The canon of knowledge on the catalytic properties of the photosynthetic enzyme Rubisco has shackled efforts to understand its diversity. Now the chains are off. While investigating the variability ...in Rubisco function among diatoms, Young et al. (see pages 3445–3456 in this issue) have demonstrated that it is our thinking, not Rubisco catalysis, that has been constrained.
Cellular exchange of carbon dioxide (CO2) is of extraordinary importance for life. Despite this significance, its molecular mechanisms are still unclear and a matter of controversy. In contrast to ...other living organisms, plants are physiologically limited by the availability of CO2. In most plants, net photosynthesis is directly dependent on CO2 diffusion from the atmosphere to the chloroplast. Thus, it is important to analyze CO2 transport with regards to its effect on photosynthesis. A mutation of the Arabidopsis thaliana AtPIP1;2 gene, which was characterized as a non‐water transporting but CO2 transport‐facilitating aquaporin in heterologous expression systems, correlated with a reduction in photosynthesis under a wide range of atmospheric CO2 concentrations. Here, we could demonstrate that the effect was caused by reduced CO2 conductivity in leaf tissue. It is concluded that the AtPIP1;2 gene product limits CO2 diffusion and photosynthesis in leaves.
Abstract
Leaf imaging via microscopy has provided critical insights into research on photosynthesis at multiple junctures, from the early understanding of the role of stomata, through elucidating C4 ...photosynthesis via Kranz anatomy and chloroplast arrangement in single cells, to detailed explorations of diffusion pathways and light utilization gradients within leaves. In recent decades, the original two-dimensional (2D) explorations have begun to be visualized in three-dimensional (3D) space, revising our understanding of structure–function relationships between internal leaf anatomy and photosynthesis. In particular, advancing new technologies and analyses are providing fresh insight into the relationship between leaf cellular components and improving the ability to model net carbon fixation, water use efficiency, and metabolite turnover rate in leaves. While ground-breaking developments in imaging tools and techniques have expanded our knowledge of leaf 3D structure via high-resolution 3D and time-series images, there is a growing need for more in vivo imaging as well as metabolite imaging. However, these advances necessitate further improvement in microscopy sciences to overcome the unique challenges a green leaf poses. In this review, we discuss the available tools, techniques, challenges, and gaps for efficient in vivo leaf 3D imaging, as well as innovations to overcome these difficulties.
We review the techniques applied in leaf imaging to model anatomy and locate metabolites, and evaluate their power and efficiency in addressing fundamental questions in photosynthetic research.
Phenotyping for photosynthetic gas exchange parameters is limiting our ability to select plants for enhanced photosynthetic carbon gain and to assess plant function in current and future natural ...environments. This is due, in part, to the time required to generate estimates of the maximum rate of ribulose‐1,5‐bisphosphate carboxylase oxygenase (Rubisco) carboxylation (Vc,max) and the maximal rate of electron transport (Jmax) from the response of photosynthesis (A) to the CO2 concentration inside leaf air spaces (Ci). To relieve this bottleneck, we developed a method for rapid photosynthetic carbon assimilation CO2 responses rapid A–Ci response (RACiR) utilizing non‐steady‐state measurements of gas exchange. Using high temporal resolution measurements under rapidly changing CO2 concentrations, we show that RACiR techniques can obtain measures of Vc,max and Jmax in ~5 min, and possibly even faster. This is a small fraction of the time required for even the most advanced gas exchange instrumentation. The RACiR technique, owing to its increased throughput, will allow for more rapid screening of crops, mutants and populations of plants in natural environments, bringing gas exchange into the phenomic era.
Photosynthetic gas exchange measurements provide fundamental, quantitative, non‐destructive data on plant function and are used to generate parameters that underpin models of leaf biochemistry through global productivity. However, measurements of photosynthetic CO2 responses (A–Ci) are slow and currently limit throughput when screening plants for desirable traits. Here, we demonstrate a new rapid A–Ci response (RACiR) technique that generates the gas exchange data that are needed to determine important parameters including maximum Rubisco carboxylation rates (Vc,max) and maximum electron transport rates (Jmax) in 5 min or less. This puts assessment of biochemical limitations to photosynthesis on the same timescale as previous measurements of net CO2 assimilation.
We present measurements of the effect of first-generation secondary organic aerosol (SOA) material on the growth of ∼10 nanometer diameter seed particles composed of sulfuric acid and water. ...Experiments were performed in an atmospheric pressure, vertically aligned flow reactor where OH was produced from HONO photolysis in the presence of either SO
or a monoterpene. For typical conditions, organic compounds at ∼300 ppbv are exposed to photooxidation for a time of ∼80 s at a OH of about 6 × 10
cm
: thus, oxidation products have minimal OH exposure. The measured size changes of the sulfuric acid seed particles can then be attributed to the uptake of first-generation products. Along with descriptions of the apparatus and the procedure, the analysis to obtain SOA yields by comparing them to growth with H
SO
(g) is detailed. Results from photooxidation experiments of αpinene, limonene, and myrcene give SOA yields of 0.040, 0.084, and 0.16, respectively. These SOA yields roughly double with each addition of a double bond to the compound. The αpinene and limonene results are in accord with the results of many previous SOA experiments, while the myrcene SOA yield stands alone. Photooxidation of myrcene also led to significant nucleation, and the species responsible is comparable to H
SO
at a 35% relative humidity in its nucleation capability.
