Plant gas exchange

Transpiration rate and stomatal resistance are the most commonly measured plant gas exchange parameters using IRGA. Their behaviour in A. thaliana plants exposed to heavy metal ion stress is demonstrated in Figure 2 B and C. 

Leaflets, stipules, and tendrils of Pisum sativum L. Improved Laxton s Progress, and cv. Curly a afila (semi-leafless) mutant have been assessed for their contribution to total plant gas exchange (Fig.1). 

Whole Plant Gas Exchange and Carbon Gain Whole plant C( exchange and C gain was deterMined using a seMi-open systeM (10). 

Fig. 1. Rates of CO2 assimilation, A (/miol s ) leaf conductance, g (mol m s ) intercellular partial pressure of CO2, Pi (Pa) soil water potential and leaf water potential, xp (MPa) during gas-exchange measurements of a 30-day-old cotton plant, plotted against day after watering was withheld. Measurements were made with 2 mmol m sec" photon flux density, 30 °C leaf temperature, and 2.0 kPa vapour pressure difference between leaf and air (S.C. Wong, unpublished data).

Bradford, K.J., Sharkey, T.D. Farquhar, G.D. (1983). Gas exchange, stomatal behaviour, and 6 C values of the acca tomato mutant in relation to abscisic acid. Plant Physiology, 72, 245-50. 

Evans, J.R., Sharkey, T.D., Berry, J.A. Farquhar, G.D. (1986). Carbon isotope discrimination measured concurrently with gas exchange to investigate CO2 diffusion in leaves of higher plants. Australian Journal of Plant Physiology 13,281-92. 

The major function of cutin is to serve as the structural component of the outer barrier of plants. As the major component of the cuticle it plays a major role in the interaction of the plant with its environment. Development of the cuticle is thought to be responsible for the ability of plants to move onto land where the cuticle limits diffusion of moisture and thus prevents desiccation [141]. The plant cuticle controls the exchange of matter between leaf and atmosphere. The transport properties of the cuticle strongly influences the loss of water and solutes from the leaf interior as well as uptake of nonvolatile chemicals from the atmosphere to the leaf surface. In the absence of stomata the cuticle controls gas exchange. The cuticle as a transport-limiting barrier is important in its physiological and ecological functions. The diffusion across plant cuticle follows basic laws of passive diffusion across lipophylic membranes [142]. Isolated cuticular membranes have been used to study this permeability and the results obtained appear to be valid... 

These gas- and water-impermeable cell layers protect the plant from desiccation, but they also hamper the uptake of carbon dioxide necessary for photosynthesis and oxygen necessary for respiration. Specialized tissues have evolved to allow passive (lenticels) and active (guard cells) modification of the permeability of the external cuticle to gas exchange. 

Armstrong W, Cousins D, Armstrong J, Turner DW, Beckett PM. 2000. Oxygen distribution in wetland plant roots and permeability barriers to gas-exchange with the rhizosphere a microelectrode and modelling study with Phragmites australis. Annals of Botany 86 687-703. 

Respiration into the lung alveoli is the most important hazard for plant workers. The average lung has 300 million alveoli with a surface area of about 70 m, which is designed for rapid gas exchange. This alveolar surface area is about 40 times larger than the external skin area of a person. There has been a systematic study of the major air pollutants associated with the protection of industrial workers, as monitored by the OSHA and the ACGIH, and there are three well-documented measurements and databases ... 

Boeing Company. (1962). Investigations of selected higher plants as gas exchange mechanisms for closed ecological systems. In Biologistics for Space Systems Symposium, Wright-Patterson Air Force Base, USA. AMRL-TDR-62-116. pp. 213-232. 

Cao, W., Tibbitts, T. W. (1991a). Potassium concentration effect on growth, gas exchange, and mineral accumulation in potatoes. J Plant Nutr, 14, 525-527. 

Another type of gas exchange process, developed to the pilot plant stage, is separation of gaseous olefin/paraffin mixtures by absorption of the olefin into silver nitrate solution. This process is related to the separation of olefin/paraffin mixtures by facilitated transport membranes described in Chapter 11. A membrane contactor provides a gas-liquid interface for gas absorption to take place a flow schematic of the process is shown in Figure 13.11 [28,29], The olefin/paraffin gas mixture is circulated on the outside of a hollow fiber membrane contactor, while a 1-5 M silver nitrate solution is circulated countercurrently down the fiber bores. Hydrophilic hollow fiber membranes, which are wetted by the aqueous silver nitrate solution, are used. 

The stomata represent the primary sites for gas exchange. Data for one clone (Table 4.2) indicate that the size of stomata are essentially the same between the adaxial (343 pm2) and abaxial (323 pm2) surfaces however, their shape varies, with lower stomata being rounder (1.3 1 length-to-width ratio) than those of the upper surface, which are more oval (1.6 1). The data represent only one clone and may not be indicative of the variation over the entire leaf surface of the plant. 

The effect of leaf position on the photosynthetic rate of Jerusalem artichoke (Soja and Haunold, 1991) is similar to that of the sunflower (English et al., 1979) in that leaf position becomes progressively more critical as the plant ages. When the plants reach their final height, only leaves in the upper 1/6 of the canopy display gas exchange rates greater than 50% of the most apical leaves (Table 10.3). 

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