Sulfated macroalgal polysaccharides λ-carrageenan and ι-carrageenan differentially alter Arabidopsis thaliana resistance to Sclerotinia sclerotiorum

We examined the effect of macroalgal polysaccharides iota- and lambda-carrageenan, which differ in sulfation, on Arabidopsis resistance to the necrotropic fungal pathogen Sclerotinia scleortiorum. Pretreatment of Arabidopsis with highly sulfated lambda-carrageenan induced resistance to S. sclerotiorum resulting in smaller leaf lesions; by contrast, the less sulfated iota-carrageenan enhanced susceptibility. lambda-carrageenan induced resistance correlated with increased expression of jasmonic acid related genes AOS, PDF1.2 and PR3. Further, lambda-carrageenan increased the oxalase oxidase activity in planta. The l-carrageenan induced resistance in the salicylic acid deficient mutant ics1, but did not rescue the susceptibility of jar1 plants suggesting that lambda-carrageenan induced resistance is independent of salicylic acid. The difference in the bioactivity of carrageenans is due, at least partly, to differences in the degree of sulfation. (C) 2010 Elsevier Ltd. All rights reserved.