Differential Production of Phenolics, Lipids, Carbohydrates and Proteins in Stressed and Unstressed Aquatic Plants, Azolla filiculoides and Azolla pinnata

SIMPLE SUMMARY: Crops are the primary feedstock for the production of food/feed and energy, and our dependency on them has been increasing over the last decade. Climate change, reduced land for active agriculture, increased population, reduced amount of clean water, and high costs of chemical fertilizers and energy make modern agriculture unsustainable. Demands are rising for the next generation of cheap and sustainable feedstock, which could be productive under existing conditions. Aquatic plants, such as the free-floating species duckweed and Azolla, have started attracting attention because of their unique features, presenting advantages over terrestrial plants. Terrestrial plants grow on the land or need to be on dry land to survive. On the other hand, aquatic plants have the ability to thrive in ponds under controlled conditions using wastewaters as a source of nutrients. Over the last decade, Azolla species became an attractive feedstock for livestock because of their accumulation of valuable products, phenolic compounds, proteins, lipids, and carbohydrates. Stress-triggered changes in these nutritional components could have a significant impact on the nutritional value of Azolla, which is used as a sustainable food supplement for livestock, poultry, and fish industries. This paper aims to assess the effects of environmental and nutrient stresses on the biosynthesis of valuable metabolites in Azolla. ABSTRACT: The metabolic plasticity of shikimate and phenylpropanoid pathways redirects carbon flow to different sink products in order to protect sessile plants from environmental stresses. This study assessed the biochemical responses of two Azolla species, A. filiculoides and A. pinnata, to the combined effects of environmental and nutritional stresses experienced while growing outdoors under Australian summer conditions. These stresses triggered a more than 2-fold increase in the production of total phenols and their representatives, anthocyanins (up to 18-fold), flavonoids (up to 4.7-fold), and condensed tannins (up to 2.7-fold), which led to intense red coloration of the leaves. These changes were also associated with an increase in the concentration of carbohydrates and a decrease in concentrations of lipids and total proteins. Changes in lipid biosynthesis did not cause significant changes in concentrations of palmitoleic acid (C16:0), linolenic acid (C18:3), and linoleic acid (C18:2), the fatty acid signatures of Azolla species. However, a reduction in protein production triggered changes in biosynthesis of alanine, arginine, leucine, tyrosine, threonine, valine, and methionine amino acids. Stress-triggered changes in key nutritional components, phenolics, lipids, proteins, and carbohydrates could have a significant impact on the nutritional value of both Azolla species, which are widely used as a sustainable food supplement for livestock, poultry, and fish industries.