Effect of Cadmium on the Level of Isoprenoid-Derived Phytohormones in Duckweed Wolffia arrhiza

Wolffia arrhiza (L.) Horkel ex Wimm. is an aquatic plant belonging to the Lemnaceae family. It does not have leaves, stems, and roots, flowers rarely occur, while body size can reach 1 mm of width and 1.3 mm of length. The present study demonstrates the endogenous level of isoprenoid-derived phytohormones and their changes under the influence of different cadmium (Cd) concentrations (0.1, 1, 10, and 100 µM). A liquid chromatography quadrupole-time-of-flight mass spectrometry analysis indicated the presence of abscisic acid, eight brassinosteroids (6-deoxocastasterone, 6-deoxotyphasterol, cathasterone, typhasterol, castasterone, 24-epicastasterone, brassinolide, and 28-homobrassinolide), seven free bases of cytokinins [ trans -zeatin ( t Z), cis -zeatin ( c Z), dihydrozeatin (DHZ), N 6 -isopentenyladenine, N 6 -isopentenyladenosine, ortho -topolin, and meta -topolin], eight conjugates of cytokinins ( t Z riboside, t Z-9-glucoside, t Z-7-glucoside, t Z- O -glucoside riboside, c Z-9-glucoside, DHZ riboside, DHZ- O -glucoside, and N 6 -isopentenyladenosine-7-glucoside) and gibberellic acid (GA 3 ) in this duckweed. The level of phytohormones in plants treated with Cd has changed, e.g., the ABA level increased while GA 3 decreased. Whereas the amount of BRs and CKs was different in Cd dose-dependent manner. Besides, it is worth noting that the distribution of 25 various phytohormones in the Wolffia arrhiza is reported for the first time.