Stomatal Behavior and CO<sub>2</sub> Exchange Characteristics in Amphistomatous Leaves

Mott, Keith A.; O’Leary, James W.

doi:10.1104/pp.74.1.47

Cited by 68 publications

(72 citation statements)

References 6 publications

(7 reference statements)

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“…1). These differences are similar to those reported by Mott and O'Leary (4). However, one can only estimate pi at the surfaces for such leaves-we know of no way to measure the actual internal gradients.…”

Section: Discussionsupporting

confidence: 72%

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Gradients of Intercellular CO₂ Levels Across the Leaf Mesophyll

Parkhurst

Wong²,

Farquhar³

et al. 1988

Plant Physiol.

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Most current photosynthesis models, and interpretations of many wholeleaf CO2 gas exchange measurements, are based on the often unstated assumption that the partial pressure of CO2 is nearly uniform throughout the airspaces of the leaf mesophyll. Here we present measurements of CO2 gradients across amphistomatous leaves allowed to assimilate CO2 through only one surface, thus simulating hypostomatous leaves. We studied five species: Eucalyptus pauciflora Sieb. ex Spreng., Brassica chinensis L., Gossypium hirsutum L., Phaseolus vulgaris L., and Spinacia oleracea L. For Eucalyptus, maximum CO2 pressure differences across the leaf mesophyll were 73 and 160 microbar when the pressures outside the lower leaf surface were 310 and 590 microbar, respectively. Using an approximate theoretical calculation, we infer that if the CO2 had been supplied equally at both surfaces then the respective mean intercellular CO2 pressures would have been roughly 12 and 27 microbar less than the pressures in the substomatal cavities in these cases. For ambient CO2 pressures near 320 microbar, the average and minimum pressure differences across the mesophyll were 45 and 13 microbar. The corresponding mean intercellular CO2 pressures would then be roughly 8 and 2 microbar less than those in the substomatal cavities. Pressure differences were generally smaller for the four agricultural species than for Eucalyptus, but they were nevertheless larger than previously reported values.there. Because no net CO2 exchange occurred through that side, the CO2 pressure measured in that cuvette would be close to the pressure in the substomatal chambers. The other chamber was operated normally, and pi was calculated for that side using the methods of Caemmerer and Farquhar (1) (a list of abbreviations used in this paper can be found in Table I). The maximum differences in CO2 pressure across the mesophyll were 10 to 14 ,ubar. These results suggest that in a 'one-sided' leaf having internal structure similar to that in cotton and cocklebur, pi should vary by no more than about 14 ,ubar across the mesophyll.Mott and O'Leary (4) performed a modified version of the Sharkey experiment using open gas exchange systems on both sides of sunflower and cocklebur leaves. They operated the system normally on one side, and adjusted the ambient CO, level at the other side until no net gas exchange occurred there. This technique allowed them to maintain small and equal positive pressures in both chambers. This method prevented room air (often high in CO2) from leaking into either chamber, and also removed any pressure difference that might drive a bulk flow of air through the leaf.In sunflower, Mott and O'Leary (4) found no measurable differences in the estimates of c; at the two surfaces. In cocklebur, c, at the surface not exchanging CO2 was always lower than c; at the other surface. The difference increased with increase in ambient CO2 concentration at the 'fed' surface. For example (K Mott, personal communication, 1985), when the upper and lower surfaces o...

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Section: Discussionsupporting

confidence: 72%

“…In sunflower, Mott and O'Leary (4) found no measurable differences in the estimates of c; at the two surfaces. In (9) estimated the resistance for cocklebur to be 1.0 m2 s mol-l.…”

mentioning

confidence: 99%

Gradients of Intercellular CO₂ Levels Across the Leaf Mesophyll

Parkhurst

Wong²,

Farquhar³

et al. 1988

Plant Physiol.

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“…For Gossypium, 1 have unpublished measurements (for one leaf) showing its porosity, i.e.. percent airspace, to be fairly high (37"" average, and over 5O'\, in the lower spongy mesophyll), so cotton would also be expected to have a lower intercellular gaseous diffusion limitation than that in many other species. Mott & O'Leary (1984) performed somewhat similar experiments, but they used separate open (flow-through) gas-exchange systems on each side of the leaf, and for some experiments adjusted />" on one surface until there was no net COj exchange through that surface. Thus all CO,, assimilated entered the leaf through the stomata on the opposite side.…”

Section: Empirical Evidencementioning

confidence: 99%

“…(It was also used by Sharkey et al, 1982 andO'Leary, 1984). Following Rand & Cooke (1980) I have argued above ( §II.4(a')) that the concepts of resistance and conductance become more confusing than useful in any region where diffusion interacts with distributed sources or sinks (i.e.…”

