Alteration in photosystem II photochemistry of thylakoids isolated from senescing leaves of wheat seedlings

Increase in the intensity of thermoluminescence Q‐band during leaf ageing is due to a block in the electron transfer from QA to QB

“…1) suggests that charge recombinations of S 2/3 Q B À and/or S 2 Q A À are affected by leaf ageing. Our results corroborate earlier reports on the decrease of these two peaks in chloroplasts isolated from primary wheat leaves senescing in either light or darkness (9).…”

“…The loss of D1 polypeptides can account for the decrease in B-band intensity. A decrease in the B-band intensity and lowering of the TL peak temperature was reported in thylakoids of senescent wheat leaves (9).…”

“…TL bands are used to study stressinduced changes in chloroplasts and the effect of exogenous agents on the electron transport phenomenon in thylakoids (2)(3)(4)(5)(6). Few studies have been done to assess changes in photosystem II during leaf ageing using TL characteristics (6,9).…”

“…A decrease in the thylakoid protein content (13), a decrease in the photochemical efficiency of photosystem II prior to that of photosystem I (11), inactivation of the oxygen-evolving system, release of manganese (14) and degradation of D1 polypeptide (15,16) to accompany leaf ageing are reported. Looking at such diverse changes, darkness-induced senescence studies were conducted and a structural modification in the Q B protein and alteration in the S state transition were predicted (9). However, these TL analyses were done in thylakoids isolated from senescing leaves.…”

Effects of temperature and irradiance on photosystem activity during Alhagi sparsifolia leaf senescence

“…It has been reported that photosynthetic capacity was inhibited by photochemical activities of photosystem (PS) I and II (Grover and Mohanty 1993), especially PSII activity (Gruszecki et al 1991, Humbeck et al 1996, Kumagai et al 2009). Furthermore, in wheat the down-regulation of PSII occurred prior to that of net photosynthetic rate (Lu and Zhang 1998), and the loss of PSII function may be due to the decreased energy transfer from carotenoids to chlorophyll (Gruszecki et al 1991), degradation of PSII reaction centre complex (Joshi et al 1993), decreased efficiency of excitation energy capture by open PSII reaction centres (Königer et al 2000), the closure of PSII reaction centres, the enhanced thermal dissipation in the PSII antennae (Lu et al 2002) and blocked electron transport (Chen et al 2010). Chlorophyll a (Chl a) fluorescence have been used to a nondestructive quantification of the damage to the leaf photosynthetic apparatus, particularly PSII, under abiotic stresses (Zhang et al 2011).…”