Atmospheric nucleation from sulfuric acid depends on the concentrations and the stabilizing effect of other trace gases, such as ammonia and amines. Diamines are an understudied class of ...atmospherically relevant compounds, and we examine how they affect sulfuric acid nucleation in both flow reactor experiments and the atmosphere. The number of particles produced from sulfuric acid and diamines in the flow reactor was equal to or greater than the number formed from monoamines, implying that diamines are more effective nucleating agents. Upper limits of diamine abundance were also monitored during three field campaigns: Lamont, OK (2013); Lewes, DE (2012); and Atlanta, GA (2009). Mixing ratios were measured as high as tens of parts per trillion by volume (GA and OK). Laboratory results suggest that diamines at these levels are important for atmospheric nucleation. Diamines likely participate in atmospheric nucleation and should be considered in nucleation measurements and models.
Key Points
Diamines stabilize sulfuric acid clusters more than monoamines like DMA
Reactions of sulfuric acid with diamines can produce more particles than with monoamines
Diamines exist in significant concentrations in the atmosphere and likely contribute to nucleation
Why small fluxes matter Hanson, David T.; Stutz, Samantha S.; Boyer, John S.
Journal of experimental botany,
05/2016, Letnik:
67, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Since its inception, the Farquhar et al. (1980) model of photosynthesis has been a mainstay for relating biochemistry to environmental conditions from chloroplast to global levels in terrestrial ...plants. Many variables could be assigned from basic enzyme kinetics, but the model also required measurements of maximum rates of photosynthetic electron transport (Jmax
), carbon assimilation (V
cmax
), conductance of CO₂ into (gs
) and through (gm
) the leaf, and the rate of respiration during the day (Rd
). This review focuses on improving the accuracy of these measurements, especially fluxes from photorespiratory CO₂, CO₂ in the transpiration stream, and through the leaf epidermis and cuticle. These fluxes, though small, affect the accuracy of all methods of estimating mesophyll conductance and several other photosynthetic parameters because they all require knowledge of CO₂ concentrations in the intercellular spaces. This review highlights modified methods that may help to reduce some of the uncertainties. The approaches are increasingly important when leaves are stressed or when fluxes are inferred at scales larger than the leaf.
Traditionally, leaves were thought to be supplied with CO₂ for photosynthesis by the atmosphere and respiration. Recent studies, however, have shown that the xylem also transports a significant ...amount of inorganic carbon into leaves through the bulk flow of water. However, little is known about the dynamics and proportion of xylem-transported CO₂ that is assimilated, vs simply lost to transpiration.
Cut leaves of Populus deltoides and Brassica napus were placed in either KCl or one of three NaH13CO₃ solutions dissolved in water to simultaneously measure the assimilation and the efflux of xylem-transported CO₂ exiting the leaf across light and CO₂ response curves in real-time using a tunable diode laser absorption spectroscope.
The rates of assimilation and efflux of xylem-transported CO₂ increased with increasing xylem 13CO₂* and transpiration. Under saturating irradiance, rates of assimilation using xylem-transported CO₂ accounted for c. 2.5% of the total assimilation in both species in the highest 13CO₂*.
The majority of xylem-transported CO₂ is assimilated, and efflux is small compared to respiration. Assimilation of xylem-transported CO₂ comprises a small portion of total photosynthesis, but may be more important when CO₂ is limiting.
Phenotyping for photosynthetic gas exchange parameters is limiting our ability to select plants for enhanced photosynthetic carbon gain and to assess plant function in current and future natural ...environments. This is due, in part, to the time required to generate estimates of the maximum rate of ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) carboxylation (V
) and the maximal rate of electron transport (J
) from the response of photosynthesis (A) to the CO
concentration inside leaf air spaces (C
). To relieve this bottleneck, we developed a method for rapid photosynthetic carbon assimilation CO
responses rapid A-C
response (RACiR) utilizing non-steady-state measurements of gas exchange. Using high temporal resolution measurements under rapidly changing CO
concentrations, we show that RACiR techniques can obtain measures of V
and J
in ~5 min, and possibly even faster. This is a small fraction of the time required for even the most advanced gas exchange instrumentation. The RACiR technique, owing to its increased throughput, will allow for more rapid screening of crops, mutants and populations of plants in natural environments, bringing gas exchange into the phenomic era.
•Discrete Element Roughness (DERM) implementation in the context of a general-purpose CFD code.•Benchmarked results for a series of canonical validation cases.•Results indicating potential to improve ...heat transfer prediction on rough surfaces compared to traditional models.
The Discrete Element Roughness Method (DERM) is evaluated as an engineering solution to the problem of convective heat transfer on rough surfaces. As part of the present work, DERM is incorporated into a general purpose compressible CFD code and explored as a way of modeling the sub-resolved roughness scales. In addition, DERM-model inputs are evaluated in detail and developed to represent sand-grain roughness (SGR). The results display good agreement in a number of validation cases. The overall results clearly indicate that DERM has potential to improve heat transfer predictions beyond the capability of SGR models, while only slightly increasing the computation time.
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