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Gas Exchange Measurements (gas + exchange_measurement)
Selected AbstractsStomatal crypts may facilitate diffusion of CO2 to adaxial mesophyll cells in thick sclerophyllsPLANT CELL & ENVIRONMENT, Issue 11 2009FOTEINI HASSIOTOU ABSTRACT In some plants, stomata are exclusively located in epidermal depressions called crypts. It has been argued that crypts function to reduce transpiration; however, the occurrence of crypts in species from both arid and wet environments suggests that crypts may play another role. The genus Banksia was chosen to examine quantitative relationships between crypt morphology and leaf structural and physiological traits to gain insight into the functional significance of crypts. Crypt resistance to water vapour and CO2 diffusion was calculated by treating crypts as an additional boundary layer partially covering one leaf surface. Gas exchange measurements of polypropylene meshes confirmed the validity of this approach. Stomatal resistance was calculated as leaf resistance minus calculated crypt resistance. Stomata contributed significantly more than crypts to leaf resistance. Crypt depth increased and accounted for an increasing proportion of leaf resistance in species with greater leaf thickness and leaf dry mass per area. All Banksia species examined with leaves thicker than 0.6 mm had their stomata in deep crypts. We propose that crypts function to facilitate CO2 diffusion from the abaxial surface to adaxial palisade cells in thick leaves. This and other possible functions of stomatal crypts, including a role in water use, are discussed. [source] The structural design of the bat wing web and its possible role in gas exchangeJOURNAL OF ANATOMY, Issue 6 2007Andrew N. Makanya Abstract The structure of the skin in the epauletted fruit bat (Epomophorus wahlbergi) wing and body trunk was studied with a view to understanding possible adaptations for gas metabolism and thermoregulation. In addition, gas exchange measurements were performed using a respirometer designed for the purpose. The body skin had an epidermis, a dermis with hair follicles and sweat glands and a fat-laden hypodermis. In contrast, the wing web skin was made up of a thin bilayered epidermis separated by a connective tissue core with collagen and elastic fibres and was devoid of hair follicles and sweat glands. The wings spanned 18,24 cm each, with about 753 cm2 of surface exposed to air. The body skin epidermis was thick (61 ± 3 µm, SEM), the stratum corneum alone taking a third of it (21 ± 3 µm). In contrast, the wing web skin epidermis was thinner at 9.8 ± 0.7 µm, with a stratum corneum measuring 4.1 ± 0.3 µm (41%). The wing capillaries in the wing web skin ran in the middle of the connective tissue core, with a resultant surface-capillary diffusion distance of 26.8 ± 3.2 µm. The rate of oxygen consumption (V,O2) of the wings alone and of the whole animal measured under light anaesthesia at ambient temperatures of 24 ºC and 33 ºC, averaged 6% and 10% of the total, respectively. Rate of carbon dioxide production had similar values. The membrane diffusing capacity for the wing web was estimated to be 0.019 ml O2 min,1 mmHg,1. We conclude that in Epomophorus wahlbergi, the wing web has structural modifications that permit a substantial contribution to the total gas exchange. [source] Growth and maintenance respiration for individual plants in hierarchically structured canopies of Medicago sativa and Helianthus annuus: the contribution of current and old assimilatesNEW PHYTOLOGIST, Issue 2 2004Markus Lötscher Summary ,,Respiratory costs of Medicago sativa and Helianthus annuus individuals growing in hierarchically structured stands in a controlled environment were analysed with regard to the daily rate of carbon (C) assimilation. ,,Net assimilation of new C (An, g C d,1) and respiration rates of new (Rnew, g C d,1) and old C (Rold, g C d,1) were assessed by 13CO2 labelling and gas exchange measurements. ,,Specific respiration rate of old C (rold, g C g,1 C d,1) decreased exponentially with increasing shoot biomass, but was not affected by the instantaneous relative growth rate (,wi). The growth coefficient g (Rnew: An) was c. 0.32. In the most severely shaded subordinate plants, g was < 0.2, but low g stimulated rold. The contribution of Rnew to total respiraton (fR, new) and the carbon use efficiency CUE (1 , R/(An +Rnew)) were c. 0.68 and 0.62 for ,wi > 0.1, respectively. For ,wi < 0.1, fR, new and CUE decreased with decreasing ,wi in both dominant and subordinate plants. ,,The results suggest that Rold was closely related to maintenance, whereas Rnew was primarily involved in growth. [source] Limitations to CO2 assimilation in ozone-exposed leaves of Plantago majorNEW PHYTOLOGIST, Issue 1 2002Y. Zheng Summary ,,The potential limitations on net leaf carbon assimilation imposed by stomatal conductance, carboxylation velocity, capacity for ribulose 1,5-bisphosphate regeneration and triose phosphate ultilization rate were derived from steady-state gas exchange measurements made over the life-span of two leaves on plants of an ,O3 -sensitive' population of Plantago major grown at contrasting atmospheric O3 concentrations. ,,Parallel measurements of chlorophyll fluorescence were used to monitor changes in the quantum efficiency of PSII photochemistry, and in vitro measurements of Rubisco activity were made to corroborate modelled gas exchange data. ,,Data indicated that a loss of Rubisco was predominantly responsible for the decline in CO2 assimilation observed in O3 -treated leaves. The quantum efficiency of PSII was unchanged by O3 exposure. ,,Stomatal aperture declined in parallel with CO2 assimilation in O3 -treated plants, but this did not account for the observed decline in photosynthesis. Findings suggested that O3 -induced shifts in stomatal conductance result from ,direct' effects on the stomatal complex as well as ,indirect effects' mediated through changes in intercellular CO2 concentration. Leaves