Vegetation monitoring of chilling stress by chlorophyll fluorescence ratio

The chlorophyll fluorescence ratio F690/F730 was deter-mined in bean seedling (Phaseolus vulgaris L., cv. Mondragone) unchilled and chilled at a low no freezing temperature of 4°C under low and high relative humidity. The two chlorophyll fluorescence emission maxima were monitored using the portable fluorometer LEAF (Laser Excited Automatic Fluorometer) developed by the Insti¬tute of Quantum Electronics. The ratio F690/F730 and the relative water content (RWC%) show a more significant decrease when the plants are chilled in light at low relative humidity, although the chlorophyll content does not change during chilling. A complete recovery of the ratio to the initial values (about 0.8-1.0) is evident after a few hours from the transfer of the plants at 20°C, while a slow increase of the relative water content was observed during the chilling treatment. The data indicate that the ratio F6901730 can be a sensitive probe to monitor chilling stress in higher plants, but it is also a useful tool to investigate the complex water relations during chilling stress. This technique, based on laser excited fluorescence spectra, could be an early stress indicator for plants and may be applied in remote sensing detection of vegetation utilizing existing fluorescence lidar systems