Up-Regulation of Antioxidants in Tobacco by Low Concentrations of H₂O₂ Suppresses Necrotic Disease Symptoms

Abstract

Pretreatment of tobacco leaves with low concentrations (5 to 10 mM) of H₂O₂ suppressed hypersensitive-type necrosis associated with resistance to Tobacco mosaic virus (TMV) or Pseudomonas syringae pv. phaseolicola. The same pretreatment resulted in suppression of normosensitive necrosis associated with susceptibility to Botrytis cinerea. This type of H₂O₂-mediated, induced disease symptom resistance correlated with enhanced host antioxidant capacity, i.e., elevated enzymatic activities of catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (POX) after viral and bacterial infections. Induction of genes that encode the antioxidants superoxide dismutase (SOD), CAT, and APX was also enhanced early after TMV infection. Artificial application of SOD and CAT suppressed necroses caused by viral, bacterial, or fungal pathogens similarly as H₂O₂ pretreatment, implying that H₂O₂-mediated symptom resistance operates through enhancement of plant antioxidant capacity. Pathogen multiplication was not significantly affected in H₂O₂-pretreated plants. Salicylic acid (SA), a central component of plant defense, does not seem to function in this type of H₂O₂-mediated symptom resistance, indicated by unchanged levels of free and bound SA and a lack of early up-regulation of an SA glucosyltransferase gene in TMV-infected H₂O₂-pretreated tobacco. Taken together, H₂O₂-mediated, induced resistance to necrotic symptoms in tobacco seems to depend on enhanced antioxidant capacity.

Reactive Oxygen Species and Plant Disease Resistance

“…Indeed, an exogenous application of relatively low concentrations (5-20 mM) of H 2 O 2 to tobacco leaves and pea seedlings stimulated the antioxidant capacity of plants, increasing thereby tolerance to abiotic stresses and enhancing seedling growth (Gechev et al 2002;Barba-Espin et al 2010). We have shown, however, that pretreatment of tobacco with 5 to 10 mM of H 2 O 2 also induces a suppression of pathogen-induced necrotic symptoms associated with either HR-type resistance to viruses and bacteria or a compatible infection by a fungus (Hafez et al 2012). This "immunization" of plant hosts was associated with the induction of transcription and activity of antioxidant enzymes and was shown to operate indeed by the enhancement of plant antioxidant capacity, since artificial, simultaneous application of superoxide dismutase and catalase suppressed necrosis caused by viral, bacterial, or fungal pathogens similarly as H 2 O 2 pretreatment.…”

“…This "immunization" of plant hosts was associated with the induction of transcription and activity of antioxidant enzymes and was shown to operate indeed by the enhancement of plant antioxidant capacity, since artificial, simultaneous application of superoxide dismutase and catalase suppressed necrosis caused by viral, bacterial, or fungal pathogens similarly as H 2 O 2 pretreatment. Remarkably, however, pathogen multiplication did not change in "immunized" tobacco plants clearly differentiating this H 2 O 2 -mediated suppression of pathogen-induced necrosis from plant disease resistance responses (Hafez et al 2012).…”

“…In fact these two types of signaling pathways (conferring inhibition of abiotic and biotic stresses) could significantly overlap, as shown, e.g., by their requirement for NADPH oxidase (RBOHD)-dependent ROS production (Miller et al 2009;Mittler et al 2011) and the necessity of proper antioxidant responses during SAR (Fodor et al 1997;Király et al 2002). Nevertheless, the fact that plant pretreatments with low concentrations of exogenous ROS cause a reduction of necrotic disease symptoms but not of pathogen levels (Hafez et al 2012) points to the existence of different types of ROS waves activated in response to abiotic and biotic stresses, respectively. In order to confer an efficient, simultaneous plant defense to pathogen infection and abiotic stress, these independently developed ROS waves should act in concert and be integrated.…”

Oxidative stress and antioxidative responses in plant–virus interactions

“…localized pathogen inhibition/oxidative stress and antioxidant/defence signalling e has been also demonstrated in virus-infected plants [see e.g. [1,11,36,63,71,91]]. The purpose of this review is to discuss how the dual role of ROS is differentially manifested during incompatible and compatible virus infections of plants.…”

Estudio integral de los mecanismos de resistencia inducida. Inductores frente a estrés biótico y abiótico

“…Another common response after virus perception is the H 2 O 2 accumulation. In plant-virus incompatible interactions, the generation of H 2 O 2 is associated with resistance to virus (Hafez et al, 2012). However, in compatible interactions the increase of H 2 O 2 is more noteworthy in the virus susceptible plant than in the resistant plant (Díaz-Vivanco et al, 2006).…”