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); PPFD ¢ , daily integral of PPFD; Rubisco, ribulose-1,5-bisphosphate carboxylase oxygenase; T leaf , leaf temperature ( ∞ C); TNC, total non-structural carbohydrate (mmol m -2 ); VPD, vapour pressure deficit (kPa).

The effects of ultraviolet-B (UV-B) radiation on water relations, leaf development, and gas-exchange characteristics in pea (Pisum sativum L. cv Meteor) plants subjected to drought were investigated. Plants grown throughout their development under a high irradiance of UV-B radiation (0.63 W m ؊2 ) were compared with those grown without UV-B radiation, and after 12 d one-half of the plants were subjected to 24 d of drought that resulted in mild water stress. UV-B radiation resulted in a decrease of adaxial stomatal conductance by approximately 65%, increasing stomatal limitation of CO 2 uptake by 10 to 15%. However, there was no loss of mesophyll light-saturated photosynthetic activity. Growth in UV-B radiation resulted in large reductions of leaf area and plant biomass, which were associated with a decline in leaf cell numbers and cell division. UV-B radiation also inhibited epidermal cell expansion of the exposed surface of leaves. There was an interaction between UV-B radiation and drought treatments: UV-B radiation both delayed and reduced the severity of drought stress through reductions in plant water-loss rates, stomatal conductance, and leaf area.Photosynthetic rate and productivity in many plant species can be reduced by increased exposure to UV-B radiation (Teramura and Ziska, 1996). To date there is no consensus on the mechanistic basis of UV-B-induced inhibition of CO 2 assimilation in mature leaves. A reduction in Rubisco activity has been suggested as a cause of the reduced CO 2 assimilation rate in leaves exposed to increased UV-B radiation. Prolonged exposure to elevated levels of UV-B radiation has been demonstrated to result in decreases of both Rubisco activity and content (Strid et al., 1990; Jordan et al., 1992; Kulandaivelu and Nedunchezhian, 1993). A primary cause of the decrease in the light-saturated rate of CO 2 assimilation induced by exposure to elevated UV-B radiation in leaves of oilseed rape has been shown to be a loss of Rubisco (Allen et al., 1997), which may also be associated with the loss of activity of other Calvin cycle enzymes (Baker et al., 1997).UV-B-induced inhibition of photosynthesis has also been attributed to a reduction in the activity of PSII photochemistry (Fiscus and Booker, 1995). However, UV-B radiation has been shown to inhibit photosynthesis without an appreciable effect on PSII photochemistry in pea (Pisum sativum L.; Nogués and Baker, 1995), oilseed rape (Allen et al., 1997), soybean (Middleton and Teramura, 1993), rice (Ziska and Teramura, 1992), and algae (Lesser, 1996). Therefore, it would appear that UV-B inhibition of PSII photochemistry is not a ubiquitous primary effect on photosynthesis. It is not clear whether changes in stomatal function play a major role in the UV-B-induced inhibition of photosynthesis. Exposure to UV-B radiation can modify the speed of stomatal opening and closing and reduce the rate of leaf transpiration (Negash, 1987; Middleton and Teramura, 1993; Day and Vogelmann, 1995), although stomatal effects have not been found to aff...

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The effectiveness of current antimicrobial interventions used in reducing the prevalence or load of Escherichia coli O157 and indicator organisms on cattle hides and carcasses at two commercial beef processing plants was evaluated. Sponge sampling of beef cattle was performed at ve locations from the initial entry of the animals to the slaughter oor to the exit of carcasses from the ''hotbox'' cooler. For each sample, E. coli O157 prevalence was determined and total aerobic bacteria, Enterobacteriaceae, and E. coli O157 were enumerated. E. coli O157 was found on 76% of animal hides coming into the plants, but no carcasses leaving the cooler were identi ed as contaminated with E. coli O157. A positive relationship was seen between the incidence of E. coli O157 in hide samples and that in preevisceration samples. Aerobic plate counts and Enterobacteriaceae counts averaged 7.8 and 6.2 log CFU/100 cm 2 , respectively, on hides, and 1.4 and 0.4 log CFU/100 cm 2 , respectively, on chilled carcasses. Aerobic plate counts and Enterobacteriaceae counts on preevisceration carcasses were signi cantly related to the respective levels on the corresponding hides; the carcasses of animals whose hides carried higher numbers of bacteria were more likely to carry higher numbers of bacteria. Implementation of the sampling protocol described here would allow processors to evaluate the ef cacy of on-line antimicrobial interventions and allow industrywide benchmarking of hygienic practices.Escherichia coli O157:H7 has been a pathogen of concern to the meat processing industry for two decades. Cases of hemorrhagic colitis caused by E. coli O157:H7 were associated with consumption of undercooked ground beef in the early 1980s (26). In the United States during 1992 and 1993, an outbreak of E. coli O157:H7 infection associated with consumption of ground beef caused hundreds of illnesses and four deaths (31). These events led the Food Safety and Inspection Service (FSIS) to declare the E. coli O157:H7 organism an adulterant in ground beef and to require that meat processors establish hazard analysis and critical control point (HACCP) plans for their plants (12). Since this time, numerous intervention strategies focusing on prevention of carcass contamination and decontamination of carcasses have been designed, tested, and put into practice at commercial processing plants.Recent studies have demonstrated that combinations of antimicrobial interventions are more effective at reducing * Author for correspondence. Tel: 402-762-4227; Fax: 402-762-4149; E-mail: arthur@email.marc.usda.gov. † Names are necessary to report factually on available data; however, the U.S. Department of Agriculture neither guarantees nor warrants the standard of the product, and the use of the name by the U.S. Department of Agriculture implies no approval of the product to the exclusion of others that may also be suitable. ‡ Present address: Room 119, Veterinary Diagnostic Center, East Campus, University of Nebraska, Lincoln, NE 68583-0907, USA.surface contami...

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Nitrogen, which is a major limiting nutrient for plant growth, is assimilated as ammonium by the concerted action of glutamine synthetase (GS) and glutamate synthase (GOGAT). GS catalyses the critical incorporation of inorganic ammonium into the amino acid glutamine. Two types of GS isozymes, located in the cytosol (GS1) and in the chloroplast (GS2) have been identified in plants. Tobacco (Nicotiana tabacum) transformants, over-expressing GS1 driven by the constitutive CaMV 35S promoter were analysed. GS in leaves of GS-5 and GS-8 plants was up-regulated, at the level of RNA and proteins. These transgenic plants had six times higher leaf GS activity than controls. Under optimum nitrogen fertilization conditions there was no effect of GS over-expression on photosynthesis or growth. However, under nitrogen starvation the GS transgenics had c. 70% higher shoot and c. 100% greater root dry weight as well as 50% more leaf area than low nitrogen controls. This was achieved by the maintenance of photosynthesis at rates indistinguishable from plants under high nitrogen, while photosynthesis in control plants was inhibited by 40-50% by nitrogen deprivation. It was demonstrated that manipulation of GS activity has the potential to maintain crop photosynthetic productivity while reducing nitrogen fertilization and the concomitant pollution.

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. Â 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. Â 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.