2.1. In vitro cultures of Riccia fluitans
Plant material was obtained from an axenic in vitro culture ofRiccia fluitans RF.1 from a previous experiment . Based on literature data and previous experiments the R. fluitans plants grew on the ½GB5 medium with 20 g · l-1 sucrose, 8 g · l-1 agar-agar and pH 6.0. The upper fragments of sterile plants of R. fluitans were used as secondary explants and were placed on the medium in the form of five small clumps separated by approx. 1-2 cm. Plants were grown in climate chambers at 24°C under long-day conditions with a 16:8 photoperiod (16 h light; 8 h dark). After four weeks of plant growth, one part of the in vitro cultures was overlaid with sterile diH20, and the second part was maintained unchanged. The proper part of the experiment was set up in four replicates and conducted for two weeks.