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

Abstract

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, κ-carrageenan, obtained from the red seaweed Kappaphycus alvarezii, as an inducer of antioxidant defense and also chloroplast proteome against leaf spot disease in tomato. к-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 κ-carrageenan (0.3%) reduced colonization of the pathogen Septoria lycopersici. In addition, κ-carrageenan pretreatment followed by pathogen infection recorded a higher accumulation of calcium oxalate crystals. The treatment of κ-carrageenan resulted in the induction of H2O2 and superoxide anion compared to control or S. lycopersici-infected plants. The tomato leaves treated with κ-carrageenan showed higher activity of peroxidase enzyme. Furthermore, chloroplast proteome analysis by 2D-PAGE of control, S. lycopersici-infected, κ-carrageenan-treated, and к-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 κ-carrageenan could be a promising inducer of antioxidant defense and modulator of chloroplast proteome in tomato plants.