Root hemiparasites are green photosynthetic plants, which parasitically acquire resources from host xylem. Mineral nutrients and water, two principal below-ground abiotic resources, were assumed to affect the interaction between hemiparasites and their hosts. The shape of these effects and the underlying physiological mechanisms have, however, remained unclear. We conducted a glasshouse experiment with root-hemiparasitic Rhinanthus alectorolophus, in which we manipulated the availability of mineral nutrients and water. Biomass production and Chl fluorescence of the hemiparasites and hosts were recorded, together with proportion of host-derived carbon in hemiparasite biomass. The abiotic resources had profound interactive effects on the performance of both the hemiparasite and the hosts, as well as the balance of above-ground biomass between them. These effects were mainly based on an increase of growth and photosynthetic efficiency under high nutrient concentrations, on the hemiparasite's ability to induce strong water stress on the hosts if water is limiting, and on release of the host from parasitism by simultaneous abundance of both resources. Hemiparasitism is a highly variable interaction, in which environmental conditions affect both the parasitic and autotrophic (and thus competitive) components. A hemiparasite's own photosynthesis plays a crucial role in the assimilation of parasitized mineral resources and their transformation into growth and fitness.

• Klíčová slova
• Orobanchaceae, Rhinanthus, autotrophy, competition, ecophysiology, hemiparasite, heterotrophy, mixotrophy,
• MeSH
• autotrofní procesy * MeSH
• biologické modely MeSH
• biomasa MeSH
• druhová specificita MeSH
• ekologie a životní prostředí - jevy * MeSH
• interakce hostitele a parazita fyziologie   MeSH
• kořeny rostlin parazitologie   fyziologie   MeSH
• Orobanchaceae parazitologie   fyziologie   MeSH
• paraziti fyziologie   MeSH
• uhlík metabolismus   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• uhlík MeSH

Melampyrum pratense is an annual root-hemiparasitic plant growing mostly in forest understorey, an environment with unstable light conditions. While photosynthetic responses of autotrophic plants to variable light conditions are in general well understood, light responses of root hemiparasites have not been investigated. We carried out gas exchange measurements (light response and photosynthetic induction curves) to assess the photosynthetic performance of M. pratense in spring and summer. These data and recorded light dynamics data were subsequently used to model carbon balance of the hemiparasite throughout the entire growth season. Summer leaves had significantly lower rates of saturated photosynthesis and dark respiration than spring leaves, a pattern expected to reflect the difference between sun- and shade-adapted leaves. However, even the summer leaves of the hemiparasite exhibited a higher rate of light-saturated photosynthesis than reported in non-parasitic understorey herbs. This is likely related to its annual life history, rare among other understorey herbs. The carbon balance model considering photosynthetic induction still indicated insufficient autotrophic carbon gain for seed production in the summer months due to limited light availability and substantial carbon loss through dark respiration. The results point to potentially high importance of heterotrophic carbon acquisition in M. pratense, which could be of at least comparable importance as in other mixotrophic plants growing in forests - mistletoes and partial mycoheterotrophs. It is remarkable that despite apparent evolutionary pressure towards improved carbon acquisition from the host, M. pratense retains efficient photosynthesis and high transpiration rate, the ecophysiological traits typical of related root hemiparasites in the Orobanchaceae.

• Klíčová slova
• carbon balance modelling, heterotrophic carbon, parasitic plant, photosynthetic response, plant ecophysiology, sunfleck,
• MeSH
• fotosyntéza * MeSH
• interakce hostitele a parazita MeSH
• kořeny rostlin parazitologie   MeSH
• lesy * MeSH
• Orobanchaceae metabolismus   fyziologie   MeSH
• roční období MeSH
• uhlík metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• uhlík MeSH

