Improvement of ex vitro transfer of tobacco plantlets by addition of abscisic acid to the last subculture

Tobacco (Nicotiana tabacum L.) plantlets were grown on Murashige and Skoog medium in ventilated Magenta boxes and for the last subculture 10 µM ABA was added to the medium. After three weeks plantlets were transferred into pots with Perlite moistened with water and grown in controlled conditions (16-h photoperiod, day/night temperature 25/20 °C, air humidity about 45 %) either under low or high irradiance of 150 (LI) and 700 (HI) µmol m⁻² s⁻¹, respectively. Content of endogenous ABA was 271.7 pmol g⁻¹(f.m.) in ABA treated plantlets, while in control plantlets it was only 53.3 pmol g⁻¹(f.m.). After ex vitro transfer, stomatal conductance and transpiration rate decreased considerably in comparison with in vitro grown plantlets and remained lower also 7 d after ex vitro transfer, especially in ABA-treated plants and so wilting of plants was practically eliminated. Net photosynthetic rate also decreased 1 d after ex vitro transfer but after 7 d it was mostly higher than that of in vitro grown plantlets. Water use efficiency significantly increased in ABA-treated plants. Chlorophyll a+b content did not change immediately after ex vitro transfer, nevertheless, after 7 d chlorophyll content was higher in ABA-treated plants. Pool of xanthophyll cycle pigments (XCP) and the degree of their deepoxidation (DEPS), which are connected with harmless dissipation of light energy, increased under high irradiance. Contents of XCP and ABA precursors (neoxanthin and violaxanthin) were lower in ABA-treated plants than in control plants indicating less stress in these plants. Most chlorophyll a fluorescence parameters did not change considerably after ex vitro transfer and so the photoinhibition was not observed even under HI. Slight increase in non-photochemical quenching under HI in ABA-treated plants suggested their better photoprotection. Thus application of ABA to the last subculture can improve acclimatization of in vitro grown plants to ex vitro conditions.