Mitochondrial alternative oxidase pathway protects plants against photoinhibition by alleviating inhibition of the repair of photodamaged PSII through preventing formation of reactive oxygen species in Rumex K‐1 leaves

Abstract

The purpose of this study was to explore how the mitochondrial AOX (alternative oxidase) pathway alleviates photoinhibition in Rumex K-1 leaves. Inhibition of the AOX pathway decreased the initial activity of NADP-malate dehydrogenase (EC 1.1.1.82, NADP-MDH) and the pool size of photosynthetic end electron acceptors, resulting in an over-reduction of the photosystem I (PSI) acceptor side. The over-reduction of the PSI acceptor side further inhibited electron transport from the photosystem II (PSII) reaction centers to the PSII acceptor side as indicated by an increase in V(J) (the relative variable fluorescence at J-step), causing an imbalance between photosynthetic light absorption and energy utilization per active reaction center (RC) under high light, which led to the over-excitation of the PSII reaction centers. The over-reduction of the PSI acceptor side and the over-excitation of the PSII reaction centers enhanced the accumulation of reactive oxygen species (ROS), which inhibited the repair of the photodamaged PSII. However, the inhibition of the AOX pathway did not change the level of photoinhibition under high light in the presence of the chloroplast D1 protein synthesis inhibitor chloramphenicol, indicating that the inhibition of the AOX pathway did not accelerate the photodamage to PSII directly. All these results suggest that the AOX pathway plays an important role in the protection of plants against photoinhibition by minimizing the inhibition of the repair of the photodamaged PSII through preventing the over-production of ROS.

Role of the mitochondrial alternative oxidase pathway in hydrogen photoproduction in Chlorella protothecoides

“…SHAM has been widely used to inhibit the AOX pathway (Yoshida et al 2006;Zhang et al 2011Zhang et al , 2012a. To confirm the role of the mitochondrial AOX pathway during H 2 photoproduction by C. protothecoides under LN and In this study, a 0.6 mM SHAM treatment inhibited about 28.7 and 27.2 % of the AOX pathway capacities in C. protothecoides after 48 h of incubation in the LN culture and LNS culture, respectively (Fig.…”

“…Respiration rates were measured at room temperature with a Clark-type O 2 electrode (Hansatech Instruments, Norfolk, UK) according to Dinakar et al (2010a, b) and Zhang et al (2011). A 1 mL sample was taken directly from the glass tube, shaken to equilibrate the culture with the atmospheric O 2 level, in the dark, and placed into the assay chamber.…”

“…Maximal photochemical efficiency of PSII (F v /F m ) and actual photochemical efficiency of PSII (U PSII ) of cultures during the process of incubation were measured using an FMS-2 pulse-modulated fluorometer (Hansatech Instruments, Norfolk, UK) integrated with a modified adapter (Zhang et al 2011(Zhang et al , 2012b. In the light, the steady-state fluorescence (F s ) and the light-adapted maximum fluorescence ðF m 0 Þ values were recorded when chlorophyll fluorescence attained steady-state levels, U PSII = 1 -F s /F m 0 .…”

“…1). Several studies have demonstrated that the AOX pathway functions as a sink for excess reducing equivalents generated by photosynthesis (Zhang et al 2011(Zhang et al , 2012a.…”

Involvement of nitric oxide-mediated alternative pathway in tolerance of wheat to drought stress by optimizing photosynthesis

“…The importance of electron transport through AP in optimizing photosynthesis under high-light condition is well known (Dinakar et al 2010;Ribas-Carbo et al 2000Strodtkötter et al 2009;Yoshida et al 2007). Under stress conditions, reducing equivalents generated by photosynthesis are often in excess in chloroplasts, which could lead to over-reduction of the photosynthetic ETC and accumulation of ROS, resulting in photoinhibition (Muller et al 2001;Zhang et al 2011). To conquer these adverse conditions, plants have developed defense systems that dissipate excess light energy (Niyogi 2000).…”