Chloride Uptake and Transport of Different Salt Status

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Abstract
The absorption, accumulation, and transport to the exudation stream of radiochloride (Cl36) by exuding onion (Allium cepa) roots as a function of the nonlabeled chloride content of the tissue and the xylem was investigated. The concentration of nonlabeled chloride in the xylem stream had no discernable effect on the transport of Cl36 from the external solution to the exudate. However, the amounts of chloride in the root tissue had a major effect on the absorption, accumulation, and transport of external C136. Small amounts of chloride in the tissue accelerated the rate of Cl36 transport to the exudation stream whereas large amounts of chloride in the tissue decreased the rate of Cl36 transport. The rate of movement of the previously accumulated chloride (vacuolar chloride) to the exudation stream progressively increased with increasing amounts of chloride in the tissue while the accumulation of Cl36 from the external solution progressively decreased. These results indicate that chloride ions reach the xylem by passing through vacuoles as well as directly through the symplast. Furthermore the data indicate that a system of transport sites exist throughout the cytoplasm which can be occupied by either internal (vacuolar released) or externally absorbed chloride. The number of sites occupied by internal ions appears to regulate the uptake, accumulation, and transport of external ions.