The Influence Of Short-day On The Frost Hardiness And Electrical Impedance Parameters In Ligustrum Vicaryi During Frost Hardening

Ligustrum vicaryi is an elite cultivar for its beauty and exotic. It is able to adapt to very low temperature, but the frost hardiness (FH) of seedlings is lower. To study the influence of short-day (SD) treatment on the FH and the parameters of electrical impedance spectroscopy (EIS) in Ligustrum vicaryi during the hardening, as well as to find the relation between the EIS parameters and the FH, and perfect EIS method for studying FH on plant, the cutting plants of Ligustrum vicaryi is short-day treated before frost hardening on 6 September, 2006, and the natural photoperiod was used as control. Then the FH of stems was assessed by methods of EIS and conventional electrolyte leakage (EL), the FH of roots and leaves were assessed by methods of EL and chlorophyll fluorescence (CF) respectively, and the FH results between different methods were compared. The EIS of stems and leaves was assessed. The water content of roots, stems and leaves were measured. The activities of Superoxide Dismutase (SOD), the activities of Peroxidase (POD), the content of Proline, the content of Soluble sugar, the content of Starch, the content of Soluble Protein and the content of chlorophyll concentration of needles were measured.The main results are as follows:1. During frost hardening, the FH of each SD treatment shows an increasing tendency. The FH of the stems in plants treated with SD was about 3℃hardier than that in control plants during the hardening. But there is no influence on FH of roots and leaves.2. With the enhancement of the FH, some changes have occurred at the EIS and the parameters of EIS in Ligustrum vicaryi during frost hardening.3. The FH of stems has high correlation with relaxation time (τ) of non-frost-exposed stems, extracellular resistance (r_e) of stems after controlled freezing tests (R~2 = 0.86, R~2 = 0.97). However, in the end of frost hardening, the FH is underestimated by the EIS than the other methods.4. During frost hardening, the water content of stems shows a decreasing tendency, and has high correlation with relaxation time (τ) of non-frost-exposed stems and with the FH of stems assessed by methods of EL (R~2 = 0.89, R~2 = 0.90), while the water content of leaves has high correlation with F_v/F_m of non-frost-exposed leaves and with the FH of stems assessed by method of CF (R~2 = 0.97, R~2 = 0.53).5. The FH of leaves assessed by method of CF has correlation with the content of carotenoid content, the content of proline, the content of soluble sugar and the activities of SOD (R~2 = 0.91, R~2 = 0.77, R~2 = 0.74, R~2 = 0.70).6. The relaxation time (τ) of non-frost-exposed leaves has correlation with the content of Proline and the content of Soluble sugar (R~2 = 0.55, R~2 = 0.54).7. The content of Proline, the contents of Soluble sugar and Soluble Protein of leaves have correlation with F_v/F_m of non-frost-exposed leaves (R~2 = 0.77, R~2 = 0.69, R~2 = 0.50).