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 s eed 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 hei ght, node count, fresh weight, dry weight, and leaf area in both culti vars. Photosynthetic rate (Pn), chlorophyll concentration, and variabl e chlorophyll fluorescence (F(v)) were lower and O3 injury and polyami ne concentrations were higher at -DIF than at +DIF. Ozone fumigation g enerally increased leaf concentration of polyamines and reduced Pn, st omatal conductance, and chlorophyll fluorescence. 'Poinsett' generally had a higher specific leaf mass and higher concentrations of chloroph yll a and polyamines than did 'Ashley', but there was no cultivar diff erence in O3 injury, growth response, Pn, or stomatal conductance.