EFFECTS OF ENVIRONMENTAL STRESS ON COMPONENTS OF REPRODUCTION IN CLARKIA UNGUICULATA

The effects of stress on reproduction in Clarkia unguiculata were investigated by monitoring flower number, seed number and seed wt after subjecting plants to drought and heavy fruit loads, and by monitoring seed number after pollinating overage flowers. Fewer main-stem flowers were produced in drought stressed plants than in non-stressed plants. Drought stress did not affect overall seed numbers and seed wt in 1981, but did significantly affect seed number and wt in different flower age classes. Overall seed numbers were not affected by drought stress in 1982, but seed wt was significantly lower in plants with stressed ovules. Fewer flowers but more seeds per pollination were produced by plants in which all or ½ the flowers were pollinated than by plants in which ¼ or 1/6 of the flowers were pollinated. Seed wts were lowest in plants with a full fruit load and in fruits produced late in the growth cycle. Seed number was variable but high following pollination of flowers with 1–7 day old stigmas, and much lower in flowers with older stigmas.     

Modeccin, the toxin of Adenia digitata. Purification, toxicity and inhibition of protein synthesis in vitro.

1. Modeccin, the toxin of Adenia digitata (Modecca digitata), was purified from the roots of this plant by affinity chromatography on Sepharose 4B. 2. This toxin is a protein with mol.wt. 57000, which on treatment with 2-mercaptoethanol can be dissociated into two subunits of mol.wts. 25000 and 32000. 3. Modeccin inhibits protein synthesis in vitro in a lysate of rabbit reticulocytes and in Ehrlich ascites cells; the effect on cells is decreased in the presence of lactose. 4. Dissociation of modeccin into subunits decreases the toxicity to animals and the inhibition of protein synthesis in cells, but enhances the inhibition of protein synthesis in the lysate system.     

BREEDING SYSTEM AND POLLINATION ECOLOGY OF TRIENTALIS BOREALIS (PRIMULACEAE)

Selfing in Trientalis borealis is reduced by spatial separation of stigma and anthers during anther dehiscence and by internal self-incompatibility. Artificial self-pollination resulted in low levels of fruit set (2.0%). Crosses made within patches of plants yielded variable (0–72.7%), but generally low fruit set (x̄ = 21.4%). This may be caused by patches often consisting of a single genet. In contrast crosses made among patches resulted in uniformly high levels of fruit set (x̄ = 84.3%). Pollinator activity was higher at open sites than at heavily shaded sites and was correlated with fruit set. Pollinator activity, however, showed no correlation with seed set. We conclude that the primary pollinators, Halictid and Andrenid bees, play an important role in the breeding system of the plant by promoting outcrossing but that availability or efficiency of pollinators may limit seed set.     

Outcrossing and paternity in Glycine argyrea by paired fruit analysis

Glycine argyrea (Fabaceae), a perennial wild relative of soybean, has a dual flowering strategy of both self-fertilized cleistogamous flowers and chasmogamous flowers on the same plant. Using allozyme polymorphisms the frequency and pattern of outcrossing was determined. The genotypes of seeds from each of several fruit (legumes) per plant were analysed by starch gel electrophoresis, and the maternal genotype inferred. The maximum likelihood estimates of outcrossing rate for the chasmogamous flowers averaged 0.38. The observed level of heterozygosity in the adult population (h = 0.25) compared with the level expected under random mating (h = 0.32) indicated that partial outcrossing was typical of this population. To analyse the mating pattern further, the pollen genotypes of several seeds per legume for pairs of legumes from the same plant were determined. About 35% of fruit from chasmogamous flowers had no genetically detectable outcross progeny, presumably because they were not cross-pollinated effectively. The majority of the remaining fruit had seed which were of mixed origin (both self-fertilized and outcrossed), suggesting that insect pollination does not preclude self-fertilization. As might be expected from this entomophilous pollination system, the pollen of outcrossed seed within one fruit usually (85% of cross-pollinated legumes) came from one male source. Evidence of pollen carry-over was found in the other legumes. The joint distribution of male sources among the pairs of legumes (paired fruit analysis) showed that non-self sources were shared in 30% of pairs. The probability that two outcrossed seeds from the same fruit would be half-sibs was estimated as 0.15, and for two seeds from different fruit on the same plant as 0.42. There is a hierarchy of genetic identity within and among legumes on the same plant, and on different plants, providing scope for the operation of selection at different levels.     

