Ionomic and metabolomic profile in Solanum lycopersicum L. ‘Micro-Tom’ under nickel stress

Crop production can no longer be sustained by rainfall due to climate change and irrigation strategies must be applied. In this contest, wastewater is an important water supply, but it could contain heavy metals that may affect both plant health and product quality and safety. Nickel (Ni) is one of 23 metal pollutants that could be a risk to the ecosystem and human health. Tomatoes are one of the most consumed vegetables and have a high nutritional value. Tomato plants are sensitive to heavy metal pollution and accumulate these elements in their organs, including fruits. This study aims to understand whether the levels of Ni allowed in irrigation water can be harmful to tomato plants and consumers. Solanum lycopersicum L. ‘Micro-Tom’ plants were watered for 52 days until fruit maturation with four treatments: 0 (control), 0.1, 0.2, and 0.4 mg L^‑1 of Ni. Dried fruit samples were digested in 65% HNO₃, using the COOLPEX Smart Microwave Reaction System. The ionomic profile, which included Ni, Cu, Mn, Zn, Fe, Mg, Ca, and K was analyzed using a Microwave Plasma Atomic Emission Spectrometer (4210 MP-AES, Agilent Technologies). Polyphenols were extracted from tomatoes’ fresh material using 80:20 (v/v, methanol/MilliQ) before performing UHPLC-MS/MS analysis. The data revealed a dose-dependent increase in Ni levels in the fruit, which, however, remained below permitted limits, ensuring consumer safety. The concentration of mineral elements in tomatoes was not altered but the polyphenols metabolic pathway was significantly affected. Caffeic acid and naringenin increased by 46 and 82% compared to the control under the higher Ni treatment. Conversely, a significant reduction in apigenin, luteolin, and quercetin concentrations was detected.