High-irradiance (HI) induced changes in heat emission, fluorescence, and photosynthetic energy storage (EST) of shade grown sugar maple (Acer saccharum Marsh.) saplings were followed using modulated photoacoustic and fluorescence spectroscopic techniques. HI-treatment at 900-4400 µmol m-2 s-1 for 15 min caused an increase in heat emission and a decrease in EST. In some leaves, HI-treatment of 900 µmol m-2 s-1 for 1 min induced a rapid increase in heat emission with a marginal decrease in EST. Parallel to the increase in heat emission, there was a decrease in fluorescence, and this phenomenon was reversible in darkness. Quenching of thermal energy dissipation and a recovery in EST were observed during the first 15 min after the HI-treatment. This down-regulation of photochemical activity and its recovery may be one of the photoprotective mechanisms in shade grown sugar maple plants. The increase in thermal energy dissipation was greater in the red absorbing long wavelength (640-700 nm) region than in the blue absorbing short wavelength region of photosynthetically active excitation radiation. The photochemical activity was affected more in short wavelengths (400-520 nm) than in the long wavelength region of the spectrum. This can be due to the migration of light-harvesting chlorophyll (Chl) a/b protein complex from photosystem (PS) 2 to PS1 and/or to the disconnection of carotenoid pool from Chls in the pigment bed of photosynthetic apparatus. and K. Veeranjaneyulu, R. M. Leblanc.
High-irradiance (HI) stress induced changes in the photosynthetic energy storage (ES) of photosystems 1 (ESPS1) and 2 (ESPS2) were studied with 650 nm modulated radiation in intact sugar maple (Acer saccharum Marsh.) leaves. HI-treatment (420 W m-2, 1 h) caused an inhibition of about 40 % in ESPS2 and an enhancement of about 60 % in ESPS1. The rate of PS1 cyclic electron transport, measured with 705 nm modulated radiation, also increased in HI-treated leaves. There was a clear state 1- state 2 transition in HI-treated leaves. ESPS1 increased significantly and ESPS2 decreased drastically in leaves preadapted to state 1 after HI (600 W m-2, 30 min) treatment. Thus, the increase in PS1 activity observed immediately after HI-treatment in leaves preadapted to state 1 can be due to the coupling of LHC2 to PS1 during the HI-treatment. Further, the dissociation of LHC2 from PS2 during the HI-treatment resulted in apparently (about 15 %) greater inhibition than the "true" inhibition of PS2 activity. The presence of LHC2 with PS2 (state 1) at the time of HI-treatment caused no additional damage to PS2 or its coupling to PS1 offered no apparent HI-treatment. Further, the dissociation of LHC2 from PS2 during the HI-treatment resulted in apparently (about 15 %) greater inhibition than the "true" inhibition of PS2 activity. The presence of LHC2 with PS2 (state 1) at the time of HI-treatment caused no additional damage to PS2 or its coupling to PS1 offered no apparent protection to the photosynthetic apparatus. and K. Veeranjaneyulu, M. Charland, R. M. Leblanc.
The review summarizes results concerning photosynthetic systems with chlorophylls and carotenoids obtained by means of spectral methods such as polarized radiation, photoacoustic spectroscopy, delayed luminescence, thermal deactivation, and leading to construction of model systems. and D. Frąckowiak, B. Smyk.
The inhibition of photosynthetic activity by bisulphite was studied in intact leaves of abscisic acid (ABA)-treated and non-treated (control) barley plants. ABA inhibited the photosynthetic process as evidenced by lower values of chlorophyll fluorescence kinetic parameters Fv/Fm (photosystem 2 activity) and Rfd (vitality index, related to the whole photosynthetic activity) compared with ABA-non-treated plants. After bisulphite treatment, the extent of inhibition was smaller in ABA-treated plants than in the control ones indicating a protective effect of ABA. The protective action sites of ABA were the QA reduction and the Calvin cycle. and C. N. N'Soukpoè-Kossi ... [et al.].
The thermal photoacoustic signal (279 Hz) and the chlorophyll (Chl) fluorescence of radish cotyledons (Raphanus sativus L.) were measured simultaneously. The signals were recorded during a photosynthetic induction with actinic radiation of different quantum fluence rates [20, 200, and 1200 µmol(PAR-quantum) m-2 s-1]. The rise of these signals upon irradiation saturating photosynthesis was followed in the steady state of the induction and during the subsequent dark-recovery (i.e., in dark periods of 1, 5, 15, and 45 min after the induction). From these values various parameters (e.g., quantum yield, photochemical loss, different types of quenching coefficients) were calculated. The results show that heat dissipation detected by photoacoustic measurements is neither low, constant, nor always parallel to Chl fluorescence. Therefore, the thermal signal should always be measured in order to fully understand the way leaves convert energy taken up by PAR absorption. This helps in the interpretation of photosynthesis under different natural and anthropogenic conditions (stress and damage effects).