Early research on anther-smut disease: A fuller view of science?

The anther-smut host-pathogen system has provided extensive insights into the evolutionary ecology of disease resistance, transmission modes, host shifts, pathogen specialization, and disease evolution in metapopulations. It also has led to unexpected insights into sex ratio distorters, sex chromosome evolution, and transposable elements in fungi. In addition, anther-smut disease played a major role in Linnaeus' germ theory and the correspondence on parasitic castration between Darwin and Becker, one of the first female botanists. Here, we explicitly highlight some of the realities in the process of science, using an unusual autobiographical approach to describe how we came to collaborate on this system in the 1980s. Using perspectives from our different career stages, we present a surprising narrative that could not be deduced from merely reading the published papers. While our work was grounded in previous ecological and evolutionary theory, it was the product as much of empirical failures and intellectual roadblocks, as the result of a progressive scientific method. Our experiences illustrate not only the "human dimension of science" but more importantly show that linear sequences of hypothesis testing do not necessarily lead to new study systems and new ideas. We suggest there is a need to re-evaluate the scientific method in ecology and evolution, especially where the challenge is to engage in a productive dialog between natural history and theory.

Urban-Soil Pedogenesis Drives Contrasting Legacies of Lead from Paint and Gasoline in City Soil

This study analyzed the impact of urban-soil pedogenesis on soil lead (Pb) contamination from paint and gasoline in the historic core of Durham, North Carolina. Total soil Pb in 1000 samples from streetsides, residential properties, and residual upland and floodplains ranged from 6 to 8825 mg/kg (mean = 211 mg/kg), with 50% of samples between 50 and 200 mg/kg soil Pb. The highest Pb concentrations were within 1 m of pre-1978 residential foundations, with concentrations inversely correlated with house age. Streetside soil Pb concentrations were elevated over the geologic background of <30 mg/kg and correlated with traffic flow. Streetside soil Pb concentrations were lower than Durham streetside soils collected in the 1970s, which was attributed to urban pedogenesis, the complex of natural and human processes that change soils over time. Accelerated erosion redistributes legacy Pb and floodplain sampling indicates sedimentation rates of up to 4 mm/year. Mixing and burial of soil with elevated Pb are also lowering soil Pb concentrations over time. These mechanisms are likely of greater significance on streetsides than near foundation soils. The development of an urban-pedogenesis framework can help guide public health approaches to Pb exposure by incorporating pedogenic processes that reduce and dissipate soil Pb contamination.

Fitter frogs from polluted ponds: The complex impacts of human-altered environments

Human-modified habitats rarely yield outcomes that are aligned with conservation ideals. Landscapes that are subdivided by roads are no exception, precipitating negative impacts on populations due to fragmentation, pollution, and road kill. Although many populations in human-modified habitats show evidence for local adaptation, rarely does environmental change yield outright benefits for populations of conservation interest. Contrary to expectations, we report surprising benefits experienced by amphibian populations breeding and dwelling in proximity to roads. We show that roadside populations of the wood frog, Rana sylvatica, exhibit better locomotor performance and higher measures of traits related to fitness compared with frogs from less disturbed environments located further away from roads. These results contrast previous evidence for maladaptation in roadside populations of wood frogs studied elsewhere. Our results indicate that altered habitats might not be unequivocally detrimental and at times might contribute to metapopulation success. While the frequency of such beneficial outcomes remains unknown, their occurrence underscores the complexity of inferring consequences of environmental change.

