Arginine decarboxylase as the source of putrescine for tobacco alkaloids

The putrescine which forms a part of nicotine and other pyrrolidine alkaloids is generally assumed to arise through the action of ornithine decarboxylase (ODC). However, we have previously noted that changes in the activity of arginine decarboxylase (ADC), an alternate source ofputrescine, parallel changes in tissue alkaloids, while changes in ODC activity do not. This led us to undertake experiments to permit discrimination between ADC and ODC as enzymatic sources of putrescine destined for alkaloids. Two kinds of evidence presented here support a major role for ADC in the generation ofputrescine going into alkaloids: (a) A specific ‘suicide inhibitor’ of ADC effectively inhibits the biosynthesis of nicotine and nornicotine in tobacco callus, while the analogous inhibitor of ODC is less effective, and (b) the flow of ¹⁴C from uniformly labelled arginine into nicotine is much more efficient than that from ornithine.     

Food security and climate change: on the potential to adapt global crop production by active selection to rising atmospheric carbon dioxide

Agricultural production is under increasing pressure by global anthropogenic changes, including rising population, diversion of cereals to biofuels, increased protein demands and climatic extremes. Because of the immediate and dynamic nature of these changes, adaptation measures are urgently needed to ensure both the stability and continued increase of the global food supply. Although potential adaption options often consider regional or sectoral variations of existing risk management (e.g. earlier planting dates, choice of crop), there may be a global-centric strategy for increasing productivity. In spite of the recognition that atmospheric carbon dioxide (CO(2)) is an essential plant resource that has increased globally by approximately 25 per cent since 1959, efforts to increase the biological conversion of atmospheric CO(2) to stimulate seed yield through crop selection is not generally recognized as an effective adaptation measure. In this review, we challenge that viewpoint through an assessment of existing studies on CO(2) and intraspecific variability to illustrate the potential biological basis for differential plant response among crop lines and demonstrate that while technical hurdles remain, active selection and breeding for CO(2) responsiveness among cereal varieties may provide one of the simplest and direct strategies for increasing global yields and maintaining food security with anthropogenic change.     

Rising atmospheric carbon dioxide concentration and the future of C4 crops for food and fuel

Crops with the C₄ photosynthetic pathway are vital to global food supply, particularly in the tropical regions where human well-being and agricultural productivity are most closely linked. While rising atmospheric [CO₂] is the driving force behind the greater temperatures and water stress, which threaten to reduce future crop yields, it also has the potential to directly benefit crop physiology. The nature of C₄ plant responses to elevated [CO₂] has been controversial. Recent evidence from free-air CO₂ enrichment (FACE) experiments suggests that elevated [CO₂] does not directly stimulate C₄ photosynthesis. Nonetheless, drought stress can be ameliorated at elevated [CO₂] as a result of lower stomatal conductance and greater intercellular [CO₂]. Therefore, unlike C₃ crops for which there is a direct enhancement of photosynthesis by elevated [CO₂], C₄ crops will only benefit from elevated [CO₂] in times and places of drought stress. Current projections of future crop yields have assumed that rising [CO₂] will directly enhance photosynthesis in all situations and, therefore, are likely to be overly optimistic. Additional experiments are needed to evaluate the extent to which amelioration of drought stress by elevated [CO₂] will improve C₄ crop yields for food and fuel over the range of C₄ crop growing conditions and genotypes.     

Facility for studying the effects of elevated carbon dioxide concentration and increased temperature on crops

The requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi-controlled plant growth facility is described which allows the study of elevated CO₂ and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO₂ concentrations of 363 and 692 cm³ m^?3 for targets of 350 and 700 cm³ m^?3 respectively. Temperatures were set to follow outside ambient or outside ambient +4°C, and hourly means were within 0.5°C of the target for 92% of the time for target temperatures greater than 6°C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifieal light with natural photoperiod) was 2% greater than the total measured outside over the same period.     

