Potassium-induced freezing tolerance is associated with endogenous abscisic acid, polyamines and soluble sugars changes in grapevine

- Potassium sulfate spray improved grapevine leaf abscission and periderm formation during acclimation phase.
- Throughout the hardening cycle freezing tolerance of all potassium treated vines considerably increased.
- Abscisic acid concentration changed with LT50 profile and always was higher in K2SO4 treated vines.
- Potassium sulfate considerably increased free polyamines, soluble sugars and phenolics concentration.
- Alleviation effect of K2SO4 on freezing stress was more effective at 3%.

Crop nutrition is a practical method against freezing injury which may improves grapevine freezing tolerance (FT) potential by increasing bud nitrogenous and carbohydrates storages. In this study the effect of foliar application of potassium sulfate (PS; K2SO4; 0, 1, 2 and 3%) on some physico-chemical properties of fruit and leaf mineral contents of 'Sultana' grapevine (Vitis vinifera L.) were studied. Moreover, to further elucidate the efficiency of foliar PS on FT and some relevant morpho-physiological changes were evaluated at four sampling dates: Nov., Jan., Mar., and Apr. following exposure to artificial freezing using electrolyte leakage and bud browning bioassay. In summer 2013 and 2014, PS was sprayed at fruit set, pea-sized berry, verison and maturity on 16 years old grapevines located in Malayer Grape Research Station (Iran) under a randomized complete block design. Based on results, foliar PS significantly affected yield, cluster weights, and berry weight and some fruit quality indices including soluble solids, titratable acidity, pH and phenolic compounds. Foliar PS significantly changed the leaf N, K, P, Mg, Zn and Fe concentrations. The effect of nutrition treatments was also significant on FT of grapevines at four sampling stages. In Jan., the highest FT (LT50 = −25.97 °C) and the lowest FT (LT50 = −20.16 °C) was found in 3% PS- treated and control untreated vines, in respectively. Moreover, PS especially at 3% resulted in higher increments in abscisic acid, total phenol, soluble sugars, and polyamines concentrations. Potassium spray increased membrane stability and decreased electrolyte leakage. The ability of Potassium in FT improvement (lower electrolyte leakage) was found to be related to change in endogenous abscisic acid concentration as a stress hormone in preliminary and subsequent changes in other metabolites such as accumulation of soluble sugars, polyamines, and phenolic acids.