INTRAPOPULATIONAL VARIATION IN POLLEN-MEDIATED GENE FLOW IN PLANTAGO LANCEOLATA L

The extent of genetic variation in pollen-mediated gene flow distance was measured for a population of the wind-pollinated herb, Plantago lanceolata. Twenty-nine genotypes were collected from a natural population, clonally replicated, and grown to reproductive maturity in a greenhouse. Relative gene flow distances were measured for each replicate and genotype in a wind tunnel. Approximately five percent of the total variation in gene flow distance was attributable to variation among genotypes. Most of the remaining variation was attributable to differences between the early part of the growing season, when most of the flowering occurs, and the remainder of the season, when flowering is sparse. The rankings of the genotypes' gene flow distances showed significant concordance between the early-season measures and measures from later in the summer. There was no correlation between the average inflorescence height for a plant and the average gene flow distance for that plant. For analysis of pollen characteristics suspected as causal factors of variation in gene flow distance, the variation in gene flow distance was divided into two components: that due to environmental (seasonal) differences, and that due to the differences among genotypes within runs. Variation in both the buoyant properties of the pollen grains and their adhesiveness was significantly partially correlated with environmental variation in gene flow distance, while only the buoyant properties of the pollen grains were significantly partially correlated with among-genotype variation in gene flow distances.

Effect of Heavy Metals Pollution on Soil Microbial Diversity and Bermudagrass Genetic Variation

Heavy metal pollution is a serious global environmental problem as it adversely affects plant growth and genetic variation. It also alters the composition and activity of soil microbial communities. The objectives of this study were to determine the soil microbial diversity, bermudagrass genetic variation in Cd contaminated or uncontaminated soils from Hunan province of China, and to evaluate Cd-tolerance of bermudagrass at different soils. The Biolog method, hydroponic experiments and simple sequence repeat markers were used to assess the functional diversity of microorganisms, Cd-tolerance and the genetic diversity of bermudagrass, respectively. Four of the sampling sites were heavily contaminated with heavy metals. The total bioactivity, richness, and microbial diversity decreased with increasing concentration of heavy metal. The hydroponic experiment revealed that bermudagrass populations collected from polluted sites have evolved, encompassing the feature of a higher resistance to Cd toxicity. Higher genetic diversity was observed to be more in contaminated populations than in uncontaminated populations. Heavy metal pollution can result in adverse effects on plant growth, soil microbial diversity and activity, and apparently has a stronger impact on the genetic structure. The results of this study provide new insights and a background to produce a genetic description of populations in a species that is suitable for use in phytoremediation practices.

Physiological basis of differential zinc and copper tolerance of Verbascum populations from metal-contaminated and uncontaminated areas

Metal contamination represents a strong selective pressure favoring tolerant genotypes and leading to differentiation between plant populations. We investigated the adaptive capacity of early-colonizer species of Verbascum recently exposed to Zn- and Cu-contaminated soils (10-20 years). Two Verbascum thapsus L. populations from uncontaminated sites (NMET1, NMET2), one V. thapsus from a zinc-contaminated site (MET1), and a Verbascum lychnitis population from an open-cast copper mine (MET2) were exposed to elevated Zn or Cu in hydroponic culture under glasshouse conditions. MET populations showed considerably higher tolerance to both Zn and Cu than NMET populations as assessed by measurements of growth and net photosynthesis, yet they accumulated higher tissue Zn concentrations in the shoot. Abscisic acid (ABA) concentration increased with Zn and Cu treatment in the NMET populations, which was correlated to stomatal closure, decrease of net photosynthesis, and nutritional imbalance, indicative of interference with xylem loading and divalent-cation homeostasis. At the cellular level, the sensitivity of NMET2 to Zn and Cu was reflected in significant metal-induced ROS accumulation and ion leakage from roots as well as strong induction of peroxidase activity (POD, EC 1.11.1.7), while Zn had no significant effect on ABA concentration and POD activity in MET1. Interestingly, MET2 had constitutively higher root ABA concentration and POD activity. We propose that ABA distribution between shoots and roots could represent an adaptive mechanism for maintaining low ABA levels and unaffected stomatal conductance. The results show that metal tolerance can occur in Verbascum populations after relatively short time of exposure to metal-contaminated soil, indicating their potential use for phytostabilization.

