Analysis of cytosolic and plastidic serine acetyltransferase mutants and subcellular metabolite distributions suggests interplay of the cellular compartments for cysteine biosynthesis in Arabidopsis

In plants, the enzymes for cysteine synthesis serine acetyltransferase (SAT) and O-acetylserine-(thiol)-lyase (OASTL) are present in the cytosol, plastids and mitochondria. However, it is still not clearly resolved to what extent the different compartments are involved in cysteine biosynthesis and how compartmentation influences the regulation of this biosynthetic pathway. To address these questions, we analysed Arabidopsis thaliana T-DNA insertion mutants for cytosolic and plastidic SAT isoforms. In addition, the subcellular distribution of enzyme activities and metabolite concentrations implicated in cysteine and glutathione biosynthesis were revealed by non-aqueous fractionation (NAF). We demonstrate that cytosolic SERAT1.1 and plastidic SERAT2.1 do not contribute to cysteine biosynthesis to a major extent, but may function to overcome transport limitations of O-acetylserine (OAS) from mitochondria. Substantiated by predominantly cytosolic cysteine pools, considerable amounts of sulphide and presence of OAS in the cytosol, our results suggest that the cytosol is the principal site for cysteine biosynthesis. Subcellular metabolite analysis further indicated efficient transport of cysteine, γ -glutamylcysteine and glutathione between the compartments. With respect to regulation of cysteine biosynthesis, estimation of subcellular OAS and sulphide concentrations established that OAS is limiting for cysteine biosynthesis and that SAT is mainly present bound in the cysteine–synthase complex.     

Local adaptation in populations of a Brachionus group plicatilis cryptic species inhabiting three deep crater lakes in Central Mexico

1. Salinity is a strong selective force for many aquatic organisms, affecting both ecological and evolutionary processes. Most of our knowledge on the effects of salinity on rotifers in the Brachionus plicatilis species complex is based mainly on populations from waterbodies that experience broad environmental changes both seasonally and annually. We tested the hypothesis that, despite the supposedly high potential for gene flow among rotifers inhabiting neighbouring environments, constant salinity has promoted local adaptation, genetic population divergence and even cryptic speciation in B. plicatilis complex populations from three deep maar lakes of distinct salinities [1.1, 6.5 and 9.0 g L^?1 total dissolved solids (TDS)] in Central Mexico. 2. To look for local adaptation, we performed common garden experiments to test the effect of different salinities on population density and intrinsic growth rate (r). Then, we evaluated the genetic divergence by sequencing the cytochrome c oxidase subunit I (COI) gene and performed reproductive trials to assess the potential gene flow among the three populations and with other closely related B. plicatilis complex species. 3. We confirmed that the rotifer populations have phenotypic plasticity in tolerance of salinity, but only rotifers from the least saline lake are adapted to low salinity. Among the populations, sequence divergence at COI was very low (just a single haplotype was found), suggesting a persistent founder effect from a relatively recent single colonisation event and a subsequent dispersal from one lake to the others, and a very restricted immigration rate. In the phylogenetic analysis, rotifers from this area of Mexico clustered in the same clade with the middle‐sized species Brachionus ibericus and B. sp. ‘Almenara’. Mexican rotifers showed successful recognition, copulation and formation of hybrids among them, but interpopulation breeding with the Spanish B. ibericus and B. sp. ‘Almenara’ was unsuccessful. 4. We conclude that the B. plicatilis complex populations from these three lakes belong to a new biological species not yet described (presently named B. sp. ‘Mexico’). To our knowledge, this is the first report of local adaptation of a natural B. plicatilis complex population living in freshwater conditions (1.1 g L^?1 TDS).     

Histological characterization of the spawning process in the catarina scallop,Argopecten ventricosus (Sowerby II, 1842) induced by thermal shock and serotonin injection

Summary

The histology of the spawning catarina scallop Argopecten ventricosus was studied to characterize cellular and anatomical changes occurring along the gonad-kidney pathway. Broodstock were conditioned for 25–30 days and induced to spawn with two methods: thermal shock and serotonin by intracardiac injection. Samples of the kidney-gonad-digestive gland complex were fixed at the sperm and oocyte stages of gamete emission and at the end of spawning. Both induction methods elicited gametes, and no particular difference in the microscopic anatomy of the acini-kidney pathway was detected. However, serotonin injection, apart from producing a rough valve opening, sporadic movement (opening and closure of valve), and pronounced foot extension, induced gamete emission in less time than thermal shock. Primary gonad ducts opened to acini to permit sperm emission; at the same time, germinal vesicles broke down in female acini and meiosis restarted. Shortly afterward, oocytes gradually changed form from typically poly-hedral to a more malleable form. This probably contributed to oocyte transport through ciliary activity along the gonad and kidney ducts. Nucleoli disintegration, chromosome condensation, and appearance of meiotic figures were observed along the acini-kidney pathway. Although sperm and oocytes were sometimes observed in gonad or kidney ducts, self-fertilization was rarely observed.     

