• abscisic acid;
  • auxin;
  • Bangiales;
  • Brazilian seaweeds;
  • cytokinin;
  • Gelidiales;
  • Gigartinales;
  • Gracilariales;
  • plant hormones

Endogenous cytokinins, auxins, and abscisic acid (ABA) were identified and quantified in 11 red algae collected from the Brazilian coast. Field materials and two isolates cultured in the laboratory were extracted with various solvents and buffers containing a mixture of appropriate internal standards, purified by solid-phase extraction followed by immunoaffinity chromatography, and analyzed by liquid chromatography–tandem mass spectrometry. Isoprenoid cytokinins (free and conjugated forms of isopentenyladenine [iP], cis-zeatin [cZ], and trans-zeatin [tZ]) were detected in all species with concentrations of cZ and iP forms being higher than tZ forms. Dihydrozeatin (DHZ) and its metabolites were only detected at very low levels in nine of the studied species. Aromatic cytokinins (6-benzylaminopurine [BA], ortho- and meta-topolin [oT and mT]) were not detected in any of the samples. The cytokinin profile of Chondracanthus teedei (Mert. ex Roth) Kütz. was distinct in comparison to other species with para-topolin (pT) derivatives detected in low concentrations. The main auxins present in all species were free indole-3-acetic acid (IAA) and indole-3-acetamide (IAM). Indole-3-ethanol (IEt), indole-3-acetyl glutamic acid (IAGlu), and indole-3-acetyl leucine (IALeu) were detected in a few species at low concentrations. ABA was present in all species analyzed except for Hypnea nigrescens Grev. ex J. Agardh. No ABA conjugates were detected in any species. These results confirm that cytokinins, auxins, and ABA were common constituents in red seaweeds, with this being the first report of the occurrence of ABA in Rhodophyta. The complexity of the hormone profiles suggests that plant hormones play a role in regulating physiological processes in Rhodophyta.