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CO2 Assimilation (co2 + assimilation)
Kinds of CO2 Assimilation Terms modified by CO2 Assimilation Selected AbstractsCarbon dioxide assimilation by a wetland sedge canopy exposed to ambient and elevated CO2: measurements and model analysisFUNCTIONAL ECOLOGY, Issue 2 2003D. P. Rasse Summary 1The wetland sedge Scirpus olneyi Gray displays fast rates of CO2 assimilation and responds positively to increased atmospheric CO2 concentration. The present study was aimed at identifying the ecophysiological traits specific to S. olneyi that drive these CO2 -assimilation patterns under ambient and elevated CO2 conditions. 2The net ecosystem exchange (NEE) of CO2 between S. olneyi communities and the atmosphere was measured in open-top chambers. 3We developed a new mechanistic model for S. olneyi communities based on published ecophysiological data and additional measurements of photosynthetic parameters. 4Our NEE measurements confirmed that S. olneyi communities have a high rate of summertime CO2 assimilation, with noontime peaks reaching 40 µmol CO2 m,2 ground s,1 on productive summer days, and that elevated CO2 increased S. olneyi CO2 assimilation by c. 35,40%. 5Using S. olneyi -specific ecophysiological parameters, comparison with measured NEE showed that the model accurately simulated these high rates of CO2 uptake under ambient or elevated CO2. 6The model pointed to the Rubisco capacity of Scirpus leaves associated with their high total nitrogen content as the primary explanation for the high rates of CO2 assimilation, and indicated that the vertical-leaf canopy structure of S. olneyi had comparatively little influence on CO2 assimilation. [source] Relative importance of microhabitat, plant form and photosynthetic physiology to carbon gain in two alpine herbsFUNCTIONAL ECOLOGY, Issue 2 2001M. J. Germino Abstract 1.,The effects of microhabitat and plant form on sunlight interception, leaf temperatures, frost occurrence and photosynthesis were evaluated for Caltha leptosepala DC and Erythronium grandiflorum Pursh. Both plants are perennials that commonly emerge from alpine snowbanks where the combination of cool temperatures and strong sunlight is among the most extreme for vascular plants. 2., Caltha leptosepala occurred in microsites where colder air accumulates, and has larger, less inclined and more densely clustered leaves compared to E. grandiflorum (which has two steeply inclined leaves). 3.,These differences in microsite and plant form led to leaf temperatures below 0 °C on 70% of nights during the summer growth season in C. leptosepala, compared to only 38% in E. grandiflorum. Leaves of C. leptosepala warmed more slowly on mornings following frosts compared to E. grandiflorum, due to less aerodynamic coupling between leaf and air temperature, and also a 45% smaller ratio of sunlit to total leaf area due to mutual shading among leaves. 4.,As a result, night frost did not affect subsequent CO2 assimilation (A) in E. grandiflorum, while frostless nights and warmer mornings led to 35% greater A in C. leptosepala in the early morning. 5.,There were no appreciable differences in the temperature and light response of photosynthesis between the two species. The apparent quantum yield of A declined only ,8% in both species following frost and exposure to strong sunlight, indicating little adjustment of photosynthetic physiology. 6.,Greater daily carbon gain probably occurs for E. grandiflorum because of its plant form and microclimate, rather than differences in photosynthetic physiology. [source] Interactive effects of water table and precipitation on net CO2 assimilation of three co-occurring Sphagnum mosses differing in distribution above the water tableGLOBAL CHANGE BIOLOGY, Issue 3 2009BJORN J. M. ROBROEK Abstract Sphagnum cuspidatum, S. magellanicum and S. rubellum are three co-occurring peat mosses, which naturally have a different distribution along the microtopographical gradient of the surface of peatlands. We set out an experiment to assess the interactive effects of water table (low: ,10 cm and high: ,1 cm) and precipitation (present or absent) on the CO2 assimilation and evaporation of these species over a 23-day period. Additionally, we measured which sections of the moss layer were responsible for light absorption and bulk carbon uptake. Thereafter, we investigated how water content affected carbon uptake by the mosses. Our results show that at high water table, CO2 assimilation of all species gradually increased over time, irrespective of the precipitation. At low water table, net CO2 assimilation of all species declined over time, with the earliest onset and highest rate of decline for S. cuspidatum. Precipitation compensated for reduced water tables and positively affected the carbon uptake of all species. Almost all light absorption occurred in the first centimeter of the Sphagnum vegetation and so did net CO2 assimilation. CO2 assimilation rate showed species-specific relationships with capitulum water content, with narrow but contrasting