Mechanisms of chloride partitioning in the leaves of salt‐stressed <i>Sorghum bicolor</i> L.

Abstract

Chloride transport in sheath and blade tissue and the cellular distribution of Cl ‐ were investigated in an attempt to determine the physiological basis of the preferential accumulation of Cl ‐ in sheaths of salt‐stressed sorghum ( Sorghum bicolor L.). Import and export of 36 Cl ‐ in leaf sheaths and blades of intact sorghum were followed over a 2 week period. X‐ray microanalysis of frozen‐hydrated bulk tissue samples was used to determine the accumulation of Cl ‐ and other elements in the vacuoles of sheath and blade cells. Sheath tissue accumulated Cl ‐ despite a relatively high Cl ‐ turnover rate. Chloride was shown to accumulate in most cell types of the sheath, particularly in adaxial epidermal cells. After an initial increase in the concentration of Cl ‐ , blade tissue regulated Cl ‐ levels within certain limits. Chloride levels in blades were greater in the abaxial and adaxial epidermal cells than in other cell types. The epidermal cells of blades accumulated Cl ‐ to approximately the same concentration as sheath epidermal cells. The Cl ‐ concentration in the photosynthetically active mesophyll and bundle sheath cells, however, remained low. Thus, the partitioning of Cl ‐ previously observed in the leaves of salinized sorghum apparently results from the ability of bundle sheath and mesophyll cells to maintain concentrations of Cl ‐ at lower levels than do epidermal cells. In addition, the relatively large sheath parenchyma cells tend to serve as reservoirs for the storage of Cl ‐ .