Seaweeds’ carbohydrate polymers as plant growth promoters

Currently, the high food demand led to a mass agriculture practices, whereas crop productivity is one of the major concerns for the producers. However, the intensification of the use of synthetic fertilizers has led to serious harmful impacts for human health and for the environment. The quest for novel and natural agricultural products is a current trend, hence seaweed polysaccharide bioactivity can contribute for this pursuit. The seaweed principal carbohydrates (agar, carrageenan and alginate) were extracted and chemically characterized from five red seaweeds, namely Gracilaria gracilis (Slender wart weed), Asparagospis armata (Harpoon weed), Calliblepharis jubata (False eyelash weed), Chondracanthus teedei var. lusitanicus and Grateloupia turuturu (Devil's tongue weed); and three brown seaweeds Colpomenia peregrina (Oyster thief), Sargassum muticum (Wireweed) and Undaria pinnatifida (Wakame). Afterwards, it was evaluated the impact of these sulphated polysaccharides on kale (Brassica oleracea) growth. Among the polymers tested, iota-carrageenan (from Calliblepharis jubata), kappa/ iota-carrageenan (from the female gametophyte of Chondracanthus teedei var. lusitanicus) and agar (from Gracilaria gracilis) showed a positive effect on kale growth. Through the quantification of polysaccharides and uronic acids, it appears that the polymer chemical structure is the decisive factor that affects the plant biostimulant activity.