Effects of climate change on productivity of cereals and legumes; model evaluation of observed year-to-year variability of the CO2 response

The effect of elevated [CO₂] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991–93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO₂ response. Measurements of the canopy gas exchange (CO₂ and water vapour) were made continuously from emergence until harvest. At an external [CO₂] of 700 μmol mol^?1 Maximum Canopy CO₂ Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 μmol mol^?1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975-88 and 1991–93 were used, assuming adequate water supply and [CO₂] at 350 and 700 μmol mol^?1. For spring wheat the simulated responses (35–50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO₂ response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO₂ response can be largely explained by differences in weather conditions (especially temperature) between growing seasons.     

A genetic selection for temperature-sensitive variants of the gene V protein of bacteriophage f1.

Complementary negative and positive genetic selections based on the activity of a plasmid-encoded bacteriophage f1 gene V are developed. The negative selection is based on an activity of the gene V protein in E. coli cells which markedly reduces the infection of those cells by f1-related viruses. In order to select against cells expressing active gene V protein, the cells are infected with the p'age R386, a derivative of f1 which confers resistance to chloramphenicol, and are plated in the presence of the antibiotic. Those cells which contain gene V protein are infrequently infected with the virus and are unable to grow in the presence of chloramphenicol; those which do not contain the gene V protein are readily infected and can grow in the presence of the antibiotic. The positive genetic selection consists of excising the gene V sequences from the plasmids and using them to replace the gene V of a bacteriophage f1 derivative containing an amber mutation in gene V. Only those genes which encode an active gene V protein can support phage growth and yield plaques. The two genetic selections can be combined in order to yield a substantial enrichment for genes encoding temperature-sensitive gene V proteins.     

Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study

Dietary supplementation with beetroot juice (BR) has been shown to reduce resting blood pressure and the O(2) cost of submaximal exercise and to increase tolerance to high-intensity cycling. We tested the hypothesis that the physiological effects of BR were consequent to its high NO(3)(-) content per se, and not the presence of other potentially bioactive compounds. We investigated changes in blood pressure, mitochondrial oxidative capacity (Q(max)), and physiological responses to walking and moderate- and severe-intensity running following dietary supplementation with BR and NO(3)(-)-depleted BR [placebo (PL)]. After control (nonsupplemented) tests, nine healthy, physically active male subjects were assigned in a randomized, double-blind, crossover design to receive BR (0.5 l/day, containing ～6.2 mmol of NO(3)(-)) and PL (0.5 l/day, containing ～0.003 mmol of NO(3)(-)) for 6 days. Subjects completed treadmill exercise tests on days 4 and 5 and knee-extension exercise tests for estimation of Q(max) (using (31)P-magnetic resonance spectroscopy) on day 6 of the supplementation periods. Relative to PL, BR elevated plasma NO(2)(-) concentration (183 ± 119 vs. 373 ± 211 nM, P < 0.05) and reduced systolic blood pressure (129 ± 9 vs. 124 ± 10 mmHg, P < 0.01). Q(max) was not different between PL and BR (0.93 ± 0.05 and 1.05 ± 0.22 mM/s, respectively). The O(2) cost of walking (0.87 ± 0.12 and 0.70 ± 0.10 l/min in PL and BR, respectively, P < 0.01), moderate-intensity running (2.26 ± 0.27 and 2.10 ± 0.28 l/min in PL and BR, respectively, P < 0.01), and severe-intensity running (end-exercise O(2) uptake = 3.77 ± 0.57 and 3.50 ± 0.62 l/min in PL and BL, respectively, P < 0.01) was reduced by BR, and time to exhaustion during severe-intensity running was increased by 15% (7.6 ± 1.5 and 8.7 ± 1.8 min in PL and BR, respectively, P < 0.01). In contrast, relative to control, PL supplementation did not alter plasma NO(2)(-) concentration, blood pressure, or the physiological responses to exercise. These results indicate that the positive effects of 6 days of BR supplementation on the physiological responses to exercise can be ascribed to the high NO(3)(-) content per se.     

The role of circulating mevalonate in nephrotic hypercholesterolemia in the rat

The cause of the hypercholesterolemia that characterizes the nephrotic syndrome has never been adequately explained. The present study examines the possibility that enhanced availability of the cholesterol precursor, mevalonic acid, to the liver in the nephrotic state may result in increased hepatic cholesterogenesis. In normal animals, the kidneys are known to be the major site of the metabolism of circulating mevalonate to both cholesterol and CO2. Previous studies, using perfusion of isolated, intact kidneys, have shown that the excretion and metabolism of mevalonate are both impaired in nephrosis. The present investigation has demonstrated in vivo that puromycin aminonucleoside nephrosis results in a 25% reduction in the oxidation of mevalonate to CO2. In the same nephrotic animals, cholesterogenesis from circulating mevalonate was significantly increased in both liver and carcass. In addition, liver slices from nephrotic animals incorporated increased amounts of [5-14C]mevalonate into cholesterol when calculated per whole liver, but not per gram of liver. Oxidation of mevalonic acid by kidney slices was significantly reduced, whether expressed as per gram of tissue or per whole organ. HMG-CoA (3-hydroxy-3-methylglutaryl) reductase activity in liver of nephrotic animals was significantly increased. We conclude that, in the nephrotic state, impaired mevalonate metabolism by the kidney may contribute to enhanced cholesterogenesis by increasing delivery of mevalonate to liver and carcass; in addition, nephrosis appears to provide an undefined stimulus for HMG-CoA reductase activity in the liver, thereby providing an additional enhancement of hepatic cholesterogenesis.     

