In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O3) exposure (70 ng g-1, 7 h d-1 for 31 d). Net photosynthetic rate (PN) of both cultivars were drastically (P<0.01) impaired by O3. Although there were significantly positive correlation between PN and stomatal conductance (gs) in both cultivars under each treatment, the decreased gs in O3 might be the result rather than the cause of decreased P N as indicated by stable or increasing the ratio of intercellular to ambient CO2 concentration(Ci/Ca). PN under saturating CO2 concentration
(PNsat) and carboxylation efficiency (CE) significantly decreased under O3 fumigation, which indicated the Calvin cycle was impaired. O3 also inhibited the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm), actual quantum yield of PSII photochemistry (ΦPSII), electron transport rate (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), the maximum in vivo rate of Rubisco carboxylation (Vcmax) and the maximal photosynthetic electron transport rate (Jmax) which demonstrated that the decrease in PN of the honeysuckle exposed to elevated O3 was probably not only due to impairment of Calvin cycle but also with respect to the light-harvesting and electron transport processes. Compared to the diploid, the tetraploid had higher relative loss in transpiration rate (E), (gs), (PNsat), Vcmax and Jmax. This result indicated that the Calvin cycle and electron transport in tetraploid was damaged more seriously than in diploid. A barely nonsignificant (P=0.086) interaction between O3 and cultivar on PN suggested a higher photosynthetic sensitivity of the tetraploid cultivar. and L. Zhang ... [et al.].