Root-hemiparasitic plants of the genus Rhinanthus acquire resources through a water-wasting physiological strategy based on high transpiration rate mediated by the accumulation of osmotically active compounds and constantly open stomata. Interestingly, they were also documented to withstand moderate water stress which agrees with their common occurrence in rather dry habitats. Here, we focused on the water-stress physiology of Rhinanthus alectorolophus by examining gas exchange, water relations, stomatal density, and biomass production and its stable isotope composition in adult plants grown on wheat under contrasting (optimal and drought-inducing) water treatments. We also tested the effect of water stress on the survival of Rhinanthus seedlings, which were watered either once (after wheat sowing), twice (after wheat sowing and the hemiparasite planting) or continuously (twice and every sixth day after that). Water shortage significantly reduced seedling survival as well as the biomass production and gas exchange of adult hemiparasites. In spite of that drought-stressed and even wilted plants from both treatments still considerably photosynthesized and transpired. Strikingly, low-irrigated plants exhibited significantly elevated photosynthetic rate compared with high-irrigated plants of the same water status. This might relate to biochemical adjustments of these plants enhancing the resource uptake from the host. Moreover, low-irrigated plants did not acclimatize to water stress by lowering their osmotic potential, perhaps due to the capability to tolerate drought without such an adjustment, as their osmotic potential at full turgor was already low. Contrary to results of previous studies, hemiparasites seem to close their stomata in response to severe drought stress and this happens probably passively after turgor is lost in guard cells. The physiological traits of hemiparasites, namely the low osmotic potential associated with their parasitic lifestyle and the ability to withstand drought and recover from the wilting likely enable them to grow in dry habitats. However, the absence of osmotic adjustment of adults and sensitivity of seedlings to severe drought stress demonstrated here may result in a substantial decline of the hemiparasitic species with ongoing climate change.

• MeSH
• biomasa MeSH
• dehydratace MeSH
• fotosyntéza MeSH
• fyziologický stres fyziologie   MeSH
• kořeny rostlin MeSH
• listy rostlin anatomie a histologie   fyziologie   MeSH
• Orobanchaceae anatomie a histologie   fyziologie   MeSH
• průduchy rostlin anatomie a histologie   fyziologie   MeSH
• semenáček anatomie a histologie   fyziologie   MeSH
• transpirace rostlin MeSH
• voda * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• voda * MeSH

BACKGROUND AND AIMS: Root hemiparasites from the rhinanthoid clade of Orobanchaceae possess metabolically active glandular trichomes that have been suggested to function as hydathode trichomes actively secreting water, a process that may facilitate resource acquisition from the host plant's root xylem. However, no direct evidence relating the trichomes to water secretion exists, and carbon budgets associated with this energy-demanding process have not been determined. METHODS: Macro- and microscopic observations of the leaves of hemiparasitic Rhinanthus alectorolophus were conducted and night-time gas exchange was measured. Correlations were examined among the intensity of guttation, respiration and transpiration, and analysis of these correlations allowed the carbon budget of the trichome activity to be quantified. We examined the intensity of guttation, respiration and transpiration, correlations among which indicate active water secretion. KEY RESULTS: Guttation was observed on the leaves of 50 % of the young, non-flowering plants that were examined, and microscopic observations revealed water secretion from the glandular trichomes present on the abaxial leaf side. Night-time rates of respiration and transpiration and the presence of guttation drops were positively correlated, which is a clear indicator of hydathode trichome activity. Subsequent physiological measurements on older, flowering plants indicated neither intense guttation nor the presence of correlations, which suggests that the peak activity of hydathodes is in the juvenile stage. CONCLUSIONS: This study provides the first unequivocal evidence for the physiological role of the hydathode trichomes in active water secretion in the rhinanthoid Orobanchaceae. Depending on the concentration of organic elements calculated to be in the host xylem sap, the direct effect of water secretion on carbon balance ranges from close to neutral to positive. However, it is likely to be positive in the xylem-only feeding holoparasites of the genus Lathraea, which is closely related to Rhinanthus. Thus, water secretion by the hydathodes might be viewed as a physiological pre-adaptation in the evolution of holoparasitism in the rhinanthoid lineage of Orobanchaceae.