optima for S. cuspidatum and S. rubellum. Assimilation by S. magellanicum was constant at a relatively low rate over a broad range of capitulum water contents. Our study indicates that prolonged drought may alter the competitive balance between species, favoring hummock species over hollow species. Moreover, this study shows that precipitation is at least equally important as water table drawdown and should be taken into account in predictions about the fate of peatlands with respect to climate change. [source] Increased leaf area dominates carbon flux response to elevated CO2 in stands of Populus deltoides (Bartr.)GLOBAL CHANGE BIOLOGY, Issue 5 2005Ramesh Murthy Abstract We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leaf- and stand-level CO2 exchange in model 3-year-old coppiced cottonwood (Populus deltoides Bartr.) plantations using the large-scale, controlled environments of the Biosphere 2 Laboratory. A short-term experiment was imposed on top of continuing, long-term CO2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6,14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25,39%). When system gross CO2 assimilation was corrected for leaf area, system net CO2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO2. The increases were mainly as a result of the larger leaf area developed during growth at high CO2, before the short-term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO2 under all treatments. Leaf-level net CO2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leaf- and stand-level gross CO2 exchange indicated that the limitation of assimilation because of canopy light environment (in well-irrigated stands; ratio of leaf : stand=3.2,3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand=0.8,1.3). These observations enabled a good prediction of whole stand assimilation from leaf-level data under water-stressed conditions; the predictive ability was less under well-watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI. [source] Lack of Interaction between Extreme High-Temperature Events at Vegetative and Reproductive Growth Stages in WheatJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 3 2003B. Wollenweber Abstract Increased climatic variability and more frequent episodes of extreme conditions may result in crops being exposed to more than one extreme temperature event in a single growing season and could decrease crop yields to the same extent as changes in mean temperature. The developmental stage of the crop exposed to increased temperatures will determine the severity of possible damage experienced by the plant. It is not known whether or not the damaging effects of heat episodes occurring at different phenological stages are additive. In the present study, the interaction of high-temperature events applied at the stages of double ridges and anthesis in Triticum aestivum (L.) cv. Chablis was investigated. Biomass accumulation of control plants and that of plants experiencing high temperatures during the double-ridge stage were similar and were reduced by 40 % when plants were subjected to a heat event at anthesis. Grain number on the main and side tillers declined by 41 %, and individual grain weight declined by 45 % with heat stress applied at the double-ridge stage and anthesis or at anthesis alone. The harvest index was reduced from 0.53 to 0.33. Nitrogen contents in leaves were reduced by 10 % at the double-ridge stage and by 25 % at anthesis. The maximum rates of CO2 assimilation increased with heat stress at the double-ridge stage and higher rates were maintained throughout the growing season. The results clearly indicate that an extreme heat event at the double-ridge stage does not affect subsequent growth or the response of wheat to heat stress at anthesis. [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] Phosphorus alleviates aluminum-induced inhibition of growth and photosynthesis in Citrus grandis seedlingsPHYSIOLOGIA PLANTARUM, Issue 3 2009Huan-Xin Jiang Limited data are available on the effects of phosphorus (P) and aluminum (Al) interactions on Citrus spp. growth and photosynthesis. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 50, 100, 250 and 500 ,M KH2PO4× 0 and 1.2 mM AlCl3· 6H2O. Thereafter, P and Al in roots, stems and leaves, and leaf chlorophyll (Chl), CO2 assimilation, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Chl a fluorescence (OJIP) transients were measured. Under Al stress, P increased root Al, but decreased stem and leaf Al. Shoot growth is more sensitive to Al than root growth, CO2 assimilation and OJIP transients. Al decreased CO2 assimilation, Rubisco activity and Chl content, whereas it increased or did not affect intercellular CO2 concentration. Al affected CO2 assimilation more than Rubisco and Chl under 250 and 500 ,M P. Al decreased root, stem and leaf P, leaf maximum quantum yield of primary photochemistry (Fv/Fm) and total performance index (PItot,abs), but increased leaf minimum fluorescence (Fo), relative variable fluorescence at K- and I-steps. P could alleviate Al-induced increase or