How do elevated CO2 and O3 affect the interception and utilization of radiation by a soybean canopy?

Net productivity of vegetation is determined by the product of the efficiencies with which it intercepts light (?_i) and converts that intercepted energy into biomass (?_c). Elevated carbon dioxide (CO₂) increases photosynthesis and leaf area index (LAI) of soybeans and thus may increase ?_i and ?_c; elevated O₃ may have the opposite effect. Knowing if elevated CO₂ and O₃ differentially affect physiological more than structural components of the ecosystem may reveal how these elements of global change will ultimately alter productivity. The effects of elevated CO₂ and O₃ on an intact soybean ecosystem were examined with Soybean Free Air Concentration Enrichment (SoyFACE) technology where large field plots (20‐m diameter) were exposed to elevated CO₂ (～550 μmol mol^?1) and elevated O₃ (1.2 × ambient) in a factorial design. Aboveground biomass, LAI and light interception were measured during the growing seasons of 2002, 2003 and 2004 to calculate ?_i and ?_c. A 15% increase in yield (averaged over 3 years) under elevated CO₂ was caused primarily by a 12% stimulation in ?_c , as ?_i increased by only 3%. Though accelerated canopy senescence under elevated O₃ caused a 3% decrease in ?_i, the primary effect of O₃ on biomass was through an 11% reduction in ?_c. When CO₂ and O₃ were elevated in combination, CO₂ partially reduced the negative effects of elevated O₃. Knowing that changes in productivity in elevated CO₂ and O₃ were influenced strongly by the efficiency of conversion of light energy into energy in plant biomass will aid in optimizing soybean yields in the future. Future modeling efforts that rely on ?_c for calculating regional and global plant productivity will need to accommodate the effects of global change on this important ecosystem attribute.     

Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality.     

Thermographic visualization of cell death in tobacco and Arabidopsis

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. 1999 Nature 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.     

The economics of monocropping and intercropping by smallholders: The case of coconuts in Indonesia

This article contains a comparison of the profits of cultivating modern and traditional varieties of coconuts as a monocrop and as an intercrop, in ideal and in average growing conditions, with good and with average management. We carry out the analysis from a private (financial) and from a national (economic) perspective. The results show that intercropping generates more income than monocropping. In the conclusion we discuss why development organizations and Third World countries encourage monocropping.     

Are the carbon costs of seed production related to the quantitative and qualitative performance? An appraisal for legumes and other crops

In the past great efforts have been made to gain a thorough understanding of the processes involved in carbon fixation but the fate of the acquired carbon has been somewhat neglected, although this aspect is crucial for improving yield performance without diminishing the quality of the harvested organs. To contribute to the crucial debate on that topic the aim of the present study was to propose some unbiased components concerning in particular grain legumes: ‘Is there any antagonism between high yield and increased nutritional quality, with a focus on protein content?’ An original approach has been used to study the impact of the modification of seed composition on the crop production, which combines theoretical calculations of energetic cost and field yield data. When applied to a wide range of species with varying seed composition, a plurispecific negative relationship between the theoretical carbon costs of seed production and the observed yields was demonstrated. The high-throughput of genetic markers could result in large-scale screening of seed quality parameters and such studies, while evaluating the impact of seed composition on crop yield, could also be used to provide data to forecast the economic impact of a new line with an original composition compared with its economically enhanced value.     

Host selection by winged colonisers within the Myzus persicae group: a contribution towards understanding host specialisation

Abstract.  1.  Myzus persicae sensu lato demonstrates considerable genetic variation in respect to adaptation to host plants. The subspecies M. persicae nicotianae shows a preference for tobacco, while M. persicae sensu stricto ( s. str. ) for other herbaceous plants. Given that winged colonisers of several aphid species play an important role in selecting host plants, here their role in the host specialisation observed in M. persicae was examined in choice and no-choice tests conducted outdoors, in performance studies, and in DC Electrical Penetration Graph (DC-EPG) studies.
2. In outdoor choice tests, 77% of spring migrants of M. persicae nicotianae chose tobacco, whereas equal proportions of M. persicae s. str. selected tobacco and pepper. In no-choice tests, spring migrants settled more quickly after alighting on host rather than on non host plants, and significantly more alate M. persicae s. str. (27%) than M. persicae nicotianae (2%) left tobacco after walking briefly on the leaf surface, whilst no significant differences were found on pepper. Cross-host transfers significantly reduced the fecundity of both summer and spring migrants of the two subspecies. Finally, the results of no-choice tests and DC-EPG studies showed that winged aphids distinguished their host through cues located on the plant surface or in subcutaneous tissues perceived prior to the initiation of feeding.
3. This study demonstrates the important role of winged colonisers in the evolution of host specialisation in M. persicae . The multifarious divergent selection that the two host forms experience, i.e. the selection against cross-migrants and their subsequent generations, is a crucial factor involved in the development and maintenance of host specialisation and promotes the parallel evolution of improved host-recognition ability.     