• Klíčová slova
• Ecophysiology, Lathraea, Rhinanthus alectorolophus, Triticum aestivum, holoparasite, hydathode trichome, orobanche, parasitic plant, respiration, rhinanthoid Orobanchaceae, root hemiparasite, transpiration, water regime, water secretion, xylem,
• MeSH
• biologická evoluce * MeSH
• buněčné dýchání MeSH
• interakce hostitele a parazita fyziologie   MeSH
• kořeny rostlin parazitologie   MeSH
• lineární modely MeSH
• listy rostlin metabolismus   MeSH
• Orobanchaceae fyziologie   MeSH
• plyny metabolismus   MeSH
• transpirace rostlin MeSH
• trichomy fyziologie   MeSH
• voda metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• plyny MeSH
• voda MeSH

Hemiparasitic plants gain virtually all mineral nutrients and water from their host plant whilst organic carbon is provided, at least in part, by their own photosynthetic activity, although their rates of assimilation are substantially lower than that found in non-parasitic plants. Hence, hemiparasites must gain at least some of their organic carbon heterotrophically from the host plant. Despite this, heterotrophic carbon gain by root hemiparasites has been investigated only for a few genera. We investigated heterotrophic carbon gain by two root hemiparasites, Rhinanthus minor L. and Euphrasia rostkoviana Hayne (Orobanchaceae), using natural abundance stable isotope (delta(13)C) profiles of both parasites attached to C(3) (wheat) and C(4) (maize) hosts coupled to a linear two-source isotope-mixing model to estimate the percentage of carbon in the parasite that was derived from the host. Both R. minor and E. rostkoviana attached to maize hosts were significantly more enriched in (13)C than those attached to wheat hosts with R. minor becoming more enriched in (13)C than E. rostkoviana. The natural abundance (13)C profiles of both parasites were not significantly different from their wheat hosts, but were less enriched in (13)C than maize hosts. Using a linear two-source isotope-mixing model, we estimated that R. minor and E. rostkoviana adult plants derive c. 50 and 25% of their carbon from their hosts, respectively. In light of these results, we hypothesise that repeatedly observed negative effect of competition for light on hemiparasites acts predominantly in early ontogenetic stages when parasites grow unattached or the abstraction of host nutrients is less effective.

• MeSH
• biomasa MeSH
• Euphrasia fyziologie   MeSH
• fotosyntéza MeSH
• heterotrofní procesy fyziologie   MeSH
• interakce hostitele a parazita MeSH
• izotopy uhlíku MeSH
• kořeny rostlin parazitologie   MeSH
• kukuřice setá růst a vývoj   parazitologie   MeSH
• Orobanchaceae fyziologie   MeSH
• Plantago růst a vývoj   parazitologie   MeSH
• pšenice růst a vývoj   parazitologie   MeSH
• uhlík metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• izotopy uhlíku MeSH
• uhlík MeSH

In their recent study, Borowicz and Armstrong (Oecologia 169:783-792, 2012) investigated effects of nutrient availability and competition for light on a perennial root hemiparasite Pedicularis canadensis. Their study showed a reduction of community productivity as a result of hemiparasite infection independently of a clear positive effect of increased nutrients. In contrast, there was a minimal effect of increased competition for light on growth of the parasite. Here, we summarize the available data on the influence of nutrient availability (closely related to productivity) on temperate grassland root hemiparasites thus expanding the discussion presented by Borowicz and Armstrong (Oecologia 169:783-792, 2012). Most studies show that root hemiparasites are highly sensitive to elevated competition for light in productive environments, which is manifested as an increase in mortality coupled to a decrease in population density. Such responses reflect increased mortality of hemiparasite seedlings that are physiologically inefficient in terms of photosynthesis and nutrient acquisition owing to a limited root network and consequently, are highly sensitive to competition for light. However, the susceptibility of hemiparasites to competition for light tends to decrease for individuals that survive the critical seedling stage. Moreover, survivors benefit from elevated nutrient availability, resulting in increased growth and fecundity. Elevated productivity can thus have opposing effects on the survival and growth of hemiparasites depending on life stage. We conclude that the findings by Borowicz and Armstrong (Oecologia 169:783-792, 2012) are not in conflict with this general view that root hemiparasite population ecology is strongly influenced by competition for light in highly productive environments.