decrease for all these parameters. We conclude that P alleviated Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from photosystem II (PSII) donor side up to the reduction of end acceptors of photosystem I (PSI), thus preventing photosynthesis inhibition through increasing Al immobilization in roots and P level in roots and shoots. Al-induced impairment of the whole photosynthetic electron transport chain may be associated with growth inhibition. [source] Effects of prolonged restriction in water supply on photosynthesis, shoot development and storage root yield in sweet potatoPHYSIOLOGIA PLANTARUM, Issue 1 2008Philippus Daniel Riekert Van Heerden Besides the paucity of information on the effects of drought stress on photosynthesis and yield in sweet potato [Ipomoea batatas (L.) Lam.], available reports are also contradictory. The aim of this study was to shed light on the effects of long-term restricted water supply on shoot development, photosynthesis and storage root yield in field-grown sweet potato. Experiments were conducted under a rainout shelter where effects of restricted water supply were assessed in two varieties (Resisto and A15). Large decreases in stomatal conductance occurred in both varieties after 5 weeks of treatment. However, continued measurements revealed a large varietal difference in persistence of this response and effects on CO2 assimilation. Although restricted water supply decreased leaf relative water content similarly in both varieties, the negative effects on stomatal conductance disappeared with time in A15 (indicating high drought acclimation capacity) but not in Resisto, thus leading to inhibition of CO2 assimilation in Resisto. Chlorophyll a fluorescence measurements, and the relationship between stomatal conductance, intercellular CO2 concentration and CO2 assimilation rate, indicated that drought stress inhibited photosynthesis primarily through stomatal closure. Although yield loss was considerably larger in Resisto, it was also reduced by up to 60% in A15, even though photosynthesis, expressed on a leaf area basis, was not inhibited in this variety. In A15 yield loss appears to be closely associated with decreased aboveground biomass accumulation, whereas in Resisto, combined effects on biomass accumulation and photosynthesis per unit leaf area are indicated, suggesting that research aimed at improving drought tolerance in sweet potato should consider both these factors. [source] The role of low soil temperature in the inhibition of growth and PSII function during dark chilling in soybean genotypes of contrasting tolerancePHYSIOLOGIA PLANTARUM, Issue 1 2007Abram J. Strauss Dark chilling affects growth and yield of warm-climate crops such as soybean [Glycine max (L.) Merr.]. Several studies have investigated chilling-stress effects on photosynthesis and other aspects of metabolism, but none have compared effects of whole-plant chilling (WPC; shoots and roots) with that of aboveground chilling in legumes. This is important because low root temperatures might induce additional constraints, such as inhibition of N2 fixation, thereby aggravating chilling-stress symptoms. Effects of dark chilling on PSII, shoot growth, leaf ureide content and photosynthetic capacity were studied in two soybean genotypes, Highveld Top (chilling tolerant) and PAN809 (chilling sensitive), in experiments comparing effects of WPC with that of shoot chilling (SC). Both treatments inhibited shoot growth in PAN809 but not Highveld Top. Also, WPC in PAN809 caused a decrease in leaf ureide content followed by severe chlorosis and alterations in O-J-I-P fluorescence-rise kinetics, distinct from SC. A noteworthy difference was the appearance of a ,K peak in the O-J-I-P fluorescence rise in response to WPC. These genotypic and treatment differences also reflected in the degree of inhibition of CO2 assimilation rates. The appearance of a ,K peak, coupled with growth inhibition, reduced ureide content, chlorosis and lower CO2 assimilation rates, provides mechanistic information about how WPC might have aggravated chilling-stress symptoms in PAN809. We introduce a model explaining how chilling soil temperatures might trigger N-limitation in sensitive genotypes and how characteristic changes in O-J-I-P fluorescence-rise kinetics are linked to changes in carbon and nitrogen metabolism. [source] Effects of long-term chilling on growth and photosynthesis of the C4 gramineae Paspalum dilatatumPHYSIOLOGIA PLANTARUM, Issue 1 2003Ana M. Cavaco Dallis grass (Paspalum dilatatum Poir.) is a C4/NADP-ME gramineae, previously classified as semi-tolerant to cold, although a complete study on this species acclimation process under a long-term chilling and controlled environmental conditions has never been conducted. In the present work, plants of the variety Raki maintained at 25/18°C (day/night) (control) were compared with plants under a long-term chilling at 10/8°C (day/night) (cold-acclimated) in order to investigate how growth and carbon assimilation mechanisms are engaged in P. dilatatum chilling tolerance. Although