Comparative Evaluation of Biochemical Changes in Tomato (Lycopersicon esculentum Mill.) Infected by Alternaria alternata and Its Toxic Metabolites (TeA, AOH, and AME).

Mukesh Meena,Andleeb Zehra,Vijai K Gupta,Ram S Upadhyay,Manish K Dubey,Mohd Aamir

doi:10.3389/fpls.2016.01408

Abstract

In the present study, we have evaluated the comparative biochemical defense response generated against Alternaria alternata and its purified toxins viz. alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TeA). The necrotic lesions developed due to treatment with toxins were almost similar as those produced by the pathogen, indicating the crucial role of these toxins in plant pathogenesis. An oxidative burst reaction characterized by the rapid and transient production of a large amount of reactive oxygen species (ROS) occurs following the pathogen infection/toxin exposure. The maximum concentration of hydrogen peroxide (H2O2) produced was reported in the pathogen infected samples (22.2-fold) at 24 h post inoculation followed by TeA (18.2-fold), AOH (15.9-fold), and AME (14.1-fold) in treated tissues. 3,3′- Diaminobenzidine staining predicted the possible sites of H2O2 accumulation while the extent of cell death was measured by Evans blue dye. The extent of lipid peroxidation and malondialdehyde (MDA) content was higher (15.8-fold) at 48 h in the sample of inoculated leaves of the pathogen when compared to control. The cellular damages were observed as increased MDA content and reduced chlorophyll. The activities of antioxidative defense enzymes increased in both the pathogen infected as well as toxin treated samples. Superoxide dismutase (SOD) activity was 5.9-fold higher at 24 h post inoculation in leaves followed by TeA (5.0-fold), AOH (4.1-fold) and AME (2.3-fold) treated leaves than control. Catalase (CAT) activity was found to be increased upto 48 h post inoculation and maximum in the pathogen challenged samples followed by other toxins. The native PAGE results showed the variations in the intensities of isozyme (SOD and CAT) bands in the pathogen infected and toxin treated samples. Ascorbate peroxidase (APx) and glutathione reductase (GR) activities followed the similar trend to scavenge the excess H2O2. The reduction in CAT activities after 48 h post inoculation demonstrate that the biochemical defense programming shown by the host against the pathogen is not well efficient resulting in the compatible host-pathogen interaction. The elicitor (toxins) induced biochemical changes depends on the potential toxic effects (extent of ROS accumulation, amount of H2O2 produced). Thus, a fine tuning occurs for the defense related antioxidative enzymes against detoxification of key ROS molecules and effectively regulated in tomato plant against the pathogen infected/toxin treated oxidative stress. The study well demonstrates the acute pathological effects of A. alternata in tomato over its phytotoxic metabolites.

Highlights

Tomato (Lycopersicon esculentum) is one of the most important widely grown vegetable crop all over the world (Abd-El Kareem et al, 2006)
The sequence was submitted to gene bank and an accession number KX118413 was assigned for the identified isolate
Our results showed that the extent of lipid peroxidation at 48 h post inoculation was maximum (15.8-fold) in pathogen-inoculated leaf samples followed by tenuazonic acid (TeA) (13.0-fold), AOH (9.5-fold) and alternariol monomethyl ether (AME) (8.2-fold) treated sample compared to control, suggesting that the biochemical defense pathway is more in the favor of pathogen

Summary

Introduction

Tomato (Lycopersicon esculentum) is one of the most important widely grown vegetable crop all over the world (Abd-El Kareem et al, 2006). A widespread natural occurrence of these toxins has been reported in various fruits and vegetables as well as their derived products, such as juices, beverages, sauces, and concentrates (Ackermann et al, 2011; Asam et al, 2011, 2013). Exposure to these toxins causes genotoxic, mutagenic, carcinogenic, and cytotoxic effects on both human and animals (Pavón et al, 2012). The toxicogenic potency of Alternaria species varies between different isolates, as some isolates have been reported to produce all the three alternariols toxins (AOH, AME, and ALT) in variable quantities (Garg and Singh, 2016). The capacity of a particular isolate to produce different mycotoxins is regulated by their genetic makeup and the amount of mycotoxins produced is well affected by cultural and environmental conditions (Garg and Singh, 2016)

Results

Discussion

Conclusion