Distribution, frequency and host patterns of European mistletoe (Viscum album subsp. album) in the major city of Lodz, Poland

The frequency of parasitism of the European mistletoe, Viscum album L. subsp. album, in the city of Lodz, a typical major city in Poland, was investigated. The infection prevalence and intensity of the mistletoe Viscum album subsp. album on its main host, Acer saccharinum as a function of host size was also investigated. The parasite showed a strong preference for alien, planted tree species (i.e. A. saccharinum, Populus×canadensis and Robinia pseudoacacia). In 2009–2011, V. album subsp. album was observed on 28 host taxa of trees and shrubs, which represents the highest diversity of host trees in a single locality in the Poland. Within the studied area 2147 trees were infested by mistletoe. The distribution of mistletoes (V. album subsp. album) among A. saccharinum hosts is significantly aggregated. The intensity of mistletoe infection in the silver maple trees was affected by the individual tree characteristics, such as the height of the tree. The overall level of aggregation as indicated by the variance to mean ratio of mistletoe numbers per host fell within the midrange of values found in other published studies of host-mistletoe interactions. The higher mistletoe infection prevalence in taller trees results from differential dispersal of mistletoe seeds to tall trees as well as differential survival of established mistletoes on tall trees. The incidence of mistletoe was higher in city centre (zone of high density development) than it was on the outskirts of a city (outer marginal zone). It was found that the abundant occurrence of mistletoe was recorded in the stands of increased nitrogen input, while other stands have little or no mistletoe infection present. Thus, this mistletoe species uses both passive and active uptake, which may be a selective advantage in a nutrient-poor environment or on a nutrient-deficient host species.     

Characterization of lignin-rich residues remaining after continuous super-critical water hydrolysis of poplar wood (Populus albaglandulosa) for conversion to fermentable sugars

Poplar wood flour (Populous albaglandulosa) was treated with sub- and super-critical water (subcritical: 325, 350 °C; super-critical: 380, 400, 425 °C) for 60 s at 220 ± 10 atm. Hydrochloric acid (0.05% v/v) was added to samples as acidic catalyst. The final products were separated into water soluble fraction and undegraded solids. The yields of undegraded solids were thoroughly dependent on temperature severity and mainly composed of lignin fragments. Average molecular weights of the lignins were between 1500 and 4400 Da, which was only 1/3-1/8-fold of poplar milled wood lignin (13,250 Da). DFRC (Derivatization Followed by Reductive Cleavage) analysis revealed that C6C3 phenols (coniferyl and sinapyl alcohol) were rarely detected in the lignins, indicating occurrence of two probable lignin reactions during SCW hydrolysis: lignin fragmentation via splitting of β-O-4 linkage and loss of propane side chains. These results were also confirmed by ¹H and ¹³C NMR spectroscopic analysis.     

Host spatial structure and disperser activity determine mistletoe infection patterns

What processes and factors are responsible for species distribution are long-standing questions in ecology and a key element for conservation and management. Mistletoes provide the opportunity to study a forest species whose occurrence is expected to be constrained by multiple factors as a consequence of their life form. We studied the mistletoe Tristerix corymbosus (Loranthaceae) on its most common hosts species in northwest Patagonia. The seeds of this mistletoe are almost exclusively dispersed by the small arboreal and endemic marsupial Dromiciops gliroides (Microbiotheridae). We assessed the underlying causes of plant spatial patterns through point pattern analysis and we used different variables that characterize the neighborhood around each host to analyze the relative effect of host availability, potential for disperser movement and canopy light conditions. We found that potential hosts were strongly aggregated and that the three most common host species were distributed independent of each other. Considering all host species together, infected and non-infected host were individually aggregated but segregated from each other. The aggregated pattern of infected hosts could be explained in part by the template of potential hosts distribution, but was subsequently modulated by the activity of the mistletoe disperser. Potential for disperser movement, the proximity to reproductive mistletoes and habitat complexity, increased mistletoe infection probability. However, neighboring host availability decreased mistletoe infection probability, and tree DBH (used as surrogate for light conditions) had no detectable effect. Our results suggested that the distribution of mistletoe infection was determined by the structure of potential host populations and by the marsupial disperser activity. Compared to bird dispersed mistletoes, the scale of the infection was smaller and the proximity to reproductive mistletoes and habitat complexity were important for seed arrival and infection. The interplay between landscape structure and disperser activity determine the spatial structure of mistletoe future generations.     