whole plant mean relative growth rate (mean RGR) and leaf growth were significantly decreased by cold exposure, chilling did not impair plant development nor favour the investment in biomass below ground. Cold-acclimated P. dilatatum cv. Raki had a lower leaf chlorophyll content, but a higher photosynthetic capacity at optimal temperatures, its range being shifted to lower values. Associated with this higher capacity to use the reducing power in CO2 assimilation, cold-acclimated plants further showed a higher capacity to oxidize the primary stable quinone electron acceptor of PSII, QA. The activity and activation of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were not significantly affected by the long-term chilling. Cold-acclimated P. dilatatum cv. Raki apparently showed a lower transfer of excitation energy from the light-harvesting complex of photosystem II to the respective reaction centre and enhancement of radiationless energy-dissipating mechanisms at suboptimal temperatures. Overall, long-term chilling resulted in several effects that comprise responses with an intermediate character of both chilling-tolerant and ,sensitive plants, which seem to play a significant role in the survival and acclimation of P. dilatatum cv. Raki at low temperature. [source] The temperature response of photosynthesis in tobacco with reduced amounts of RubiscoPLANT CELL & ENVIRONMENT, Issue 4 2008DAVID S. KUBIEN ABSTRACT The reasons for the decline in net CO2 assimilation (A) above its thermal optimum are controversial. We tested the hypothesis that increasing the ratio of Rubisco activase to Rubisco catalytic site concentration would increase the activation state of Rubisco at high temperatures. We measured photosynthetic gas exchange, in vivo electron transport (J) and the activation state of Rubisco between 15 and 45 °C, at 38 and 76 Pa ambient CO2, in wild-type (WT) and anti- rbcS tobacco. The Rubisco content of the anti- rbcS lines was 30% (S7-1) or 6% (S7-2) of WT, but activase levels were the same in the three genotypes. Anti- rbcS plants had lower A than WT at all temperatures, but had a similar thermal optimum for photosynthesis as WT at both CO2 levels. In WT plants, Rubisco was fully activated at 32 °C, but the activation state declined to 64% at 42 °C. By contrast, the activation state of Rubisco was above 90% in the S7-1 line, between 15 and 42 °C. Both A and J declined about 20% from Topt to the highest measurement temperatures in WT and the S7-1 line, but this was fully reversed after a 20 min recovery at 35 °C. At 76 Pa CO2, predicted rates of RuBP regeneration-limited photosynthesis corresponded with measured A in WT tobacco at all temperatures, and in S7-1 tobacco above 40 °C. Our observations are consistent with the hypothesis that the high temperature decline in A in the WT is because of an RuBP regeneration limitation, rather than the capacity of Rubisco activase to maintain high Rubisco activation state. [source] Transgenic approaches to manipulate the environmental responses of the C3 carbon fixation cyclePLANT CELL & ENVIRONMENT, Issue 3 2006CHRISTINE A. RAINES ABSTRACT The limitation to photosynthetic CO2 assimilation in C3 plants in hot, dry environments is dominated by ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) because CO2 availability is restricted and photorespiration is stimulated. Using a combination of genetic engineering and transgenic technology, three approaches to reduce photorespiration have been taken; two of these focused on increasing the carboxylation efficiency of Rubisco either by reducing the oxygenase reaction directly or by manipulating the Rubisco enzyme by concentrating CO2 in the region of Rubisco through the introduction of enzymes of the C4 pathway. The third approach attempted to reduce photorespiration directly by manipulation of enzymes in this pathway. The progress in each of these areas is discussed, and the most promising approaches are highlighted. Under saturating CO2 conditions, Rubisco did not limit photosynthesis, and limitation shifted to ribulose bisphosphate (RuBP) regeneration capacity of the C3 cycle. Transgenic analysis was used to identify the specific enzymes that may be targets for improving carbon fixation, and the way this may be exploited in the high CO2 future is considered. [source] A coupled model of stomatal conductance, photosynthesis and transpirationPLANT CELL & ENVIRONMENT, Issue 7 2003A. TUZET ABSTRACT A model that couples stomatal conductance, photosynthesis, leaf energy balance and transport of water through the soil,plant,atmosphere continuum is presented. Stomatal conductance in the model depends on light, temperature and intercellular CO2 concentration via photosynthesis and on leaf water potential, which in turn is a function of soil water potential, the rate of water flow through the soil and plant, and on xylem hydraulic resistance. Water transport from soil to roots is simulated through solution of Richards' equation. The model captures the observed hysteresis in diurnal variations in stomatal