Drought stress provokes the down‐regulation of methionine and ethylene biosynthesis pathways in Medicago truncatula roots and nodules

Symbiotic nitrogen fixation is one of the first physiological processes inhibited in legume plants under water‐deficit conditions. Despite the progress made in the last decades, the molecular mechanisms behind this regulation are not fully understood yet. Recent proteomic work carried out in the model legume Medicago truncatula provided the first indications of a possible involvement of nodule methionine (Met) biosynthesis and related pathways in response to water‐deficit conditions. To better understand this involvement, the drought‐induced changes in expression and content of enzymes involved in the biosynthesis of Met, S‐adenosyl‐L‐methionine (SAM) and ethylene in M. truncatula root and nodules were analyzed using targeted approaches. Nitrogen‐fixing plants were subjected to a progressive water deficit and a subsequent recovery period. Besides the physiological characterization of the plants, the content of total sulphur, sulphate and main S‐containing metabolites was measured. Results presented here show that S availability is not a limiting factor in the drought‐induced decline of nitrogen fixation rates in M. truncatula plants and provide evidences for a down‐regulation of the Met and ethylene biosynthesis pathways in roots and nodules in response to water‐deficit conditions.     

LOCALIZATION AND IDENTIFICATION OF GALACTOSE/N-ACETYLGALACTOSAMINE AND SIALIC ACID-CONTAINING PROTEINS IN CHINESE HAMSTER METAPHASE CHROMOSOMES

Four lectins were used to recognize galactose/N-acetyl-galactosamine (Gal/GalNAc) and sialic acid residues in proteins of Chinese hamster metaphase chromosomes. In situ binding pattern of a fluorescein isothiocyanate-labelled (Gal/GalNAc)-specific lectin Sophora japonica agglutinin (SJA) showed that chromosomal SJA-binding proteins are primarily localized to the helically coiled substructure of chromatids. Numerous SJA-binding proteins were identified in Western blots of chromosomal proteins, their molecular weights ranging from 26 to 200kDa. Another Gal/GalNAc-specific lectin, peanut agglutinin (PNA), with a slightly different sugar binding specificity, did not bind to Chinese hamster metaphase chromosomes, and in Western blots only two chromosomal protein bands were faintly stained. The in situ labelling patterns of two sialic acid-specific lectins, Maackia amurensis (MAA) and Sambucus nigra (SNA) agglutinins, both showed that the helically coiled substructure of chromatids is also enriched in sialylated proteins. In Western blot analysis 11 MAA-binding protein bands with molecular weights ranging from 54 to 215kDa were identified, while SNA only bound to one protein band of 67kDa. MAA and SNA are specific for α (2|ad3)- and α (2|ad6)-linked sialic acid residues, respectively. Thus, it is likely that α (2|ad3)-linked sialic acid residues are more common in chromosomal proteins than α(2|ad6)-linked sialic acid residues. These data suggest that Gal/GalNAc and sialic acid-containing glycoproteins exist in metaphase chromosomes and that these proteins may have a role in the formation of higher order metaphase chromosome structures.     

A method for sampling the populations of large termite nests

A method for sampling the population of large Macrotermes nests is described. Fumigation with methyl bromide was followed by complete extraction of the nest contents. Termites and fungus comb fragments were separated from soil by flotation in water. Results for fumigated and live-dug nests were compared. Sampling without prior fumigation caused the population and biomass to be underestimated by up to an order of magnitude. Caste and instar ratios were also distorted in ways that were not consistent but were affected by the size of the nest. It is therefore concluded that methyl bromide fumigation is a valuable technique for sampling the populations of Macrotermes nests.     

