Fig. 1. Freezing of Arabidopsis plants expressing the DAFP-1 antifreeze protein (AFP) with (line 340) and without (line 270) a signal peptide targeting the protein for secretion
to the appoplast. The gene coding the DAFP-1 protein was obtained from the beetle, Dendroides canadensis. Individual plants were removed from the soil, mounted on
cardboard with silicon grease, and cooled at approximately 5 ◦ C/h. Plants were not sprayed with water and so supercooled to very low temperatures before freezing. Freezing
was monitored using high resolution infrared thermography and is visualized as an exothermic event that raises the temperature of the plant above ambient air temperature.
Top left—Wild-type and transformed Arabidopsis plants prior to conducting the freezing test. Top right—Freezing of a wild type plant at −9.4 ◦ C. Average freezing temperature
of wild type plants was −13.3 ◦ C. Bottom left—Freezing of a 270-23 transgenic plant (DAFP-1 without a signal peptide) at −11.6 ◦ C. Average freezing temperature of transgenic
270-23 plants was −13.8 ◦ C. No significant difference was observed between wild-type and 270 transgenic plants. Bottom right—Freezing of two 340-29 plants (DAFP-1 with
a signal peptide) at −17.9 ◦ C. Average freezing temperature of 340-29 plants was −16.6 ◦ C which was significantly different (p ≤ 0.05) than the wild-type and 270-23 plants.
The high level of supercooling indicates that the DAFP-1 may have inhibited ice nucleators present in the apoplast.