Transport Across Chloroplast Membranes: Optimizing Photosynthesis for Adverse Environmental Conditions

Abstract

Chloroplasts are central to solar light harvesting and photosynthesis. Optimal chloroplast functioning is vitally dependent on a very intensive traffic of metabolites and ions between the cytosol and stroma, and should be attuned for adverse environmental conditions. This is achieved by an orchestrated regulation of a variety of transport systems located at chloroplast membranes such as porines, solute channels, ion-specific cation and anion channels, and various primary and secondary active transport systems. In this review we describe the molecular nature and functional properties of the inner and outer envelope and thylakoid membrane channels and transporters. We then discuss how their orchestrated regulation affects thylakoid structure, electron transport and excitation energy transfer, proton-motive force partition, ion homeostasis, stromal pH regulation, and volume regulation. We link the activity of key cation and anion transport systems with stress-specific signaling processes in chloroplasts, and discuss how these signals interact with the signals generated in other organelles to optimize the cell performance, with a special emphasis on Ca(2+) and reactive oxygen species signaling.

Dynamic photosynthesis under a fluctuating environment: a modelling-based analysis

“…In the last two decades, genetic approaches have been extensively used in the study of the Calvin cycle and photorespiration (Raines, 2003;Stitt et al, 2010;Carmo-Silva et al, 2015), and the regulation of the electron transport chain (Horton, 2014;Pottosin and Shabala, 2016). This has, to a large extent, substituted the earlier work on the biochemistry and biophysics of photosynthesis.…”

“…Chloroplasts are separated from the cellular medium (cytosol) by a double membrane (chloroplast envelope). The envelope of the chloroplast contains numerous transporters that allow the exchange of specific metabolites with the cytosol (Pottosin and Shabala, 2016). Inside the chloroplasts, there is a membrane of complex structure called thylakoid.…”

“…Additionally, the electrical component of the pmf affects the internal electron transport through PSII (Lebedeva et al, 2002), whereas the pH component of pmf regulates the kinetics of PQH2 oxidation by cyt b6f as well as qE. In addition to H % , other ions (Mg (% , Cl ) , and K % , among others) may also move across the thylakoid membrane through different channels (Pottosin and Shabala, 2016) and alter the partitioning of pmf into its electrical and pH component ).…”

“…From a mechanistic point of view, such behaviour could be achieved by regulating the activities of channels that facilitate transport of ions, additional ion transport across the chloroplast envelope, and Z ) /`) counterion transport across the thylakoid membrane (Finazzi et al, 2015;Pottosin and Shabala, 2016). Recent experimental evidence indicates that the partitioning of pmf into its pH and electrical components is regulated by the activities of such channels (Armbruster et al, 2014;Kunz et al, 2014;Herdean et al, 2016).…”

“…Or, the detailed description of the PSII reaction centre means that, by adding one (or more) reactions the model could simulate acceptor-side photoinhibition (Aro et al, 1993), and explore the effects of the electrical field across the thylakoid membrane on photoinhibition of PSII (Davis et al, 2016). Other possible extensions would include more mechanistic treatments of the buffering of H ( in the lumen (van Kooten et al, 1986), the transport of ions across the thylakoid membrane by different channels (Pottosin and Shabala, 2016), or state transitions regulated by the redox state of the PQ/PQH2 pool and thioredoxin (Rintamäki et al, 2000). Regarding the stromal metabolism, many processes could be added, including the Calvin cycle, photorespiration and sucrose synthesis (Zhu et al, 2007;Laisk et al, 2009a).…”