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

Abstract

Nicotiana tabacum L. plantlets were grown in glass vessels or in Magenta boxes with better CO2 supply. To improve the ex vitro transfer we tested application of abscisic acid and elevated CO2 concentration. In the first two weeks 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 almost 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, PN was always higher at CE than at CA, but when measured under CA, positive effect of CE was found 2 and 16 days after transfer in M-plants and only 16 days after transfer in G-plants. Slightly increased Chl a content was found in all ABA-treated plants, and in M-plants grown under CE. The content of xanthophyll cycle pigments was lower under 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) was 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 efficiency of PS2 (variable to maximum fluorescence ratio, Fv/Fm) after ex vitro transfer was similar to that in in vitro grown plants. This together with the values of DEPS indicated that no photodamage during ex vitro transfer occurred.