Chlorophyll fluorescence of a model plant - and a mutant that doesn't behave.
Chlorophyll is the green pigment that harvests and converts light in photosynthesis. Chlorophyll also emits light, as fluorescence, and variations in fluorescence emission report on changes in the efficiency of photosynthesis. We have developed a way to film changes in chlorophyll fluorescence, by computer acquisition of fluorescence images. The coloured pea leaf image that is used in these pages as a link to the Plant Cell Biology home page, was obtained in this way, using leaves that had begun to take up a herbicide that inhibits electron transport in photosynthesis, increasing fluorescence emission from regions around the veins that transport substances into the leaf. In the picture you now see, leaves of the small plant thale cress were imaged by a camera that detects chlorophyll fluorescence. Fluorescence is initially high (seen as the red colour in image 1), and falls after six minutes in the light (image 2), as the light-harvesting protein becomes phosphorylated. A far-red light, unseen by the camera, is switched on, and fluorescence falls further (image 3), to rise slightly after a further two minutes (image 4), as the phosphate group is removed from the light-harvesting protein. One plant, whose two leaves are seen near the centre, behaves differently, and its fluorescence stays high. This plant has a mutation. Paul Davison, who found the mutant plant using fluorescence imaging, is isolating the tagged gene that causes the defect.
This page with a Quicktime animation (4.3 MB, suitable only for wide-band connections) of the fluorescence changes in Arabidopsis, in place of the graphic.
A Quicktime animation (3.6 MB, suitable only for wide-band connections) of state 1-state 2 transitions in pea leaves.
The Kautsky effect.Fugue in D minor, BWV 948.