Determination of morphological variation in subspecies of Isatis glauca Aucher ex Boiss. from Central Anatolia

Isatis glauca Aucher ex Boiss. has four subspecies: glauca, galatica Y?ld?r?ml?, sivasica (Davis) Y?ld?r?ml? and iconia (Boiss.) Davis, naturally growing in Turkey. In this study, 77 accessions from nine I. glauca ssp. populations were characterised in terms of variation in morphological characters, including the number of branches per plant, plant height, diameter of stem base, diameter of middle stem, diameter of apical stem, width and length of fruit, length of fruit stalk, fruit shape, fruit base shape, fruit apices shape, loculus, ondulation, apical process of fruit, fruit weight, basal length of fruit, apical length of fruit, wing width of fruit, loculus length, loculus width, length of seed, dorsal width of seed, lateral width of seed and seed weight. The number of branches had the highest value of coefficient of variation (CV), 0.21–0.86, while the fruit width had the lowest value of CV 0.08–0.20. According to Pearson’s correlation and multiple regression analyses, eco-geographical factors had a substantial effect on morphological variation. A principal component analysis explained 90.61 % of morphological variation through the study of five extracted components. A dendrogram, which was constructed according to the between-group linkages method, based on squared Euclidean distances, represented a hierarchical cluster analysis of 77 accessions. The results of the principal coordinate analysis, which showed differentiation according to morphological characters between nine populations, were consistent with the dendrogram. Consequently, morphological variation of I. glauca ssp. and the significant effects of eco-geographical factors on its morphological variation were discussed.     

The haemocyanin of the whelk, Busycon contrarium (Conrad): aggregation states and subunit structure

1. The haemocyanin of the left-handed whelk Busycon contrarium (Conrad) exists largely as six or more multi-decameric aggregates characterized by sedimentation coefficients of approximately 105S, 132S, 155S, 170S, 185S and about 200-220S. 2. These aggregates represent di- to hepta- or octa-decameric assemblies of the basic haemocyanin decamer having a mol. wt of 4.3 x 10(6)-4.5 x 10(6). 3. The fully dissociated subunits in 8.0 M urea (pH 8.5) and at pH 11.1, 0.01 M EDTA have mol. wts of 4.78 x 10(5) and 4.62 x 10(5), close to one-tenth of the mol. wt of the basic decameric unit of most gastropod haemocyanins. 4. The pH dependence of the mol. wts (Mw), studied by light-scattering at the constant protein concentration of 0.010%, exhibit bell-shaped pH transition profiles with mol. wt values of about 16 x 10(6) in the presence of 0.01 M Mg2+, in the pH region from about pH 4.5-8.0; in the absence of stabilizing divalent ions the observed mol. wt is about 10 x 10(6) at pH 4.5-7.0. Below pH 4.5 and above 7.0-8.0 there is a sharp drop in mol. wt to about 4 x 10(5)-4.5 x 10(5). 5. The transition profiles observed with both the urea and salt series of probes investigated at concentration = 0.010% are found to produce aggregation at low reagent concentrations with mol. wt changes from about 9 x 10(6)-12 x 10(6)-14 x 10(6), followed by a decrease in mol. wt below 4.3 x 10(6)-4.5 x 10(6) of the haemocyanin decamers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Moist-Soil Seed Abundance in Managed Wetlands in the Mississippi Alluvial Valley

