Journal Article•
Stomatal and mesophyll conductances control CO2 transfer to chloroplasts in leaves of grapevine (Vitis vinifera L.)
21 Apr 2015-Vitis: Journal of Grapevine Research (Institut für Rebenzüchtung Geilweilerhof = Institute of Grapevine Breeding Geilweilerhof)-Vol. 42, Iss: 2, pp 65-68
TL;DR: It is hypothesized that both stomatal and mesophyll conductance are involved in the adaptation of the CO 2 supply to the CO 2 demand at the site of carboxylation in chloroplasts.
Abstract: From simultaneous determination of net CO 2 assimilation and transpiration at the abaxial side and of the photosynthetic electron transport rate at the adaxial side of fieldgrown, light-saturated leaves of grapevine (cv. Riesling) photorespiration, stomatal conductance for CO2, mesophyll conductance and the CO 2 concentration in intercellular spaces (Ci) and in chloroplasts (Cc) were estimated. CO 2 assimilation was saturated at about Ci = 340 ppm. At increasing ambient CO 2 concentration (Ca) photorespiration decreased (less negative values); stomatal conductance decreased significantly (- 45 %) limiting CO2 uptake into intercellular spaces. Rates of total photosynthetic electron transport were constant between Ci = 340 and 800 ppm and decreased by 34 % at low Ci. Electron flow to carboxylation was closely correlated to CO 2 assimilation rates (R 2 = 0.999). When Ca was raised, the CO 2 concentration in chloroplasts (Cc) increased but at smaller rates than Ci. Presumably due to the distinct decline of the mesophyll conductance Cc remained constant at Ci >340 ppm. At Ca = 400 ppm the Cc/Ca ratio was 0.46 - 0.48, corroborating data reported for other species (CORNIC and FRESNEAU 2002). At 2 % ambient O 2 and 400 ppm CO 2 decreased rates of photorespiration (- 69 %) were associated with a decline of total photosynthetic electron flow (- 6 %); higher stomatal and mesophyll conductances, however, led to increases of Cc and CO2 assimilation rates (+ 49 %). It is hypothesized that both stomatal and mesophyll conductance are involved in the adaptation of the CO 2 supply to the CO 2 demand at the site of carboxylation in chloroplasts.
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TL;DR: There is now evidence that g(liq) and, in some cases, g(w), are the main determinants of g(m).
Abstract: During photosynthesis, CO2 moves from the atmosphere (Ca) surrounding the leaf to the sub-stomatal internal cavi- ties (Ci) through stomata, and from there to the site of carboxylation inside the chloroplast stroma (Cc) through the leaf mesophyll. The latter CO2 diffusion component is called mesophyll conductance (gm), and can be divided in at least three components, that is, conductance through intercellular air spaces (gias), through cell wall (gw) and through the liquid phase inside cells (gliq). A large body of evidence has accumulated in the past two decades indicat- ing that gm is sufficiently small as to significantly decrease Cc relative to Ci, therefore limiting photosynthesis. More- over, gm is not constant, and it changes among species and in response to environmental factors. In addition, there is now evidence that gliq and, in some cases, gw, are the main determinants of gm. Mesophyll conductance is very dynamic, changing in response to environmental variables as rapid or even faster than stomatal conductance (i.e. within seconds to minutes). A revision of current knowl- edge on gm is presented. Firstly, a historical perspective is given, highlighting the founding works and methods, fol- lowed by a re-examination of the range of variation of gm among plant species and functional groups, and a revision of the responses of gm to different external (biotic and abiotic) and internal (developmental, structural and meta- bolic) factors. The possible physiological bases for gm, including aquaporins and carbonic anhydrases, are dis- cussed. Possible ecological implications for variable gm are indicated, and the errors induced by neglecting gm when interpreting photosynthesis and carbon isotope discrimi- nation models are highlighted. Finally, a series of research priorities for the near future are proposed.
942 citations
TL;DR: New evidence shows that anatomical traits, such as cell wall thickness and chloroplast distribution are amongst the stronger determinants of mesophyll conductance, although rapid variations in response to environmental changes might be regulated by other factors such as aquaporin conductance.
580 citations
TL;DR: Transgenic tobacco plants differing in the amounts of aquaporin NtAQP1 showed different slopes of the gm-Ci response, suggesting a possible role for aquaporins in mediating CO2 responsiveness of gm, and the importance of these findings is discussed in terms of their effects on parameterization of AN-CI curves.