Section: Empirical Evidencementioning

confidence: 99%

Diffusion of CO₂and other gases inside leaves

1994

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SUMMARY Diffusion of CO2 in the intercellular airspaces of the leaf mesophyll is one of the many processes that can limit photosynthetic carbon assimilation there. This limitation has been largely neglected in recent years, but both theoretical and empirical evidence is presented showing that it can be substantial, reducing CO2 assimilation rates by 25% or more in some leaves. Intercellular diffusion is fundamentally a three‐dimensional process, because CO2 enters the leaf through discrete stomata, and not through a uniformly porous epidermis. Modelling it in one dimension can cause major underestimation of its limiting effects. Resistance and conductance models often fail to account well for the limitation, in part because they are usually one‐dimensional representations, but also because they treat continuously interacting processes as if they were sequential. A three‐dimensional diffusion model is used to estimate the intercellular limitation in leaves of different structural types. Intercellular gaseous diffusion probably limits CO2 assimilation by at most a few percent in many of the agricultural plants commonly studied by laboratory physiologists, as they usually have thin, amphistaomatous leaves. However, it may cause substantial limitations in the thicker, often hypostomatous leaves of the wild plants that occupy large areas of the earth. Several physiological implications of intercellular diffusion are discussed. I close by reiterating published suggestions that the gas‐exchange parameter commonly termed pi should be renamed pes (es for evaporating surfaces) to avoid the confusing implication that p1, is‘the’intercellular CO2 pressure.

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“…Differences across the leaf depend on the coordination between photosynthesis and stomatal conductance by each leaf surface and the extent to which CO, diffusion across the leaf is restricted. With 330 pbar of CO, outside the leaf, differences between the upper and lower surface p , values amount to O to 20 pbar, oí-less than 10 pbar on average (Mott and OLeary, 1984;Wong et al, 1985;Parkhurst et al, 1988). A more direct way to assess the restriction to diffusion across the leaf is to follow an inert gas such as helium or N,O.…”

Section: Vertical Resistancementioning

confidence: 99%

Carbon Dioxide Diffusion inside Leaves

Evans¹,

Caemmerer²

1996

Plant Physiol.

376

301

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Leaves are beautifully specialized organs that enable plants to intercept light necessary for photosynthesis. The light is dispersed among a large array of chloroplasts that are in close proximity to air and yet not too far from vascular tissue, which supplies water and exports sugars and other metabolites. To control water loss from the leaf, gas exchange occurs through pores in the leaf surface, stomata, which are able to rapidly change their aperture. Once inside the leaf, CO, has to diffuse from the intercellular air spaces to the sites of carboxylation in the chloroplast (for C, species) (Fig. 1) or the cytosol (for C, species). These internal diffusion paths are the topic of this article.There are several reasons why internal diffusion is of interest. First, Rubisco has a poor affinity for CO, and operates at only a fraction of its catalytic capacity in C, leaves. The CO, gradient within the leaf thus affects the efficiency of Rubisco and the overall nitrogen use efficiency of the leaf. Second, prediction of photosynthetic rates of leaves from their biochemical properties requires a good estimate of the partial pressure of CO, at the sites of carboxylation, pc. Third, internal resistance to CO, diffusion results in a lower pc and reduces carbon gain relative to water loss during photosynthesis (water-use efficiency). Considerable effort is being invested selecting and identifying plants with improved water-use efficiency using the surrogate measure of carbon isotope discrimination, A, of plant dry matter (Ehleringer et al., 1993). The ratio of intercellular to ambient CO, partial pressure, pi/p,, and A are both linearly related to water-use efficiency if pc/pi is constant. To date, we have little knowledge of genetic variation in p c / p i .Until recently, it was not possible to directly measure the gradient in CO, partial pressure to the sites of carboxylation. The gradient could be inferred from a theoretical analysis of the diffusion pathway, but because several steps have unknown permeability constants, the values are uncertain. Opinion has oscillated from the existence of large to small gradients over the last 30 years. There are now two techniques that enable the gradient to be measured in C, leaves. After describing these techniques, we will consider diffusion through intercellular air spaces and diffusion across cell walls and liquid phase to sites of carboxylation. Finally, we will examine CO, diffusion into mesophyll cells and across the bundle sheath in C, leaves.* Corresponding author; e-mail evans8rsbs-centra1.anu.edu.au; fax 61-(0)6-249-4919. 339 TECHNIQUES FOR MEASURING CO, TRANSFER CON D UCTANC EConventional gas-exchange techniques measure fluxes of water and CO, into and out of a leaf. The gradient in partial pressure of CO, from ambient air to the substomatal cavities (usually referred to as p,) is derived using Ficks law of diffusion, which states that the gradient in partial pressure is equal to the flux divided by the conductance, i.e. pa -pi = A/g, where A is the rate of CO, assimilat...

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Stomatal Behavior and CO₂ Exchange Characteristics in Amphistomatous Leaves

Cited by 68 publications

References 6 publications

Gradients of Intercellular CO₂ Levels Across the Leaf Mesophyll

Gradients of Intercellular CO₂ Levels Across the Leaf Mesophyll

Diffusion of CO₂and other gases inside leaves

Carbon Dioxide Diffusion inside Leaves

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Stomatal Behavior and CO2 Exchange Characteristics in Amphistomatous Leaves

Cited by 68 publications

References 6 publications

Gradients of Intercellular CO2 Levels Across the Leaf Mesophyll

Gradients of Intercellular CO2 Levels Across the Leaf Mesophyll

Diffusion of CO2and other gases inside leaves

Carbon Dioxide Diffusion inside Leaves

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Product

Resources

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Stomatal Behavior and CO₂ Exchange Characteristics in Amphistomatous Leaves

Gradients of Intercellular CO₂ Levels Across the Leaf Mesophyll

Gradients of Intercellular CO₂ Levels Across the Leaf Mesophyll

Diffusion of CO₂and other gases inside leaves