Light, temperature and nutrients as factors in photosynthetic adjustment to an elevated concentration of carbon dioxide

The short-term stimulation of the net rate of carbon dioxide exchange of leaves by elevated concentrations of CO₂ usually observed in C₃ plants sometimes does not persist. Experiments were conducted to test whether the patterns of response to the environment during growth were consistent with the hypotheses that photosynthetic adjustment to elevated CO₂ concentration is due to (1) feedback inhibition or (2) nutrient stress. Soybean [Glycine max (L.) Merr. cv. Williams] and sugar beet (Best vulgaris L. cv. Mono Hye-4) were grown from seed at 350 and 700 μl^? CO₂, at 20 and 25°C, at a photon flux density of 0.5 and 1.0 mmol m^?2 S^?1 and with three nutrient regimes until the third trifoliolate leaf of soybean or the sixth leaf of sugar beet had finished expanding. Net rates of CO₂ exchange of the most recently expanded leaves were then measured at both 350 and 700 μl 1^?1 CO₂. Plants grown at the elevated CO₂ concentration had net rates of leaf CO₂ exchange which were reduced by 33% in sugar beet and 23% in soybean when measured at 350 μl 1^?1 CO₂ and when averaged over all treatments. Negative photosynthetic adjustment to elevated CO₂ concentration was not greater at 20 than at 25°C, was not greater at a photon flux density of 1.0 than at 0.5 mmol m^?2 S^?1 and was not greater with limiting nutrients. Furthermore, in soybean, negative photosynthetic adjustment could be induced by a single night at elevated CO₂ concentration, with net rates of CO₂ exchange the next day equal to those of leaves of plants grown from seed at the elevated concentration of CO₂. These patterns do not support either the feedback-inhibition or the nutrient-stress hypothesis of photosynthetic adjustment to elevated concentrations of CO₂.     

Exhaled air temperature as a function of ambient temperature in flying and resting ducks

Exhaled air temperature (T _exh) has a paramount effect on respiratory water loss during flight. For migratory birds, low T _exh potentially reduces water loss and increases flight range. However, only three studies provide empirical data on T _exh during flight. The aim of this study was to record T _exh of birds during rest and flight at a range of controlled ambient temperatures (T _amb). One wigeon and two teal flew a total of 20 times in a wind tunnel at T _amb ranging from 1° to 24°C. T _exh during flight did not differ between the two species and was strongly correlated with T _amb (T _exh=1.036 T _amb + 13.426; R²=0.58). In addition, body temperature had a weak positive effect on T _exh. At a given T _amb, T _exh was about 5°C higher during flight than at rest.     

Effects of doubled atmospheric carbon dioxide concentration on the responses of assimilation and conductance to humidity

Experiments were performed to determine if growth at elevated partial pressure of CO₂ altered the sensitivity of leaf water vapour conductance and rate of CO₂ assimilation to the leaf-to-air difference in the partial pressure of water vapour (Δw). Comparisons were made between plants grown and measured at 350 and 700 μPa Pa^?1 partial pressures of CO₂ for amaranth, soybean and sunflower grown in controlled environment chambers, soybean grown outdoors in pots, and orchard grass grown in field plots. In amaranth, soybean and orchard grass, both the absolute and the relative sensitivity of conductance to Δw at the leaf surface were less in plants grown and measured at the elevated CO₂. In sunflower, there was no change in the sensitivity of conductance to Δw for the two CO₂ partial pressures. Tests in soybeans and amaranth showed that the change in sensitivity resulted from elevated CO₂ during the measurement of the Δw response. Assimilation rate of CO₂ was not altered by Δw in amaranth, which has C₄ metabolism. In sunflower, the assimilation rate of plants grown and measured at elevated CO₂ was insensitive to Δw, consistent with the response of assimilation rate to intercellular CO₂ partial pressure in the prevailing range. In soybean, the sensitivity of assimilation rate to Δw was not different between CO₂ treatments, in contrast to what would be expected from the response of assimilation rate to intercellular CO₂ partial pressure.     

Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and elevated ozone concentration

Rice is arguably the most important food source on the planet and is consumed by over half of the world's population. Considerable increases in yield are required over this century to continue feeding the world's growing population. This meta-analysis synthesizes the research to date on rice responses to two elements of global change, rising atmospheric carbon dioxide concentration ([CO₂]) and rising tropospheric ozone concentration ([O₃]). On an average, elevated [CO₂] (627 ppm) increased rice yields by 23%. Modest increases in grain mass and larger increases in panicle and grain number contributed to this response. The response of rice to elevated [CO₂] varied with fumigation technique. The more closely the fumigation conditions mimicked field conditions, the smaller was the stimulation of yield by elevated [CO₂]. Free air concentration enrichment (FACE) experiments showed only a 12% increase in rice yield. The rise in atmospheric [CO₂] will be accompanied by increases in tropospheric O₃ and temperature. When compared with rice grown in charcoal-filtered air, rice exposed to 62 ppb O₃ showed a 14% decrease in yield. Many determinants of yield, including photosynthesis, biomass, leaf area index, grain number and grain mass, were reduced by elevated [O₃]. While there have been too few studies of the interaction of CO₂ and O₃ for meta-analysis, the interaction of temperature and CO₂ has been studied more widely. Elevated temperature treatments negated any enhancement in rice yield at elevated [CO₂], which suggests that identifying high temperature tolerant germplasm will be key to realizing yield benefits in the future.     

Latency of oxygen toxicity of the central nervous system in rats as a function of carbon dioxide production and partial pressure of oxygen

Oxygen toxicity of the central nervous system (CNS) can occur as convulsions and loss of consciousness, with no warning symptoms. A quantitative study of the effect of metabolic rate on sensitivity to oxygen toxicity was made in the rat. A group of 19 rats were exposed (126 exposures) to 12 combinations of four pressures (456, 507, 608 and 709 kPa) and three ambient temperatures (15, 23 and 29°C) until the appearance of the first electrical discharge (FED) preceding clinical convulsions. Carbon dioxide production (V˙CO₂) was also measured. A thermoneutral zone (mean V˙CO₂ 0.87 ml · g⁻¹ · h⁻¹) existed between the temperatures of 24 and 29°C; at temperatures lower than this, the metabolic rate increased by 1.2 to 4 times the resting level. Latency of FED decreased linearly with the increase in V˙CO₂ at all four oxygen pressures. The slopes (absolute value) and intercepts decreased with the increase in oxygen pressure. This linear relationship made possible the derivation of an equation which described latency of the FED as a function of both oxygen pressure and metabolic rate. Various environmental and other physiological factors that have been said to influence sensitivity to CNS oxygen toxicity, enhancing the effect of the partial pressure of oxygen, can be explained by their effect on metabolic rate. It is suggested that in situations where there is a risk of oxygen toxicity of the CNS, that risk would be reduced by a lower metabolic rate. Accepted: 4 May 1998     

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale

The relative stimulation of photosynthesis by elevated carbon dioxide in C₃ species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C₃ species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 °C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 – 25 °C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 °C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of increasing carbon dioxide concentration on the photosynthetic and growth stimulation of selected C4crops and weeds

Plants of six weedy species (Amaranthus retroflexus, Echinochloa crus-galli, Panicum dichotomiflorum, Setaria faberi, Setaria viridis, Sorghum halapense) and 4 crop species (Amaranthus hypochondriacus, Saccharum officinarum, Sorghum bicolor and Zea mays) possessing the C₄type of photosynthesis were grown at ambient (38 Pa) and elevated (69 Pa) carbon dioxide during early development (i.e. up to 60 days after sowing) to determine: (a) if plants possessing the C₄photosynthetic pathway could respond photosynthetically or in biomass production to future increases in global carbon dioxide and (b) whether differences exist between weeds and crops in the degree of response. Based on observations in the response of photosynthesis (measured as A, CO₂assimilation rate) to the growth CO₂condition as well as to a range of internal CO₂(C_i) concentrations, eight of ten C₄species showed a significant increase in photosynthesis. The largest and smallest increases observed were for A. retroflexus (+30%) and Z. mays (+5%), respectively. Weed species (+19%) showed approximately twice the degree of photosynthetic stimulation as that of crop species (+10%) at the higher CO₂concentration. Elevated carbon dioxide also resulted in significant increases in whole plant biomass for four C₄weeds (A. retroflexus, E. crus-galli, P. dichotomiflorum, S. viridis) relative to the ambient CO₂condition. Leaf water potentials for three selected species (A. retroflexus, A. hypochondriacus, Z. mays) indicated that differences in photosynthetic stimulation were not due solely to improved leaf water status. Data from this study indicate that C₄plants may respond directly to increasing CO₂concentration, and in the case of some C₄weeds (e.g. A. retroflexus) may show photosynthetic increases similar to those published for C₃species.     

