Abstract
ABSTRACTElectron probe X‐ray microanalysis was used to analyse the effects of sub‐zero temperatures on K+ distribution in compartments within non‐acclimated and cold acclimated rye (Secale cereale L. cv Voima) leaf cells and to evaluate membrane leakage of ions caused by freezing‐injury. The specimens were rapidly frozen from growing temperatures and from two different sub‐zero temperatures (LT50 and LT100) to which the leaves had already been slowly cooled. Measurements were made in the cytoplasm, vacuole and cell walls in freeze‐substituted mesophyll cells. At ambient temperatures, the mean K+ concentration in the cytoplasm (100 mol m−3) differed significantly from that of the vacuole (49 mol m−3) in the non‐acclimated (NA) cells, while in cold acclimated (A) cells, the concentrations were similar (109 vs 93 mol m−3, respectively). At LT50 temperatures, the K+ concentration in NA‐cells decreased significantly in the cytoplasm (59 mol m−3) but increased in the cell walls. In the A‐cells, on the other hand, the mean K+ concentration increased significantly (about three‐fold) in all major compartments. At LT100 temperatures, K+ concentrations in the cytoplasm and cell walls decreased when compared with corresponding LT50 values in the A‐cells but increased in the NA‐cells. The increased potassium concentration in the cytoplasm of A‐cells at LT50 temperature is compatible with the observed cell shrinkage and an absence of plasma membrane damage. The decreased potassium concentration in the cytoplasm of NA‐cells at LT50 temperature is compatible with the slight cell shrinkage and suggests that the plasma membrane in these cells shows increased permeability due to freeze injury.
Published Version
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