Variation in active and passive resource inputs to experimental pools: mechanisms and possible consequences for food webs

1. Cross‐ecosystem movements of resources, including detritus, nutrients and living prey, can strongly influence food web dynamics in recipient habitats. Variation in resource inputs is thought to be driven by factors external to the recipient habitat (e.g. donor habitat productivity and boundary conditions). However, inputs of or by ‘active’ living resources may be strongly influenced by recipient habitat quality when organisms exhibit behavioural habitat selection when crossing ecosystem boundaries. 2. To examine whether behavioural responses to recipient habitat quality alter the relative inputs of ‘active’ living and ‘passive’ detrital resources to recipient food webs, we manipulated the presence of caged predatory fish and measured biomass, energy and organic content of inputs to outdoor experimental pools of adult aquatic insects, frog eggs, terrestrial plant matter and terrestrial arthropods. 3. Caged fish reduced the biomass, energy and organic matter donated to pools by tree frog eggs by ～70%, but did not alter insect colonisation or passive allochthonous inputs of terrestrial arthropods and plant material. Terrestrial plant matter and adult aquatic insects provided the most energy and organic matter inputs to the pools (40–50%), while terrestrial arthropods provided the least (7%). Inputs of frog egg were relatively small but varied considerably among pools and over time (3%, range = 0–20%). Absolute and proportional amounts varied by input type. 4. Aquatic predators can strongly affect the magnitude of active, but not passive, inputs and that the effect of recipient habitat quality on active inputs is variable. Furthermore, some active inputs (i.e. aquatic insect colonists) can provide similar amounts of energy and organic matter as passive inputs of terrestrial plant matter, which are well known to be important. Because inputs differ in quality and the trophic level they subsidise, proportional changes in input type could have strong effects on recipient food webs. 5. Cross‐ecosystem resource inputs have previously been characterised as donor‐controlled. However, control by the recipient food web could lead to greater feedback between resource flow and consumer dynamics than has been appreciated so far.     

Influence of male mating history on female reproductive success among monandrous Naryciinae (Lepidoptera: Psychidae)

1. Multiple male copulations can have detrimental effects on female fitness due to sperm limitation. 2. Monandrous Naryciinae females are immobile while the males are short‐lived and do not feed. Multiple male mating is therefore expected to lead to sperm limitation in females. Sperm limitation and male limitation are hypothesised as causes of the repeated evolution of parthenogenetic reproduction in the Psychidae. 3. In this study, the effects of multiple male mating on female reproduction are investigated in several species of Naryciinae by allowing males multiple copulations. The results for two species, Siederia listerella and Dahlica lichenella, are compared. The sex ratios of 53 natural populations are examined for indications of male limitation. 4. Previous copulations by the male increased the female's risk of remaining unfertilised. However, contrary to expectations, those unfertilised females were capable of successful re‐mating. 5. In S. listerella, the number of previous copulations of males negatively influenced female fitness. Females produced 30% fewer offspring if they mated with a previously mated male. In D. lichenella, the older the male and the lower its number of total lifetime copulations, the higher the female's reproductive success. 6. Only a fraction of the investigated populations had a female‐skewed sex ratio, but differences in development time between males and females could lead to reproductive asynchrony. 7. In conclusion, male mating history did not lead to strong sperm limitation in Naryciinae as had been suggested by their life history.     

Unequal maternal investment in offspring quality in relation to predation risk

Equal investment within broods does not always maximize parental reproductive value if the reproductive value of some of the young is low. We examined maternal investment in terms of offspring size in relation to the prospects of survival from predation within broods of the shield bug Elasmucha ferrugata Fabr. (Heteroptera; Acanthosomatidae). Shield bug females guard eggs and first instar nymphs against invertebrate predators by covering the clutch with their body and by behaving aggressively towards their enemies. Survival of eggs was not possible without maternal care. When females were allowed to guard their brood, eggs at the periphery were more vulnerable to predators than eggs at the centre. We found that females laid significantly larger eggs in the safest, central part of the clutch. There seems to be an advantage of large nymph size, since when nymphs were reared separately with low food resources, the larger ones were more likely to survive. Larger nymphs were also more likely to push themselves to the safest, central part of the clutch. Females seem to allocate their resources more to the offspring with the highest probability of avoiding predation. Thus our study supports unequal maternal investment within broods of E.ferrugata.