Tomato plant response under atmospheric particulate matter stress

Urban particulate matter (PM) can affect green plants either via deposition on the above-ground biomass, where the contaminants can penetrate the leaf surface, or indirectly via soil-root interaction. In our investigation, a model experiment was carried out to demonstrate the direct effect of PM on tomato (Solanum lycopersicum L.) plant growth. A monitoring campaign of PM10 was conducted at an urban background site of Canosa (Apulia, Southern Italy) in four different days (1, 2, 3, 4). PM10 samples were collected for 24 hours on quartz fiber filter. The filters were then cut into two parts, one of which was used for the chemical characterization of the PM10 and one for the growth of tomato. Organic and elemental carbon and polycyclic aromatic hydrocarbons (PAHs) content were analysed for all the tested filters. Tomato plants were grown for 18 days directly on filters absorbed with PM10. The germination rate of tomato seeds and some parameters of seedlings primary growth of this plant species (length of root and shoot, their fresh weight and content of photosynthetic pigments in shoot) were used as laboratory indicators of phytotoxicity. Substantial differences were found in the growth of root apparatus respect to that of control plants. A significant decrease of primary root elongation, a large amount of secondary roots and a decrease in plant and root weights were found. To assess if the direct exposition of roots to PM10 induced an oxidative stress, reactive oxygen species (ROS) concentration was evaluated by measuring the fluorescence arising from oxidation of DCFH-DA in both control and treated roots. Quantitative analysis of ROS indicated that an oxidative burst in response to abiotic stress occurred in roots directly grown on PM10, whose detrimental effect was also confirmed by the findings on chlorophyll content and chlorophyll-to-carotenoid ratio.