SENSITIVITY OF THE RELATIVE F-PL LEVEL OF CHLOROPHYLL FLUORESCENCE INDUCTION IN LEAVES TO THE HEAT-STRESS

The (F-pl - F-o)/F-v value of the fluorescence induction curve is show n to be a more suitable parameter to detect a wider range of heat stre ss damage to thylakoid membranes as compared to quantities t(1/2) (tim e of fluorescence rise from F-o to (F-o + F-m)/2 level) and ($) over b ar r (the fluorescence induction time defined as the area above the in duction curve normalized to F-v = 1). A method for exact and automatic F-pl determination is presented. A break point in the quality and beh aviour of the fluorescence induction curve of barley leaves incubated at 49 degrees C was reached at the moment (about 240 s) when the trans formation of PS II active (Q(B)-reducing) to PSII inactive (Q(B)-non-r educing) centres was completed. The meaning of the standard F-v and F- v/F-m parameter was then changed. The method of F-pl determination des cribed here may help to increase the analytical value of the standard chlorophyll fluorometers.