Current Insights into the Molecular Mode of Action of Seaweed-Based Biostimulants and the Sustainability of Seaweeds as Raw Material Resources

Abstract

Natural biostimulants, such as seaweed extracts, can stimulate plant growth and development in both model and crop plants. Due to the increasing demands for their use in agriculture, it is crucial to ensure the sustainability of the sources from which they are produced. Furthermore, some seaweed extracts were recently shown to prime and protect from adverse environmental factors such as drought, salinity and extreme temperatures, as well as from oxidative stress. The molecular mode of action of these biostimulants has still not been fully elucidated, but there has been significant progress in this direction in the last years. Firstly, this review examines the sustainability aspects of harvesting seaweed resources as raw materials for manufacturing biostimulants and provides an overview of the regulatory landscape pertaining to seaweed-based biostimulants. The review then summarises the recent advances in determining the genetic and molecular mechanisms activated by seaweed-based biostimulants, their influence on transcriptome reconfiguration, metabolite adjustment, and ultimately stress protection, improved nutrient uptake, and plant growth and performance. This knowledge is important for deciphering the intricate stress signalling network modulated by seaweed-based biostimulants and can aid in designing molecular priming technologies for crop improvement.

Keywords: abiotic stress; biostimulants; oxidative stress; plant priming; seaweed extracts; sustainability.

Figure 1

Examples of intertidal, subtidal and beach/storm-cast seaweeds. (a) A. nodosum growing in the intertidal zone in County Kerry, Ireland (source: BioAtlantis Ltd.), (b) Laminaria growing in subtidal waters of Bantry Bay, County Cork, Ireland (Crowe et al. [43]; unpublished image), and (c) beach/storm-cast seaweeds on Derrymore Strand, County Kerry, Ireland (source: BioAtlantis Ltd.).

Figure 2

Commercially available A. nodosum-based seaweed extracts are proven to induce plant priming and abiotic stress tolerance in the model plant Arabidopsis and in crops. Molecular, biochemical and physiological level stress adaptations that occur in seaweed based biostimulant primed plants during oxidative, drought, salt and freezing stress challenges are also summarised above [144,155,165,166,167]. The tomato plants in the figure were primed with A. nodosum extract, SuperFiffty, SF or untreated, with both treatment groups subsequently exposed to drought stress. Red and green arrows show processes, genes, metabolites that are repressed/downregulated and activated/upregulated, respectively.