Carbon dioxide exchange and phytochrome control of flowering in Xanthium pennsylvanicum

Abstract

The presence of CO2 at sufficiently high concentrations is necessary for red light night interruptions to affect flowering in Xanthium pennsylvanicum L. The present study investigated the involvement of CO2 exchange in the effects of night interruptions on flowering. Brief red or far-red treatments were applied to Xanthium plants under inductive night conditions, and flowering response was assessed according to bud morphology 10 days after light treatment. The occurrence of flowering depended on the timing, wavelength, and intensity of the light treatments and on the CO2 concentration during the treatments. During the night interruptions CO2 exchange was measured in single attached leaves. CO2 exchange was influenced by the conditions during the night interruptions, but there was no apparent relationship between the patterns of CO2 exchange observed and the subsequent flowering responses to the night interruptions. Brief (10–60 s) high-intensity red light interruptions at 350 ppm CO2 had much less effect on CO2 exchange than did 5 min of low-intensity red light interruptions given at 20 ppm CO2. The brief light interruptions inhibited flowering, while the longer interruptions at low CO2 concentrations were ineffective. Moreover, far-red reversal of red light effects was not accompanied by alterations in CO2 exchange. It appears that the action of CO2 in night interruptions is not associated with CO2 exchange during the interruptions.