Rapid bioassays to evaluate the plant growth promoting activity of Ascophyllum nodosum (L.) Le Jol. using a model plant, Arabidopsis thaliana (L.) Heynh

Ascophyllum nodosum extract products are used commercially in the form of liquid concentrate and soluble powder. These formulations are manufactured from seaweeds that are harvested from natural habitats with inherent environmental variability. The seaweeds by themselves are at different stages of their development life-cycle. Owing to these differences, there could be variability in chemical composition that could in turn affect product consistency and performance. Here, we have tested the applicability of using Arabidopsis thaliana as a model to study the activity of two different extracts from A. nodosum. Three different bioassays: Arabidopsis root-tip elongation bioassay, Arabidopsis liquid growth bioassay and greenhouse growth bioassay were evaluated as growth assays. Our results indicate that both extracts promoted root and shoot growth in comparison to controls. Further, using Arabidopsis plants with a DR5:GUS reporter gene construct, we provide evidence that components of the commercial A. nodosum extracts modulates the concentration and localisation of auxins which could account, at least in part, for the enhanced plant growth. The results suggest that A. thaliana could be used effectively as a rapid means to test the bioactivity of seaweed extracts and fractions.