Effect of elevated CO2 concentration on acclimation of tobacco plantlets to ex vitro conditions

Nicotiana tabacum L, plants grown in vitro were transferred to ex vitro conditions and grown for 28 d in a greenhouse under normal CO(2) concentration (C, 330 pmol mol(-1)) or elevated CO(2) concentration (E, 1000 mu mol mol(-1)). Stomatal conductances of abaxial and adaxial epidermes measured under optimal conditions were not significantly affected by growth under E, but the stomatal regulation of gas exchange was better. Leaf photosynthetic rate (A) of elevated CO(2) plants was similar to that of control plants when both were measured under normal CO(2), but higher when both were measured under elevated CO(2). The A of elevated CO(2) plants was much higher than the A of control plants when measured under their respective growth CO(2) concentration, which resulted in their higher growth rate. Chlorophyll a and b contents, and activities of whole electron transport chain and of photosystem (PS) II were not markedly affected by growth under E, and the maximum efficiency of PSII measured as the ratio of variable to maximum fluorescence was even slightly increased. Hence no down-regulation of photosynthesis occurred in transplanted plants grown for 4 weeks under E. The contents of p-carotene and of xanthophyll cycle pigments (violaxanthin + antheraxanthin+zeaxanthin) were lower in E plants. The degree of de-epoxidation of xanthophyll cycle pigments was not changed or was even lower after transfer to ex vitro conditions, which indicated that no photoinhibition occurred, Therefore, CO(2) enrichment can improve acclimation of in vitro-grown plantlets to ex vitro conditions.