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.