Abstract: The effects of short-term (minutes) variations of CO2 concentration on mesophyll conductance to CO2 (gm) were evaluated in six different C3 species by simultaneous measurements of gas exchange, chlorophyll fluorescence, online carbon isotope discrimination and a novel curve-fitting method. Depending on the species, gm varied from five- to ninefold, along the range of sub-stomatal CO2 concentrations typically used in photosynthesis CO2-response curves (AN)-Ci curves; where AN is the net photosynthetic flux and Ci is the CO2 concentrations in the sub-stomatal cavity), that is, 50 to 1500 micromol CO2 mol(-1) air. Although the pattern was species-dependent, gm strongly declined at high Ci, where photosynthesis was not limited by CO2, but by regeneration of ribulose-1,5-bisphosphate or triose phosphate utilization. Moreover, these changes on gm were found to be totally independent of the velocity and direction of the Ci changes. The response of gm to Ci resembled that of stomatal conductance (gs), but kinetic experiments suggested that the response of gm was actually faster than that of gs. Transgenic tobacco plants differing in the amounts of aquaporin NtAQP1 showed different slopes of the gm-Ci response, suggesting a possible role for aquaporins in mediating CO2 responsiveness of gm. The importance of these findings is discussed in terms of their effects on parameterization of AN-Ci curves.
513 citations
TL;DR: Evidence is provided for the in vivo involvement of aquaporin NtAQP1 in mesophyll conductance to CO(2) using plants either deficient in or overexpressing Nt aqP1.
Abstract: *† These authors contributed equally to this work. Summary Leaf mesophyll conductance to CO 2 (gm) has been recognized to be finite and variable, rapidly adapting to environmental conditions. The physiological basis for fast changes in g m is poorly understood, but current reports suggest the involvement of protein-facilitated CO 2 diffusion across cell membranes. A good candidate for this could be the Nicotiana tabacum L. aquaporin NtAQP1, which was shown to increase membrane permeability to CO 2 in Xenopus oocytes. The objective of the present work was to evaluate its effect on the in vivo mesophyll conductance to CO 2, using plants either deficient in or overexpressing NtAQP1. Antisense plants deficient in NtAQP1 (AS) and NtAQP1 overexpressing tobacco plants (O) were compared with their respective wild-type (WT) genotypes (CAS and CO). Plants grown under optimum conditions showed different photosynthetic rates at saturating light, with a decrease of 13% in AS and an increase of 20% in O, compared with their respective controls. CO 2 response curves of photosynthesis also showed significant differences among genotypes. However, in vitro analysis demonstrated that these differences could not be attributed to alterations in Rubisco activity or ribulose-1,5-bisphosphate content. Analyses of chlorophyll fluorescence and on-line 13 C discrimination indicated that the observed differences in net photosynthesis (AN) among genotypes were due to different leaf mesophyll conductances to CO2, which was estimated to be 30% lower in AS and 20% higher in O compared with their respective WT. These results provide evidence for the in vivo involvement of aquaporin NtAQP1 in mesophyll conductance to CO 2.
405 citations
TL;DR: In this article, the authors investigated physiological and structural mechanisms underpinning the leaf economics spectrum (LES) by analysing a novel data compilation incorporating rarely considered traits such as the dry mass fraction in cell walls, nitrogen allocation, mesophyll CO2 diffusion and associated anatomical traits for hundreds of species covering major growth forms.
Abstract: The leaf economics spectrum (LES) represents a suite of intercorrelated leaf traits concerning construction costs per unit leaf area, nutrient concentrations, and rates of carbon fixation and tissue turnover. Although broad trade-offs among leaf structural and physiological traits have been demonstrated, we still do not have a comprehensive view of the fundamental constraints underlying the LES trade-offs. Here, we investigated physiological and structural mechanisms underpinning the LES by analysing a novel data compilation incorporating rarely considered traits such as the dry mass fraction in cell walls, nitrogen allocation, mesophyll CO2 diffusion and associated anatomical traits for hundreds of species covering major growth forms. The analysis demonstrates that cell wall constituents are major components of leaf dry mass (18-70%), especially in leaves with high leaf mass per unit area (LMA) and long lifespan. A greater fraction of leaf mass in cell walls is typically associated with a lower fraction of leaf nitrogen (N) invested in photosynthetic proteins; and lower within-leaf CO2 diffusion rates, as a result of thicker mesophyll cell walls. The costs associated with greater investments in cell walls underpin the LES: long leaf lifespans are achieved via higher LMA and in turn by higher cell wall mass fraction, but this inevitably reduces the efficiency of photosynthesis.
