Importance of AOX pathway in optimizing photosynthesis under high light stress: role of pyruvate and malate in activating AOX

Abstract

The present study shows the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under high light (HL). The responses of photosynthesis and respiration were monitored as O(2) evolution and O(2) uptake in mesophyll protoplasts of pea pre-incubated under different light intensities. Under HL (3000 micromol m(-2) s(-1)), mesophyll protoplasts showed remarkable decrease in the rates of NaHCO(3)-dependent O(2) evolution (indicator of photosynthetic carbon assimilation), while decrease in the rates of respiratory O(2) uptake were marginal. While the capacity of AOX pathway increased significantly by two fold under HL, the capacity of cytochrome oxidase (COX) pathway decreased by >50% compared with capacities under darkness and normal light (NL). Further, the total cellular levels of pyruvate and malate, which are assimilatory products of active photosynthesis and stimulators of AOX activity, were increased remarkably parallel to the increase in AOX protein under HL. Upon restriction of AOX pathway using salicylhydroxamic acid (SHAM), the observed decrease in NaHCO(3)-dependent O(2) evolution or p-benzoquinone (BQ)-dependent O(2) evolution [indicator of photosystem II (PSII) activity] and the increase in total cellular levels of pyruvate and malate were further aggravated/promoted under HL. The significance of raised malate and pyruvate levels in activation of AOX protein/AOX pathway, which in turn play an important role in dissipating excess chloroplastic reducing equivalents and sustenance of photosynthetic carbon assimilation to balance the effects of HL stress on photosynthesis, was depicted as a model.

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

“…Supporting this, the observation that a lack of AOX in tobacco leaf mitochondria increased ROS levels was found (Cvetkovska and Vanlerberghe 2012), and our results also indicated that stress-induced increase in AP reduces ROS accumulation in Arabidopsis (Wang et al 2012). Also, the role of AP in optimizing photosynthesis has recently attracted much attention in plants (Dinakar et al 2010;Raghavendra and Padmasree 2003). Evidence of the interaction between AP and photosynthesis comes from observations that inhibition of AOX causes a decrease in the photosynthesis and the over-reduction of the photosynthetic electron transport chain (ETC) in plant leaves (Bartoli et al 2005;Yoshida et al 2006).…”

“…A major function of the AP is to balance the requirements of carbon metabolism and mitochondrial electron transport (Vanlerberghe and McIntosh 1997). Although the role of mitochondrial electron transport in optimizing photosynthesis is now well documented (Dinakar et al 2010;Padmasree and Raghavendra 1999;Strodtkötter et al 2009), the literature on the importance of AP in the protection of photosynthetic apparatus under drought stress is still limited. In this study, we observed that photosynthesis was inhibited in both wheat cultivars under drought stress as indicated by the decreased Fv/Fm, UPSII, and qP (Fig.…”

“…It has been reported that AP is involved in responses to abiotic stress, supported by the fact that AP activity and AOX expression could be induced under various stress conditions, such as high light (Dinakar et al 2010), salinity (Wang et al 2010a), low temperature (Wang et al 2012), drought (Bartoli et al 2005), nutrients supply (Escobar et al 2006;Gonzàlez-Meler et al 2001), and CO 2 concentration (Gonzàlez-Meler et al 2009). These results suggest that AP may have a close relationship with photosynthesis under stress conditions.…”

“…In the last several years, interest in the relationships between respiration and photosynthesis has been growing rapidly. 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).…”

Alternative Oxidase in Resistance to Biotic Stresses: Nicotiana attenuata AOX Contributes to Resistance to a Pathogen and a Piercing-Sucking Insect But Not Manduca sexta Larvae

“…1A). In particular, AOX transcripts appeared to be higher during the light periods than during dark periods, which could be associated with a previously reported AOX function in buffering high photosynthetic and respiration rates in response to high light (Dinakar et al, 2010). To examine the function of NaAOX in resistance of N. attenuata against its specialist herbivore M. sexta caterpillars, we generated stably AOX-silenced N. attenuata plants (irAOX) using RNAi and inverted repeat fragment of the NaAOX1 gene (Supplemental Fig.…”