Passive and Active Components of Chloride Absorption in the Bark and the Wood of Citrus Roots

The characteristics of chloride absorption by the tap root of citrus (Citrus spp.) seedlings were compared in isolated disks of the bark and in segments of the wood. Analysis of elution curves of the isotope following saturation of the tissue shows that there are at least two components of the chloride absorption system: one typical of the free space (“passive”) and the other of the non‐free space (“active”). These two components are present in the bark only, while the wood has essentially the characteristics of a free space absorption (the slow component of the efflux being less evident). The nature of the bark as an actively collecting tissue for chloride from 10 mM Na36Cl, in contrast to the wood, was established on the basis of uptake curves. Examination of the uptake in the bark of 3 citrus varieties revealed considerable differences with regard to the magnitude of the two components of chloride absorption. These findings are discussed in relation to the role of the cortex and the stele in the transport of ions.