Physiological Changes in the Hemiparasite Rhinanthus serotinus before and after Attachment

Growth of the hemiparasite Rhinanthus serotinus (Schönh.) Oborny was greatly stimulated after attachment of the parasite to the roots of the host plant, Hordeum vulgare L. In order to find the limiting factors for the growth of Rhinanthus without a host, unattached and attached Rhinanthus plants were compared. Within I day after attachment the contents of nitrogen, phosphorus, potassium, magnesium, and sodium increased considerably. Organic nitrogen and phosphorus compounds were rapidly synthesized in attached Rhinanthus. The accumulation of sugars in unattached Rhinanthus and the decrease in sugar content after attachment suggested that the main requirement from the host was not for carbohydrates.     

Maintenance of species integrity in sympatrically occurring Rhinanthus minor and R. serotinus in The Netherlands

Summary In certain localities, R. minor and R. serotinus grow sympatrically and the flowering-periods overlap. The species hybridize but can still be recognized as distinct taxonomic entities. In the field s x m crosses can be expected to occur more frequently than the reverse, on the basis of flower morphology and pollinator (bumblebee) efficiency. Observation of pollen germination, pollen tube growth, seed set, and seed germination in artificial, reciprocal crosses permits the conclusion that a single m x s pollination leads to more offspring than a single s x m pollination. The two species are isolated from each other by a series of mechanisms none of which is 100% effective by itself, but their combined action comes close to that figure. The leakages in the ethological barrier against hybridization are closed, partly, by physiological mechanisms.     

Water flows in the parasitic association Rhinanthus minor/Hordeum vulgare

Using the facultative root hemiparasite Rhinanthus minor and its host Hordeum vulgare several aspects of water relations have been measured in this parasitic association. Extraction of xylem sap by the parasite from the host's roots is facilitated by con siderably higher transpiration per leaf area in the parasite than in the host and by the fact that stomata of attached Rhinanthus were open all day and night despite extremely high ABA concentrations in the leaves. By comparison, another root hemiparasite, Melampyrum arvense, parasitizing various grasses in the field, showed normal diurnal stomatal behaviour. The abnormal behaviour of Rhinanthus stomata was not due to anatomical reasons as closure could be induced by applying high external ABA concentrations. Remarkable differences have been detected between the hydraulic conductance of barley seminal roots showing relatively low values and that of Rhinanthus seminal roots showing very high values. The latter could be related to the observed high ABA concentrations in these roots. Whole plant water uptake, transpirational losses, growth-dependent deposition, and the flows of water within the plants have been measured in singly growing Rhinanthus and Hordeum plants and in the parasitic association between the two. Water uptake, deposition and transpiration in Rhinanthus were dramatically increased after attachment to the barley host; most of the water used by the parasite was extracted as xylem sap from the host, thereby scavenging 20% of the total water taken up by the host's roots. This water uptake by the parasitized host, however, due to a parasite-induced reduction in the host's growth, was decreased by 22% as compared to non-parasitized barley. The overall changes in growth-related water deposition in the host and parasite pointed to decreased shoot growth and relatively favoured root growth in the host and to strongly favoured shoot growth in the parasite. These changes in the host became more severe, when more than one Rhinanthus was parasitizing one barley plant.     

Effects of intensity and duration of infection by a hemiparasitic plant, Rhinanthus serotinus, on growth and reproduction of a perennial grass, Agrostis capillaris

Arising from annual variation in parasitic plant population densities, substantial yearly changes may occur in the parasitic load of an individual perennial host. We conducted two two-year greenhouse pot experiments to examine the effects of varying intensities and duration of infection by an annual root hemiparasitic plant. Rhinanthus serotinus, on the growth and reproduction of its perennial host grass. Agrostis capillaris. In the first experiment, one host plant was growing either alone or under a load of 1 or 3 root hemiparasitic plants for one growing season, and during the next season all hosts continued their life free of hemiparasites. In the second experiment, the host plants either grew alone or were parasitised by 1 or 2 root hemiparasitic plants either during the first growing season only or during two successive seasons (the parasitic load being the same in the two seasons). In both experiments, the root hemiparasites markedly reduced the growth and reproduction of their perennial hosts. In the first experiment, the negative effects of parasites on host performance increased with the increase in intensity of parasitic infection from one to three parasites. The harmful effects of hemiparasitim were carried over to the following season; hosts parasitised during the previous season with one or three parasites produced significantly less biomass than those without parasites. In addition, hosts parasitised by three parasites during the first season produced significantly less panicles in the second season than those parasitised by one parasite and those without parasites. The second experiment showed that the production of biomass of A. capillaris during the second season was, but the production of panicles was not affected by the duration of parasitic infection. In addition, in this experiment, the second season biomass of A. capillaris depended on the intensity of infection (1 vs 2 parasites), but the production of panicles was unaffected by the number of parasites.     

