Cysteine and glutathione in orange juice

The major part of the sulfhydryl compounds of both Valencia and Navel orange juice was found to exist as cysteine and glutathione. These two compounds were isolated and analyzed as their crystalline S-benzyl derivatives from concentrates prepared by preferential mercuric ion precipitation. Cysteine analysis before and after hydrolysis showed that all of the sulfhydryl of the concentrates was cysteine and glutathione. The glutathione analysis was confirmed by Woodward's glyoxalase method.     

Drought tolerance of two black poplar (Populus nigra L.) clones: contribution of carbohydrates and oxidative stress defence

Drought is expected to become an increasingly important factor limiting tree growth caused by climate change. Two divergent clones of Populus nigra (58-861 and Poli) originating from contrasting environments were subjected to water limitation (WL) to elucidate whether they differ in tolerance to drought, which mechanisms to avoid stress they exhibit and whether drought has an impact on the interactions between roots and shoots. Limiting water availability caused photosynthetic rate and total non-structural carbohydrate (TNC) levels to decrease in 58-861. However, starch-degrading enzyme activity and gene expression were induced in roots, and soluble sugar levels were higher than in well-watered (WW) plants. These data suggest that assimilation and partitioning of carbon to the roots are decreased, resulting in mobilization of stored starch. In contrast, the photosynthetic rate of Poli was reduced only late in the treatment, and carbohydrate levels in WL plants were higher than in WW plants. Superoxide dismutase (SOD) activity and gene expression were higher in Poli than in 58-861, even in WW plants, leading to a higher capacity to defend against oxidative stress.     

Local adaptation to higher temperatures reduces immigration success of genotypes from a warmer region in the water flea Daphnia

There is growing awareness that microevolutionary dynamics may alter ecological processes. Rising temperatures under global change are expected to open windows for establishment of species and genotypes from warmer regions. Yet, microevolutionary tracking of temperature change by local populations may reduce establishment success of these immigrants. We exposed a UK population of the water flea, Daphnia magna , to two temperature regimes during a 1.5-year experimental evolution trial, and subsequently compared competitive strength of non-warm-adapted and warm-adapted D. magna in competition with French genotypes. Our results indicate that local microevolutionary responses to global warming may reduce establishment success of immigrant genotypes that are preadapted to warmer climate. Simulation modeling shows that microevolution results in a reduced likelihood and speed of displacement of local populations by immigrant genotypes under realistic immigrant/resident ratios. We conclude that local evolutionary dynamics may shift the relative impact of local and regional processes in response to global change.     

Ammonium Tolerance and Carbohydrate Status in Maize Cultivars

Four maize (Zea mays L.) hybrids were grown hydroponically for4 weeks with 20 mM ammonium or nitrate as the sole nitrogensource. Dry matter production was strongly depressed by ammoniumnutrition in the hybrid Helga relative to plants grown on nitrate,and moderately decreased in the hybrid Melina. Ammonium hadno inhibitory effect on total yield in the other two hybrids(Ramses and DK 261). The relative growth rate (RGR) of rootsand shoots of the sensitive hybrid Helga decreased significantlyunder ammonium nutrition during the first 2 weeks of the experiment,while at the end of the experiment nitrogen form had no effecton the RGR in any of the four hybrids. The strong reductionin RGR of Helga in the early seedling stage was correlated withthe accumulation of twice the concentration of free ammoniumin the shoot tissue relative to the other hybrids. Helga wastherefore unable to sufficiently detoxify ammonia in the roots.Root concentrations of water soluble carbohydrates (WSC) inHelga and Melina in the early seedling stage did not differunder ammonium and nitrate nutrition. In contrast, Ramses andDK 261 both had elevated WSC concentrations in ammonium-fedroots. It is hypothesized that a sufficient supply of carbonskeletons for ammonium assimilation in the roots is requiredfor maximum growth under high ammonium concentrations, and thatthere is genotypic variability in this physiological trait. Ammonium; carbohydrates; growth rate; maize; nitrate; roots; Zea mays L     

Factors contributing to the loss of seed from the seed-bank of Trifolium balansae and Trifolium resupinatum over summer

Abstract The influence of predation, fungi and germination of seed of the annual legumes Trifolium balansae and Trifolium resupinatum was investigated by placing known quantities of seed in bags in the field; combinations of all three factors were imposed. It was found that rainfall was the most important factor contributing to the loss of seed over summer (up to 76%), followed by predation (up to 15%); fungi had only a very small influence (0.1–0.2%). Predation contributed to a larger percentage of loss over summer in T. resupinatum line SA14433 than in T. balansae cv. Paradana, which is attributed to seed size. The effect of summer grazing on the size of the seed-bank was investigated. It was found that summer grazing did not influence the amount of seed present in the seed-bank in March. Removal of all surface material in December resulted in a significant drop in seed reserves compared with the ungrazed or grazed areas. Hardseededness in March was not affected by any of the treatments; the seedling density after regeneration was not affected by summer grazing, but was reduced when all surface material was removed. The data were incorporated in a model to describe seed loss from the seed bank over summer quantitatively; the utility of such models is discussed.