Acclimation of tobacco plantlets to ex vitro conditions as affected by application of abscisic acid

Plantlets of Nicotiana tabacum L. cv, Petit Havana SR1 were grown in vitro on Murashige and Skoog medium containing 2% saccharose, and then transplanted ex vitro into pots with coarse sand and Hewitt nutrient solution, In the first day after transplantation, the antitranspirant abscisic acid (ABA; 0.01, 0.05 or 0.10 mM) was added to the substrate. Leaf stomatal conductance (g(s)), which was high in plants during the first days after transplantation similarly as in plantlets grown in vitro, was considerably decreased by ABA-treatment, However, in the further days g(s) decreased more quickly in control than in ABA-treated plants, and after 2 or 3 weeks g(s) was significantly lower than that of plantlets grown in vitro but similar in control and ABA-treated plants. Two weeks after transplantation, net photosynthetic rate, chlorophyll a + b content, maximal photochemical efficiency, and actual quantum yield of photosystem II in plant leaves were higher in comparison with those in plantlets grown in vitro. ABA-treatment had slight positive or insignificant effect on photosynthetic parameters and enhanced plant growth. Thus ABA application can alleviate 'transplant shock' and speed up acclimation of plantlets to ex vitro conditions.