The effects of Piriformospora indica (Pi) inoculation and zinc (Zn) soil- application on mitigation of cold stress in grapevine (Vitis vinifera L. cv Sultana) plants were investigated. Fungal mycelium (1% w/v) suspension was added to each cutting and Zn (5.0 mg/l Zn-EDTA) applied to each pot every 15 day. At the end of experiment, half of the pots (control and Pi and Zn-treated vines) were subjected to 4°C for 24 h. The remaining vines in each treatment group were kept at 24°C. Cold stress (4°C) markedly decrease leaf photosynthetic pigments and relative water content however, Pi and Zn resulted in higher stability of photosynthetic pigments and higher relative water content in treated vines compared to control vines. Cold stress increased leaf electrolyte leakage, lipid peroxidation and hydrogen peroxide contents in vines, whereas Pi colonization and Zn treatments considerably reduced their levels. Moreover, leaf superoxide dismutase, catalase, guaiacol peroxidase, and ascorbate peroxidase activities markedly increased in Pi- and Zn-treated vines under cold stress. Decreasing the temperature from 24°C to 4°C increased leaf abscisic acid (ABA), polyamines (PAs), soluble carbohydrate, proline, soluble proteins and total phenol content in all vines. However, vines treated with Pi + Zn showed marked increases in these compounds compared to control vines under cold stress. The nutrient content of leaves in vines under low temperature stress decreased compared to vines grown at 24°C. Interestingly, in vines inoculated with Pi and Zn, the amounts of nutrients decreased to a lesser extent. Therefore, application of Pi and Zn allowed chilled vines to absorb higher nutrient during normal temperatures, enabling them to attenuate cold stress by stimulating antioxidant enzymes and plant growth regulators (ABA and PAs) accumulation in their tissues.