Daily variations in the optical properties of a small lake

1. The major components of the underwater light field (ULF: vertical attenuation, absorption, scattering and suspensoids including plankton fractions) of Las Madres Lake, a small wind‐sheltered, oligohumic lake in Central Spain, were investigated daily over a period of 3 months at the onset of vernal circulation. 2. Gilvin, arising mostly from the decomposition of reeds in the littoral in autumn, was the main component of vertical attenuation, and its variability explained the highest fraction of absorption variability. Tripton appeared to be the main factor responsible for scattering, and might have resulted from dust deposition from the surrounding mining land. The plankton community played a minor role in attenuation, absorption or scattering throughout the investigation period. 3. Vertical and horizontal mixing dynamics may control the ULF to a certain extent, as most optical properties changed within different mixing periods and poor advective exchanges may have resulted in uneven distribution of water colour in this small lake. 4. Time series analysis showed that most autocorrelations were shorter than a week, inherent properties (absorption, scattering) being delayed longer than apparent properties (attenuation, transparency) as a result of their lower dependence on solar irradiance. A 2‐day lag was observed in cross‐correlations between either gilvin and absorption or tripton and scattering. When different mixing periods at early circulation were considered, however, ULF components changed their relationships and delays with suspensoids and dissolved substances over such periods, probably tracking the dynamics of their controlling factors. 5. Our study, and others at daily, weekly, seasonal, interannual and long‐term scales, demonstrates that ULF is a system upon which different processes are operating at different time scales. Contrary to expectations, however, the variability in the ULF does not increase with time scale and depends partly upon the trophic status of lakes.     

Karyomorphology, heterochromatin patterns and evolution in the genus Ophrys (Orchidaceae)

Karyotype structures and heterochromatin distribution in representative taxa of the genus Ophrys are compared, based on Feulgen-stained and banded somatic metaphase chromosomes. The karyotypes of Ophrys iricolor , O. lupercalis , O. caesiella , O. lutea , O. lunulata , O. x. tardans , O. apifera , O. praecox , O. lacaitae and O. insectifera are described for the first time. The karyological analyses indicate the relationships among the species with respect to asymmetry indices and heterochromatin content. Chromosomal differences have been helpful in clarifying the taxonomic position of Ophrys species that do not have clear affinities. The representative species of Araniferae , Fuciflorae and Ophrys sections exhibited the most asymmetrical karyotypes, while chromosome complements of the O. fusca–O. lutea group, of O. tenthredinifera and of O. bombyliflora proved to be less asymmetrical. Weakly heterochromatic chromosomes, with heterochromatin present mostly in thin centromeric bands, characterize Ophrys C-banded karyotypes. Chromomycin A₃ (CMA) staining revealed that the analysed species exhibit a weak pattern of CMA⁺ bands at centromeric, intercalary or telomeric regions. No DAPI bright blocks were observed. The significance of the karyological data is discussed with regard to the relationships between the analysed species. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 87–99.     

Seasonal clutch size variation of multi-brooded bird species: comparisons between breeding season and latitudes

Single- and multi-brooded species of birds differ in their seasonal patterns of clutch size. Single-brooded species start with a maximum clutch size that declines continuously as the season progresses, whereas the clutch sizes of multi-brooded species usually increase to a mid-season maximum peak and then decrease progressively until the end of the breeding season. Previous studies have shown that multi-brooded migrant species present seasonal patterns that are similar to single-brooded species at high latitudes but similar to multi-brooded non-migratory species at lower latitudes. We studied the Greenfinch Carduelis chloris and Goldfinch C. carduelis populations in eastern Spain (Sagunto, Valencia) between 1975 and 2002 to compare seasonal variations in clutch sizes between years with early and late starts to the breeding season. The period over which clutch sizes increase was longer when the breeding season started earlier. The Goldfinch population showed no pattern of initial increase in clutch size when there was a late start to the breeding season: a late start shortens the season giving them less time to breed, and may also coincide with maximum food availability. Thus, the pattern of single-brooded species was observed. In the Greenfinch population, a trend toward the seasonal pattern of single-brooded species was also observed when the following indices were compared: clutch size increase, modal timing, initial slope and timing of maximum clutch size. We have also compared the seasonal patterns of clutch size of both species in eastern Spain with the patterns observed in Britain. Our results show that for both Goldfinches and Greenfinches, the non-migrant southern populations of Sagunto in eastern Spain do not tend towards a more multi-brooded seasonal pattern of clutch size than the migrant Goldfinches of Britain.     

Climate-driven changes on phytoplankton–zooplankton coupling and nutrient availability in high mountain lakes of Southern Europe

1. The effect of climate variability on phytoplankton and zooplankton dynamics and nutrient availability was studied in two high mountain fishless lakes (La Caldera and Río Seco) of contrasting morphology, hydrology and dissolved inorganic nitrogen : soluble reactive phosphate (DIN : SRP) ratios during 1986 and after a 10‐year‐long drought in 1996 and 1997. 2. Thaw was delayed and water temperatures were lower in both lakes in 1996 than in 1986 and 1997. However, the lake‐specific DIN : SRP ratio was maintained in the 3 years studied, reflecting its local control. 3. On other hand, the presumptive limiting nutrient in each lake, P in La Caldera and N in Río Seco, showed higher concentrations in 1996 versus 1986 and 1997. Significant positive correlations between temperature and chlorophyll a were found in both lakes in 1996 but these relationships were negative or not significant in 1986 and 1997. Zooplankton biomass showed lower values in 1996 than in 1986 or 1997. 4. These findings can be explained by a decoupling of the phytoplankton–zooplankton interaction because of a constraint on zooplankton growth by low temperatures in the coldest year studied. This observation furnishes evidence that regional climatic control on the phytoplankton–zooplankton link can modulate the overall demand for nutrients.