• MeSH
• Andropogon parazitologie   MeSH
• ekosystém * MeSH
• interakce hostitele a parazita * MeSH
• lipnicovité parazitologie   MeSH
• Pedicularis fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• komentáře MeSH
• práce podpořená grantem MeSH

The heterotrophic lifestyle of parasitic plants relies on the development of the haustorium, a specific infectious organ required for attachment to host roots. While haustorium development is initiated upon chemodetection of host-derived molecules in hemiparasitic plants, the induction of haustorium formation remains largely unknown in holoparasitic species such as Phelipanche ramosa. This work demonstrates that the root exudates of the host plant Brassica napus contain allelochemicals displaying haustorium-inducing activity on P. ramosa germinating seeds, which increases the parasite aggressiveness. A de novo assembled transcriptome and microarray approach with P. ramosa during early haustorium formation upon treatment with B. napus root exudates allowed the identification of differentially expressed genes involved in hormone signaling. Bioassays using exogenous cytokinins and the specific cytokinin receptor inhibitor PI-55 showed that cytokinins induced haustorium formation and increased parasite aggressiveness. Root exudates triggered the expression of cytokinin-responsive genes during early haustorium development in germinated seeds, and bio-guided UPLC-ESI(+)-/MS/MS analysis showed that these exudates contain a cytokinin with dihydrozeatin characteristics. These results suggest that cytokinins constitutively exudated from host roots play a major role in haustorium formation and aggressiveness in P. ramosa.

• Klíčová slova
• Brassica napus, Phelipanche ramosa, broomrape, cytokinins, haustorium, microarray, parasitic plant, root development, root exudates,
• MeSH
• Brassica napus parazitologie   MeSH
• cytokininy metabolismus   MeSH
• kořeny rostlin růst a vývoj   fyziologie   MeSH
• Orobanche růst a vývoj   fyziologie   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• cytokininy MeSH
• regulátory růstu rostlin MeSH

Root-hemiparasitic interaction between the dominant grass Calamagrostis epigejos and the hemiparasite Thesium linophyllon was studied to assess the potential of the parasite to regulate dominance of the grass, which is expanding into species-rich steppe grasslands. First, we aimed to identify physiological links between the two species as a principal indicator of the parasitic relationship. Second, we analysed the dynamics of the two species in the vegetation of a steppe grassland at the foot of the Bükk Mountains, Hungary, where their joint presence is recorded in a long-term permanent plot monitoring dataset to detect patterns associated with the parasitic ecological interaction. Numerous well-developed functional haustoria of Th. linophyllon were identified on the root systems of C. epigejos. The joint dynamics of C. epigejos and Th. linophyllon displayed clear signs of the parasitic interaction: (1) the dynamics of Th. linophyllon frequency was positively associated with the initial cover of C. epigejos; (2) maximum recorded cover values of the two species were strongly positively correlated; and (3) the extent of C. epigejos decrease in the vegetation was significantly positively associated with maximum Th. linophyllon cover recorded throughout the monitoring period. We demonstrate that C. epigejos can be parasitized by Th. linophyllon, which restricts abundance of the grass. Th. linophyllon thus has potential to act as a native biological control of C. epigejos in steppe grasslands.

• Klíčová slova
• Biological control, conservation management, expansive grass, haustorium, landfill restoration, species rich grassland,
• MeSH
• cévnaté rostliny fyziologie   MeSH
• interakce hostitele a parazita fyziologie   MeSH
• kořeny rostlin parazitologie   MeSH
• lipnicovité parazitologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Maďarsko MeSH

PREMISE OF THE STUDY: Microsatellite primers were developed for the first time in the root hemiparasite herb Odontites vernus (Orobanchaceae). These markers will be useful to investigate the role of polyploidization in the evolution of this diploid-tetraploid complex, as well as the extent of gene flow between different ploidy levels. METHODS AND RESULTS: Fourteen polymorphic and reproducible loci were identified and optimized from O. vernus using a microsatellite-enriched library and 454 Junior sequencing. The set of primers amplified di- to pentanucleotide repeats and showed two to 13 alleles per locus. Transferability was tested in 30 taxa (19 belonging to Odontites and 11 from eight other genera of Orobanchaceae tribe Rhinantheae). CONCLUSIONS: The results indicate the utility of the newly developed microsatellites in O. vernus and several other species, which will be useful for taxon delimitation and conservation genetics studies.

• Klíčová slova
• Odontites vernus, Orobanchaceae, Rhinantheae, conservation, diploid-tetraploid complex, microsatellite,
• Publikační typ
• časopisecké články MeSH