Ethylene and cytokinin interaction in the morphogenesis of Pelargonium x hortorum LH Bailey in vitro

Pelargonium x hortorum 'Grand Prix' which is susceptible to leaf yellowing and 'Bergpalais' which is not susceptible to leaf yellowing were chosen for the experiments. Ethylene production and action as well as the associated morphological response of Pelargonium shoots grown in the presence of a precursor of ethylene biosynthesis 1-aminocyclopropane-1-carboxylic acid (ACC), ethylene inhibitors: alpha-aminooxyacetic acid (AOA) and silver nitrate (AgNO3) and different cytokinins: (meta-topolin) (mT) or 6-benzylaminopurine (BAP) were studied. It was found that 'Grand Prix' was more sensitive to ethylene than 'Bergpalais' and it showed the leaf yellowing in response to 0.1 mg l(-1) ACC. Moreover, it was noted that ACC added separately or together with cytokinin influenced Pelargonium morphogenesis. Depending on the concentration of ACC (0.1-2.0 mg l(-1)), it either stimulated or inhibited shoot and root formation as well as the growth of shoots and leaf blades. ACC-induced leaf yellowing in 'Grand Prix' was effectively inhibited by mT. In contrast, BAP did not enhance shoot quality. Simultaneously, the presence of mT in the medium resulted in up to a twofold increase in the ethylene production by 'Grand Prix' shoots throughout the culture period compared with the shoots growing on the BAP-medium. The inhibitor of ethylene action (AgNO3) added with cytokinin prevented the yellowing of Pelargonium shoots, but simultaneously influenced the formation of mature shoots with limited long-term multiplication potential. The shoots of P. x hortorum 'Grand Prix' treated with AgNO3 and mT emitted two- and sevenfold more ethylene after 11th and 21st day of culture compared with those treated with AgNO3 and BAP. It is suggested that mT inhibits the early senescence of Pelargonium in vitro by decreasing its sensitivity to ethylene.