BASIC PROPERTIES OF THE CHLOROPHYLL FLUORESCENCE TEMPERATURE CURVE INBARLEY LEAVES

The basic slow kinetics and spectral properties of the chlorophyll flu orescence temperature curve (FTC) under low actinic radiation excitati on (is-approximately-equal-to 2 W m-2) were measured in primary barley leaves of shade-grown plants. In contrast to the usual F(o) temperatu re dependence, two distinct regions and two maxima of FTC were documen ted upon a linear heating regime. The first maximum situated between 4 9.5 and 51-degrees-C was less sensitive, whereas the position of the s econd maximum (between 53 and 63-degrees-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 effect of partial light-harvesting complex LHCII disconnection from the PS 2 complex at 480 nm excitation. A new fluor escence emission around 700 nm appeared upon heating. The excitation s pectra in the 400 nm to 500 nm region for the 685 nm fluorescence emis sion 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 the second FTC band were measured us ing the triggering experiments with an incubation of 58-degrees-C. A d isconnection of LHCI from other pigment-protein complexes is suggested as a concomitant effect of the second FTC maximum.