Leaf day respiration: low CO₂ flux but high significance for metabolism and carbon balance

Abstract

Contents 986I.987II.987III.988IV.991V.992VI.995VII.997VIII.998References998 Summary It has been 75 yr since leaf respiratory metabolism in the light (day respiration) was identified as a low‐flux metabolic pathway that accompanies photosynthesis. In principle, it provides carbon backbones for nitrogen assimilation and evolves CO2 and thus impacts on plant carbon and nitrogen balances. However, for a long time, uncertainties have remained as to whether techniques used to measure day respiratory efflux were valid and whether day respiration responded to environmental gaseous conditions. In the past few years, significant advances have been made using carbon isotopes, ‘omics’ analyses and surveys of respiration rates in mesocosms or ecosystems. There is substantial evidence that day respiration should be viewed as a highly dynamic metabolic pathway that interacts with photosynthesis and photorespiration and responds to atmospheric CO2 mole fraction. The view of leaf day respiration as a constant and/or negligible parameter of net carbon exchange is now outdated and it should now be regarded as a central actor of plant carbon‐use efficiency.

Thioredoxin h2 contributes to the redox regulation of mitochondrial photorespiratory metabolism

“…This fact apart, it is important to highlight that plant respiration and photosynthetic carbon assimilation, including photorespiration, are dynamically regulated during the day/night cycle (Timm et al, ). Thus, although photorespiratory pathway is light regulated (Timm et al, ; Walker & Oliver, ), the TCA cycle flux is mostly restricted in the light (Kromer, ; Sweetlove, Beard, Nunes‐Nesi, Fernie, & Ratcliffe, ; Tcherkez et al, , ). That being said, the carbon flux through photorespiration is likely much higher than the flux through respiration in illuminated leaves, which means that TRX h2 ‐mediated redox‐regulation of mtLPD would mainly, if not only, affect photorespiration during the day.…”

Three physiological parameters capture variation in leaf respiration of Eucalyptus grandis, as elicited by short‐term changes in ambient temperature, and differing nitrogen supply

“…R ref seemingly scales with foliar nitrogen concentration (Jones, Leafe, Stiles, & Collet, ; Lee et al, ; Tjoelker, Oleksyn, Reich, & Zytowiak, ; Tjoelker, Reich, & Oleksyn, ; Vose & Ryan, ; Weih & Karlsson, ; Xu & Griffin, ), and “Type II acclimation” is mostly described as a long‐term response to growth temperature (i.e., weeks to months). Type II acclimation is regulated by transcriptional/translational control of glycolytic and mitochondrial enzymes (Kruse, Alfarraj, Rennenberg, & Adams, ; Tcherkez et al, ) and is prevalent in newly developed leaves (Loveys et al, ; Slot & Kitajima, ). Type I acclimation has been defined as a short‐term response to growth temperature (i.e., hours to days) and is described by changing temperature sensitivity, that is, the exponent of the response function (Atkin & Tjoelker, ; Smith & Dukes, ).…”

“…By extension, we hypothesize that δ RCO2 (abbreviated δ R in the present study; see Table for a list of abbreviations) is related to the mode of carbon flux through respiratory pathways. It is thus axiomatic that regulation of carbon fluxes via biochemical pathways of glycolysis and the tricarboxylic acid (TCA) cycle (which liberate the bulk of the CO 2 respired by leaves) is complex and that we know little about controlling mechanisms in vivo (Araujo, Nunes‐Nesi, Nikoloski, Sweetlove, & Fernie, ; Buchanan, Gruissem, & Jones, ; Smith & Dukes, , see Tcherkez et al, , for a recent review). Nonetheless, observations of TCA “cycle” operating in modular fashion (i.e., Sweetlove, Beard, Nunes‐Nesi, Fernie, & Ratcliffe, ; Tcherkez et al, ) allow for some generalization.…”

“…Complete cyclic oxidation of organic acids prevails when cellular demand for ATP is high, whereas non‐cyclic fluxes are stronger when organic acids are withdrawn for anabolic reactions (Sweetlove et al, ). For example, assimilation of inorganic nitrogen requires the operation of phosphoenolpyruvate carboxylase, in order to partially bypass pyruvate kinase and supplement the TCA cycle with sufficient intermediates (i.e., malate), which are not completely oxidized but withdrawn for synthesis of amino acids (i.e., 2‐oxoglutarate for synthesis of glutamate; Plaxton & Podesta, ; Tcherkez et al, ).…”

Metabolome and molecular basis for carbohydrate increase and nitrate reduction in burley tobacco seedlings by glycerol through upregulating carbon and nitrogen metabolism

“…Photosynthesis carbohydrates provide carbon backbones for nitrogen assimilation 9 . Most enzymes involved in nitrogen assimilation require reducing powers for their reactions in chloroplasts, and their activities are highly regulated by photosynthesis and its products 10 .…”