Queuine in plants and plant tRNAs: Differences between embryonic tissue and mature leaves

In eubacterial and eukaryotic tRNAs specific for Asn, Asp, His and Tyr the modified deazaguanosinederivative queuosine occurs in position 34, the first position of the anticodon. Analysis of unfractionated tRNAs from wheat and from tobacco leaves shows that these tRNAs contain high amounts of guanosine (G) in place of queuosine (Q). This was measured by the exchange of G34 for [³H]guanine catalysed by the specific tRNA guanine transglycosylase from E. coli. Upon gel electrophoretic separation of the labeled tRNAs, seven Q-deficient tRNA species including isoacceptors are detectable. Two are identified as cytoplasmic tRNAs^Tyr and tRNA^Asp and two represent chloroplast tRNA^Tyr isoacceptors. In contrast to leaf cytoplasm and chloroplasts, wheat germ has low amounts of tRNAs with G34 in place of Q.A new enzymatic assay is described for quantitation of free queuine in cells and tissues. Analysis of queuine in plant tissues shows that wheat germ contains about 200 ng queuine per g wet weight. In wheat and tobacco leaves queuine is present, if at all, in amounts lower than 10 ng/g wet weight. The absence of Q in tRNAs from plant leaves is therefore caused by a deficiency of queuine. Tobacco cells cultivated in a synthetic medium without added queuine do not contain Q in tRNA, indicating that these rapidly growing cells do not synthesize queuine de novo.     

Identification,purification, and characterization of pathogenesis-related proteins from virus-infected Samsun NN tobacco leaves

Ten pH-3 soluble, low-molecular-weight pathogenesis-related proteins (PRs) were found to accumulate in leaves of tobacco cv. Samsun NN reacting hypersensitively to tobacco mosaic virus. Besides the previously characterized PRs 1a, 1b, 1c and 2, these proteins were provisionally designated N, O, P, Q, R, and S in order of decreasing electrophoretic mobility in native polyacrylamide gels. Two-dimensional gel electrophoresis indicated that the PRs consist of single polypeptides, except for R, which is composed of two components with slightly different molecular weights. Estimated molecular weights in SDS-containing gels were: PRs 1a and 1b 17 kD, 1c 16.5 kD, 2 31 kD, N 33 kD, O 35 kD, P 27 kD, Q 28 kD, R 13 and 15 kD, and S 25 kD. However, based on their elution from gel filtration columns and relative moblities in native gels of different acrylamide concentrations, P and Q appeared to have molecular weights similar to those of the PR 1 group. Upon chromatofocusing no additional components were resolved. The PRs were eluted between pH 7 and 4; except for R, their pIs, as judged from isoelectric focusing, appeared to lie in the range from pH 4 to 5.2. In the presence of 6 M urea PR 1a was split into two components, one of which was strongly retarded on gels, as were P and Q. None of the PRs was detected when gels were stained for glycoproteins.By combinations of gel filtration, DEAE-cellulose chromatography, and chromatofocusing, PRs 1a, 1b, 1c, 2 and N were purified, their amino acid compositions determined, and antisera raised against each of these components. By Western blotting, antisera against either PR 1a, 1b, or 1c reacted with each of the components of the PR 1 group, as well as with PR S. Similarly, the antisera against either PR 2 or N reacted with both 2 and N, as well as with O and R. On the basis of major similarities in molecular weight characteristics, amino acid compositions, and serological relationships, it is proposed to classify tobacco PRs into five groups: 1: PRs 1a, 1b, and 1c; 2: 2a (formerly 2), 2b (N), and 2c (O); 3: 3a (P), and 3b (Q); 4: 4a and 4b (the two components of R); and 5: PR 5 (S).     

A simple system for plant cell microinjection and culture

Microinjection of plant protoplasts and cells has been recently reported, however a system that combines simplicity of design, harmless immobilization, high resolution visibility and ability to monitor individual target cells is lacking. This report describes a system which combines these features. It consists of a microinjection-microculture dish containing immobilized protoplasts and a simple chamber that maintains sterility and humidity during injection. Highly purified protoplast preparations are plated at low population density as a thin monolayer of widely separated cells embedded in agarose layered over a thicker (0.2 mm at center to 1 mm at edge) layer of agarose-solidified medium. This physical arrangement allows for rapid location, mapping and injection of the immobilized protoplasts and also their subsequent location for growth monitoring. The double layers of agarose provide adequate nutrition for culturing injected cells to the microcalli stage. In addition to protoplast injection, this system was also used to inject 3- to 4-day old nonspherical cells derived from protoplasts. Colony formation rates from injected protoplasts and cells with regenerated walls were equivalent to those of uninjected controls. Furthermore, tobacco protoplasts stored at 4°C in liquid medium for up to two weeks remained fully competent for plating and injection. These cold-stored protoplasts, when injected, formed colonies at rates similar to those from fresh preparations. The ability to store protoplasts without loss of viability considerably increases the ease and convenience of cell injection experiments.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of the other products that may also be suitable.