The basic slow Idnetics and spectral properties of the chlorophyll fluorescence temperature curve (FTC) under low actinic radíation excitation (s 2 W m"2) were measured in primary barley leaves of shade-grown plants. In contrast to the usual Fo temperature dependence, two distinct regions and two maxima of FTC were documented upon a linear heating regime. The fírst maximum situated between 49.5 and 51 °C was less sensitive, whereas Ihe position of the second maximum (between 53 and 63 “C) was strongly dependent on the heating rate. The spectral resolution of the fluorescence emission suggested a presence of photosystem (PS) 1 emission in the FTC at 436 nm excitation and an efíect of partial light-harvesting complex LHCII disconnection from the PS 2 complex at 480 nm excitation. A new fluorescence emission around 700 nm appeared upon heating. The excitation spectra in the 400 nm to 500 nm region for the 685 nm fluorescence emission wavelength indicated that only one emission form was responsible for both of the FTC bands. The 77 K fluorescence spectra at increasing, maximal and decreasing parts of Ihe second FTC band were measured using the triggering expeiiments wilh an incubation temperature of 58 oC. A disconnection of LHCI firom otiier pigment-protein complexes is suggested as a concomitant effect of Ihe second FTC maximum.
Chlorophyll (Chl) fluorescence temperature cinve (FTC) of primary leaves of spring barley (Hordeum vulgare L.), cultivated imder a low irradiance, was studied at low actinic radiation excitation (436 nm, 2 W m'^) under a heating regime consisting of a linear increase of temperature (0.083 °C s’*), 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 distinct temperature and kinetic regions expressed by two discemible temperature maxima were observed for ťhis type of the FTC. Two triggering temperatures of successive irreversible changes are postulated at 45-48 “C and 53-55 °C temperature intervals, respectively; they may correlate with the heat inactivation of photosystem 2 and with changes of the chloroplast and cytoplasmic membrane integrity.