Tomato fruit antioxidants in relation to salinity and greenhouse climate.

A two-year study of antioxidants in greenhouse tomato was conducted. Plants were treated continuously with nutrient solution electrical conductivities (EC) of 2, 4, or 6 dS m⁻¹. Increasing EC reduced yield per plant and fruit size. Oxygen radical absorbance capacity (ORAC), lutein, β-carotene, lycopene, and vitamin C concentrations were evaluated in harvested fruit. ORAC and all antioxidants with the exception of lutein increased with EC. None of the 10 genes involved in antioxidant metabolism were affected by salinity in ripe fruit, but the expression of three of them (ZDS, CrtR-b1, and NCED1) varied with the stage of fruit development. Antioxidant concentrations were related to greenhouse climatic conditions. β-Carotene, lycopene, lutein, and vitamin C responded negatively to light and positively to temperature, whereas ORAC was unresponsive. Multiple regressions of antioxidants in relation to EC and climatic factors showed that antioxidants responded more strongly to light and temperature than to EC.