OBSERVATIONS OF ICE NUCLEATION AND PROPAGATION IN PLANTS USING INFRARED VIDEO THERMOGRAPHY

We evaluated the use of infrared (IR) video thermography to observe di rectly ice nucleation and propagation in plants. An imaging radiometer with an HgCdTe long-wave (8-12 mu m) detector was utilized to image t he thermal response of plants during freezing. IR images were analyzed in real time and recorded on videotape. Information on the videotape was subsequently accessed and analyzed utilizing IR image analysis sof tware. Freezing of water droplets as small as 0.5 mu L was clearly det ectable with the radiometer. Additionally, a comparison of temperature tracking data collected by the radiometer with data collected with th ermocouples showed close correspondence. Monitoring of an array of pla nt species under different freezing conditions revealed that ice nucle ation and propagation are readily observable by thermal imaging. In ma ny instances, the ice nucleation-active bacterium Pseudomonas syringae placed on test plants could be seen to initiate freezing of the whole plant. Apparent ice nucleation by intrinsic nucleators, despite the p resence of ice nucleation-active bacteria, was also evident in some sp ecies. Floral bud tissues of peach (Prunus persica) could be seen to s upercool below the temperature of stem tissues, and ice nucleation at the site of insertion of the thermocouple was frequently observed. Rat es of propagation of ice in different tissues were also easily measure d by thermal imaging. This study demonstrates that IR thermography is an excellent method for studying ice nucleation and propagation in pla nts.