Abstract

The large differences in freezing tolerance that exist between winter and spring wheat cultivars suggest that the regulation of the initiation of reproductive organs and development plays an important role in the potential of the plant to cold acclimate, which is a process of treating the plants at low non-freezing temperatures in order to increase its freezing tolerance ability. Because of the advantages of analyzing in model species, we have studied the changes in the capacity of Arabidopsis thaliana to cold acclimate at different stages of development. We have found that freezing tolerance decreases after flowering, with a critical and abrupt drop in the tolerance two days after the opening of the first flowers. Freezing tolerance was increased after flowering by the exogenous application of abscisic acid (ABA) and by sodium nitroprusside (SNP) which produces NO, thus implicating ABA and NO in the signaling pathways involved in cold acclimation. In addition, we have found that the expression of three wheat sulfotransferases (ST) namely: TaST2, TaST3 and TaST4 are regulated during cold acclimation. Molecular characterization of TaST2, TaST3 and TaST4 revealed that the deduced amino acid sequences of all three enzymes contained the conserved regions and amino acids involved in 3'-phosphoadenosine 5'-phosphosulfate (PAPS) binding and catalysis (Varin, 1992 and Marsolais, 1995). All three sulfotransferases were found to be differentially regulated by cold in winter and spring wheat. Wheat EST clone collections were used to sub-clone TaST2, TaST3 and TaST4 in a bacterial expression vector pQE30. The purified recombinant proteins were tested for purity by SDS-PAGE and various ranges of compounds were tested as possible substrates