Salinity Resistance of Citrus Seedlings in Relation to Hydraulic Conductance, Plasma Membrane ATPase and Anatomy of the Roots

The evaluation of the response of three rootstocks to conditions of high salinity (NaCl 90 mmol/L) and the relationship with different parameters was the objective of this study. The three rootstocks were Cleopatra Mandarin, considered to be tolerant to salinity, Citrange Carrizo and Citrus Macrophylla, considered to be sensitive to salinity. We related the differences in salinity resistance to water and nutrient uptake, ATPase and anatomy of roots. For this, root hydraulic conductivity, ion concentrations in the xylem obtained under transpiration flow, root plasma membrane ATPase activity and anatomy of the root tips were determined in seedlings grown in a controlled environment. We found that under saline conditions, the Cleopatra M. rootstock showed less alteration of L0 and nutrient uptake and better maintenance of the root anatomy when they were compared with controls. The increase observed in the ATPase activity of this rootstock could be closely related to the increase in Na+ and Cl− uptake observed, indicating that a higher resistance to those ions must have occurred. Therefore, a whole succession of mechanisms and reactions can determine the degree of salt resistance in citrus plants.