**2.3 Cold**

Cold stress, as an abiotic stress, has been shown to be one of the most important abiotic stresses that reduce agricultural crop output by altering crop quality and post-harvest life. Many crop plant species have been found to be substantially hampered in their reproductive growth by chilling such as rice displaying sterility when exposed to chilling temperatures during anthesis [11]. Plants are sessile in nature; therefore, they have evolved unique ways to cope with temperature variations in their habitat [12]. In temperate conditions, plants are encountered by chilling and freezing conditions that are very harmful to plants as stress.

In order to adapt themselves, plants acquire chilling and freezing tolerance against such lethal cold stresses by a process called acclimation [13]. However, many important crops are still incompetent to the process of cold acclimation.
