Hormonal profiles in shoot apices in (sub)tropical populations of the aquatic carnivorous plant Aldrovanda vesiculosa in summer and winter

We compared hormonal profiles (cytokinins, auxins, ABA) in shoot apices in six (sub)tropical populations of the aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae; one from Botswana, five from Australia) growing in cultures during summer and then in frosty conditions at the beginning of winter. One Australian population (Armidale, E Australia, NSW) formed dormant turions. No crucial differences in cytokinin and auxin profiles (for both total and active forms) were found between summer and winter shoots within single populations or between non-dormant and dormant populations in the summer or the winter. The ABA content, as a hormonal criterion for plant dormancy, was consistently nearly zero in summer growing plants in all populations. In winter plants, a nearly zero ABA content occurred only in African plants from Botswana, whereas medium-high ABA contents (3.5–7.0 µmol kg⁻¹; dry weight) were found in all Australian plants regardless of their dormancy. Different Quaternary migration history from southern Europe and subsequent separate evolution and genetic changes might explain the difference between these Australian and African plants. Generally, these results raise questions about how turion formation and dormancy are regulated in plant species with turions with zero ABA content and how other non-dormant subtropical or temperate species overwinter with high ABA content.