Oscillating Yield of Flash-Induced Chlorophyll Fluorescence Decay in Intact Cells of Thermosynechococcus elongatus

Abstract

Increase And Subsequent Decay Of Flash-Induced Chlorophyll Fluorescence Provides A Useful Tool In Psii Electron Transport Studies In A Wide Range Of Experimental Objects Ranging From Isolated Psii Core Complexes To Cyanobacterial Or Algal Cells And Intact Leaves. Typically, Increased Fluorescence Yield Reached Upon Excitation By A Saturating Light Pulse Decreases Monotonically In Time From Its Maximal Level To Fo. This Behaviour Can Be Explained By Assuming The Well-Known Two-Electron Gate Model Of The Psii Acceptor Side. Intact Cells Of The Thermophilic Cyanobacterium Thermosynechococcus Elongatus Do Not Show The Monotonically Decreasing Yield Of Flash-Induced Fluorescence Decay. Instead The Relaxation Curves Possess A Transient Drop With A Minimum Around 100 Ms After The Flash, Followed By An Overshoot After Few Seconds, Resulting In Dampened Oscillation Of The Fluorescence Yield. This Interesting Phenomenon Was Investigated Utilizing Different Acceptors And/Or Inhibitors Of Electron Transport As Well As Temperature-Dependence And Light/Dark Adaptation Conditions. Possible Mechanisms Behind The Oscillating Yield Of Flash-Induced Fluorescence Decay In Intact Cells Of Thermosynechococcus Elongatus Are Discussed.