A method for determination of carbon dioxide specific radioactivity and concentration in blood, rumen fluid, and expired air

A method is described for determining specific radioactivity and concentration of CO₂ in blood, rumen fluid, and expired air. The CO₂ of blood and rumen fluid samples is liberated selectively by 1 m phosphate buffer (pH 5.8) containing 1 mm NaN₃ and 5 mm NaF. Liberated CO₂ is quantitatively trapped in 0.3 n Ba(OH)₂, and amounts of CO₂ are determined by titration of residual hydroxide ion. The resulting BaCO₃ is solubilized with 10% EDTA in 1 m Tris (pH 9), and radioactivity is determined by liquid scintillation. For quantitative determination of expired CO₂, a measured fraction of expired air is bubbled through 0.3 n Ba(OH)₂. The amount of trapped CO₂ is determined by titrating residual hydroxide ion in an aliquot of trapping solution after BaCO₃ is precipitated by centrifugation. Radioactivity is determined by liquid scintillation spectrophotometry of ethanolamine carbamate after CO₂ is regenerated from BaCO₃ by addition of acid and quantitatively retrapped in ethanolamine.     

Invasiveness potential of Miscanthus sinensis: implications for bioenergy production in the United States

Miscanthus sinensis (Anderss.) is a perennial grass species that has been grown widely as an ornamental since the late 1800s and is now being considered for bioenergy production in the United States. With its ability to be grown from seed and tolerate cold climates, this species offers practical advantages over current cultivars of the higher‐yielding hybrid species, M.×giganteus. Yet a large‐scale release of M. sinensis for bioenergy production in colder northern regions could result in new invasions into natural areas. We show, with reference to historical records and data collected in six wild US populations of M. sinensis in 2009, that ornamental varieties of this species have a long history of localized escape in the Eastern United States, primarily within the Appalachian region. To prevent further escape and gene flow, we recommend the development of sterile or functionally sterile varieties of M. sinensis or the restriction of its usage as a donor of genetic material to new sterile cultivars of M. ×giganteus. Other appropriate precautions for new biomass varieties include experimental demonstration of low invasiveness in the target region ahead of commercial production, along with postintroduction stewardship programs.     

Carcinoma of buccal mucosa in smokeless tobacco users: a preliminary study of the use of cytology for early detection

A type of smokeless tobacco, known as Maras powder, is widely used in lieu of cigarettes in the south-eastern region of Turkey. In the present study, we evaluated cytological smears obtained from the lesion of lower lip mucosa of 80 smokeless tobacco users. There were severe epithelial abnormalities in seven out of the 80 subjects. Punch biopsies from these cases disclosed dysplasia in three cases, carcinoma in situ in two, and carcinoma in the other two cases. There was mild dysplasia in two punch biopsies of the remaining 73 cases. Oral cancer in tobacco powder users appeared to be related to the length of use, as it was observed only in subjects with 15 or more years of exposure.     

