Enhancement of local plant immunity against tobacco mosaic virus infection after treatment with sulphated-carrageenan from red alga (Hypnea musciformis)

• Chemical identification of SPS4, sulphated carrageenan extracted from a red alga.
• SPS4 capacity to induce plant defence related-secondary metabolites biosynthesis.
• SPS4 application on tobacco plants induces of SA- and JA/ET-dependent defence genes.
• Significant enhancement of local plant immunity to TMV after treatment with SPS4.
• Depending on dose, SPS4 plays dual role “replication inhibitor/immunity enhancer”.

In the course of development, plants adapted variant defence mechanisms against their infecting pathogens. Some biological molecules miming pathogen effectors mode-of-action are called “plant elicitors” and resides in organisms of marine milieu especially marine algae. In this work, we present the chemical identification of SPS4 “sulphated polysaccharide 4” extracted from the red alga Hypnea musciformis and its eliciting biological activity against TMV “tobacco mosaic virus”. FT-IR analysis indicated that SPS4 mainly contains kappa-carrageenan (98%). Unlike to many algal polysaccharidic elicitors, biological assay on SPS4 showed its ability in tobacco plant to activate SA- and JA/ET-pathways-dependent defence mechanisms. The presented data indicated that SPS4 is also capable of activating the mechanisms of strengthening cell walls and produce variant metabolites like phenolic compounds that have an active role in plant defence. Subsequent plant bioassays showed a significant reduction of TMV spots number to nil when inoculated with virus after SPS4 treatment. Furthermore, the dose of SPS4 affecting TMV accumulation was determined by applying three different concentrations. The results indicated a dual effect of SPS4 biological activity on TMV infection by affecting of virus accumulation/infectivity and enhancing locally plant immunity against TMV.