Ice crystal formation temperature was determined in the region of the crown in one group of 7-day-old intact unhardened high-salt plants of winter wheat (
Triticum aestivum L. cv. Weibulls Starke II) with TA (Thermal Analysis) and DTA (Differential Thermal Analysis) methods. After exposure of another group of plants, grown for the first 7 days in the same way as the first group, to various sub-zero temperatures (-1 to 5°C), influx in roots of Rb
+(
86Rb
+) and Ca
2+(
45Ca
2+) and contents of K
+ and Ca
2+ were determined at intervals during 7 days of recovery. Ice crystal formation in the crown tissue was probably extracellular and took place at about -4°C. There was a large loss of K
+ from the roots after treatment at sub-zero temperatures. This loss increased as the temperature of the sub-zero treatment decreased. During recovery, roots of plants exposed to -1, -2 and -3°C gradually reabsorbed K
+. Reabsorption of K
+ in roots of plants exposed to -4°C was greatly impaired. Rb
+ influx decreased and Ca
2+ influx increased after sub-zero temperature treatments of the plants. Active Rb
+ influx mechanisms and active extrusion of Ca
2+ were impaired or irreversibly damaged by the exposure. While Rb
+ influx mechanisms were apparently repaired during recovery in plants exposed to temperatures down to -3°C, Ca
2+ extrusion mechanisms were not. The temperature for ice crystal formation in the region of the crown tissue coincides with the temperature at which the plants lost the ability to reabsorb K
+ and to repair Rb
+ influx mechanisms during the recovery period. Plants were lethally damaged at temperatures below ?4°C.
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