Uncorrelated mistletoe infection patterns and mating success with local host specialization in <Emphasis Type="Italic">Psittacanthus calyculatus</Emphasis> (Loranthaceae)

Mistletoe infection between conspecific and interspecific hosts can be restricted by seed dispersal, host-mistletoe compatibility and abiotic factors, yet no studies have linked mistletoe infection patterns and pollination together for understanding mistletoe distribution at a local scale. Psittacanthus calyculatus (Loranthaceae) is a hemiparasitic plant with a broad host range across its geographic distribution. The potential for local host adaptation has been shown using cross-inoculation experiments, in which plants of mistletoe seeds collected from a given host are more likely to survive when they are inoculated on conspecific host trees compared with those inoculated on other host provenances. Here we evaluate host adaptation by describing the local patterns of infection (prevalence and intensity) of P. calyculatus mistletoes on three native host tree species (Alnus acuminata, Quercus crassipes, Salix bonplandiana) and one introduced species (Populus alba) and carried out cross-pollination experiments to examine how pollination affects infection patterns of different host species. Mistletoe infection prevalence (proportion of infection) and infection intensity (mean number of mistletoes per tree) were in general disproportional with respect to the availability of native host tree species but higher to that of non-native host tree species. Cross-pollination experiments showed higher mating success on the native host tree species, suggesting higher local adaptation to specially Q. crassipes. The observed spatial distribution of host tree species and mistletoe infection along with the non-random mating could contribute to local genetic structuring of mistletoe populations.     

Carbon and nitrogen parasitism by a xylem‐tapping mistletoe (Tapinanthus oleifolius) along the Kalahari Transect: a stable isotope study

The present study explores the xylem‐tapping parasitism by mistletoe (Tapinanthus oleifolius) on native tree species along the Kalahari Transect (KT) using the stable isotopes of carbon and nitrogen. Mistletoe‐host pairs were collected at three geographical locations along the KT rainfall gradient in the 2005 and 2006 wet seasons. Foliar total carbon, total nitrogen and their stable isotope compositions (δ¹³C and δ¹⁵N) were measured. Heterotrophy (H) was calculated using foliar δ¹³C values of mistletoes and their hosts as an indicator of proportion of carbon in the mistletoes derived from host photosynthate. Based on the mistletoe H‐value and relationship between the mistletoe foliar δ¹⁵N and their host foliar δ¹⁵N, the results showed that mistletoes along the KT derived both nitrogen and carbon from their hosts. Mistletoes may regulate water use in relation to nitrogen supply. The proportion of carbon in the mistletoes derived from host photosynthate was between 35% and 78%, and the degree of heterotrophy was species‐specific with only limited annual variation. The study emphasizes the importance of incorporating parasitic associations in future studies on studying carbon, water and nutrient cycling along the Kalahari.     

The pentose phosphate pathway as a source of NADPH for lignin synthesis

The aim of this work was to investigate whether the pentose phosphate pathway provides reducing power for lignin synthesis. Explants of the stem of Coleus blumei and the storage tissue of Helianthus tuberosus were cultured for 4 days on media which caused extensive lignification. [3-³H]-glucose and either [3-¹⁴C]- or [U-¹⁴C]-glucose were supplied to such 4-day-cultured explants, and also to the roots of 5-day-old seedlings of Pisum sativum. Significant amounts of ³H and ¹⁴C were recovered in syringaldehyde, vanillin, p-hydroxybenzaldehyde, and ligothio-glycollic acid from the explants of Coleus and Helianthus; and in vanillin, p-hydroxybenzaldehyde, and milled-wood lignin from pea roots. The ³H/¹⁴C ratios in these derivatives and preparations of lignin are held to indicate that much of the reducing power for lignin synthesis comes from the pentose phosphate pathway.     

NUTRIENT AND WATER RELATIONS OF THE MISTLETOE PHORADENDRON LEUCARPUM (VISCACEAE): HOW TIGHTLY ARE THEY INTEGRATED?

Tissue mineral concentrations of calcium, copper, iron, magnesium, manganese, nitrogen, phosphorus, potassium, sodium, and zinc, and long-term water-use efficiency (as estimated by δ¹³C±) were measured in the mistletoe Phoradendron leucarpum and its hosts to investigate the relationship between nutrient concentrations and water economies of the parasite and hosts. The mistletoe had mineral concentrations 0.97 to 2.88 times greater than the hosts. Mean long-term mistletoe water-use efficiency (-27.89±) was comparable to mean long-term host water-use efficiency (-27.69±) and generally greater than the water-use efficiency reported for most mistletoe species. Differences between mistletoe and host water-use efficiency ranged from +0.65 to -0.75± and were more similar to mistletoes found growing on nitrogen-fixing host species as reported in other studies. Mistletoe nutrient concentrations, in particular nitrogen, were not related to changes in mistletoe water-use efficiencies. Nutrient: calcium ratios indicated that mistletoes acquire nutrients in excess of that which can be delivered by the host xylem. These data are discussed relative to the passive vs. active theories of nutrient uptake.     