Abstract: Managed moist-soil units support early succession herbaceous vegetation that produces seeds, tubers, and other plant parts used by waterfowl in the Mississippi Alluvial Valley (MAV), USA. We conducted a stratified multi-stage sample survey on state and federal lands in the MAV of Arkansas, Louisiana, Mississippi, and Missouri during autumns 2002–2004 to generate a contemporary estimate of combined dry mass of seeds and tubers (herein seed abundance) in managed moist-soil units for use by the Lower Mississippi Valley Joint Venture (LMVJV) of the North American Waterfowl Management Plan. We also examined variation in mean seed abundance among moist-soil units in 2003 and 2004 in relation to management intensity (active or passive), soil pH and nutrient levels, proportional occurrence of plant life-forms (e.g., grass, flatsedge, and forb; vine; woody plants), and unit area. Estimates of mean seed abundance were similar in 2002 (x̄ = 537.1 kg/ha, SE = 100.1) and 2004 (x̄ = 555.2 kg/ha, SE = 105.2) but 35–40% less in 2003 (x̄ = 396.8 kg/ha, SE = 116.1). Averaged over years, seed abundance was 496.3 kg/ha (SE = 62.0; CV = 12.5%). Multiple regression analysis indicated seed abundance varied among moist-soil units inversely with proportional occurrence of woody vegetation and unit area and was greater in actively than passively managed units (R²_adj = 0.37). Species of early succession grasses occurred more frequently in actively than passively managed units (P ≤ 0.09), whereas mid- and late-succession plants occurred more often in passively managed units (P ≤ 0.02). We recommend the LMVJV consider 556 kg/ha as a measure of seed abundance for use in estimating carrying capacity in managed moist-soil units on public lands in the MAV. We recommend active management of moist-soil units to achieve maximum potential seed production and further research to determine recovery rates of seeds of various sizes from core samples and the relationship between seed abundance and unit area. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):707–714; 2008)     

Measuring mast seeding behavior: relationships among population variation,individual variation and synchrony

Mast seeding, or masting, is the variable production of flowers, seeds, or fruit across years more or less synchronously by individuals within a population. A critical issue is the extent to which temporal variation in seed production over a collection of individuals can be viewed as arising from a combination of individual variation and synchrony among individuals. Studies of masting typically quantify such variation in terms of the coefficient of variation (CV). In this paper we examine mathematically how the population CV relates to the mean individual CV and synchrony, concluding that the relationship is a complex one which cannot isolate an overall measure of synchrony, and involves additional factors, principally the number of plants sampled and the mean productivity per plant. Our development suggests some simple approximate relationships of population CV to individual variability, synchrony and the number of individuals. These were found to fit quite well when applied to data from 59 studies which included seed production at the individual level.     

FERTILIZATION DYNAMICS AND PARENTAL EFFECTS UPON FRUIT DEVELOPMENT IN RAPHANUS RAPHANISTRUM: CONSEQUENCES FOR SEED SIZE VARIATION

Seed weight varies significantly within and among fruits of wild radish (Raphanus raphanistrum). To determine sources of this variation, we studied fertilization and seed development following controlled pollinations. Within fruits, central ovules were fertilized prior to distal ovules and attained greater seed size. Ninety-seven percent of the variation in mean seed wt per fruit was explained by an analysis of variance incorporating parental effects, pollination date, and the number of seeds per fruit. We document strong maternal effects on the number of ovules per ovary, the number of fertilized ovules per ovary, the number of seeds per fruit, and mean individual seed wt per fruit. Across females, pollen donor had a slight but significant effect on seed wt; no paternal effects on fertilization rate, zygote number, or seed number per fruit were detected. Within females, with one exception, pollen donor had no significant effect on these components of seed development. Stronger maternal main effects may be due to donor x recipient interactions, cytoplasmic factors, the genetic inequity within triploid endosperm, and/or strict maternal control over resource allocation. The large maternal effects relative to paternal effects may limit the rate at which natural selection acts on paternal traits expressed prior to seed maturation.     