on the same plant exposed to equivalent levels of O3 showed striking differences in their response to the pollutant. [source] Carbon use efficiency depends on growth respiration, maintenance respiration, and relative growth rate.PLANT CELL & ENVIRONMENT, Issue 9 2003A case study with lettuce ABSTRACT Carbon use efficiency (CUE, the ratio between the amount of carbon incorporated into dry matter to the amount of carbon fixed in gross photosynthesis) is an important parameter in estimating growth rate from photosynthesis data or models. It previously has been found to be relatively constant among species and under different environmental conditions. Here it is shown that CUE can be expressed as a function of the relative growth rate (rGR) and the growth (gr) and maintenance respiration coefficients (mr): 1/CUE = 1 + gr + mr/rGR. Net daily carbon gain (Cdg), rGR, and CUE were estimated from whole-plant gas exchange measurements on lettuce (Lactuca sativa L.) ranging from 24 to 66 d old. Carbon use efficiency decreased from 0.6 to 0.2 with increasing dry mass, but there was no correlation between CUE and Cdg. The decrease in CUE with increasing dry mass was correlated with a simultaneous decrease in rGR. From the above equation, gr and mr were estimated to be 0.48 mol mol,1 and 0.039 g glucose g,1 dry matter d,1, respectively. Based on the gr estimate, the theoretical upper limit for CUE of these plants was 0.68. The importance of maintenance respiration in the carbon balance of the plants increased with increasing plant size. Maintenance accounted for 25% of total respiration in small plants and 90% in large plants. [source] Thermographic visualization of cell death in tobacco and ArabidopsisPLANT CELL & ENVIRONMENT, Issue 1 2001L. Chaerle ABSTRACT Pending cell death was visualized by thermographic imaging in bacterio-opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) (Chaerle et al. 1999Nature Biotechnology 17, 813,816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco,TMV interaction (Chaerle et al. 1999), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant. [source] Substrate oxidation and retention in pigs and poultryANIMAL SCIENCE JOURNAL, Issue 2 2002André CHWALIBOG ABSTRACT A model combining data from gas exchange measurements with nutrient balances, demonstrating energy transfer between the pools of protein, carbohydrate and fat and their partition in the body, is described. Data from energy metabolism experiments with growing pigs and laying hens is incorporated into the model in order to illustrate methods of calculations and interpretations of the model. The experiments with pigs were carried out with growing pigs (20,100 kg) measured alternately on high (ad libitum) and low (near maintenance) feed levels on diets with low or high fat concentration. When energy intake from digested carbohydrate covered the requirements for growth, heat from oxidation of carbohydrate contributed 85,90% to the total heat production, while there was no net oxidation of fat. When the intake of digested carbohydrate was not sufficient to cover requirements, fat was mobilized from the body and oxidized. Energy from oxidation of carbohydrate was in all measurements below the energy in the carbohydrate pool, indicating transfer of energy from carbohydrate to fat metabolism in the process of de novo lipogeneis. The experiments with hens were carried out with 62 hens during the laying period from 26 to 47 weeks of age. The hens originated from two strains (A and B); they were kept in battery cages either individually or 3 hens/cage and fed ad libitum with an identical commercial diet. The partition of the protein pool between oxidation and retention was not influenced by the housing system. However, the genetic origin of hens effected protein utilization with relatively lower oxidation and higher retention in Strain B. The main part of the carbohydrate pool was oxidized (45,60%), but the hens kept individually oxidized more carbohydrate than those kept 3 hens/cage. Further, there were significant differences between the strains. Generally, about half of the fat pool originated from de novo lipogenesis from carbohydrate, indicating the importance of this process for fat retention in eggs. Fat oxidation depended on the energy supply from carbohydrate, hence with higher use of carbohydrate for oxidation in Strain B less fat was oxidized and more was used for fat synthesis. The presented results indicate that by combining results from gas exchange measurements with nitrogen and energy balances it is possible to evaluate the contribution of nutrients to the oxidative processes and the energy transfer between substrate pools. [source] Photosynthesis light curves: a method for screening water deficit resistance in the model legume Medicago truncatulaANNALS OF APPLIED BIOLOGY, Issue 3 2009C. Nunes Abstract The photosynthetic performance of two transgenic Medicago truncatula lines engineered for water deficit (WD) resistance and a non-transformed line was assessed in a growth chamber experiment in well-watered, WD and stress recovery conditions. Direct gas exchange measurements showed that the transgenic plants had lower photosynthetic rates under well-hydrated conditions when compared to the non-transformed line. Photosynthesis light curves confirmed this difference but more importantly showed a progressive change in photosynthetic behaviour with intensity of dehydration. Dehydration led to sharp decreases of maximum photosynthesis (Amax), photosynthetic apparent quantum yield (,) and apparent light compensation point. The recovery rates showed that all plant lines had a similar capacity to regain control photosynthetic values. Furthermore, results suggested that light was more limiting for photosynthesis than atmospheric CO2 concentration. The results are discussed in terms of the use of photosynthesis light response curves as a non-destructive and expeditious approach to select M. truncatula transformants with improved WD resistance. [source] | ||||||||||