Heat-induced changes in photosystem I activity as measured with different electron donors in isolated spinach thylakoid membranes

Abstract

Heat-induced changes in photosystem I (PSI) have been studied in terms of rates of oxygen consumption using various donors (DCPIPH2, TMPDred and DADred), formation of photo-oxidized P700 and changes in Chl a fluorescence emission at 77 K. Linear heating of thylakoid membranes from 35 degrees C to 70 degrees C caused an enhancement in PSI-mediated electron transfer rates (DCPIPH2-->MV) up to 55 degrees C. However, no change was observed in PSI rates when other electron donors were used (TMPDred and DADred). Similarly, Chl a fluorescence emission spectra at 77 K of heat-treated thylakoid membranes did not show any increase in peak at 735 nm, however, a significant decrease was observed as a function of temperature in the peaks at 685 and 694 nm. In DCMU-treated control thylakoid membranes maximum photo-oxidized P700 was generated at g = 2.0025. In heat-treated thylakoid membranes maximum intensity of photo-oxidized P700 signal was observed at approximately 50-55 degrees C without DCMU treatment. The steady-state signal of the photo-oxidized P700 was studied in the presence of DCPIPH2 and TMPDred as electron donors in DCMU-treated control and in 50 degrees C treated thylakoid membranes. We present here the first of such comparative study of PSI activity in terms of the rates of oxygen consumption and re-reduction kinetics of photo-oxidized P700 in the presence of different electron donors. It appears that the formation of the P700+ signal in heat-treated thylakoid membranes is due to an inhibited electron supply from PSII and not due to spillover or antenna migration.

Design of New Extraction Surfactants for Membrane Proteins from Peptide Gemini Surfactants

“…To examine the degrees of denaturation at the extracellular domains of PSI and PSII, such as the [4Fe-4S] clusters F a and F b in PsaE for PSI and the oxygen-evolution complex (OEC) for PSII, we examined the light-induced electron transfer activities of PSI and PSII and the lifetimes of the charge-separated state at the special pairs P700 of PSI. The light-induced electron transfer activities of PSI and PSII can be estimated by the rates of O 2 consumption and O 2 evolution using an O 2 electrode, respectively. ,− The lifetime of P700 +• can be estimated from a nonlinear curve-fitting analysis of the time-course decay in A 689 after a pulse of photo excitation at 400 nm . The elimination or damage to PsaE, including the [4Fe-4S] clusters F a and F b , shortens the lifetime of P700 +• to 1 ms, instead of 30 ms (on native state).…”

Prompt chlorophyll fluorescence as a tool for crop phenotyping: an example of barley landraces exposed to various abiotic stress factors

“…Although the heat stress has the negative effects on PSI (Tiwari et al 2008(Tiwari et al , Živčák et al 2015 or other components of ETC, the effects of high temperature on PSII are the most prominent. It is well known that the oxygenevolving complex is one of the most sensitive components of PSII, which is reflected also at the level of OJIP kinetics (Srivastava et al 1997, Mathur et al 2011.…”

Effects of high temperature and low pH on photosystem 2 photochemistry in spinach thylakoid membranes

“…Our earlier results (Tiwari et al 2008) have shown that F 685 decreased with increasing temperature while F 730 is largely unaffected. Thus, although the ratio (F 730 /F 685 ) increased, no energy transfer at the expense of PS 2 took place at high temperature.…”