Fitness of reciprocal F1 hybrids between Rhinanthus minor and Rhinanthus major under controlled conditions and in the field

The performance of first‐generation hybrids determines to a large extent the long‐term outcome of hybridization in natural populations. F₁ hybrids can facilitate further gene flow between the two parental species, especially in animal‐pollinated flowering plants. We studied the performance of reciprocal F₁ hybrids between Rhinanthus minor and R. major, two hemiparasitic, annual, self‐compatible plant species, from seed germination to seed production under controlled conditions and in the field. We sowed seeds with known ancestry outdoors before winter and followed the complete life cycle until plant death in July the following season. Germination under laboratory conditions was much lower for the F₁ hybrid formed on R. major compared with the reciprocal hybrid formed on R. minor, and this confirmed previous results from similar experiments. However, this difference was not found under field conditions, which seems to indicate that the experimental conditions used for germination in the laboratory are not representative for the germination behaviour of the hybrids under more natural conditions. The earlier interpretation that F₁ hybrid seeds formed on R. major face intrinsic genetic incompatibilities therefore appears to be incorrect. Both F₁ hybrids performed at least as well as and sometimes better than R. minor, which had a higher fitness than R. major in one of the two years in the greenhouse and in the field transplant experiment. The high fitness of the F₁ hybrids confirms findings from naturally mixed populations, where F₁ hybrids appear in the first year after the two species meet, which leads to extensive advanced‐hybrid formation and introgression in subsequent generations.     

Role of Ethylene in the Germination of the Hemiparasite Striga hermonthica

Seed germination of the hemiparasitic angiosperm Striga hermonthica (Del.) Benth is elicited by compounds present in the root exudates of the host plant. Although a variety of compounds can substitute for the host-derived signal, the mechanism through which these act is unknown. In the present study, an inhibitor of ethylene biosynthesis, aminoethoxyvinyl glycine, was found to inhibit germination. Addition of an intermediate in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid, was found to override this inhibition and to act as a substitute for the host-derived signal. 2,5-Norbornadiene, an inhibitor of ethylene action, was also found to inhibit germination. Ethylene is rapidly produced by Striga seeds after treatment with host root exudates. These results are consistent with a model for Striga seed germination in which host-derived signals and other compounds act by eliciting the synthesis of ethylene and in which ethylene itself initiates the biochemical changes leading to germination.     

Positive and Negative Interactions among Individuals of a Root Hemiparasite

Abstract: I studied the effects of a wide range of densities on establishment, survival, growth and reproduction of the annual root hemiparasite Rhinanthus alectorolophus in a field experiment. Seeds of the parasite were sown with those of a mixture of grassland plants as potential hosts. In most plants, seedling survival is strongly reduced by self-thinning at high densities, but in R. alectorolophus the proportion of seeds producing a young plant increased linearly with sowing density, indicating positive interactions among seedlings. Because survival to maturity was not influenced by density, the number of flowering plants per seed sown also increased with density. In contrast, mean plant size and reproduction were strongly reduced at high densities. It is suggested that resource sharing among parasites connected by haustoria is the most likely mechanism responsible for the reduced mortality of seedlings at high densities. The results indicate that facilitation among cohorts of conspecific root hemiparasites can increase the recruitment of young plants. The number of seeds produced per seed sown (a multiplicative fitness measure) was, however, independent of density in Rhinanthus because the early positive effects of density on recruitment were compensated later by the negative effects of crowding on growth and reproduction. Increased survival of seedlings could, however, indirectly increase fitness because it will increase the genetic diversity of offspring and may thus, for instance, reduce the impact of pathogens.     

