TRANSITIONS IN THE THYLAKOID MEMBRANES OF BARLEY LEAVES STUDIED BY CHLOROPHYLL FLUORESCENCE TEMPERATURE CURVE

Chlorophyll (Chl) fluorescence temperature curve (FTC) of primary leav es of spring barley (Hordeum vulgare L.), cultivated under a low irrad iance, was studied at low actinic radiation excitation (436 nm, 2 W m- 2) under a heating regime consisting of a linear increase of temperatu re (0.083-degrees-C s-1), followed by a period of constant temperature . After prompt cooling of the sample to 77 K, Chl fluorescence spectra at defined points of the temperature regime were measured. Two distin ct temperature and kinetic regions expressed by two discernible temper ature maxima were observed for this type of the FTC. Two triggering te mperatures of successive irreversible changes are postulated at 45-48- degrees-C and 53-55-degrees-C temperature intervals, respectively; the y may correlate with the heat inactivation of photosystem 2 and with c hanges of the chloroplast and cytoplasmic membrane integrity.