Citrus rootstocks regulate the nutritional status and antioxidant system of trees under copper stress

• Citrus rootstock influences copper stress resistance of orange trees.
• Cu/Zn-SOD activity in leaves depends on signalling regulated by rootstocks.
• Copper stress impairs nutrient uptake, assimilation and nutritional status of trees.
• Copper accumulates in roots of trees in response to metal homeostasis maintenance.
• Copper toxicity affects iron transport to the shoot causing Fe-deficiency symptoms.

Copper (Cu) deficiency and toxicity cause stresses in citrus orchards and limited information is available about which rootstocks and associated mechanisms would enhance plant resistance to such nutritional disorders. Therefore, this study evaluated the nutritional status and antioxidant system responses of citrus grafted onto selected rootstocks differing in horticultural performance [Swingle citrumelo (SW) or Rangpur lime (RL)], grown in nutrient solution with varying concentrations of Cu (0.015, 0.60 or 24.0 μM). The experiment was carried out in a greenhouse using young sweet orange trees. Once taken up, Cu mostly accumulated in roots (75% of total plant Cu content). Trees grafted onto RL were more responsive to enzyme activities related to oxidative stress and to nitrogen metabolism in leaves when grown in the presence of either the lowest or the highest Cu concentrations used. Those grown in 24.0 μM Cu displayed decreased overall nutrient uptake and accumulation, with the exception of iron, which was predominantly found in roots. Cu/Zn superoxide dismutase activity in leaves was dependent upon signalling regulated by rootstocks, being lower in SW than in RL. Therefore, the use of appropriate rootstock varieties contributes to alleviate the effects of Cu stress on the metabolism and nutritional status of citrus plants.