A European phylogeography of Rhinanthus minor compared to Rhinanthus angustifolius: unexpected splits and signs of hybridization

Rhinanthus minor and Rhinanthus angustifolius (Orobanchaceae) are annual hemiparasites, which occur sympatrically in Europe and are known to hybridize. We studied chloroplast and nuclear (amplified fragment length polymorphism [AFLP]) diversity in R. minor and compared genetic structuring in this species with R. angustifolius by analyzing the AFLP data for both species simultaneously. The AFLP data revealed that populations in Italy, Greece, and southeast Russia initially identified as R. minor were so distant from the other R. minor populations that they probably belong to another, yet unidentified taxon, and we refer to them as Rhinanthus sp. R. minor s.s. showed a clear geographic genetic structure in both the chloroplast DNA (cpDNA) and nuclear genome. The simultaneous analysis of both species shed new light on the previously published findings for R. angustifolius, because some populations now turned out to belong to R. minor. The admixture analysis revealed very few individuals of mixed R. minor-R.angustifolius ancestry in the natural populations in the west of Europe, while admixture levels were higher in the east. The combined haplotype network showed that haplotype H1 was shared among all species and is likely to be ancestral. H2 was more abundant in R. angustifolius and H3 in R. minor, and the latter probably arose from H1 in this species in the east of Europe. The occurrence of H3 in R. angustifolius may be explained by introgression from R. minor, but without interspecific admixture, these are likely to have been old hybridization events. Our study underlines the importance of including related species in phylogeographic studies.     

The Germination of the Seeds of Rhinanthus Crista-galli

The germination of the seeds of Rhinanthus Crista-galli hasbeen induced by exposing them to moisture at 2° C. for periodsof from 17 weeks to over a year, depending on the amount ofdry storage to which the seeds had previously been subjected.Germination could not be brought about by moisture-treatmentat 20° C. During moisture-treatment at 2° C. the respirationrate falls significantly after an initial increase, and thengradually rises, after which germination takes place. Generally,respiration is significantly lower during moisture-treatmentat 20° C. Analyses of the treated seeds suggest that therespiratory substrate might be protein. It was found by paperchromatography that during moisture-treatment at 2° C. thenumber of amino-acids in the alcohol extract first diminishesand then increases, reaching a maximum in the ungerminated seedjust before germination becomes apparent. Differences were detectedin the amino-acids found in the alcohol extracts of seeds treatedat 2° C. compared with those moisture-treated at 20°C. Reasons are given which suggest that the limiting factorin the germination process may be the nature and rate of thehydrolysis of the reserve proteins of the seeds.     

Suppression of host photosynthesis by the parasitic plant Rhinanthus minor

BACKGROUND AND AIMS: Parasitism is well understood to have wide-ranging deleterious effects on host performance in species thus far characterized. Photosynthetic performance reductions have been noted in the Striga-Zea mays association; however, no such information exists for facultative hemiparasitic plants and their hosts, nor are the effects of host species understood. METHODS: Chlorophyll fluorimetry was used to study the effects of parasitism by the hemiparasite Rhinanthus minor on the grass Phleum bertolinii and the forb Plantago lanceolata, and the effects of host species on the photosynthetic apparatus of R. minor. KEY RESULTS: Parasitism by Rhinanthus led to a significant decrease in the host, and total (host + parasite) biomass in Phleum; however, in Plantago, no significant repression of growth was noted. Maximum quantum yield (F(v)/F(m)) was reduced in parasitized Plantago, relative to control plants, but not in Phleum. F(v)/F(m) was significantly lower in R. minor parasitizing Phleum than Plantago, suggesting Phleum to be a superior host to Plantago for R. minor. Steady-state quantum yield (Phi(PSII)) was significantly depressed in parasitized Phleum, but only at low irradiances in Plantago. Phi(PSII) was very low for R. minor grown on Plantago, but not Phleum. CONCLUSIONS: Shown here is the first evidence of the suppression of host photosynthesis by a facultative hemiparasitic plant, which has significant effects on total biomass production. Host identity is a significant factor in parasite success, with the forb Plantago lanceolata exhibiting apparent chemical as well as previously identified physical defences to parasitism. It is proposed that the electron transport rate (as denoted by Phi(PSII)) represents the limiting factor for biomass accumulation in this system, and that Plantago is able to suppress the growth of Rhinanthus by suppressing the electron transport rate.     