Classification of genetic variation for cadmium tolerance in Bermudagrass [Cynodon dactylon (L.) Pers.] using physiological traits and molecular markers

Cadmium (Cd) is one of the most toxic pollutants that caused severe threats to animal and human health. Bermudagrass is a dominant species in Cd contaminated soils, which can prevent Cd flow and spread. The objectives of this study were to determine the genetic variations in major physiological traits related to Cd tolerance in six populations of Bermudagrass collected from China, and to examine the genetic diversity and relationships among these accessions that vary in Cd tolerance using molecular markers. Plants of 120 accessions (116 natural accessions and 4 commercial cultivars) were exposed to 0 (i.e. control) or 1.5 mM CdSO4·8/3H2O for 3 weeks in hydroponic culture. Turf quality, transpiration rate, chlorophyll content, leaf water content and growth rate showed wide phenotypic variation. The membership function method was used to comprehensively evaluate Cd-tolerance. According to the average subordinate function value, four accessions were classified as the most tolerant genotypes and four accessions as Cd-sensitive genotypes. The trend of Cd tolerance among the six studied populations was as follows: Hunan > South China > North China > Central China > West South China and Xinjiang population. Phylogenetic analysis revealed that the majority of accessions from the same or adjacent regions were clustered into the same groups or subgroups, and the accessions with similar cadmium tolerance displayed a close phylogenetic relationship. Screening genetically diverse germplasm by combining the physiological traits and molecular markers could prove useful in developing Cd-tolerant Bermudagrass for the remediation of mill tailings and heavy metal polluted soils.

Effect of different arbuscular mycorrhizal fungal isolates on growth and arsenic accumulation in Plantago lanceolata L

The role of indigenous and non-indigenous arbuscular mycorrhizal fungi (AMF) on As uptake by Plantago lanceolata L. growing on substrate originating from mine waste rich in As was assessed in a pot experiment. P. lanceolata inoculated with AMF had higher shoot and root biomass and lower concentrations of As in roots than the non-inoculated plants. There were significant differences in As concentration and uptake between different AMF isolates. Inoculation with the indigenous isolate resulted in increased transfer of As from roots to shoots; AMF from non-polluted area apparently restricted plants from absorbing As to the tissue; and plants inoculated with an AMF isolate from Zn-Pb waste showed strong As retainment within the roots. Staining with dithizone indicated that AMF might be actively involved in As accumulation. The mycorrhizal colonization affected also the concentration of Cd and Zn in roots and Pb concentration, both in shoots and roots.

Effects of lead on the growth, lead accumulation and physiological responses of Pluchea sagittalis

This work aimed to study the process of stress adaptation in root and leaves of different developmental stages (apex, middle and basal regions) of Pluchea sagittalis (Lam.) Cabrera plants grown under exposure to five Pb levels (0, 200, 400, 600 and 1000 μM) for 30 days. Pb concentration and content in roots, stems, and leaves of different developmental stages increased with external Pb level. Consumption of nutrient solution, transpiration ratio, leaf fresh weight, leaf area, and shoot length decreased upon addition of Pb treatments. However, dry weight of shoot parts and roots did not decrease upon addition of Pb treatments. Based on index of tolerance, the roots were much more tolerant to Pb than shoots. δ-aminolevulinic acid dehydratase activity was decreased by Pb treatments, whereas carotenoid and chlorophyll concentrations were not affected. Lipid peroxidation and hydrogen peroxide concentration both in roots and leaves increased with increasing Pb levels. Pb treatments increased ascorbate peroxidase activity in all plant parts, while superoxide dismutase activity increased in leaves and did not change in roots. Catalase activity in leaves from the apex shoot was not affected by Pb, but in other plant parts it was increased. Pb toxicity caused increase in non-protein thiol groups concentration in shoot parts, whereas no significant difference was observed in roots. Both root and shoot ascorbic acid concentration increased with increasing Pb level. Therefore, it seems that Pb stress triggered an efficient defense mechanism against oxidative stress in P. sagittalis but its magnitude was depending on the plant organ and of their physiological status. In addition, these results suggest that P. sagittalis is Pb-tolerant. In conclusion, P. sagittalis is able to accumulate on average 6730 and 550 μg Pb g(-1) dry weight, respectively, in the roots and shoot, a physiological trait which may be exploited for the phytoremediation of contaminated soils and waters.

