Adjustment of growth, starch turnover, protein content and central metabolism to a decrease of the carbon supply when Arabidopsis is grown in very short photoperiods

Arabidopsis was grown in a 12, 8, 4 or 3 h photoperiod to investigate how metabolism and growth adjust to a decreased carbon supply. There was a progressive increase in the rate of starch synthesis, decrease in the rate of starch degradation, decrease of malate and fumarate, decrease of the protein content and decrease of the relative growth rate. Carbohydrate and amino acids levels at the end of the night did not change. Activities of enzymes involved in photosynthesis, starch and sucrose synthesis and inorganic nitrogen assimilation remained high, whereas five of eight enzymes from glycolysis and organic acid metabolism showed a significant decrease of activity on a protein basis. Glutamate dehydrogenase activity increased. In a 2 h photoperiod, the total protein content and most enzyme activities decreased strongly, starch synthesis was inhibited, and sugars and amino acids levels rose at the end of the night and growth was completely inhibited. The rate of starch degradation correlated with the protein content and the relative growth rate across all the photoperiod treatments. It is discussed how a close coordination of starch turnover, the protein content and growth allows Arabidopsis to avoid carbon starvation, even in very short photoperiods.     

Adjustment of growth and central metabolism to a mild but sustained nitrogen-limitation in Arabidopsis

We have established a simple soil-based experimental system that allows a small and sustained restriction of growth of Arabidopsis by low nitrogen (N). Plants were grown in a large volume of a peat–vermiculite mix that contained very low levels of inorganic N. As a control, inorganic N was added in solid form to the peat–vermiculite mix, or plants were grown in conventional nutrient-rich solids. The low N growth regime led to a sustained 20% decrease of the relative growth rate over a period of 2 weeks, resulting in a two- to threefold decrease in biomass in 35- to 40-day-old plants. Plants in the low N regime contained lower levels of nitrate, lower nitrate reductase activity, lower levels of malate, fumarate and other organic acids and slightly higher levels of starch, as expected from published studies of N-limited plants. However, their rosette protein content was unaltered, and total and many individual amino acid levels increased compared with N-replete plants. This metabolic phenotype reveals that Arabidopsis responds adaptively to low N by decreasing the rate of growth, while maintaining the overall protein content, and maintaining or even increasing the levels of many amino acids.     

Evolution and determinants of host specificity in the genus Lamellodiscus (Monogenea)

The evolution and determinants of host specificity in Lamellodiscus species (Monogenea, Diplectanidae) were investigated. The 20 known Mediterranean species were studied, all parasites of fishes from the family Sparidae (Teleostei). An index of specificity, which takes into account the phylogenetic relationships of their fish host species, was defined. The link between specificity and its potential determinants was investigated in a phylogenetic context using the method of independent contrasts. Host specificity in Lamellodiscus species appeared to be highly constrained by phylogeny, but also linked to host size. Mapping specificity onto the parasite phylogenetic tree suggests that specialist species do not represent an evolutionary dead end, and that specialization is not a derived condition. It is hypothesized that the ability to be generalist or specialist in Lamellodiscus is controlled by intrinsic, phylogenetically-related characteristics, and that specialist species tend to use large hosts, which may be more predictable.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 431−443.     

Rapid morphological change in stream beetle museum specimens correlates with climate change

Abstract 1. Climate change has been occurring at unprecedented rates and its impacts on biological populations is beginning to be well documented in the literature. For many species, however, long‐term records are not available, and trends have not been documented. 2. Using museum specimens from southern USA, we show that the stream‐dwelling beetle Gyretes sinuatus has shown an 8% increase in body size and change in body shape (fineness ratio) from 1928 to 1988. Any directional morphological change observed over time could be an indicator of a microevolutionary response. 3. During these 60 years, there have also been changes in temperature, precipitation, and location of collection sites. Unlike the global trend, mean annual temperature in the region has decreased, and furthermore, total annual precipitation has increased. By investigating how these various ecological and geographical variables may affect body size and shape, we can examine which pressures may promote larger and/or thinner beetles. 4. Results indicate that mean annual temperature was the most predictive variable for the change in size and shape. We suggest there is an adaptive role for temperature on body size and shape of stream dwelling organisms. 5. We found that museum specimens can be invaluable resources of information when collection date and location information is available. We promote the use of such specimens for future studies of the morphological response to climate change.     

