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 th ese signals, which are distributed unevenly across the leaf, it is nec essary to image the signal distribution. Leaf tissues generate complex , two-dimensional, changing, time-dependent patterns of fluorescence t hat 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 p rovides two-dimensional images of time-dependent fluorescence in photo synthetic tissue. The instrument was built with the use of parts of ou r recently constructed imaging spectrophotometer. This instrument empl oys a charge-coupled device (CCD) camera, which can acquire spectra fo r 31,680 positions per sample. Two simple filters remove excitation em ission overlap. Software based on a novel approximation allows imaging of time-dependent fluorescence of photosystem II across the surface o f a leaf. A simple reconfiguration of this instrument to image at a di stance of seven meters was used to test: potential remote sensing appl ications. The instrument's use in agriculture is demonstrated by very early determination of freeze damage, herbicide effects, and invasion by fungal pathogens.