Effects of carbon dioxide concentration on the interactive effects of temperature and water vapour on stomatal conductance in soybean

Soybeans were grown at three CO₂ concentrations in outdoor growth chambers and at two concentrations in controlled-environment growth chambers to investigate the interactive effects of CO₂, temperature and leaf-to-air vapour pressure difference (LAVPD) on stomatal conductance. The decline in stomatal conductance with CO₂ was a function of both leaf temperature and LAVPD. In the field measurements, stomatal conductance was more sensitive to LAVPD at low CO₂ at 30 °C but not at 35 °C. There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations. Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO₂. Measurements in the environmental growth chamber were also performed at the opposing CO₂, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO₂ than by measurement CO₂. Two models that describe stomatal responses to LAVPD were compared with the outdoor data to evaluate whether these models described adequately the interactive effects of CO₂, LAVPD and temperature.     

Reconstructing atmospheric carbon dioxide with stomata: possibilities and limitations of a botanical pCO2-sensor

Stomatal frequency is often observed to vary inversely with atmospheric CO₂ concentration (pCO₂). The response is due to (1) individual phenotypic plasticity and (2) evolutionary change, depending on the time scale. Evolutionary responses occur more frequently than individual responses and individual responses are more pronounced under subambient pCO₂ levels than under elevated pCO₂ (CO₂ ceiling). The evolutionary response appears therefore to be a valuable device for determining past pCO₂. Since tree leaves often represent a conspicuous and rich resource of fossil material, they are increasingly important in this respect. Additionally, certain tree species are considered to represent living fossils and therefore valuable sources of ancient stomatal data. There are, however, numerous difficulties which have to be considered such as: (1) high variance of the data, especially for fossil material, (2) interspecific differences of the response, (3) the CO₂ ceiling and (4) differences between short-term and long-term responses. Whereas the qualitative pCO₂ signal of stomatal frequency appears to be reliable, quantitative pCO₂ reconstruction has to be performed with caution. The results of a number of studies which used stomatal frequency as a pCO₂ sensor demonstrate good agreement with the results obtained with other proxy data. Current techniques are based on transfer functions which calibrate the fossil data with extant material. It is suggested that a mechanistic approach including physical as well as physiological processes could improve pCO₂ reconstruction. Furthermore, the topic of the influence of pCO₂ on stomatal frequency is significant not only for reconstructing past pCO₂ but also with respect to the climate-biosphere interrelationship.     

Evaluating soil microbial carbon use efficiency explicitly as a function of cellular processes: implications for measurements and models

Carbon use efficiency (CUE), the proportion of carbon (C) consumed by microbes that is converted into biomass, is an important parameter for soil C models with explicit microbial controls. While often considered as a single parameter, CUE is an emergent property of multiple microbial processes, including assimilation efficiency, biomass-specific respiration, enzyme production, and respiratory costs of enzyme production. These processes occur over variable time scales and imply different fates for C, and the same emergent CUE value can result when C is allocated in fundamentally different ways (e.g. a high investment in enzyme production vs. a high assimilation cost). We developed a model that represents the individual processes underlying emergent CUE to test how shifts in microbial allocation alter equilibrium soil C pool sizes. We found that an increase in emergent CUE that results from a change in assimilation efficiency, biomass specific respiration, or respiration costs from enzyme production causes soil organic C (SOC) to decline, while the same change in emergent CUE resulting from a change in enzyme production causes SOC to increase. We also used the model to test the sensitivity of CUE from isotopic C tracer estimates to changes in microbial allocation processes. We found that these estimates do not account for the same microbial processes represented by emergent CUE in models. We propose that considering microbial processes explicitly rather than representing CUE as a single parameter can improve data-model integration. In addition, modeling microbial processes explicitly will account for a wider range of possible outcomes from shifts in microbial C allocation, such as when increased SOC results from increasing CUE.     

Control of carbon dioxide in exhaust air as a method for equal biomass yields at different bed heights in a column fermentor

Summary The rate of aeration of the medium in a solid state fermentation system for biomass production by Schwanniomyces castellii in a large column fermentor was found to influence the gradient of biomass yield at different bed heights. The variations were lower with a higher rate of aeration. These trends were used to formulate a successful strategy to ensure equal biomass yield at all the bed heights by controlling the level of CO₂ at about 2% in exhaust air from the fermentor. Correspondence to: B. K. Lonsane