Carbon dioxide fixation and translocation of photoassimilates in Vicia Faba following X-irradiation

Abstract

At 14 days post initiation of germination, seedlings of Vicia faba were exposed to 250 R of 250 kVp X-ray which resulted in approximately 50 per cent reduction in accumulation of biomass by 28 days following irradiation. The assimilation of 14CO 2 by irradiated plants during 15-min feeding periods was less than in control plants from 8 to 24 days following irradiation. Likewise, the proportion of 14C-photoassimilate which was translocated to the roots of irradiated plants was significantly smaller than that of control plants from 4 to 24 days following irradiation. At 8 and 12 days post irradiation, stomatal opening on all leaves of irradiated plants was reduced relative to that of control plants and the degree of stomatal opening was found to be significantly correlated with reduced CO 2 fixation. At this time, the difference in 14CO 2 assimilation between control and irradiated plants was greater at higher light intensity, and also this difference in assimilation rate was eliminated by increasing atmospheric CO 2 to 0·09 per cent. Evidence for a physiological limitation in CO 2 availability in irradiated plants at 8–12 days post irradiation is discussed in terms of the Blackman saturation effect (limiting factors) and impairment of stomatal opening.