Optimization of photosynthesis by multiple metabolic pathways involving interorganelle interactions: resource sharing and ROS maintenance as the bases

Abstract

The bioenergetic processes of photosynthesis and respiration are mutually beneficial. Their interaction extends to photorespiration, which is linked to optimize photosynthesis. The interplay of these three pathways is facilitated by two major phenomena: sharing of energy/metabolite resources and maintenance of optimal levels of reactive oxygen species (ROS). The resource sharing among different compartments of plant cells is based on the production/utilization of reducing equivalents (NADPH, NADH) and ATP as well as on the metabolite exchange. The responsibility of generating the cellular requirements of ATP and NAD(P)H is mostly by the chloroplasts and mitochondria. In turn, besides the chloroplasts, the mitochondria, cytosol and peroxisomes are common sinks for reduced equivalents. Transporters located in membranes ensure the coordinated movement of metabolites across the cellular compartments. The present review emphasizes the beneficial interactions among photosynthesis, dark respiration and photorespiration, in relation to metabolism of C, N and S. Since the bioenergetic reactions tend to generate ROS, the cells modulate chloroplast and mitochondrial reactions, so as to ensure that the ROS levels do not rise to toxic levels. The patterns of minimization of ROS production and scavenging of excess ROS in intracellular compartments are highlighted. Some of the emerging developments are pointed out, such as model plants, orientation/movement of organelles and metabolomics.

Nitrogen Metabolism in Adaptation of Photosynthesis to Water Stress in Rice Grown under Different Nitrogen Levels

“…N assimilation, especially the reduction of nitrate, is a highly energy dependent reaction (Bloom et al, 2010). Incorporation of inorganic N into amide and amino acid consumes energy and reducing equivalents produced in photosynthesis, mitochondrial oxidative metabolism, or other cytosolic reactions, depending on the site of reaction (Sunil et al, 2013). Reduction of nitrate in leaves could use the excessive reducing power derived from photosynthesis, and it is more efficient than the reduction which takes place in roots in water stress situation (Gonzalez-Dugo et al, 2010).…”

How Does Chloroplast Protect Chlorophyll Against Excessive Light?

“…On the other hand, reduced Fd can release electrons also to ferredoxin:nitrite reductase and sulphite reductase for the reductive assimilation of nitrite [37] and sulphur [38]. Finally, reduced Fd represents an electron donor for fatty acid desaturases [39] and glutamine:oxoglutarate amino transferase [40]. However, when NADP + is not available, reduced Fd releases its electron to different acceptors whose function is to avoid an overreduction of PSI [41].…”

Reactive Oxygen Species and Photosynthesis

“…Generation of H 2 O 2 and 1 O 2 at PS I and PS II respectively, as well as photorespiratory H 2 O 2 , is associated with the control of nuclear gene expression (Op den Camp et al, (2003); Vandenabeele et al, 2004;Pitzschke et al, 2006;Pfannschmidt et al, 2009;Sunil et al, 2013;Fischer et al, 2013;Foyer and Noctor, 2013).…”