Phytohormone profiles in leaves and traps of three Genlisea (Lentibulariaceae) species

Abstract

Genlisea (Lentibulariaceae) is a tropical genus of rootless wetland carnivorous plants. The belowground leaf (rhizophyll) is a Y-shaped organ which functions as an ‘eel trap‘ for soil microorganisms. We compared phytohormonal profiles (cytokinins, auxins, ABA) in green photosynthetic leaves, upper trap segments (including the vesicle for prey digestion) and lower branched trap segments functioning as trap entrances, in three Genlisea species from a pot culture. Relatively low contents of total cytokinins (35–1017 nmol kg⁻¹; dry weight) and active cytokinins (7–213 nmol kg⁻¹) occurred in the species. Those in upper trap segments, which fulfill demanding physiological functions, usually exceeded several times those in branched trap segments or green leaves. Generally, auxin contents were enormously variable across the species. Auxin contents (both IAA and total contents) in both organ types in G. hispidula and G. uncinata exceeded those in the G. lobata × flexuosa hybrid by one–three orders of magnitude. The highest free IAA content was usually in green leaves followed by upper and branched trap segments. However, the ABA content, as a hormonal criterion for plant dormancy, was consistently very low in all organs and species, indicating no growth limitation by this inhibitory hormone. The comparison of these hormone profiles with those from the literature in the phylogenetically related sister genus Utricularia (six aquatic species) has indicated that the very low cytokinin contents in Genlisea organs could reflect their very low growth rate as compared to rapidly growing aquatic Utricularia species.