines and reduced Pn, stomatal conductance, and chlorophyll fluorescence. 'Poinsett' generally had a higher specific leaf mass and higher concentrations of chlorophyll a and polyamines than did 'Ashley', but there was no cultivar difference in O3 injury, growth response, Pn, or stomatal conductance.