Mechanisms Regulating Photosynthesis in Pennisetum Typhoides

Mcpherson, HG; Slatyer, R. O.

doi:10.1071/bi9730329

Cited by 55 publications

(28 citation statements)

References 23 publications

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“…where g1(H20) was determined according to Equation 1, and the factor 1.6 is the ratio of the diffusivities of CO, and water vapor in air (McPherson and Slatyer, 1973;Nobel, 1983). The correction was 4 to 6 pmol CO, mol-I when this equation was used and, thus, very small.…”

Section: Materials a N D Methodsmentioning

confidence: 99%

CO2 and Water Vapor Exchange across Leaf Cuticle (Epidermis) at Various Water Potentials

1997

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~ ~Cuticular properties affect the gas exchange of leaves, but little is known about how much CO, and water vapor cross the cuticular barrier or whether low water potentials affect the process. Therefore, we measured the cuticular conductances for CO, and water vapor in grape (Vitis vinifera 1.) leaves having various water potentials. l h e lower leaf surface was sealed to force all gas exchange through the upper surface, which was stoma-free. In this condition both gases passed through the cuticle, and the CO, conductance could be directly determined from the interna1 mole fraction of CO, near the compensation point, the externa1 mole fraction of CO,, and the CO, flux. The cuticle allowed small amounts of CO, and water vapor to pass through, indicating that gas exchange occurs in grape leaves no matter how tightly the stomata are closed. However, the CO, conductance was only 5.7% of that for water vapor. This discrimination against CO, markedly affected calculations of the mole fraction of CO, in leaves as stomatal apertures decreased. When the leaf dehydrated, the cuticular conductance to water vapor decreased, and transpiration and assimilation diminished. This dehydration effect was largest when turgor decreased, which suggests that cuticular gas exchange may have been influenced by epidermal stretching.The waxy cuticle of leaves serves to inhibit water loss and thus to decrease the dehydration of the underlying cells (Scott, 1964(Scott, ,1966Norris and Bukovac, 1968; Leon and Bukovac, 1978). The waxes vary in thickness and composition, and the inhibition of water loss varies accordingly (Bengtson et al., 1978; OToole et al., 1979; OToole, 1982; Jordan et al., 1983 Jordan et al., , 1984 von Wettstein-Knowles, 1989; Jenks et al., 1994). Holmgren et al. (1965) found that water loss through the cuticle was 1.7 to 28.6% of that through open stomata, depending on the species. This indicates that gas exchange through the cuticle can be a small or substantia1 fraction of the exchange through open stomata. As stomata close, the fraction becomes larger and the control of gas exchange shifts increasingly to the cuticle. Leaves that are darkened or that dehydrate and close their stomata experience this shift from stomatal control to cuticular control.As water loss becomes increasingly dependent on the cuticle, the exchange of CO, becomes similarly dependent on cuticular properties. Dugger (1952) found that 14C02 passes through the cuticle. Woolley (1967) observed that artificial films discriminate against CO, and predicted that the cuticle would show the same behavior. However, the C0,-exchange properties have not been reported for cuticles. This issue is important because CO, in the intercellular spaces is the substrate for photosynthesis and the concentration is generally calculated from the diffusion of water vapor through the leaf (Moss and Rawlins, 1963; von Caemmerer and Farquhar, 1981). Similarly, the diffusive conductance for CO, is calculated from water vapor diffusion (Gaastra, 1959; von Caemmerer and...

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Section: Materials a N D Methodsmentioning

confidence: 99%

CO2 and Water Vapor Exchange across Leaf Cuticle (Epidermis) at Various Water Potentials

1997

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“…Photosynthetic resistances were measured and calculated by a modification of the original technique of Gaastra (6). A multiplier (1.59) which relates the diffusion coefficients of CO2 and H20 (16) was used to calculate CO2 diffusive resistances from the H20 diffusive resistances. In this study, the CO2 mesophyll resistance term originally defined by Gaastra was replaced by the residual resistance term, since this includes all diffusive and metabolic components of the total CO2 resistance apart from stomatal and boundary layer resistances (9).…”

Section: Methodsmentioning

confidence: 99%

Net Photosynthesis, Electron Transport Capacity, and Ultrastructure of Pisum sativum L. Exposed to Ultraviolet-B Radiation

Brandle¹,

Campbell²,

Sisson³

et al. 1977

Plant Physiol.

