[Occurrence and metabolism of auxin in multicellular algae of the Baltic Sea : I. On the occurrence of indole-3-acetic acid]

HIGH-THROUGHPUT SCREENING TECHNOLOGY FOR MONITORING PHYTOHORMONE PRODUCTION IN MICROALGAE(1)

New miniaturized techniques for multiplying microalgae and estimating their phytohormone production were developed; in these methods, the strains to be tested are cultivated in microtitre plates, and the phytohormones in suspensions of the cultures are measured by direct ELISAs. Specific and sensitive ELISAs for determining abscisic acid (ABA), indole-3-acetic acid (IAA), cis- and trans-zeatin riboside, isopentenyladenosine (iPR), and other less common cytokinins were developed for this purpose. Polyclonal antibodies used in the ABA and IAA assays were raised against C1- and C1'- conjugates of the compounds with BSA, respectively, and thus were specific for the free acids and their respective C1-derivatives. The use of cytokinin ribosides coupled via their sugar residues to BSA as haptens generally led to antibodies that bound free bases, 9-glycosides and nucleotides, but with high specificity for the corresponding N(6) -side chains. Using internal standards, dilution assays, and authentic [(2) H] and [(3) H] recovery markers, it was shown that the ELISAs could be used to estimate contents of the selected phytohormones in the cultures. The ELISAs provided reliable and very fast estimates of the selected phytohormones, at concentrations ranging from 0.01 to 10 pmol · mL(-1) in various microalgal strains. In addition, a recently developed HPLC selected ion monitoring mass spectrometry (HPLC-SIM-MS) method was used to calibrate and validate the ELISA results and confirm the presence of the detected phytohormones in immunoaffinity-purified extracts. Where independent validation of results is deemed necessary, the use of quantitative HPLC-MS is recommended for each new microalgal strain to be tested.

Evaluation of evidence for the presence of indole-3-acetic acid in marine algae

Using a two-dimensional thin layer chromatography system (TLC) we have been unable to detect endogenous indole-3-acetic acid (IAA) (as an Ehrlichpositive spot on TLC plates) in the acidic, ether-soluble fraction of alkaline hydrolysates of 10 species of marine algae. Exogenously added IAA, admixed with algal extracts, was completely separated on chromatograms from other Ehrlich-positive compounds which were present in the extracts. Several regions of auxin-like activity were located on chromatograms of Fucus extracts. From experiments on the recovery of exogenously added IAA from algal extracts, we calculate that if IAA is present in algae, the levels are below 0.1 μg IAA/g fresh weight. The claim by previous workers that IAA is present in marine algae is critically discussed.

[Occurrence and metabolism of auxin in multicellular algae of the Baltic sea]

1. Unsterile and sterile green algae (2 species tested) and red algae (3 species) were able to hydrolize indole-3-acetonitrile (IAN) to indole-3-acetic acid (IES). Indole-3-acetamide (IAAm), detected together with IES, seemed to be an intermediate. Brown algae (3 species) incubated with IAN could produce neither IES nor IAAm. All algae oxidized IAN to indole-3-carboxaldehyde (IA) and indole-3-carboxylic acid (ICS). 2. IES destruction by living algae was mainly due to the activity of marine microorganisms. Sterile algae showed low activity; but sea-water previously incubated with unsterile algae, was active. IA and ICS, together with unidentified substances, were products of the IES-destruction. 3. All but one tested species of algae showed peroxidase activity in vivo. Enzyme preparations made of red and brown algae possessed neither peroxidase nor IES-oxidase activity, but preparations of 5 species of green algae (with one exception: Cladophora rupestris) showed peroxidase and IES-oxidase activity. IES-oxidase of these algae was active only in the presence of the cofactors Mn(++) and 2.4-dichlorophenol. Natural inhibitors of IES-oxidase were present in the enzyme preparations made of several (but not all) red and brown algae; they were absent in all green algae preparations.