Water relations and growth of shrubs before and after fire in a semi-arid woodland

Summary Plant water relations and shoot growth rate of shrubs resprouting after fire or unburnt were measured in a semi-arid poplar box (Eucalyptus populnea) shrub woodland of eastern Australia. In vegetation unburnt for about 60 years, the dawn xylem water potential (_x) of the dominant shrub species was about-1.0 MPa when the soil was wet and-8.0 MPa when the soil was very dry. At any one time, the dominant shrub species,Eremophila mitchellii, E. sturtii, Geijera parviflora andCassia nemophila, were similar in _x butAcacia aneura andDodonaea viscosa were consistently higher in _x than this group when the soil was moist and lower when the soil was dry. The dominant tree species,Eucalyptus populnea andE. intertexta, appeared to have access to additional water beneath the hardpan which is located 60–80 cm below the surface. When shrubs were under extreme water stress (_x of-8 MPa), the trees had a _x of-3 to-3.6 MPa. Following a fire, both _x and leaf stomatal conductance (g _s) of resprouting shrubs were higher for about 5 years than comparable-aged unburnt vegetation, with relative differences in _x increasing with drought stress. Elongation rate of resprouts was positively linked to prefire shrub height in 3 of 4 species. However, shrubs resprouting after high intensity fires had substantially higher rates of shoot elongation than after low intensity fires which were in turn higher than for foliar expansion of unburnt shrubs. It is concluded that the growth rate of resprouting shrubs is primarily determined by physiological/ morphological factors associated with plant size but is also assisted by greater availability of water and possibly nutrients for a period after fire.     

Water Relations of Nitella Translucens

Summary

Volume changes in interodal cells of Nitella translucens have been measured by three methods: weight changes, static length changes and kinetic changes. We have obtained consistent results by the different methods which indicate that the volume change between incipient plasmolysis and full turgor is usually in the range 2 1/2–5 per cent. In addition, our confirm the values for the hydraulic conductivity (L_p) of these cells which have previously been obtained in transcellular osmosis experiments, and we have observed an apparent polarity of L_p similar to that found in these experiments.     

Host selectivity and the mediation of competition by the root hemiparasite Rhinanthus minor

Summary Rhinanthus minor (Yellow-rattle) was grown in replacement series mixtures with Lolium perenne and Trifolium repens. The hemiparasitic interaction resulted in Relative Yield Totals (the sum of the yields in mixture relative to those in monoculture) considerably above 2. The hemiparasite caused a greater decrease in the yield of the legume and also performed better on the legume, indicating that T. repens was a better host for R. minor than L. perenne under the experimental conditions. When L. perenne and T. repens were grown in binary mixture with or without R. minor the hemiparasite affected considerably the competitive relationship between the two species by selectively parasitizing the legume. The effect of R. minor on competition between the two species was, however, dependent upon the nutrient status of the soil: the higher the level of soil nitrogen the fewer haustorial connections were made with T. repens and the less was the depression in its yield. In another series of experiments in which Festuca rubra, Holcus lanatus and L. perenne were grown in various binary mixtures with or without R. minor it was also shown that the yield of a preferred host was depressed to the advantage of a non-preferred host. It is suggested that the mediation of competition by the hemiparasite provides a mechanism by which it might affect the structure and diversity of plant communities.     