3个香榧单株的种实性状变异分析

对浙江宁海3个香榧单株种实种长、种径、种长径比(种形系数)、单种重、鲜出核率、核长、核径、核长径比(核形指数)、单核重9个性状指标进行了测定和统计分析,为香榧优株选育提供理论依据。结果表明:单种重平均值最大的是宁榧1号(9.17 g),单种重极大值出现在宁榧1号(13.6 g);单核重平均值最大的为宁榧1号(2.93 g)。平均鲜出核率最大的是宁榧3号,达到40.86%,鲜出核率极大值出现在宁榧2号(51.06%)。株间种长、种径、种长径比、核长、核长径比、单种重、单核重、鲜出核率指标均存在显著差异,而核径差异性不显著。种实性状变异幅度最大的指标为单核重(变异系数CV为22.68%),单种重(变异系数CV为21.18%)次之,最小的为种长径比(变异系数CV为4.49%)。种长、种径、核长、核径均与单种重和单核重有显著相关性,鲜出核率与种长、种径、单种重、呈极显著负相关,与种长径比呈极显著正相关。     

五角枫种群表型多样性

为揭示五角枫种群的表型分化程度、变异模式及地理变异规律,以山西19个种群为研究对象,采用巢式方差分析、相关分析、聚类分析等方法从形态学角度对五角枫种群的叶片、果实、种子等23个表型性状进行了系统分析。结果表明:(1)五角枫23个表型性状中除果柄长、着生痕、种子长/宽以外,其余20个表型性状在种群间和种群内均存在显著和极显著差异。(2)19个种群的平均变异系数为18.07。叶片、果实、种子的平均表型变异系数依次为:果实19.78%叶片18.77%种子10.25%。(3)五角枫种群间表型分化系数(VST)均值为48.82%,种群内变异(51.18%)与种群间变异(48.82%)基本相当。叶片、果实、种子表型分化系数的平均值为:叶片58.08%果实41.24%种子25.87%。(4)五角枫叶片、果实和种子的信息多样性指数(H)为:叶片6.1079果实5.9118种子5.2855;多样性指数平均值(D)分别为:果实0.9967叶片0.9961种子0.9948。(5)主成分分析结果显示:五角枫种群表型多样性基本来源为:叶片贡献率果实贡献率种子贡献率。(6)五角枫表型变异呈现出以经度和纬度变异并存的趋势,少数表型性状与经度和纬度呈现显著或极显著相关。(7)利用欧氏距离对五角枫种群进行UPGMA聚类分析,将五角枫19个种群划分为两大类群。五角枫种群具有较高的表型多样性,种群间和种群内均存在丰富的表型变异,与其遗传特点和分布生境等密切相关,研究结果为今后五角枫种质资源的保护和利用奠定了基础。     

Pathogenic effects of Salmonella enterica subspecies enterica serovar Typhimurium on sprouting and growth of maize

The study was undertaken to understand effects and survival of S. enterica subspecies enterica serovar Typhimurium (S. Typhimurium), a zoonotic serovar, on maize seed germination and plant growth. All the four strains of S. enterica subspecies enterica serovar Typhimurium significantly reduced germination of maize seeds in sprouting plates as well as in soil. About > or =2.7x10(3) Salmonella cfu ml(-1) of soaking water, while > or =2.7x10(7) Salmonella cfu g(-1) soil were required to significantly inhibit germination of maize. Similar inhibition of germination could be observed using > or = 16 mg of bacteria free Salmonella cell lysate (CL) protein per g of soil or > or =0.5 mg of CL protein per ml of soaking water in sprouting plates. At the constant dose of 3.6x10(7) to 3.8x10(7) Salmonella cfu or 5 mg cell lysate protein ml(-1) of soaking water, four strains of Salmonella significantly reduced germination, however difference between strains was insignificant. After germination too, maize growth was affected both by Salmonella organism and CL with little strain-to-strain variation. All Salmonella persisted in growing plants from 15 to 35 days of plant age and up to 190 days in soil. Maize plants once grown for a week in sterile soil were resistant to invasion of S. enterica subspecies enterica serovar Typhimurium in their leaves even in doses as high as 7.6x10(9) cfu g(-1) of soil. Salmonella persisted better and longer in plants grown from contaminated seed sown in loam soil, but rarely in plants grew in sandy soil. All maize plants had Salmonella in their stumps even after 35 days of sowing irrespective of kind of soil, primary source of infection (soil or seed) and type of S. enterica subspecies enterica serovar Typhimurium strain. The study revealed that Salmonella is not only zoonotic but a phytopathogen also.     

