Steering stomatal dynamics by chemicals or LED lighting during acclimatization of micropropagated plantlets

Acclimatization of micropropagated plants is one of the crucial phases for success of a tissue culture protocol. Tissue cultured plants have no functional stomata, a reduced root system and a underdeveloped cuticula. By steering the stomatal dynamics or minimizing respiration, acclimatization might be optimized. In this research, we try to regulate stomatal behavior and respiration either by chemical or physical triggers. In the experiments we used micropropagated Bromeliads, Spathiphyllum and Rhododendron. In a first experiment, plant growth regulators and antitranspirants were used as chemical triggers. Plantlets were drenched in different plant growth regulators before transfer to the greenhouse. Afterwards stomatal conductance and water retention were measured during the acclimatization. In a second experiment the effect of different LED light regimes during the acclimatization [100% red (R); 100% R + supplemental far-red (FR) Φ 0.7, 100% R + supplemental FR Φ 0.8; 50% R + 50% blue (B) light + supplemental FR Φ 0,7, fluorescent light (FL); PAR 60 µmol/m².s in all cases] was investigated. The water retention measurements demonstrated that the crucial phase during acclimatization takes place between day four and day seven. Promising effects of abscisic acid, antitranspirants, paclobutrazol and putrescine on acclimatization of the tissue cultured plantlets were observed during the first experiment. For the physical regulation, the number of stomata at the end of acclimatization was increased under R + FR (Φ 0.7) light, but the roots were shorter for Spathiphyllum and Bromelia. In Bromelia significantly less roots were present under R + FR (Φ 0.7) light. FL resulted in a significant higher percentage of dry matter for the upper part of all the ornamentals tested, while for the lower root part no difference between the light treatments was observed.