Role of CaCl₂ in Cold Acclimation-Induced Freezing Resistance of Populus tomentosa Cuttings

Populus tomentosa cuttings were treated with 1 mmol·L^-1, 5 mmol·L^-1, 10 mmol·L^-1 or 15 mmol·L^-1 of CaCl₂ for 1-7 d, respectively, for studying the effects of different concentrations of CaCl₂ on freezing resistance. Results indicated that 10 mmol·L^-1 of CaCl₂ has greater effect than other concentrations on the enhancement of freezing resistance, and the optimum time of pretreatment was 5 d. In addition, cuttings used for cold acclimation at -3℃ were pretreated with or without 10 mmol·L^-1 of CaCl₂, 3 mmol·L^-1 of Ca²⁺ chelator EGTA, 0.05 mmol·L^-1 of CaM antagonist CPZ or 0.1 mmol·L^-1 of Ca²⁺ channel inhibitor LaCl₃.The changes in CaM and freezing resistance of all cuttings were investigated. The results showed that cold acclimation at -3℃ increased CaM content and decreased the minimum temperature for 100% survival. The CaCl₂ pretreatment enhanced the effect of cold acclimation and obviously increased CaM content and decreased the minimum temperature for 100% survival, but this effect was strongly inhibited by the EGTA, CPZ or LaCl₃.It is concluded that the effect of CaCl₂ on freezing resistance is associated with its concentration and time of pretreatment, Ca²⁺-CaM may be involved in the induction of freezing resistance of the cuttings.