Influence of low temperature on regulation of Rb+ and Ca2+ influx in roots of winter wheat

Abstract

Influx of Rb+(86Rb+) and Ca2+(45Ca2+) was determined in roots of winter wheat (Triticum aestivum L. cv. Weibulls Starke II) after 14 days at 16°C/16 h light, after 1 and 8 weeks of cold acclimation (2°C/8 h light) and at intervals after deacclimation (16°C/16 h light) for up to 14 days. The plants were cultivated at 3 ionic strengths: 100, 10 and 1% of a full strength nutrient solution, containing 3.0 mM K+ and 1.0 mM Ca2+.K+ concentrations in roots and shoots increased during cold treatment, while Ca2+ in the roots decreased. In the shoots Ca2+ concentrations remained the same. Influx of Rb+ as a function of average K+ concentration in the roots of 14‐day‐old, non‐cold‐treated plants was high at a certain K+ level in the root and decreased at higher root K+ levels (negative feedback). The pattern for Ca2+ influx versus average concentration of Ca2+ in the root was the reverse. Independent of duration of treatment (1–8 weeks), cold acclimation partly changed the regulation of Rb+ influx, so that it became less dependent upon negative feedback and more dependent on the ionic strength of the cultivation solution. After exposure to 2°C, Ca2+ influx increased at high Ca2+ concentrations in the root as compared with influx in roots of 14‐day‐old non‐cold‐treated plants. Under deacclimation, Ca2+ influx gradually decreased again, and reached the level observed before cold treatment within 7–14 days at 16°C; the number of days depending on the exposure time at 2°C. It is suggested that Rb+(K+) influx became adjusted to low temperature and that abscisic acid (ABA) may be involved in this mechanism. It is also suggested that extrusion of Ca2+ was impaired and/or Ca2+ channels were activated at 2°C in roots of plants grown in the full‐strength solution and that extrusion was gradually restored and/or Ca2+ channels were closed under deacclimation conditions.