Specificity of translational regulation by two DNA-binding proteins

The gene V protein of the filamentous bacteriophages f1, fd and M13, and the gene 32 protein of bacteriophage T4 share the property of binding strongly and co-operatively to single-stranded nucleic acids, especially DNA. Moreover, both are capable of repressing the translation of specific mRNAs (gene 32 protein its own, and gene V protein that of the filamentous phage gene II), both in vivo and in vitro. If the mechanism of repression by either of these proteins were based solely on its ability to bind single strands co-operatively, then the other would be expected to mimic or interfere with its effect in vitro. We have found no such mimicry or interference, even at protein concentrations high enough to have substantial non-specific effects on translation. This suggests that the sites of repression on the mRNAs must offer something other than simple “unstructuredness” for binding and repression to occur.     

The metapopulation dynamics of an infectious disease: tuberculosis in possums

An SEI metapopulation model is developed for the spread of an infectious agent by migration. The model portrays two age classes on a number of patches connected by migration routes which are used as host animals mature. A feature of this model is that the basic reproduction ratio may be computed directly, using a scheme that separates topography, demography, and epidemiology. We also provide formulas for individual patch basic reproduction numbers and discuss their connection with the basic reproduction ratio for the system. The model is applied to the problem of spatial spread of bovine tuberculosis in a possum population. The temporal dynamics of infection are investigated for some generic networks of migration links, and the basic reproduction ratio is computed-its value is not greatly different from that for a homogeneous model. Three scenarios are considered for the control of bovine tuberculosis in possums where the spatial aspect is shown to be crucial for the design of disease management operations.     

Periodic triggering of an inducible gene for control of a wild population

A possible method of control for the management of wild populations consists of continual introgression of an inducible transgene by releasing transgenic individuals, with periodic exposure of the population to a trigger. Exposure to the trigger causes death or sterility in carriers of the transgene, but is otherwise benign. We investigate the effectiveness of various strategies for control. We show that suppression of the population density below any pre-specified level is possible using this technique. At the same time we show that too frequent or too efficient exposure to the trigger can select for non-transgenic genotypes at an intensity such that the population density will be largely unaffected by the trigger. Choices for management parameters can ensure that the latter scenario is avoided. We show that releasing individuals carrying the transgene at more than one locus facilitates density control.     

Seasonal changes in the response of winter wheat to elevated atmospheric CO2 concentration grown in Open-Top Chambers and field tracking enclosures

Winter wheat was grown at ambient and elevated (ambient plus 350 μL L^–1) CO₂ concentrations in open top chambers and in field-tracking sun-lit climatized enclosures (elevated is 718 μL L^–1). There was no significant effect of CO₂ concentration on sheath, leaf and root biomass and leaf area in the early spring (January to April). 24-h canopy CO₂ exchange rate (CCER) was not significantly affected either. However, elevated CO₂ concentration increased CCER at midday, decreased evapotranspiration rate and increased instantaneous water-use-efficiency during early spring. Leaf, sheath and root nitrogen concentration per unit dry weight decreased and nonstructural carbohydrate concentration increased under elevated CO₂, and N-uptake per unit ground area decreased significantly (– 22%) towards the end of this period. These results contrast with results from the final harvest, when grain yield and biomass were increased by 19% under elevated CO₂. N concentration per dry weight was reduced by 5%, but N-uptake per unit ground area was significantly higher (+ 11%) for the elevated CO₂ treatment. 24-h and midday-CCER increased significantly more in late spring (period of 21 April to 30 May) (respectively by + 40% and 53%) than in the early spring (respectively 5% and 19%) in response to elevated CO₂. Midday evapotranspiration rate was reduced less by elevated CO₂ in the late spring (– 13%) than in early spring (– 21%). The CO₂ response of midday and 24-h CCER decreased again (+ 27% and + 23% resp.) towards the end of the growing season. We conclude that the low response to CO₂ concentration during the early spring was associated with a growth-restriction, caused by low temperature and irradiance levels. The reduction of nitrogen concentration, the increase of nonstructural carbohydrate, and the lower evapotranspiration indicated that CO₂ did have an effect towards the end of early spring, but not on biomass accumulation. Regression analysis showed that both irradiance and temperature affected the response to CO₂.