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 sa linity (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 Macrophyl la, considered to be sensitive to salinity. We related the differences in s alinity resistance to water and nutrient uptake, ATPase and anatomy of root s. For this, root hydraulic conductivity, ion concentrations in the xylem o btained under transpiration flow, root plasma membrane ATPase activity and anatomy of che root tips were determined in seedlings grown in a controlled environment. We found that under saline conditions, the Cleopatra M. roots tock showed less alteration of L-0 and nutrient uptake and better maintenan ce 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 re sistance to those ions must have occurred. Therefore, a whole succession of mechanisms and reactions can determine the degree of salt resistance in ci trus plants.