The Mechanisms and Applications of Plant Stress Mitigation by Seaweed Extracts

Extract of the brown macroalga (seaweed), Ascophyllum nodosum, has been used widely as foliar and soil fertigation on field and horticultural crops. A. nodosum extracts improve plant growth, yield, and quality of plant produce and alleviate abiotic stresses such as salinity, low temperature, and water stress. Recent studies using the model plant, Arabidopsis thaliana, have revealed that the extracts affect a specific subset of plant genes at the transcriptional level leading to stress tolerance. Root treatment with A. nodosum extract significantly improved plant performance under 150mM NaCl stress.  Treated plants recorded a significant increase in the number of leaves, leaf area, and biomass. Transcriptome analysis revealed that 184 genes were up regulated on day one after the extract treatment, the number increased to 257 on day 5. However, A. nodosum extract treatment attenuated the transcript abundance of 91 and 262 genes on day one and day five, respectively. Similarly, lipophilic components of A. nodosum extracts protected A. thaliana against low temperature stress. This induced tolerance against low temperatures was a result of coordinated transcriptome and metabolomic changes. For example, treated plants accumulated high concentrations of unsaturated fatty acids and sugar alcohols. Further, the chemical components in the extract affected the expression of genes involved in the biosynthesis of plant growth regulators. This suggests that A. nodosum extracts mitigate stress, at least in part, through changes in concentration of plant growth regulators. This research opens up a novel area of chemical regulation of gene expression to improve plant growth and stress tolerance. This potential will be discussed.