Variation in arsenic, lead and zinc tolerance and accumulation in six populations of Pteris vittata L. from China

Arsenic, Pb and Zn tolerance and accumulation were investigated in six populations of Pteris vittata collected from As-contaminated and uncontaminated sites in southeast China compared with Pteris semipinnata (a non-As hyperaccumulator) in hydroponics and on As-contaminated soils. The results showed that both metallicolous and nonmetallicolous population of P. vittata possessed high-level As tolerance, and that the former exhibited higher As tolerance (but not Pb and Zn tolerance) than the latter. In hydroponic culture, nonmetallicolous population clearly showed significantly higher As concentrations in fronds than those in metallicolous populations. In pot trials, As concentrations in fronds of nonmetallicolous population ranged from 1060 to 1639 mg kg(-1), about 2.6- to 5.4-folds as those in metallicolous populations. It was concluded that As tolerance in P. vittata resulted from both constitutive and adaptive traits, Pb and Zn tolerances were constitutive properties, and that nonmetallicolous population possesses more effective As hyperaccumulation than metallicolous populations.

Genetic structure and differentiation inMetrosideros polymorpha(Myrtaceae) along altitudinal gradients in Maui, Hawaii

The level and distribution of genetic variability within and amongMetrosideros polymorphapopulations along altitudinal gradients on the island of Maui, Hawaii were examined to assess the extent of genetic differentiation. Sixteen loci encoding 11 enzymes were scored in 17 populations along the NE wet slope of Mt. Haleakala and Kipahulu Valley in East Maui and six populations along the Puu Kukui trail in West Maui. On average, 50% of the loci were polymorphic within populations with an overall mean of 2·15 alleles per locus. The observed heterozygosities for different populations were moderate (0·108–0·220) and conformed to panmixia except for one of the mid-elevation populations. The distribution of allozyme variation indicates that very little differentiation has occurred along altitudinal gradients. Approximately 90% of the total variation resides within populations in East Maui while 95% was found within West Maui populations. The mean populational pair-wise genetic identities (Nei's I) ranged from 0·909 to 0·998. The UPGMA cluster analysis on genetic identity matrices and PCA on allele frequencies revealed marginal altitudinal differentiation. Twenty one alleles out of a total 63 showed statistically significant correlations with environmental variables.

Lead and zinc accumulation and tolerance in populations of six wetland plants

Wetland plants such as Typha latifolia and Phragmites australis have been indicated to show a lack of evolution of metal tolerance in metal-contaminated populations. The aim of the present study is to verify whether other common wetland plants such as Alternanthera philoxeroides and Beckmannia syzigachne, also possess the same characteristics. Lead and zinc tolerances in populations of six species collected from contaminated and clean sites were examined by hydroponics. In general, the contaminated populations did not show higher metal tolerance and accumulation than the controls. Similar growth responses and tolerance indices in the same metal treatment solution between contaminated and control populations suggest that metal tolerance in wetland plants are generally not further evolved by contaminated environment. The reasons may be related to the special root anatomy in wetland plants, the alleviated metal toxicity by the reduced rooting conditions and the relatively high innate metal tolerance in some species.

