Application of ABA and kinetin on the aquatic carnivorous plant Aldrovanda vesiculosa affects the morphology and phytohormone profiles in shoot apices

Aldrovanda vesiculosa is a rootless aquatic carnivorous plant forming turions (winter buds) as specific overwintering organs containing high abscisic acid (ABA) content. The high ABA content has the key role in regulating turion formation and maintaining turion dormancy. Here, we compared hormonal profiles (cytokinins, auxins, ABA) in shoot apices in A. vesiculosa grown in mini aquaria in a greenhouse at the end of the summer season after a 2-day priming with ABA (2 µM) and ABA together with an artificial cytokinin kinetin (KIN, 20 µM), to find out their effects and interactions on turion formation and morphology. During the next 11 days (without added hormones), the ABA application gently boosted the turion development but the rapid apical shoot growth was not influenced. The shoot apices were narrower and more condensed. The ABA+KIN application almost ceased the apical growth and retarded the turion development. Shoot apices were robust and wide. Turion development may thus interfere with apical shoot growth. The application of ABA alone did not significantly change the contents of cytokinins, auxins or ABA in shoot apices, but +ABA+KIN significantly decreased the total and active endogenous cytokinins and increased the ABA content threefold compared to the control. Thus, both added hormones affected the developing turions in a similar way which is known and expected in dormant organs of terrestrial plants. These results suggest that the coordination between ABA and cytokinins might be crucial for hormonal regulation of the onset of turion dormancy and turion development in aquatic plants.