ABSTRACT
During the initial hardening period, the activity of free auxins markedly increases and precedes the development of cold resistance. The more cold - adaptive/tolerant plants have higher levels of abscisic acid (ABA) in addition to other changes. Role of ABA in cold tolerance of plants has been discussed before at some length, but this chapter describes field-food and vegetable crops. The induction of freezing tolerance by exogenous ABA application and a transient increase in endogenous ABA levels during low temperature induced acclimation led T. H. H. Chen et al. to propose that the transient increase in ABA concentration might function as a trigger for the subsequent events in cold acclimation. Inhibition of ABA biosynthesis with fluridone abolished acclimation-induced chilling tolerance, and exogenous application of ABA to fluridone-treated seedlings restored chilling tolerance. Both low temperature and exogenous ABA induced larger increases in free proline content and stability of cell membranes in frost resistant wheat genotypes than in the frost sensitive ones.
