Physiological Responses of Cabbage to Incipient Copper Toxicity

Three-week-old seedlings of the cabbage ( Brassica oleracea L. Capitata group) cultivars Wisconsin All Seasons and Globe King were exposed for 3 weeks to Cu 2+ concentrations ranging from 1.2 to 2.5 mg Cu 2+ /liter. Plants were harvested after 14, 16, 19, or 22 days of exposure. During Cu 2+ treatment, shoots appeared healthy, but roots turned golden, with increased lateral branching and tip browning. Cultivars responded identically for all characteristics measured. Root Cu concentrations were >3000 μg·g −1 or 300 times the control after Cu 2+ treatment. Shoot Cu concentrations (13 μg·g −1 ), while significantly higher than the control, were not above critical values associated with yield reductions. The high root Cu concentrations were not associated with lower shoot or root yields. The initial symptoms of Cu 2+ toxicity in the first fully expanded leaves were elevated leaf Cu concentrations and lower total chlorophyll and chlorophyll a : b ratios. There was no effect on leaf fresh weight per unit area, transpiration, respiration, net photosynthesis, or apparent photosynthetic quantum yields.