Wintering behaviour and spatial ecology of Eurasian Woodcock Scolopax rusticola in western France

The spatial ecology of wintering Eurasian Woodcocks Scolopax rusticola was investigated to determine whether hunting-free forest reserves offer adequate protection to all individuals. The analysis of movements performed by 65 radiotagged Woodcocks during three consecutive winters in Brittany revealed the existence of three types of individual strategies. During daylight hours, 34% of birds remained in a unique core area (of 1.1 ha) during January and February while 18% used several core areas successively (never came back to a previously used core) and 48% alternated between several core areas (exploratory movements around several core areas visited several times). Alternating diurnal strategies seemed to result from a lower abundance of food (earthworms), whereas this was not the case in the unique core-use strategy. The successive core-use strategy was considered as a subset of the 'unique' strategy, for which birds were forced to change sites because of a lower abundance of food after depletion. During the night, 62% of birds showed alternative core-use whereas 33% lived in a unique core and the 'successive' strategy was almost absent. As food abundance was similar in the night cores used by birds under each strategy, we discuss the reasons for the nocturnal strategies in relation to individual differences in territoriality or the ability to detect predators. Both diurnal and nocturnal strategies led most of the birds to leave the reserve, and the important use of bocage and hedges by day (by 39% of birds) and meadows at night (83% of birds used meadows on more than 70% of nights), around the protected forest, call for their inclusion in management plans around reserves.     

The tobacco Ntann12 gene, encoding an annexin, is induced upon Rhodoccocus fascians infection and during leafy gall development

Annexins are calcium-binding proteins that have been associated in plants with different biological processes such as responses to abiotic stress and early nodulation stages. Until now, the implication of annexins during plant–pathogen interactions has not been reported. Here, a novel plant annexin gene induced in tobacco BY-2 cell suspension cultures infected with the phytopathogenic bacterium Rhodococcus fascians (strain D188) has been identified . Expression of this gene, called Ntann12 , is also induced, but to a lower extent, by a strain (D188-5) that is unable to induce leafy gall formation. This gene was also induced in BY-2 cells infected with Pseudomonas syringae but not in cells infected with Agrobacterium tumefaciens or Escherichia coli. Ntann12 expression was also found to be stimulated by abiotic stress, including NaCl and abscissic acid, confirming a putative role in stress signal transduction pathways. In addition, promoter- GUS analyses using homozygous transgenic tobacco seedlings showed that the developmentally controlled expression of Ntann12 is altered upon R. fascians infection. Finally, up-regulation of Ntann12 during leafy gall ontogenesis was confirmed by RT-qPCR. Discussion is focused on the potential role of Ntann12 in biotic and abiotic stress responses and in plant development, both processes that may involve Ca²⁺-dependent signalling.     

Molecular analysis of Gigaspora (Glomales, Gigasporaceae)

This work presents a cooperative effort to integrate new molecular (isozyme and SSU analyses) characters into the morphological taxonomy of the genus Gigaspora (Glomales). Previous analyses of published Gigaspora SSU sequences indicated the presence of a few polymorphic nucleotides in the region delimited by primers NS71-SSU 1492'. In our study, the SSU of 24 isolates of arbuscular mycorrhizal (AM) fungi from the Gigasporaceae were amplified and the NS71-SSU 1492' region was directly sequenced. The corresponding sequences of four more isolates of AM fungi from Gigasporaceae, already published, were also included in our analyses. Three Gigaspora groups were identified on the basis of a 6 nucleotide-long 'molecular signature': Gigaspora rosea group ( G. rosea + G. albida ), Gigaspora margarita group ( G. margarita + G. decipiens ) and Gigaspora gigantea , which constituted a group by itself. The isozyme profiles (malate dehydrogenase, MDH) of 12 of these 28 isolates, and seven other isolates not sequenced, were compared. The results obtained further supported the grouping of isolates provided by the SSU analysis. Both SSU and MDH analysis indicated that two out of the 35 isolates had been misidentified, which was confirmed when their morphology was reassessed. The use of the Gigaspora intrageneric molecular signature as a quick, unambiguous and objective method to recognize Gigaspora isolates under any (field or laboratory) experimental conditions is suggested.