Tomato is one of the most economically important vegetables worldwide and is constantly threatened by various biotic and abiotic stress factors reducing the quality and quantity in the production of this crop. As an alternative to mitigate stress in plants, carbon nanomaterials (CNMs) have been used in agricultural areas. Therefore, the objective of the present work was to evaluate the antioxidant responses of tomato seedlings to the application via foliar and drench of carbon nanotubes (CNTs) and graphene (GP). Different doses (10, 50, 100, 250, 500, and 1000 mg L⁻¹) and a control were evaluated. The results showed that the fresh and dry root weight increased with the application of CNMs. Regarding the antioxidant responses of tomato seedlings, the application of CNMs increased the content of phenols, flavonoids, ascorbic acid, glutathione, photosynthetic pigments, activity of the enzyme’s ascorbate peroxidase, glutathione peroxidase, catalase, and phenylalanine ammonia lyase as well as the content of proteins. Therefore, the use of carbon-based nanomaterials could be a good alternative to induce tolerance to different stress in tomato crop.

Summary: Enterotoxigenic Escherichia coli (ETEC) strains are important pathogens in developing countries. Some vaccine formulations containing the heat labile toxin B subunit (LTB) have been used in clinical trials; however, the induction of neutralizing antibodies against the heat‐stable toxin (ST), a poor immunogenic peptide, is necessary, as most ETEC strains can produce both toxins. In this study, a plant optimized synthetic gene encoding for the LTB‐ST fusion protein has been introduced into plastids of tobacco leaf tissues, using biolistic microprojectile bombardment, in an effort to develop a single plant‐based candidate vaccine against both toxins. Transplastomic tobacco plants carrying the LTB‐ST transgene have been recovered. Transgene insertion into the plastid was confirmed by both PCR and Southern blot analysis. GM1‐ELISA revealed that the LTB‐ST fusion protein retained its oligomeric structure, and displayed antigenic determinants for both LTB and ST. Western blot analysis, using LTB antisera, confirmed the presence of a 17‐KDa protein in transplastomic lines, with the correct antigenicity of the fusion protein. Expression levels of this fusion protein in different lines reached up to 2.3% total soluble protein. Oral immunization of mice with freeze‐dried transplastomic tobacco leaves led to the induction of both serum and mucosal LTB‐ST specific antibodies. Following cholera toxin challenge, a decrease of intestinal fluid accumulation was observed in mice immunized with LTB‐ST‐containing tobacco. These findings suggest that tobacco plants expressing LTB‐ST could serve as a plant‐based candidate vaccine model providing broad‐spectrum protection against ETEC‐induced diarrhoeal disease.

The diseases that attack the tomato crop are a limiting factor for its production and are difficult to control or eradicate. Stem and fruit rot and leaf blight caused by Alternaria solani causes severe damage and substantial yield losses. Carbon nanotubes (CNTs) could be an alternative for the control of pathogens since they have strong antimicrobial activity, in addition to inducing the activation of the antioxidant defense system in plants. In the present study, multi-walled carbon nanotubes were evaluated on the incidence and severity of A. solani. Moreover, to the impact they have on the antioxidant defense system and the photosynthetic capacity of the tomato crop. The results show that the application of CNTs had multiple positive effects on tomato crop. CNTs decreased the incidence and severity of A. solani. Furthermore, CNTs increased the fruit yield of tomato crop and dry shoot biomass. The antioxidant system was improved, since the content of ascorbic acid, flavonoids, and the activity of the glutathione peroxidase enzyme were increased. The net photosynthesis and water use efficiency were also increased by the application of CNTs. CNTs can be an option to control A. solani in tomato crop, and diminish the negative impact of this pathogen.