Analysis of temperature-jump chlorophyll fluorescence induction in plants.
A newly observed general chlorophyll fluorescence induction effect in plants is described. Fluorescence yield can rise through as many as four different phases (alpha, beta, gamma, ) in the dark, when intact cells or leaves are rapidly heated (within approx. 2.5 s) from 20 to 40-50 degrees C. An analysis of this temperature-jump fluorescence induction in Scenedesmus obliquus leads to the following: 1. Phase alpha is due to removal of S-quenching and appears to be related to heat deactivation of the water-splitting enzyme system. With prolonged heating, irreversibility of alpha upon recooling reflects irreversible damage to the water-splitting enzyme system. 2. beta is independent of the S-states and of the redox state of primary System II acceptor Q. It is suggested that beta parallels functional separation of Q from the System II trapping centre. This effect is highly reversible. 3. gamma and beta reflect reduction of primary System II acceptor Q by a heat-induced endogenous reductant, which is probably identical to hydrogenase. Critical temperatures for pronounced alpha and beta phases differ markedly in different plants. Possible correlations between temperature-jump fluorescence inductio, thylakoid membrane lipid composition, lipid phase transition and lipid-protein interactions are discussed.
D002734:Chlorophyll / Q000378:metabolism*; D000460:Chlorophyta / Q000378:metabolism; D003486:Cyanides / Q000494:pharmacology; D003624:Darkness; D004237:Diuron / Q000494:pharmacology; D007700:Kinetics; D010944:Plants / Q000187:drug effects / Q000378:metabolism*; D013045:Species Specificity; D013050:Spectrometry, Fluorescence; D013696:Temperature
D003486:Cyanides; D002734:Chlorophyll; D004237:Diuron