Tolerance to paraquat-mediated oxidative and environmental stresses in squash (Cucurbita spp.) leaves of various ages

► The level of paraquat injury was lower in younger leaves than in older leaves. ► Differential leaf response to paraquat was partially correlated with the change in catalase, peroxidase, ascorbate peroxidase, and glutathione reductase activities. ► Higher tolerance to paraquat-mediated oxidative and abiotic stresses in young leaves of most squash cultivars might contribute to the differential prevention of oxidative damage in leaves of various ages.