View larger version (207K):
[in a new window]
|
Fig. 4. Progression of freezing events in turfgrass plants viewed with infrared thermal imaging radiometer (camera) in real time. Plants were placed into a controlled environment room, held at 0°C for 20 min, then inoculated by placing water droplets containing ice-nucleating bacteria (Pseudomonas syringae strain Cit7) on leaf and root surfaces. Air temperature was reduced 0.5°C at 3-min intervals. Time is shown in the upper right corner of the image while temperature range being sensed by the camera is shown on the bottom of the image. Only selected freezing events are indicated in the figures. Fig. 4A shows three perennial ryegrass plants on the left and three supina bluegrass plants on the right as their images appear at an air temperature of -1°C 6 min after beginning the freezing test. Twenty seconds later (B), heat emission as water freezes inside plant tissues is indicated by the color change of roots on the sixth plant from the left. In another 69 s, freezing progressed acropetally toward the crown on the sixth plant, then basipetally into other roots, and the root system of the third plant began to freeze (C). When room temperature reached -2°C 12 min after the test began, freezing had started in roots of the second plant, proceeded acropetally from roots on the third plant into the crown, and was progressing through roots of Plants 4 and 6 (D). Note the red color of the crown in the third plant from the left, indicating greater heat loss due to higher moisture content compared with roots. At a room temperature of -5°C, 30 min after the test began, crowns and shoots of all plants were freezing, and freezing in root tissues was finished. The yellow circle on the sixth plant is a water droplet containing P. syringae freezing.
|