conductance, assimilation rate and transpiration for plant canopies. Hysteresis arises because atmospheric demand for water from the leaves typically peaks in mid-afternoon and because of uneven distribution of soil matric potentials with distance from the roots. Potentials at the root surfaces are lower than in the bulk soil, and once soil water supply starts to limit transpiration, root potentials are substantially less negative in the morning than in the afternoon. This leads to higher stomatal conductances, CO2 assimilation and transpiration in the morning compared to later in the day. Stomatal conductance is sensitive to soil and plant hydraulic properties and to root length density only after approximately 10 d of soil drying, when supply of water by the soil to the roots becomes limiting. High atmospheric demand causes transpiration rates, LE, to decline at a slightly higher soil water content, ,s, than at low atmospheric demand, but all curves of LE versus ,s fall on the same line when soil water supply limits transpiration. Stomatal conductance cannot be modelled in isolation, but must be fully coupled with models of photosynthesis/respiration and the transport of water from soil, through roots, stems and leaves to the atmosphere. [source] Improved temperature response functions for models of Rubisco-limited photosynthesisPLANT CELL & ENVIRONMENT, Issue 2 2001C. J. Bernacchi ABSTRACT Predicting the environmental responses of leaf photosynthesis is central to many models of changes in the future global carbon cycle and terrestrial biosphere. The steady-state biochemical model of C3 photosynthesis of Farquhar et al. (Planta 149, 78,90, 1980) provides a basis for these larger scale predictions; but a weakness in the application of the model as currently parameterized is the inability to accurately predict carbon assimilation at the range of temperatures over which significant photosynthesis occurs in the natural environment. The temperature functions used in this model have been based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Since photosynthetic rates are often Rubisco-limited (ribulose, 1-5 bisphosphate carboxylase/oxygenase) under natural steady-state conditions, inaccuracies in the functions predicting Rubisco kinetic properties at different temperatures may cause significant error. In this study, transgenic tobacco containing only 10% normal levels of Rubisco were used to measure Rubisco-limited photosynthesis over a large range of CO2 concentrations. From the responses of the rate of CO2 assimilation at a wide range of temperatures, and CO2 and O2 concentrations, the temperature functions of Rubisco kinetic properties were estimated in vivo. These differed substantially from previously published functions. These new functions were then used to predict photosynthesis in lemon and found to faithfully mimic the observed pattern of temperature response. There was also a close correspondence with published C3 photosynthesis temperature responses. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10,40 °C) necessary for predicting carbon uptake by terrestrial C3 systems. [source] Growth in elevated CO2 protects photosynthesis against high-temperature damagePLANT CELL & ENVIRONMENT, Issue 6 2000Daniel R. Taub ABSTRACT We present evidence that plant growth at elevated atmospheric CO2 increases the high-temperature tolerance of photosynthesis in a wide variety of plant species under both greenhouse and field conditions. We grew plants at ambient CO2 (~ 360 ,mol mol,1) and elevated CO2 (550,1000 ,mol mol,1) in three separate growth facilities, including the Nevada Desert Free-Air Carbon Dioxide Enrichment (FACE) facility. Excised leaves from both the ambient and elevated CO2 treatments were exposed to temperatures ranging from 28 to 48 °C. In more than half the species examined (4 of 7, 3 of 5, and 3 of 5 species in the three facilities), leaves from elevated CO2 -grown plants maintained PSII efficiency (Fv/Fm) to significantly higher temperatures than ambient-grown leaves. This enhanced PSII thermotolerance was found in both woody and herbaceous species and in both monocots and dicots. Detailed experiments conducted with Cucumis sativus showed that the greater Fv/Fm in elevated versus ambient CO2 -grown leaves following heat stress was due to both a higher Fm and a lower Fo, and that Fv/Fm differences between elevated and ambient CO2 -grown leaves persisted for at least 20 h following heat shock. Cucumis sativus leaves from elevated CO2 -grown plants had a critical temperature for the rapid rise in Fo that averaged 2·9 °C higher than leaves from ambient CO2 -grown plants, and maintained a higher maximal rate of net CO2 assimilation following heat shock. Given that photosynthesis is considered to be the physiological process most sensitive to high-temperature damage and that rising atmospheric CO2 content will drive temperature increases in many already stressful environments, this CO2 -induced increase in plant high-temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century. [source] Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)PLANT