Uptake of hexavalent chromium by tomato (Solanum lycopersicum L.) plants and mediated effects on their physiology and productivity, along with fruit quality and safety

Cr(VI) is known to induce hormesis in plants. Nevertheless, its effects on the quality of agricultural produce are poorly studied. In the present study, tomato (Solanum lycopersicum L.) plants were exposed to incremental Cr(VI) concentrations through irrigation with water containing K2Cr2O7 in escalating concentrations (0.05, 0.5, 1, 5 and 10 mg L-1), aiming at investigating potential mediated effects on (1) yield, (2) stress responses in leaves, (3) the biosafety of fruits and (4) the mediated alterations in tomato fruit quality attributes. Plants in all Cr(VI) treatments displayed similar phenotype, with no modulations in fruit setting. Plants irrigated with water containing 10 mg L-1 K2Cr2O7 had lower photosynthetic pigment concentration and suffered from oxidative stress in their leaves (evidenced by increased MDA and H2O2 content). Elevated Cr(VI) treatments (5 or 10 mg L-1 K2Cr2O7) resulted in the production of fruits with lower weight and smaller size, along with increased ripening index and soluble solids, lycopene, beta-carotene and soluble carbohydrate (fructose, sucrose, total sugars) content. Alterations in fruit quality attributes were at least in part corroborated by the abundance of transcripts related to sucrose (SlSuSys, SlLin5, SlLin6, SlLin7) and carotenoid (SlZDS, SlCRTISO, SlbLCY) biosynthesis. The concentration of total Cr in all fruit samples was far below the maximum permissible limits, thus indicating safety for human consumption. Overall, results presented herein provide novel evidence that Cr(VI) can exert significant effects on the quality of agricultural produce at the biochemical and molecular level, indicating that Cr(VI)-contaminated water should be cautiously used after rigorous investigation.