Photosynthetic pigments and gas exchange during ex vitro acclimation of tobacco plants as affected by CO2 supply and abscisic acid

Nicotiana tabacum L. plantlets were grown in glass vessels or in Magenta bo xes with better CO2 supply. To improve the ex vitro transfer we tested appl ication of abscisic acid and elevated CO2 concentration. In the first two w eeks after transfer, net photosynthetic rate, chlorophyll a+b content, and Chl a/b ratio were higher, and content of xanthophyll cycle pigments lower in M-plants than in G-plants, but during further growth the differences alm ost disappeared. ABA application alleviated the risk of wilting because it decreased stomatal conductance. The effect of ABA was enhanced under CE (28 days after transfer). In situ, P-N was always higher at CE than at CA, but when measured under CA, positive effect of CE was found 2 and 16 days afte r transfer in M-plants and only 16 days after transfer in G-plants. Slightl y increased Chl a content was found in all ABA-treated plants, and in M-pla nts grown under CE. The content of xanthophyll cycle pigments was lower und er CE compared to CA, and the lowest one was found in ABA-treated M-plants grown under CE. On the contrary, the degree of their deepoxidation (DEPS) w as slightly higher in plants grown under CE. No significant effects of ABA- treatment or growth under CE on fluorescence kinetic parameters were found and inconsistent effects on photochemical activities. The photochemical eff iciency of PS2 (variable to maximum fluorescence ratio, F-v/F-m) after ex v itro transfer was similar to that in in vitro grown plants. This together w ith the values of DEPS indicated that no photodamage during ex vitro transf er occurred.