CELL & ENVIRONMENT, Issue 4 2000M. M. Gonzalez-Real ABSTRACT This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO2 assimilation (Al) and total nitrogen content (Nl) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO2 partial pressure (pa) at saturating photosynthetic photon flux density (I about 1000 ,mol m,2 s,1) and (ii) to saturating CO2 partial pressure (pa about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20,38 °C). A biochemical model of leaf photosynthesis relating Al to intercellular CO2 partial pressure (pi) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (Vlm) and the maximum rate of electron transport (Jm). The results indicated that rose leaves growing at the top of the canopy had higher values of Jm and Vlm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, Nl, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non-photosynthetic nitrogen, Nb, varied from 76 mmolN m,2leaf (layer 1) to 60 mmolN m,2leaf (layer 4), representing a large fraction of Nl (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (Np=Nl,Nb) and I profiles supports the hypothesis that rose leaves acclimate to the time-integrated absorbed I. The relationships between I and Np, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer. [source] Utilization of O2 in the metabolic optimization of C4 photosynthesisPLANT CELL & ENVIRONMENT, Issue 1 2000J. P. Maroco ABSTRACT The combined effects of O2 on net rates of photosynthesis, photosystem II activity, steady-state pool size of key metabolites of photosynthetic metabolism in the C4 pathway, C3 pathway and C2 photorespiratory cycle and on growth were evaluated in the C4 species Amaranthus edulis and the C3 species Flaveria pringlei. Increasing O2 reduced net CO2 assimilation in F. pringlei due to an increased flux of C through the photorespiratory pathway. However, in A. edulis increasing O2 up to 5,10% stimulated photosynthesis. Analysis of the pool size of key metabolites in A. edulis suggests that while there is some O2 dependent photorespiration, O2 is required for maximizing C4 cycle activity to concentrate CO2 in bundle sheath cells. Therefore, the response of net photosynthesis to O2 in C4 plants may result from the balance of these two opposing effects. Under 21 versus 5% O2, growth of A. edulis was stimulated about 30% whereas that of F. pringlei was inhibited about 40%. [source] Photochemical reflectance index as a mean of monitoring early water stressANNALS OF APPLIED BIOLOGY, Issue 1 2010V. Sarlikioti Water stress in plants affects a number of physiological processes such as photosynthetic rate, stomatal conductance as well as the operating efficiency of photosystem II (PSII) and non-photochemical quenching (NPQ). Photochemical reflectance index (PRI) is reported to be sensitive to changes in xanthophyll cycle which occur during stress and could possibly be used to monitor changes in the parameters mentioned before. Therefore, the aim of this study was to evaluate the use of PRI as an early water stress indicator. Water stress treatment was imposed in a greenhouse tomato crop. CO2 assimilation, stomatal conductance, light-adapted and dark-adapted fluorescence as well as PRI and relative water content (RWCs%) of the rooting medium were repeatedly measured. The same measurements were also performed on well-irrigated plants that acted as a reference. The experiment was repeated in four consecutive weeks. Results showed a strong correlation between RWCs% and photosynthetic rate, stomatal conductance, NPQ and operating efficiency of PSII but not with PRI when the whole dataset was considered. Nevertheless, more detailed analysis revealed that PRI gave a good correlation when light levels were above 700 µmol m,2 s,1. Therefore, the use of PRI as a water stress indicator cannot be independent of the ambient light conditions. [source] Stoichiometric model and metabolic flux analysis for Leptospirillum ferrooxidansBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010M.P. Merino Abstract A metabolic model for Leptospirillum ferrooxidans was developed based on the genomic information of an analogous iron oxidizing bacteria and on the pathways of ferrous iron oxidation, nitrogen and CO2 assimilation based on experimental evidence for L. ferrooxidans found in the literature. From this metabolic reconstruction, a stoichiometric model was built, which includes 86 reactions describing the main catabolic and anabolic aspects of its metabolism. The model obtained has 2 degrees of freedom, so two external fluxes were estimated to achieve a determined and observable system. By using the external oxygen consumption rate and the generation flux biomass as input data, a metabolic flux map with a distribution of internal fluxes was obtained. The results obtained were verified with experimental data from the literature, achieving a very good prediction of the metabolic behavior of this bacterium at steady state. Biotechnol. Bioeng. 2010;107:696,706. © 2010 Wiley Periodicals, Inc. [source] | ||||||||||