Cold hardiness of olive (Olea europaeaL.) cultivars in cold-acclimated and non-acclimated stages: seasonal alteration of soluble sugars and phospholipids

Abstract

SUMMARYIn many plant species, several physiological and biochemical changes occur during low-temperature-induced cold acclimation. A previous study with olive cultivars (Cansevet al.2009) demonstrated a correlation between the level of accumulation of certain leaf proteins besides antioxidative enzyme activities and cold hardiness of the cultivars. The present paper analysed soluble sugar (SS) and phospholipid (PL) contents of cold-acclimated (CA) and non-acclimated (NA) leaf tissues in order to explain the mechanism of cultivar-dependent response to cold in olive. In general, cold acclimation significantly increased total soluble sugar (TSS), reducing sugars and sucrose contents of all cultivars to various extents depending on the cold hardiness of cultivars. In addition, TSS, reducing sugars and sucrose contents in cold-tolerant cultivars were significantly increased, whereas TSS, reducing sugars and sucrose contents in cold-sensitive cultivars either did not change or increased slightly in CA stage compared with those in NA stage. Even though reducing sugars were the major soluble sugar in olive leaves, levels of sucrose accumulations in CA stage compared with those in NA stage were greater than those observed in reducing sugars accumulation. Changes in levels of total PL, as well as the three individual PL fractions phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), were investigated in olive leaf tissues. Significant increases in levels of PC and PE fractions during CA compared with those in NA stage suggested that PC and PE maintained the cold hardiness of olive cultivars more effectively than did PI. Although the precise mechanisms by which olive responds to cold may still be open to discussion, soluble sugars and PL are clearly important in the ability of olive cultivars to stand against cold stress.