Detection of photosynthetic activity and water stress by imaging the red chlorophyll fluorescence

It is shown that with a new flash-lamp chlorophyll (Chl) fluorescence imaging system (FL-FIS), the photosynthetic activity of several thousand points of an intact attached leaf can be screened in a non-destructive way within a few seconds. The method allows the detection of the gradients in photosynthetic capacity over different parts of the leaf. The photosynthetic activity is sensed via imaging the Chi fluorescence at its maximum Fm and at steady state Chi fluorescence Fs of the induction kinetics and by the subsequent determination of the image of the fluorescence decrease ratio (R-Fd) which is known as the vitality index of the photosynthetic apparatus. Under water stress the photosynthetic activity decreases as seen in the images of the two fluorescence ratios R-Fd and Fm/Fs. Histogram and profile analysis of Chi fluorescence images and Chi fluorescence ratios allow the quantification of the differences between normal and stressed leaves with a high statistical significance. (C) 2000 Editions scientifiques et medicales Elsevier SAS.