AN INSTRUMENT CAPABLE OF IMAGING CHLOROPHYLL-ALPHA FLUORESCENCE FROM INTACT LEAVES AT VERY-LOW IRRADIANCE AND AT CELLULAR AND SUBCELLULAR LEVELS OF ORGANIZATION

An instrument capable of imaging chlorophyll a fluorescence, from inta ct leaves, and generating images of widely used fluorescence parameter s is described, This instrument, which is based around a fluorescence microscope and a Peltier-cooled charge-coupled device (CCD) camera, di ffers from those described previously in two important ways, First, th e instrument has a large dynamic range and is capable of generating im ages of chlorophyll a fluorescence at levels of incident irradiance as low as 0.1 mu mol m(-2) s(-1). Secondly, chlorophyll fluorescence, an d consequently photosynthetic performance, can be resolved down to the level of individual cells and chloroplasts, Control of the instrument , as well as image capture, manipulation, analysis and presentation, a re executed through an integrated computer application, developed spec ifically for the task, Possible applications for this instrument inclu de detection of early and differential responses to environmental stim uli, including various types of stress, Images illustrating the instru ment's capabilities are presented.