Abstract
Some polyphenolic compounds isolated in xylem tissues of woody plant, Katsura tree, showed anti-ice nucleation (supercooling-facilitating) activity in a solution containing ice nucleator such as silver iodide or ice-nucleation bacterial cells, resulting in maintenance of a supercooling state of the solution for a long time and decline of freezing temperature of the solution. Levels of these supercooling-facilitating activities were dependent on types of both the polyphenolic compounds and ice-nucleators used in the assay solution. To study the mechanism of supercooling-facilitating activity by these polyphenolic compounds, characterization of ice-nucleators should be necessary in addition to these polyphenolic compounds resulting in decline of freezing temperature. In the present study, a gene of ice-nucleation inaA protein, of Erwinia ananas was cloned and recombinant inaA protein with histidine-tag was expressed in Escherichia coli cells for further characterization. Freezing temperature of a cell suspension culture of E. coli cells transformed with recombinant inaA gene was higher than that of E. coli cells transformed with recombinant lacZ gene with histidine-tag, a negative control sample, suggesting acquirement of ice-nucleation activity by expression of recombinant inaA gene in transformed E. coli cells.