357 citations
Additional excerpts
...In some studies the petiole is included when measuring LMA, in others it is excluded, and in others still the authors do not make clear what protocol was followed (see Supporting Information). In general, LMA including the petiole can be higher by c. 10%, but there is considerable variation across species. In this study, we used the published/measured values without conversion, and we note that this difference can be a source of error in trait–LMA relationships. Total leaf N content was typically measured with a CN analyser. Cell walls are made up of complex macromolecules consisting of pectin, hemicellulose, cellulose, lignin and structural proteins. Cell walls can be extracted by various methods such as alcohol extraction, detergent extraction and organic solvent extraction from ground samples at cold or heated temperatures (Fry, 1988). Neutral detergent fibre (NDF) is the most popular indicator of cell wall content in plant ecological studies. NDF is typically extracted from ground dried material with neutral detergent at a boiling temperature for 1 h (Van Soest, 1994). NDF represents most of the cell wall components but pectin is inevitably removed by this method. Pectin accounts for 20–35% of primary cell walls in forb species and 2–10% in graminoid species but very little of secondary cell walls (Vogel, 2008), and therefore the hot extraction method may underestimate the cell wall fraction by up to 10% of leaf mass if primary cell walls occupy 30% of leaf mass. In contrast, some starch, cuticle compounds (e.g. cutin) and some minerals (e.g. silica) may also be contained in NDF. The fraction of leaf mass in cutin is usually small (0.5–4%; Go~ ni & Hedges, 1990) and some species such as some graminoids accumulate silica up to 9% (Cooke & Leishman, 2011). In short, NDF represents a conservative estimate of cell wall mass except for some graminoid species. As it is not straightforward to convert cell wall mass data among different protocols because of variation in chemical composition among species, we used raw values without conversion in our analysis. Cell wall N is normally measured from extracted cell walls with a CN analyser (Onoda et al., 2004) or with amino acid analysis after digestion (Takashima et al., 2004). To measure cell wall N mass, it is important to extract cell walls without contamination of cytosolic proteins. In particular, cytosolic proteins can become insoluble with heat or drying or by binding with polyphenolics, and contaminate the cell wall N fraction. Therefore, oven-dried samples should not be used for quantification of cell wall N for studies of leaf economy. Fresh frozen samples may be the best for the cell wall extraction but freeze-dried samples could be used (Harrison et al., 2009). Some cell wall proteins are strongly or covalently attached to the polysaccharides while others are weakly bound to cell walls, and therefore cell wall N recovery rates depend on the strength of the solvents used (Lamport, 1965; Fry, 1988). If a weak extraction solvent is used, weakly bound cell wall proteins can be extracted, but contamination of the cell wall N fraction by cytosolic proteins will remain a concern. In contrast, when a strong solvent is used, the amount of cell wall N is underestimated because of loss of weakly bound cell wall proteins. Most data in this study were obtained with strong solvents, and therefore the value reported in this study may be a conservative estimate of cell wall N. The amount of Rubisco can be measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), capillary electrophoresis or immunoblotting methods (Makino et al., 1986; Warren, 2004). Some studies have also estimated the amount of Rubisco from the maximum carboxylation capacity of Rubisco by inverting the Farquhar et al. (1980) photosynthesis model (Niinemets & Tenhunen, 1997)....
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References
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TL;DR: It was found that the response of the rate of CO2 Assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at lowand high inter cellular p (CO2).
Abstract: A series of experiments is presented investigating short term and long term changes of the nature of the response of rate of CO2 assimilation to intercellular p(CO2). The relationships between CO2 assimilation rate and biochemical components of leaf photosynthesis, such as ribulose-bisphosphate (RuP2) carboxylase-oxygenase activity and electron transport capacity are examined and related to current theory of CO2 assimilation in leaves of C3 species. It was found that the response of the rate of CO2 assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at low and high intercellular p(CO2). In longer term changes in CO2 assimilation rate, induced by different growth conditions, the initial slope of the response of CO2 assimilation rate to intercellular p(CO2) could be correlated to in vitro measurements of RuP2 carboxylase activity. Also, CO2 assimilation rate at high p(CO2) could be correlated to in vitro measurements of electron transport rate. These results are consistent with the hypothesis that CO2 assimilation rate is limited by the RuP2 saturated rate of the RuP2 carboxylase-oxygenase at low intercellular p(CO2) and by the rate allowed by RuP2 regeneration capacity at high intercellular p(CO2).
4,385 citations
TL;DR: Under optimal conditions, the most outstanding genotype was ICS-1, both in plant height, number of leaves, and stomatal conductance, this being proof that this genotype develops excellently and stands out if it has the right conditions and water availability.
