Effects of Silicon Nanoparticles on the Activity of Antioxidant Enzymes in Tomato Roots Invaded by Meloidogyne incognita (Kofoid et White, 1919) Chitwood, 1949

In plants, pathogen attack can induce an immune response known as systemic acquired resistance (SAR) that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO 2 -NPs, food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO 2 -NP-induced disease resistance are unknown. Here, we show that SiO 2 -NPs, as well as soluble orthosilicic acid (Si(OH) 4 ), can induce SAR in a dose-dependent manner, that involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in leaf air spaces of the spongy mesophyll. In contrast to treatment with SiO 2 -NPs, induction of SAR by Si(OH) 4 was problematic, since high concentrations caused stress. We conclude that SiO 2 -NPs have the potential to serve as an inexpensive, highly efficient, safe, and sustainable alternative for plant disease protection.

Here, the interaction of Melodoigyne incognita virulent and avirulent pathotypes with susceptible and Mi-resistant tomato (Solanum lycopersicon) has been studied. Significant differences in nematode penetration occurred 2 days postinoculation (dpi) and became stable from 3 dpi onwards. The hypersensitive cell response (HR) in resistant plants prevented the installation of the avirulent pathotype. The virulent pathotype overcame the Mi (nematode) resistance and induced feeding sites in root cells without triggering HR. Reactive oxygen species (ROS), visualized by subcellular reduction of nitroblue tetrazolium, accumulated in nematode penetrated cells. Quantitative analyses with dichlorofluorescein indicated that the oxidative burst occurred very early with both pathotypes, with an enhanced rate in hyper-responsive cells. Hydrogen peroxide (H(2)O(2)), detected by cerium chloride reaction, accumulated in the cell walls and especially in cells neighbouring HR. The apoplastic location of cerium perhydroxide indicated that either the plasma membrane or the cell wall was the primary site of the superoxide/H(2)O(2) generator. The data provide evidence, for the first time, for ROS-generated signals and their spatiotemporal expression in the host and nonhost interaction of tomato with nematodes.

Silicon (Si) is considered a non-essential element similar to cadmium, arsenic, lead, etc., for plants, yet Si is beneficial to plant growth, so it is also referred to as a quasi-essential element (similar to aluminum, cobalt, sodium and selenium). An element is considered quasi-essential if it is not required by plants but its absence results in significant negative consequences or anomalies in plant growth, reproduction and development. Si is reported to reduce the negative impacts of different stresses in plants. The significant accumulation of Si on the plant tissue surface is primarily responsible for these positive influences in plants, such as increasing antioxidant activity while reducing soil pollutant absorption. Because of these advantageous properties, the application of Si-based nanoparticles (Si-NPs) in agricultural and food production has received a great deal of interest. Furthermore, conventional Si fertilizers are reported to have low bioavailability; therefore, the development and implementation of nano-Si fertilizers with high bioavailability could be crucial for viable agricultural production. Thus, in this context, the objectives of this review are to summarize the effects of both Si and Si-NPs on soil microbes, soil properties, plant growth and various plant pathogens and diseases. Si-NPs and Si are reported to change the microbial colonies and biomass, could influence rhizospheric microbes and biomass content and are able to improve soil fertility.