Seasonal responses of photosynthetic electron transport in Scots pine ( Pinus sylvestris L.) studied by thermoluminescence

Abstract

The potential of photosynthesis to recover from winter stress was studied by following the thermoluminescence (TL) and chlorophyll fluorescence changes of winter pine needles during the exposure to room temperature (20 degrees C) and an irradiance of 100 micromol m(-2) s(-1). TL measurements of photosystem II (PSII) revealed that the S(2)Q(B)(-) charge recombinations (the B-band) were shifted to lower temperatures in winter pine needles, while the S(2)Q(A)(-) recombinations (the Q-band) remained close to 0 degrees C. This was accompanied by a drastically reduced (65%) PSII photochemical efficiency measured as F(v)/ F(m,) and a 20-fold faster rate of the fluorescence transient from F(o) to F(m) as compared to summer pine. A strong positive correlation between the increase in the photochemical efficiency of PSII and the increase in the relative contribution of the B-band was found during the time course of the recovery process. The seasonal dynamics of TL in Scots pine needles studied under field conditions revealed that between November and April, the contribution of the Q- and B-bands to the overall TL emission was very low (less than 5%). During spring, the relative contribution of the Q- and B-bands, corresponding to charge recombination events between the acceptor and donor sides of PSII, rapidly increased, reaching maximal values in late July. A sharp decline of the B-band was observed in late summer, followed by a gradual decrease, reaching minimal values in November. Possible mechanisms of the seasonally induced changes in the redox properties of S(2)/S(3)Q(B)(-) recombinations are discussed. It is proposed that the lowered redox potential of Q(B) in winter needles increases the population of Q(A)(-), thus enhancing the probability for non-radiative P680(+)Q(A)(-) recombination. This is suggested to enhance the radiationless dissipation of excess light within the PSII reaction center during cold acclimation and during cold winter periods.

Excess manganese differentially inhibits photosystem I versus II inArabidopsis thaliana

“…3 and Table 3) confirms the suggestion of altered reduction state of PSII acceptor side in Mn-stressed plants (Kitao et al , 1997b). Since Q A is in quasi-equilibrium with Q B and the PQ pool, the present results imply that lowering the redox potential of Q B will decrease the probability for forward electron transfer between the two quinone acceptors by shifting the redox equilibrium between Q A – Q B and Q A Q B – towards Q A – Q B (Minagawa et al , 1999; Ivanov et al , 2002, 2003) in plants exposed to high Mn concentrations.…”

Zeaxanthin-independent energy quenching and alternative electron sinks cause a decoupling of the relationship between the photochemical reflectance index (PRI) and photosynthesis in an evergreen conifer during spring

“…Alternative electron sinks can include plastid terminal oxidase (PTOX)-mediated electron transport to oxygen ( Savitch et al , 2010 ) or photorespiration ( Takahashi and Badger, 2011 ). Cyclic electron transport around PSI can also contribute significantly to the removal of excess energy during winter and early spring ( Ivanov et al , 2002 ). Recently it was suggested that the provision of ATP produced from cyclic electron transport maintains chloroplast integrity during chilling stress ( Huang et al , 2010 ) and supports the recovery from chilling stress.…”

Photosystem II of Ligustrum lucidum in response to different levels of manganese exposure

“…Lower redox state of Q B implies altered reduction potential of PSII at the acceptor side in Mn-stressed plants 17 . Since Q A is in quasi-equilibrium with Q B and the PQ pool, the lower redox potential of Q B will decrease the probability of forward electron transfer between the two quinone acceptors by shifting the redox equilibrium between Q A − Q B and Q A Q B − towards Q A − Q B 33,34 .…”