Abstract: This research is part of an effort that the ICT (Institute of Tropical Cultivation) has been doing for several years tending to develop superior genotypes of cocoa (Theobroma cacao L.). That is why this study aims to find tolerant or moderately tolerant cocoa genotypes and accessions to water stress with resistance to pests and diseases and high production and industrial quality. Twenty genotypes of cocoa seedlings were investigated, during the period of 6 months, in a soil with sandy-loam texture under nursery conditions, of controlled irrigation. A split plot design was used, with 40 treatments and 3 repetitions. In addition, daily data of the micro climatic characteristics (T °, HR) were taken, in which different indicators of variable were evaluated such as the stomatal conductance (CE) that is greatly influenced by the T ° and HR. The results obtained indicate that the genotypes that showed moderate tolerance to water stress were UNG - 77, UNG - 53, ICT - 1281 and ICT - 1112; the non-tolerant ones were PAS - 93, CEPEC - 2002, ICT - 2142, ICT - 1092, CP - 2005 - C10, TSH - 1188, CCN - 51, IMC - 67, PH - 17, AYP - 15, ICS - 6, BN - 34, ICT - 1506, PAS - 91, PH - 990 and ICS - 1. Under optimal conditions, the most outstanding genotype was ICS-1, both in plant height, number of leaves, and stomatal conductance, this being proof that this genotype develops excellently and stands out if it has the right conditions and water availability.
3,693 citations
Book•
01 Jan 1980
TL;DR: Life in the Solar System, and Beyond, and beyond, and In the Right Place at the Right Time.
Abstract: Prolog: The Big Guns of Kugluktuk.- Life in the Solar System, and Beyond.- The Limits of the World.- In the Right Place at the Right Time.- The Terraforming of Mars.- The Terraforming of Venus.- An Abundance of Habitats.
3,663 citations
TL;DR: The primary effect of low RWC on Apot is most probably caused by limited RuBP synthesis, as a result of decreased ATP synthesis, either through inhibition of Coupling Factor activity or amount due to increased ion concentration.
Abstract: Summary
Experimental studies on CO2 assimilation of mesophytic C3 plants in relation to relative water content (RWC) are discussed. Decreasing RWC slows the actual rate of photosynthetic CO2 assimilation (A) and decreases the potential rate (Apot). Generally, as RWC falls from c. 100 to c. 75%, the stomatal conductance (gs) decreases, and with it A. However, there are two general types of relation of Apot to RWC, which are called Type 1 and Type 2. Type 1 has two main phases. As RWC decreases from 100 to c. 75%, Apot is unaffected, but decreasing stomatal conductance (gs) results in smaller A, and lower CO2 concentration inside the leaf (Ci) and in the chloroplast (Cc), the latter falling possibly to the compensation point. Down-regulation of electron transport occurs by energy quenching mechanisms, and changes in carbohydrate and nitrogen metabolism are considered acclimatory, caused by low Ci and reversible by elevated CO2. Below 75% RWC, there is metabolic inhibition of Apot, inhibition of A then being partly (but progressively less) reversible by elevated CO2; gs regulates A progressively less, and Ci and CO2 compensation point, Γ rise. It is suggested that this is the true stress phase, where the decrease in Apot is caused by decreased ATP synthesis and a consequent decreased synthesis of RuBP. In the Type 2 response, Apot decreases progressively at RWC 100 to 75%, with A being progressively less restored to the unstressed value by elevated CO2. Decreased gs leads to a lower Ci and Cc but they probably do not reach compensation point: gs becomes progressively less important and metabolic limitations more important as RWC falls. The primary effect of low RWC on Apot is most probably caused by limited RuBP synthesis, as a result of decreased ATP synthesis, either through inhibition of Coupling Factor activity or amount due to increased ion concentration. Carbohydrate synthesis and accumulation decrease. Type 2 response is considered equivalent to Type 1 at RWC below c. 75%, with Apot inhibited by limited ATP and RuBP synthesis, respiratory metabolism dominates and Ci and Γ rise. The importance of inhibited ATP synthesis as a primary cause of decreasing Apot is discussed. Factors determining the Type 1 and Type 2 responses are unknown. Electron transport is maintained (but down-regulated) in Types 1 and 2 over a wide range of RWC, and a large reduced/oxidized adenylate ratio results. Metabolic imbalance results in amino acid accumulation and decreased and altered protein synthesis. These conditions profoundly affect cell functions and ultimately cause cell death. Type 1 and 2 responses may reflect differences in gs and in sensitivity of metabolism to decreasing RWC.
1,791 citations