Inbreeding alters a plant-predispersal seed predator interaction

The effect of inbreeding on genetic diversity is expected to decrease plant defences or vigour-related traits that, in turn, can modify the pattern of attack by herbivores. The selective damage caused by herbivores can produce variable fitness costs between inbred and outcrossed progenies influencing the evolution of a species’ plant mating system. By exposing inbred and outcrossed plants to natural conditions of seed predation, we assessed whether inbreeding increases weevil incidence and infestation, and how weevil seed predation affects the fitness of inbred and outcrossed progeny. To test if inbreeding affected the host’s plant quality, we weighed the biomass of weevils developed in inbred and outcrossed progenies. An additional experiment was carried out to examine whether weevils preferentially attack vigorous plants regardless from the level of inbreeding. The average value of leaf size was 21% larger in outcrossed plants than in inbred plants. Likewise, weevil incidence and infestation were 13 and 40%, respectively, higher on outcrossed plants relative to their inbred counterparts. However, the relative impact of seed predation was significantly lower in outcrossed progeny than in inbred progeny. In contrast, inbreeding did not alter host plant quality and weevils developed in inbred and outcrossed plants had a similar biomass. Variations in fruit number were consistently associated with the infestation level in both experiments, whereas leaf size only predicted the number of weevils in one experiment, suggesting that fruit number is the most influential vigour-related characteristic of a weevil attack. These findings indicate that the costs of inbreeding of the interaction D. stramonium-T. soror were higher for inbred plants than for outcrossed plants. The interaction between seed predation and inbreeding depression could prevent the fixation of selfing as a unique reproductive strategy in D. stramonium.     

Reproductive isolation of a new hybrid species, Senecio eboracensis Abbott & Lowe (Asteraceae)

The nature and extent of reproductive isolation was examined between a new self-compatible hybrid species Senecio eboracensis (2n=40) and its parents, self-incompatible S. squalidus (2n=20) and self-compatible S. vulgaris (2n=40). The triploid F(1) of S. eboracensis x S. squalidus exhibited very low seed set (x=0.63%), and F(2) and F(3) progeny were able to recover nominal levels of fertility (x=23.9 and 9.7%), while F(1) and F(2) offspring of S. eboracensis x S. vulgaris showed reduced seed set (x=63.8 and 58.8%). In both cases, evidence from previous work indicates that reduced fertility is associated with meiotic chromosome mispairing, and is a likely consequence of recombining both parental genomes within this new taxon. No hybrid offspring between S. eboracensis and S. squalidus were found in the wild, and only one such hybrid was recorded among 769 progeny produced by S. eboracensis surrounded by S. squalidus on an experimental plot. Natural crossing between S. eboracensis and S. vulgaris was recorded to be very low (between 0 and 1.46%) in the wild, but rose to 18.3% when individuals of S. eboracensis were surrounded by plants of S. vulgaris. It was concluded that strong breeding barriers exist between the new hybrid species and its two parents. Prezygotic isolation between S. eboracensis and S. vulgaris is likely to be largely due to both species reproducing by predominant self-fertilisation. However, differences recorded for germination, seedling survival, time of flowering and characters associated with pollinator attraction, plus significant clumping of juvenile and adult conspecifics in the wild, probably also contribute to reproductive isolation and ecological differentiation.     

