Low-temperature Acclimation and the Correlation of Vernalization Requirement with Accumulation of Some Compatible Solutes and Physiological Mechanisms in Bread Wheat

Cold tolerance is an adaptative mechanism that plants in temperate climates require to survive and grow in suboptimal temperatures. Exposed plant to low temperature produces a myriad of measurable changes in biochemical characters that are often highly correlated with plant cold tolerance. A key element of cereal adaptation to cold is represented by the capacity for physiological adjustments that allows plants to retain growth and photosynthetic capacity at low temperature. Four bread wheat cultivars were planted to examine the frost tolerance and its relationship with accumulation of cryoprotectant and some of the biochemical changes in controlled environment and field conditions. Prolonged cold treatment accelerated the transition to reproductive development in winter and facultative cultivars but not in the spring one. Exposure to low-temperatures also enhanced frost tolerance of the winter and facultative wheats. Maximum frost tolerance was detected around the vernalization fulfilment. The highest frost tolerance potential was observed in the winter cultivar، where the longest cold treatments were necessary for fulfilment of vernalization response. Frost tolerance responses were highly correlated with chlorophyll concentration and proline accumulation in cultivars. Frost tolerance capacity was associated with reduced malondialdehyde content and hydrogen peroxide accumulation in cultivars. According to the chlorophyll fluorescence parameters، cold acclimation treatments in controlled environment condition had no effect on induction of cold stress symptoms. These data support the hypothesis that vernalization fulfilment is the critical point in the down-regulation of cold tolerance expression، and vernalization with cold acclimation pathways are interconnected in cereals to delay the spring floral-development allowing acclimation to low-temperatures and accumulation of cryoprotectants during the vegetative stage.