186

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Pisum sativum L. was exposed to ultraviolet-B (UV-B) radiation (280-315 nm) in greenhouse and controOled environment chambers to examine the effect of this radiation on photosynthetic processes. Net photosynthetic rates of intact leaves were reduced by UV-B irradiation. Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO2 diffusion into the leaf. Dark respiration rates were increased by previous exposure to this radiation. Electron transport capacity as indicated by methylviologen reduction was also sensitive to UV-B irradiation. The ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with photosystem II than with photosystem I. Electron micrographs indicated structural damage to chloroplasts as well as other organelles. Plant tissue irradiated for only 15 minutes exhibited dilation of thylakoid membranes of the chloroplast in some cells. Some reduction in Hill reaction activity was also evidenced in these plant materials which had been irradiated for periods as short as 15 minutes.Ultraviolet radiation in the 280 to 315 nm waveband, usually denoted as UV-B radiation, is readily absorbed by nucleic acid and protein chromophores (8) and effectively inhibits many plant processes (5), including photosynthesis (2, 22). Ultraviolet radiation of this waveband is of particular interest to photobiologists because this radiation occurs in normal sunlight and would be intensified if the atmospheric ozone layer were reduced (3,10). Although the action of intense 254 nm UV radiation on photosynthetic processes has been well studied (7), this radiation would not reach the Earth's surface even in the event of severe ozone radiation.The present study was initiated to evaluate effects of UV-B radiation on photosynthesis and aspects of the electron transport system, and to define morphological changes of chloroplasts in Pisum sativum L. plants exposed to Results of this study tend to support the hypothesis that photosynthetic processes primarily associated with PSII are affected by the levels of UV-B radiation tested in this study. MATERIALS AND METHODSP. sativum L. cv. Early Alaska plants were grown under greenhouse conditions with an approximate 14-hr photoperiod and PAR4 of about 400 ,ueinsteins m-2 sec-'. Studies of the effects of plant biomass were initiated when the seedlings were 7 days old. In all other experiments, the seedlings were 14 days old upon initiation of treatment.Spectral irradiance for the controlled environment studies was provided by the lamp filter system previously described (21). The PAR was 800 ,ueinsteins -m-2 -sec-1 with a 16-hr photoperiod. Temperatures were programmed to simulate a July day in northern Utah (13 to 37 C). Spectral irradiance for both the control and UV radiation treatments are illustrated in Figure 1.The biomass study was carried out i...

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“…Leaf diffusive resistances were measured and calculated by a modification of the technique of Gaastra (10). A multiplier (1.594) which relates the diffusion coefficients of CO2 and H20 (21) was used to calculate CO2 diffusive resistances from the H20 diffusive resistances. In this study, the CO2 mesophyll resistance originally defined by Gaastra (10) was replaced by the residual resistance term, since this includes all diffusive and metabolic components of the total CO2 resistance apart from stomatal and boundary layer resistances (12).…”

Section: Methodsmentioning

confidence: 99%

Photosynthesis, Dark Respiration, and Growth of Rumex patientia L. Exposed to Ultraviolet Irradiance (288 to 315 Nanometers) Simulating a Reduced Atmospheric Ozone Column

Sisson¹,

Caldwell²

1976

Plant Physiol.

125

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Net photosynthesis, dark respiration, and growth of Rumexpatientia L. exposed to a ultraviolet irradiance (288-315 nanometers) simulating a 0.18 atm-cm stratospheric ozone column were determined. The ultraviolet irradiance corresponding to this 38% ozone decrease from normal was shown to be an effective inhibitor of photosynthesis and leaf growth.The repressive action on photosynthesis accumulated through time whereas leaf growth was retarded only during the initial few days of exposure. Small increases in dark respiration rates occurred but did not continue to increase with longer exposure periods. A reduction in total plant dry weight and leaf area of approximately 50% occurred after 22 days of treatment, whereas chlorophyll concentrations remained unaltered.Global UV irradiance on the earth's surface fluctuates with changes in solar altitude, cloud cover, stratospheric ozone concentration, and atmospheric turbidity. No appreciable UV radiation below 295 nm is received on the earth's surface due to absorption of UV radiation by the stratospheric ozone layer. A reduction of the stratospheric ozone column would result in a predictable shift in the terrestrial global spectrum to include shorter UV wavelengths below 295 nm (3,13). Such a reduction could result from catalytic interactions of ozone with oxides of nitrogen released in the stratosphere by aircraft (14, 16), halomethanes diffusing from the troposphere (6, 15, 22) or other man-induced perturbations of the stratosphere. Although the resulting shift in the global UV radiation spectrum resulting from partial ozone reduction would be small (3, 13), any added increment of shorter wavelength UV radiation might prove significant since it is effectively absorbed by chromophores such as nucleic acids and proteins (11).Historically, UV radiation photobiological research has dealt principally with monochromatic 254-nm radiation. From these studies, an array of deleterious effects on plants has been shown.These effects include such responses as reduced growth (25) partial ozone reduction does not, at the present time, appear plausible for three reasons. First, biological response to UV radiation tends to be highly wavelength-specific with respect to efficiency of photobiological action (5, 11). Second, the biologically potent waveband shorter than 280 nm would not be transmitted to the earth's surface even if the ozone column were reduced to 40% of its present thickness (13). Finally, there may be qualitative as well as quantitative differences in the response to 254-nm radiation and radiation in the 288-to 315-nm waveband as has been reported for Chlamydomonas reinhardi (23).This paper reports on evaluation of net photosynthesis, dark respiration, and growth of Rumex patientia L. exposed to UV irradiation corresponding to the global UV spectral irradiance which would occur with partial ozone reduction. The level of ozone reduction simulated was approximately 38% from normal, and resulted in an almost immediate detrimental effect on those plant processes wh...

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Mechanisms Regulating Photosynthesis in Pennisetum Typhoides

Abstract: Leaf chamber studies were conducted on single attached leaves of Pennisetum typhoides (Burm.) S. & H. (bulrush millet) to identify and describe the processes regulating photosynthesis.

Cited by 55 publications

References 23 publications

CO2 and Water Vapor Exchange across Leaf Cuticle (Epidermis) at Various Water Potentials

CO2 and Water Vapor Exchange across Leaf Cuticle (Epidermis) at Various Water Potentials

Net Photosynthesis, Electron Transport Capacity, and Ultrastructure of Pisum sativum L. Exposed to Ultraviolet-B Radiation

Photosynthesis, Dark Respiration, and Growth of Rumex patientia L. Exposed to Ultraviolet Irradiance (288 to 315 Nanometers) Simulating a Reduced Atmospheric Ozone Column

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