The Role of Geographic Analysis in Locating, Understanding, and Using Plant Genetic Diversity

The genetic structure of an organism is shaped by various factors, many of which vary significantly over space. In this chapter, we provide insight on how studying geographic patterns may contribute to an improved understanding of variability in genetic structure. We first review the theoretical background on how differences in genetic structure may be generated through processes that are inherently variable over space. We then present novices with some basics on how geographic information systems (GIS) may be adopted to study this variation, including advice on software, data, and the type of research questions that might be addressed. The chapter finishes with a brief review of how spatial analysis has contributed to the conservation and use of plant genetic resources, through an understanding of spatial patterns in species distribution and genetic structure. We conclude that spatial variation is a factor often overlooked in genetic studies and one that merits greater consideration. With the advent of functional genomics and improved quantification of adaptive traits, spatial analysis may be key in understanding variation in genetic structure through careful analysis of genotype-environment interactions.

Lead, zinc and copper accumulation and tolerance in populations of Paspalum distichum and Cynodon dactylon

Both Fankou and Lechang lead/zinc (Pb/Zn) mine tailings located at Guangdong Province contained high levels of total and DTPA-extractable Pb, Zn and Cu. Paspalum distichum and Cynodon dactylon were dominant species colonized naturally on the tailings. Lead, zinc and copper accumulation and tolerance of different populations of the two grasses growing on the tailings were investigated. Tillers of these populations including those from an uncontaminated area were subjected to the following concentrations: 5, 10, 20, 30 and 40 mg l(-1) Pb, 2.5, 5, 10, 20 and 30 mg (l-1) Zn, or 0.25, 0.50, 1 and 2 mg l(-1) Cu for 14 days, respectively, then tolerance index (TI) and EC50 (the concentrations of metals in solutions which reduce 50% of normal root growth) were calculated. The results indicated that both Lechang and Fankou populations of the two grasses showed a greater tolerance to the three metals than those growing on the uncontaminated area, which suggested that co-tolerant ecotypes have evolved in the two grasses. P. distichum collected from Fankou tailings had the highest tolerance to Cu while Lechang population the highest tolerance to Pb and Zn among the tested populations, and tolerance levels in P. distichum were related to metal concentrations in the plants. P. distichum had a better growth performance than C. dactylon when both of them were grown on the tailings sites. Tolerant populations of these species would serve as potential candidates for re-vegetation of wastelands contaminated with Pb, Zn and Cu.

Antimony accumulation in Achillea ageratum, Plantago lanceolata and Silene vulgaris growing in an old Sb-mining area

Preliminary data of a biogeochemical survey concerning antimony transfer from soil to plants in an abandoned Sb-mining area are presented. Achillea ageratum, Plantago lanceolata and Silene vulgaris can strongly accumulate antimony when its extractable fraction in the soil is high (139-793 mg/kg). A. ageratum accumulates in basal leaves (1367 mg/kg) and inflorescences (1105 mg/kg), P. lanceolata in roots (1150 mg/kg) and S. vulgaris in shoots (1164 mg/kg). In these plant species, the efficiency of antimony accumulation decreases when the antimony availability in the soil is high. In A. ageratum and S. vulgaris, the death of the epigeal target part at the end of the growing season contributes to a reduction of the antimony load in the plant. A study to test the use of these species as bioindicators of antimony availability in soil is suggested by our results.

Response of higher plants to lead contaminated environment

Lead concentration is increasing rapidly in the environment due to increased use of its sources by human society. Alarming concentrations of the metal have been reported in dust of densely populated urban areas and, water and land of various areas near the industrial waste disposals. Plants absorb lead and accumulation of the metal have been reported in roots, stems, leaves, root nodules and seeds etc. which increases with the increase in the exogenous lead level. Lead affects plant growth and productivity and the magnitude of the effects depend upon the plant species. Photosynthesis has been found to be one of the most sensitive plant processes and the effect of the metal is multifacial. Nitrate reduction is inhibited drastically in roots by the metal but in the leaves a differential effect is observed in various cultivars. Lead also inhibits nodulation, N-fixation and ammonium assimilation in the root nodules. It appears that the toxic effect of the metal is primarily at physiological level and provision of certain inorganic salts can antagonize the toxic effects to some extent. Further responses of plants to the metal depend on various endogenous, environmental and nutritional factors. Some plants are able to tolerate excess of Pb+2 by involving processes like exclusion, compartmentalization or synthesizing metal detoxifying peptides-the phytochelatins.

