Cysteine, Glutathione, Nicotiana tabacum, Salicylic acid, Sulfur induced resistance, Tobacco mosaic virus, APR, adenosine 5′-phosphosulfate reductase, BSA, bovine serum albumin, CATSAB, salicylic acid-binding catalase, CP, coat protein, dpi, days post inoculation, GSH1, γ-glutamyl cysteine synthetase, GSH2, glutathione synthetase, GSTTau1, Tau class glutathione S-transferase, HR, hypersensitive response, PBS, phosphate buffered saline, PCD, programmed cell death, ROS, reactive oxygen species, S, sulfate, SIR, sulfur induced resistance, SED, sulfur enhanced defense, TMV, Tobacco mosaic virus
Sufficient sulfate supply has been linked to the development of sulfur induced resistance or sulfur enhanced defense (SIR/SED) in plants. In this study we investigated the effects of sulfate (S) supply on the response of genetically resistant tobacco ( Nicotiana tabacum cv. Samsun NN) to Tobacco mosaic virus (TMV). Plants grown with sufficient sulfate (+S plants) developed significantly less necrotic lesions during a hypersensitive response (HR) when compared to plants grown without sulfate (−S plants). In +S plants reduced TMV accumulation was evident on the level of viral RNA. Enhanced virus resistance correlated with elevated levels of cysteine and glutathione and early induction of a Tau class glutathione S-transferase and a salicylic acid-binding catalase gene. These data indicate that the elevated antioxidant capacity of +S plants was able to reduce the effects of HR, leading to enhanced virus resistance. Expression of pathogenesis-related genes was also markedly up-regulated in +S plants after TMV-inoculation. On the subcellular level, comparison of TMV-inoculated +S and −S plants revealed that +S plants contained 55–132 % higher glutathione levels in mitochondria, chloroplasts, nuclei, peroxisomes and the cytosol than −S plants. Interestingly, mitochondria were the only organelles where TMV-inoculation resulted in a decrease of glutathione levels when compared to mock-inoculated plants. This was particularly obvious in −S plants, where the development of necrotic lesions was more pronounced. In summary, the overall higher antioxidative capacity and elevated activation of defense genes in +S plants indicate that sufficient sulfate supply enhances a preexisting plant defense reaction resulting in reduced symptom development and virus accumulation.
► Sulfate as possible enhancer of plant defense during virus infection. ► Sulfate fertilization reduces symptom severity and virus contents. ► Enhanced cysteine and glutathione metabolism up-regulates defense gene expression. ► Sulfate fertilization enhances plant defense during virus infection.