Intercellular Airspaces

FIGURE 7.6 Swamp tupelo seedling showing lenticels and waterroots. (Redrawn from Hook and Scholtens, 1978.) 

FIGURE 7.7 Porosity of rice roots as a function of distance from apex. (Redrawn from Armstrong, 1971.) 

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The rate of water vapor diffusion per unit leaf area, Jw> equals the difference in water vapor concentration multiplied by the conductance across which Acm occurs (// = g/Ac - Eq. 8.2). In the steady state (Chapter 3, Section 3.2B), when the flux density of water vapor and the conductance of each component are constant with time, this relation holds both for the overall pathway and for any individual segment of it. Because some water evaporates from the cell walls of mesophyll cells along the pathway within the leaf, is actually not spatially constant in the intercellular airspaces. For simplicity, however, we generally assume that Jm, is unchanging from the mesophyll cell walls out to the turbulent air outside a leaf. When water vapor moves out only across the lower epidermis of the leaf and when cuticular transpiration is negligible, we obtain the following relations in the... 

Mesophytes.— These are plants that grow in soil of an intermediate character which is neither specially acid, cold or saline, but is sufficiently well supplied with water and rich in the elements required for plant growth. Plants which grow under such conditions do not have structures by which transpiration is closely controlled. They have large leaves frequently toothed and incised, with numerous stomata usually on the lower surface and small intercellular -airspaces. The leaves and stems are usually of a fresh green color. Typical of the mesophytes are the grasses and most of the annual and biennial herbs of temperate regions. 

Transport of oxygen within the plant requires continuity of the intercellular airspaces to create a flow path with low resistance. Two major pathways are recognized for O2 transport into and within the plant. These are... 

These early observations, followed by recent reports by several researchers indicate that greater gas fluxes in intercellular airspaces of some wetland plants are due to pressurized convective flow (Dacey, 1981, 1987 Armstrong and Armstrong, 1991 Armstrong and Beckett, 1996 Brix et al.,... 

Mass flow of gases in intercellular airspaces of wetland plants can be generated by several processes ... 

The pressure induced by humidity in the intercellular airspaces is the difference in water vapor pressure inside and outside the leaf (Brix et al., 1992) ... 

FIGURE 7.19 Influence of leaf temperature on pressurization of gases in intercellular airspaces. (Redrawn from Grosse, 1989.)... 

FIGU RE 7.21 Influence of relative humidity on pressurization in the intercellular airspaces of wetland plants. 

Mass flows mediated by thermal transpiration and humidity-induced pressurization require Knudsen s regime (i.e., pore diameter <0.1 pm). Static pressure in intercellular airspaces decreases... 

Sulfide is oxidized in the rhizosphere and the resulting sulfate is taken up by the plants. Alternatively, sulfide can be taken by the plant and oxidized in the intercellular airspaces of roots (Carlson and Forrest, 1982). Sulfide precipitation with metals as metal sulfides (insoluble precipitates under anaerobic conditions) decreases pore water concentrations. However, metal sulfides formed in... 

Fig. 3. Primary carbon metabolism in a photosynthetic C3 leaf. An abbreviated depiction of foliar C02 uptake, chloroplastic light-reactions, chloroplastic carbon fixation (Calvin cycle), chloroplastic starch synthesis, cytosolic sucrose synthesis, cytosolic glycolysis, mitochondrial citric acid cycle, and mitochondrial electron transport. The photorespiration cycle spans reactions localized in the chloroplast, the peroxisome, and the mitochondria. Stacked green ovals (chloroplast) represent thylakoid membranes. Dashed arrows near figure top represent the C02 diffusion path from the atmosphere (Ca), into the leaf intercellular airspace (Ci), and into the stroma of the chloroplast (Cc).SoHd black arrows represent biochemical reactions. Enzyme names and some substrates and biochemical steps have been omitted for simplicity. The dotted line in the mitochondria represents the electron transport pathway. Energy equivalent intermediates (e.g., ADP, UTP, inorganic phosphate Pi) and reducing equivalents (e.g., NADPH, FADH2, NADH) are labeled in red. Membrane transporters Aqp (CO2 conducting aquaporins) and TPT (triose phosphate transporter) are labeled in italics. Mitochondrial irmer-membrane electron transport and proton transport proteins are labeled in small case italics.

Fig. 5. Leaf anatomy differs among species in ways that affect the mesophyll conductance to CO2 diffusion. Thin mesophytic Nicotiana tabacum leaves (left) have abundant intercellular air space, thin mesophyll cell walls, and, presumably a high mesophyll conductance that could sustain high rates of photosynthesis. Thick sclerophyllous Agave schidigeri leaves (right) have large, tightly packed, thick-walled cells, and, presumably a low mesophyll conductance that could restrict photosynthesis. E =epidermis, M=mesophyll cells, SSC=sub-stomatal cavity, IAS=intercellular airspace. (Micrographs by Bruce Campbell.)...

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