Patterns of seed mass variation and their effects on seedling traits inAlliaria petiolata (Brassicaceae)

Seed mass is considered to be the least plastic component of reproductive yield. Yet, in invasive populations of garlic mustard, Alliaria petiolata, seed mass was highly variable (eightfold among populations, 2.5-7.5 fold within populations, two-threefold within individuals, and 1.4-1.8 fold within fruits). Variation in seed mass among populations explained nearly half of the total variance. Variation among seeds within fruits accounted for a further 25% of variance. Individual seed mass within a plant decreased with increased distance from the main stem, suggesting that access to parental resources limits seed size in a predictable manner. MANOVAs and Roy-Bargmann stepdown analyses revealed significant effects of seed mass, but not seed position (within a fruit or within an infructescence), on an array of subsequent seedling traits. Smaller seeds germinated significantly earlier, and seedlings from small seeds produced their first primary leaves significantly later and grew significantly taller. After accounting for seed mass as a covariate, only one seedling trait, date of first leaf emergence, was affected by seed position in a fruit. Differences in seed mass may therefore affect seedling recruitment via effects on early seedling growth in this weedy species.     

Clumped planting arrangements improve seed production in a revegetated eucalypt woodland

The arrangement of plants within revegetated sites is rarely considered an important characteristic of these communities. However, in natural systems, plant spatial arrangements can influence a range of ecological processes, including pollination and seed set. Pollinators tend to preferentially visit larger and/or more closely spaced populations, with plants in these populations generally receiving more outcrossed pollen, resulting in increased seed set and better quality seed. Similar trends may occur in revegetated populations, but little is known about the influence of planting arrangement on seed production in restored systems. Here, we quantified the effect of plant abundance (number of conspecifics within 100 m) and distance to nearest reproductive conspecific on the level of seed set for six eucalypt species (n = 422 trees in total) in 1 year and for one of these species (Eucalyptus leucoxylon), across three additional years. Seed number per fruit was highly variable both between individuals and within individuals across years. Despite this variability, there was a consistent trend of higher seed production (seed number per fruit) when another reproductive conspecific was within 20 m. In contrast, plant abundance had little influence on seed production. Further investigation of nearest neighbor arrangements found the distance to either the first, second, third, or fourth reproductive neighbors were the key predictors of seed production. Therefore, revegetation designs that consider plant spacing and aggregation, rather than only planting to overall density criteria (i.e. trees/ha), at least for the eucalypts studied here, has the potential to improve seed production in revegetated populations.     

Paternal plastid DNA can be inherited in lentil

Restriction fragment analysis was used to study the inheritance of chloroplast DNA (cpDNA) in F₁ progeny from crosses between Lens culinaris ssp. orientalis and L. culinaris ssp. culinaris. Twenty-five combinations of 11 restriction enzymes and three heterologous probes from Petunia hybrida cpDNA were used to screen six accessions of L.c. culinaris and one accession of L. c. orientalis for restriction fragment length polymorphisms (RFLPs). No variation in cpDNA was observed within the subspecies L. c. culinaris, but the L. c. orientalis accession was unambiguously distinguished from all six L. c. culinaris accessions by two RFLPs. Of ten F₁ progeny from L. c. orientalis x L. c. culinaris crosses, nine had only maternal cpDNA restriction fragments but one F₁ plant inherited cpDNA fragments from both parents. Nuclear DNA inheritance was biparental in all ten F₁ progeny.     

