Imaging Fluorometer to Detect Pathological and Physiological Change in Plants

Fluorescence signals from plant leaves have considerable potential for improving agricultural investigations; however, to fully interpret these signals, which are distributed unevenly across the leaf, it is necessary to image the signal distribution. Leaf tissues generate complex, two-dimensional, changing, time-dependent patterns of fluorescence that occur immediately after illumination of a dark-adapted leaf. These patterns are very sensitive measures of plant photosynthetic function. Thus, we built a novel, fully computer-interfaced instrument which provides two-dimensional images of time-dependent fluorescence in photosynthetic tissue. The instrument was built with the use of parts of our recently constructed imaging spectrophotometer. This instrument employs a charge-coupled device (CCD) camera, which can acquire spectra for 31,680 positions per sample. Two simple filters remove excitation emission overlap. Software based on a novel approximation allows imaging of time-dependent fluorescence of photosystem II across the surface of a leaf. A simple reconfiguration of this instrument to image at a distance of seven meters was used to test potential remote sensing applications. The instrument's use in agriculture is demonstrated by very early determination of freeze damage, herbicide effects, and invasion by fungal pathogens.