A sulfated polysaccharide κ-carrageenan induced antioxidant defense and proteomic changes in chloroplast against leaf spot disease of tomato

Ecofriendly approaches to control plant diseases using biopolymers are gaining momentum due to their non-toxic nature to the environment. The present study elucidates the potency of a sulfated polysaccharide, kappa-carrageenan, obtained from the red seaweed Kappaphycus alvarezii, as an inducer of antioxidant defense and also chloroplast proteome against leaf spot disease in tomato. k-carrageenan (0.3%) treatment was very effective in reducing disease scores in tomato plants. Fluorescent microscopy of tomato leaves stained with Uvitex 2B (a chitin specific stain) revealed that foliar application of kappa-carrageenan (0.3%) reduced colonization of the pathogen Septoria lycopersici. In addition, kappa-carrageenan pretreatment followed by pathogen infection recorded a higher accumulation of calcium oxalate crystals. The treatment of kappa-carrageenan resulted in the induction of H2O2 and superoxide anion compared to control or S. lycopersici-infected plants. The tomato leaves treated with kappa-carrageenan showed higher activity of peroxidase enzyme. Furthermore, chloroplast proteome analysis by 2D-PAGE of control, S. lycopersici-infected, kappa-carrageenan-treated, and k-carrageenan treatment followed by S. lycopersici-infected leaves of tomato showed differential expression of 31 proteins, of which 11 proteins were upregulated including acid phosphatase 1-like, C- terminal processing peptidase, GATA transcription factor 5, Calvin cycle protein CP12-1, Photosystem I reaction center subunit PSAK, and subunit of cytochrome B6-F complex iron-sulfur centers. These results indicated that kappa-carrageenan could be a promising inducer of antioxidant defense and modulator of chloroplast proteome in tomato plants.

Automated summary

The study demonstrated that kappa-carrageenan effectively reduced leaf spot disease in tomato plants, inhibited pathogen colonization, enhanced peroxidase activity, and modulated chloroplast proteome expression. This biopolymer shows promise as an inducer of antioxidant defense and a regulator of chloroplast proteome in tomato plants.