POPULATION VARIATION AND HYBRIDIZATION IN SEA-ROCKETS (CAKILE,CRUCIFERAE): SEED GLUCOSINOLATE CHARACTERS

In a study of intra- and interpopulation variation in seed glucosinolates, remarkable uniformity was found among individuals within the two chemically distinct subspecies of East Coast Cakile edentula. Glucosinolates were used as taxonomic markers in a study of hybridization between ssp. edentula and ssp. harperi where they form mixed populations on the Outer Banks of North Carolina. Thirteen plants with hybrid chemical profiles were detected in a sample of 89 individuals from four populations; the zone of hybridization is narrow, and has persisted for at least eight years. Artificial hybrids of the two subspecies are additive for kinds and intermediate for proportions of seed glucosinolates, and families of F₂'s show a range of recombinant chemical profiles. Natural hybridization was confirmed by recovering hybrid and parental types in 47 progeny of three presumptive wild hybrids. Glucosinolate profile characteristics segregated independently of the segregation patterns for fruit length and seed weight. Selection against particular glucosinolate phenotypes is one possible mechanism maintaining this narrow hybrid zone on the Outer Banks.     

Purification and properties of different forms of modeccin, the toxin of Adenia digitata. Separation of subunits with inhibitory and lectin activity.

1. The subunits were isolated of modeccin (subsequently referred to as modeccin 4B), the toxin purified from the roots of Adenia digitata by affinity chromatography on Sepharose 4B [Gasperi-Campani, Barbieri, Lorenzoni, Montanaro, Sperti, Bonetti & Stirpe (1978) Biochem J. 174, 491-496]. They are an A subunit (mol.wt. 26 000), which inhibits protein synthesis, and a B subunit (mol.wt. 31 000), which binds to cells. Both sununits, as well as intact modeccin, gave single bands on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, but showed some heterogeneity on isoelectric focusing and on polyacrylamide-gel electrophoresis at pH 9.5. 2. A second form of modeccin, not retained by Sepharose 4B, was purified by affinity chromatography on acid-treated Sepharose 6B: this form is subsequently termed modeccin 6B 3. Modeccin 6B has a molecular weight indistinguishable from that of modeccin 4B, and consists of two subunits of mol.wts. 27 000 and 31 000, joined by a disulphide bond. The subunits were not isolated because of their high insolubility in the absence of sodium dodecyl sulphate. 4. As compared with modeccin 4B, modeccin 6B is slightly less toxic to animals, does not agglutinate erythrocytes, and is a more potent inhibitor of protein synthesis in a lysate of rabbit reticulocytes, giving 50% inhibition at the concentration of 0.31 microgram/ml.     

Patterns of genetic diversity in outcrossing and selfing populations of Arabidopsis lyrata

Arabidopsis lyrata is normally considered an obligately outcrossing species with a strong self-incompatibility system, but a shift in mating system towards inbreeding has been found in some North American populations (subspecies A. lyrata ssp. lyrata). This study provides a survey of the Great Lakes region of Canada to determine the extent of this mating system variation and how outcrossing rates are related to current population density, geographical distribution, and genetic diversity. Based on variation at microsatellite markers (progeny arrays to estimate multilocus outcrossing rates and population samples to estimate diversity measures) and controlled greenhouse pollinations, populations can be divided into two groups: (i) group A, consisting of individuals capable of setting selfed seed (including autogamous fruit set in the absence of pollinators), showing depressed outcrossing rates (T(m) = 0.2-0.6), heterozygosity (H(O) = 0.02-0.06) and genetic diversity (H(E) = 0.08-0.10); and (ii) group B, consisting of individuals that are predominantly self-incompatible (T(m) > 0.8), require pollinators for seeds set, and showing higher levels of heterozygosity (H(O) = 0.13-0.31) and diversity (H(E) = 0.19-0.410). Current population density is not related to the shift in mating system but does vary with latitude. Restricted gene flow among populations was evident among all but two populations (F(ST) = 0.11-0.8). Group A populations were more differentiated from one another (F(ST) = 0.78) than they were from group B populations (F(ST) = 0.59), with 41% of the variation partitioned within populations, 47% between populations, and 12% between groups. No significant relationship was found between genetic and geographical distance. Results are discussed in the context of possible postglacial expansion scenarios in relation to loss of self-incompatibility.