Cold Stress Effects on PSI Photochemistry in Zea mays: Differential Increase of FQR-Dependent Cyclic Electron Flow and Functional Implications

Abstract

Cold-induced inhibition of CO(2) assimilation in maize (Zea mays L.) is associated with a persistent depression of the photochemical efficiency of PSII. However, very limited information is available on PSI photochemistry and PSI-dependent electron flow in cold-stressed maize. The extent of the absorbance change (ΔA(820)) used for in vivo quantitative estimation of photooxidizable P700(+) indicated a 32% lower steady-state oxidation level of the PSI reaction center P700 (P700(+)) in cold-stressed compared with control maize leaves. This was accompanied by a 2-fold faster re-reduction rate of P700(+) in the dark, indicating a higher capacity for cyclic electron flow (CEF) around PSI in cold-stressed maize leaves. Furthermore, the increased PSI-dependent CEF(s) was associated with a much higher stromal electron pool size and 56% lower capacity for state transitions compared with control plants. To examine NADP(H) dehydrogenase (NDH)- and ferredoxin:plastoquinone oxidoreductase (FQR)-dependent CEF in vivo, the post-illumination transient increase of F(o)' was measured in the presence of electron transport inhibitors. The results indicate that under optimal growth conditions the relatively low CEF in the maize mesophyll cells is mostly due to the NDH-dependent pathway. However, the increased CEF in cold-stressed plants appears to originate from the up-regulated FQR pathway. The physiological role of PSI down-regulation, the increased capacity for CEF and the shift of preferred CEF mode in modulating the photosynthetic electron fluxes and distribution of excitation light energy in maize plants under cold stress conditions are discussed.

High Light-Dependent Phosphorylation of Photosystem II Inner Antenna CP29 in Monocots Is STN7 Independent and Enhances Nonphotochemical Quenching

“…This hypothesis is supported by the report that STN8 activity is not inhibited by HL (Bonardi et al, 2005;Vainonen et al, 2005) and is the only Ser/Thr kinase enzyme associated with thylakoid in corn through MS analysis, in addition to STN7 (Friso et al, 2010). Moreover, the highest P-CP29 accumulation level was reported in cold and HL (Bergantino et al, 1995), a condition known to induce overreduction of electron transport chain due to a decreased demand for reducing equivalent by the CalvinBenson cycle (Savitch et al, 2011). The alignment of STN8 protein of Arabidopsis and rice (Supplemental Fig.…”

Proton Gradient Regulation5-Like1-Mediated Cyclic Electron Flow Is Crucial for Acclimation to Anoxia and Complementary to Nonphotochemical Quenching in Stress Adaptation

“…were challenged with HL cold (HLC) stress (400 mE m -2 s -1 at 4°C; Cornic et al, 2000;Savitch et al, 2011;Ivanov et al, 2012). Seven-day-old protonema liquid cultures of the two genotypes were transferred from optimal to HLC growth conditions.…”

Regulation of the photosynthetic apparatus under fluctuating growth light

“…During these seasons, their needles continue to absorb light, even though it cannot be used for CO 2 assimilation because the enzyme systems are largely inhibited at low temperatures. Survival of evergreens in these conditions involves reduction of the light-harvesting antenna size [16], as well as a marked reduction in the amount of PSII complexes, while the amount of PSI remains unchanged [17][18][19]. More generally, it is highly possible that slowing down PSII photochemistry and the accompanying redox chemistry can function as a protection system for the entire photosynthetic machinery against photodamage.…”