Tolerance to SO2, NO2 and their mixture in Plantago major L. populations

The possible evolution of tolerance to NO2, alone or in combination with SO2 was investigated in three populations of Plantago major L., originating from Hyde Park in central London (polluted site), Ascot (clean site) and The Netherlands. Screening for sensitivity to the pollutants was carried out by means of chronic fumigations with NO2 or NO2 plus SO2 and acute fumigations with SO2, NO2 or their mixture. The Hyde Park population showed smaller growth reductions induced by the pollutant mixture, than did the other populations. In contrast no differential response in terms of foliar injury was observed after an acute fumigation with SO2+ NO2, but the Hyde Park population was the most sensitive to NO2 alone. The results indicate that selection for tolerance to SO2 does not confer tolerance to NO2 alone or the pollutant mixture.

Arsenic, cobalt and nickel tolerances in two populations of Silene vulgaris (Moench) Garcke from Ontario, Canada

A population of Silene vulgaris (Moench) Garcke collected from mine tailings near the town of Cobalt, Ontario was compared in its metal tolerance with a population collected at an uncontaminated site (Baymouth, Ontario). Seedlings of the Cobalt population were tolerant to elevated levels of arsenic, cobalt and nickel, both compared with the Baymouth population and with other literature reports for this species. However, the tolerance indices in the Cobalt plants for these toxic elements did not correlate well with their concentration in water extractions in the mine soils. Indices of arsenic tolerance, based on the inhibition of root growth in 12 d experiments, showed a similar response to that in a 28 d experiment for both populations. The latter however, appeared to be a more accurate indicator of As tolerance in S. vulgaris, because the longer-term tolerance indices had lower standard deviations and higher probabilities for tolerance than the short-term tolerance indices. Reduced uptake of As occurred in the roots of tolerant individuals compared with non-tolerant individuals at a low As treatment. At a higher arsenic exposure, however, arsenic entered the roots of tolerant individuals. A partial exclusion or reduced translocation of arsenic to the shoots then appeared to operate in the shoots of tolerant individuals, i.e. arsenic levels were higher in shoots of non-tolerant plants. At the highest arsenic exposure, where the individuals from the Cobalt population were no longer tolerant, this exclusion pattern broke down. From a preliminary selection experiment, some arsenic tolerant individuals occurred in the Baymouth population. This suggests that under circumstances of arsenic contamination this population also has the potential to develop a tolerance to high arsenic exposure.

Cadmium tolerance and co-tolerance in Silene vulgaris (Moench.) Garcke [=S. cucubalus (L.) Wib.]

This paper is the first to report cadmium tolerance in a dicotyledonous species, Silene vulgaris (Moench.) Garcke. The response to cadmium of five populations originating from one uncontaminated and various heavy-metal contaminated sites was examined under standardized conditions for three weeks. The tolerance index (TI), based on the mean relative growth rate (R), was determined. Populations originating from cadmium-contaminated sites showed a distinct tolerance to cadmium. A population from a site enriched only with copper also exhibited a marked co-tolerance to cadmium. A clear difference in biomass production between the sensitive and tolerant populations was attained at 1 μM cadmium. An optimum biomass production in tolerant populations at a metal concentration higher than in the control, as demonstrated for zinc and copper, could not be established for cadmium. The pattern of cadmium uptake and translocation differed between tolerant and sensitive populations. All tolerant populations accumulated cadmium in the roots and showed some degree of restricted transport to the shoots. The effect of cadmium on the elemental distribution in roots and shoots was population-independent for some elements (copper, zinc, potassium) and population-specific for others (phosphorus, magnesium and sodium). The phenomenon of co-tolerance to cadmium is discussed in relation to possible tolerance mechanisms, especially with regard to metal-binding compounds (metallothioneins, phytochelatins).