The digital video on this page shows two leaves.The right one is control
(untreated) , the left one is treated with a herbicide - diuron. For the
shooting of the video, the leaves were excited with #051FB0
light and a red
filter was placed between the leaves and the camera.
Credits: Brad Sherman; Fred Chow and Govindjee for making the video. Govindjee
thanks Matej Lexa for digitizing and transferring it to the Web page.
The browser is encouraged to read : Govindjee (1995) Sixty-three years since
Kautsky: chlorophyll a fluorescence. Australian Journal of Plant Physiology,
volume 22, pages 131-160.
The video shows "instant" rise in chlorophyll a fluorescence
in both leaves. In the treated leaf fluorescence remains high and does not
decay, whereas in the untreated leaf it decays. This is because diuron blocks
electron flow beyond QA- (QA being
an electron acceptor of PSII and a quencher of chlorophyll a fluorescence);
thus in treated leaves, QA remains as QA-.
In untreated leaf, photosynthesis competes with fluorescence, and the latter
goes down, it is said.