Water Relations of Evergreen Sclerophylls. I. Seasonal Changes in the Water Relations of Eleven Species from the Same Environment

Leaf water relationships were studied in eleven evergreen sclerophyllspecies from a macchia near Athens, Greece. Water (     

The Water Relations of Pinus sylvestris

Comparative field studies of transpiration rate and drying-transpiration in Scots pine were carried out in the autumns of 1964 and 1965 and in the early summer of 1966. The experimentl material was nineteen to twinty year old grafts, of the same clone but growing on different types of ground, or of different clones but growing in close proximity and under the same environmental conditions. Transpiration rates were measured on detached shoots. The results indicated that the type of ground did not very much modify the responses of the shoots to illumination-darkness treatment. Drying-transpiration is here defined as the transpiration occurring when detached shoots are prevented from water uptake. Measurements were made of the rate of loss of weight and the amount of water given off from illuminated shoots. Defferences were found both in the rate of weight loss, and in the amount of water given off, between pine trees of the same clone but growing on different types of ground, and between pine trees of different clones but growing on the same type of ground.     

The Water Relations of Pinus sylvestris

The water potential (β) in ten-year-old Scots pine trees (Pinus sylvestris L.) from four different latitudinal provenances ranging from 57° N to 67° N, growing in close proximity to each other, was measured in a pressure chamber during five selected periods between May 1972 and March 1973. Diurnal and seasonal patterns of φ are presented in relation to irradiance, air temperature and vapour pressure deficit (D) for one cloudy and one clear day in each experimental period. The largest daily amplitude in φ was found at the beginning and end of summer, indicating a larger resistance to water flow from soil to needles. As the soil water potentials (measured as pre-dawn values) were, at the same time, the highest for the year, it is suggested that these changes in resistance from period to period mainly take place in the trees. Plots of φ against D during clear days, showed marked hysteresis as the result of the simultaneous influence on φ of several environmental factors. Close linear relations resulted when φ was plotted against potential evaporation rate (calculated from the Pennman-Monteith formula). The slopes of these regression lines, essentially the flow resistance, showed marked seasonal variations, with the largest resistance found at the beginning and end of summer. In most periods the water relations of the trees from different provenances were strikingly similar. A continuous change in the water relations of the remote provenances towards the situation for the “home-provenance” is indicated by the experimental results. It is concluded that trees from different latitudes after ten years of growth have about the same chance as the home provenance to survive periods during which their water balance might become critical.     

Genetic variation changes the interactions between the parasitic plant-ecosystem engineer Rhinanthus and its hosts

Within-species genetic variation is a potent factor influencing between-species interactions and community-level structure. Species of the hemi-parasitic plant genus Rhinanthus act as ecosystem engineers, significantly altering above- and below-ground community structure in grasslands. Here, we show the importance of genotypic variation within a single host species (barley-Hordeum vulgare), and population-level variation among two species of parasite (Rhinanthus minor and Rhinanthus angustifolius) on the outcome of parasite infection for both partners. We measured host fitness (number of seeds) and calculated parasite virulence as the difference in seed set between infected and uninfected hosts (the inverse of host tolerance). Virulence was determined by genetic variation within the host species and among the parasite species, but R. angustifolius was consistently more virulent than R. minor. The most tolerant host had the lowest inherent fitness and did not gain a fitness advantage over other infected hosts. We measured parasite size as a proxy for transmission ability (ability to infect further hosts) and host resistance. Parasite size depended on the specific combination of host genotype, parasite species and parasite population, and no species was consistently larger. We demonstrate that the outcome of infection by Rhinanthus depends not only on the host species, but also on the underlying genetics of both host and parasite. Thus, genetic variations within host and parasite are probably essential components of the ecosystem-altering effects of Rhinanthus.     

大棕蝠江南亚种回声定位声波特征与分析

在自建录音棚内录制大棕蝠汀南亚种Eptesicus serotinus andersoni不同状态下的同声定位声波,使用单因素方差分析(One-Way ANOVA)方法埘小同状态下的声波参数进行显著性差异分析和均值的多重比较,结果表明,大棕蝠江南亚种回声定位声波为短的、宽带的且能量大部分集中在第1谐波的调频型声波,伴有3～4个谐波.并且飞行、悬挂和手持状态的各声波参数均存在显著差异(P<0.05).悬挂状态同声定位声波的声脉冲持续时间大于飞行和手持状态,飞行状态下回声定位声波声脉冲间隔最小,但同声定位声波的主频率为所有状态中最高的.回声定位声波的这些特征及差异体现了与其捕食策略和捕食生境的适应性.