Mistletoe host-resemblance: A study of herbivory,nitrogen and moisture in two Australian mistletoes and their host trees

Abstract For 150 years mistletoe host-resemblance has been an unsolved puzzle. Mimicry, camouflage, host protection and shape modification by the host tree have all been advanced as possible solutions. No extended examination of herbivory of host-parasite pairs has ever been done, however, to put these explanations to the test. The study was carried out in northeastern Australia from March to July 1994. Rates of leaf herbivory were estimated for seven individuals of Amyema biniflora Barlow (a cryptic mistletoe species), Dendrophthoe glabrescens (Blakely) Barlow (a non-cryptic mistletoe species) and their host trees (Eucalyptus tessellaris F. Muell. and Eucalyptus platyphylla F. Muell., respectively). In addition three measures of leaf palatability–nitrogen content, moisture content and toughness–were also assessed. Variability in mistletoe leaf shape was quantified by measuring the leaf widths of mistletoes on a variety of host tree species. Mistletoes sustained greater levels of herbivory compared to their host trees, but herbivory did not differ between mistletoe species. The non-cryptic mistletoe had lower levels of nitrogen compared to its host tree, but there was no difference in nitrogen levels between the cryptic mistletoe and its host. The moisture content of mistletoe leaves was greater than that of their hosts but not between mistletoe or host species. The mistletoe species had tougher leaves than their host trees. Leaf shape was different for one species of mistletoe growing on different host trees, but constant for another species of mistletoe. The results contradict, in some crucial aspect, all of the mimicry hypotheses currently on offer.     

The influence of mistletoes on nutrient cycling in a semi-arid savanna, southwest Zimbabwe

Parasitic plants are increasingly becoming the focus of research in many ecosystems. They have been shown to alter litterfall properties and decomposition rates in environments where they occur. Despite this recognition, the role of mistletoes in nutrient cycling in semi-arid savanna remains poorly understood. We investigated the litter input, element returns, and associated below-canopy soil nutrient concentrations of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) that parasitize Acacia karroo trees in a semi-arid savanna, southwest Zimbabwe. Element concentrations in mistletoe leaf litter were enriched relative to the host. Litterfall from mistletoes significantly increased overall litterfall by up to 173 %, with E. ngamicum and P. kalachariensis having greater litterfall than their host trees. Associated with these changes in litterfall was an increase in element returns and the below-canopy soil nutrient concentrations. The increase in nutrient returns was due to both the effect of enriched mistletoe litter and increased volumes of litterfall beneath host trees. Litterfall, element returns, and the below-canopy soil nutrient concentrations were significantly influenced by mistletoe density, with higher values at high mistletoe density. Overall, E. ngamicum and P. kalachariensis had greater influence on litterfall, element returns, and soil nutrient concentrations than V. verrucosum. These findings are consistent with current understanding of enhanced nutrient cycling in the presence of parasitic plants particularly in nutrient-poor ecosystems. We conclude that the introduction of nutrients and associated increase in resource heterogeneity play an important role in determining ecosystem structure and function in semi-arid savannas.     

寄主植物的功能性状对桑寄生寄主专一性的影响初探

为探讨寄主多样性和寄主功能性状对桑寄生植物的寄主专一性的影响,调查了西双版纳热带植物园内桑寄生和寄主植物种类。结果表明,桑寄生植物共有2科5属6种1变种,感染隶属于58科190属286种寄主植物1 323株。桑寄生在不同生境的寄生强度具有极显著差异(P0.01),单一种植园的寄生强度最高,而在森林的分布最少。不同种类桑寄生的寄主范围存在较大差异,专一性程度(H′)为1.92～7.05,多度较高的植物更容易被感染。冗余分析表明,寄主植物的胸径、树皮含水量和树皮粗糙度对不同桑寄生的寄主利用差异有显著影响,而木质密度和树皮pH的影响不显著。因此,不同种类桑寄生在热带植物群落的寄主专一性程度有较大差异,对寄主植物特定功能性状的偏好能解释部分差异。     

Characterization of Dye-decolorizing Peroxidase (DyP) from Thermomonospora curvata Reveals Unique Catalytic Properties of A-type DyPs

Dye-decolorizing peroxidases (DyPs) comprise a new family of heme peroxidases, which has received much attention due to their potential applications in lignin degradation. A new DyP from Thermomonospora curvata (TcDyP) was identified and characterized. Unlike other A-type enzymes, TcDyP is highly active toward a wide range of substrates including model lignin compounds, in which the catalytic efficiency with ABTS (k_cat^app/K_m^app = (1.7 × 10⁷) m⁻¹ s⁻¹) is close to that of fungal DyPs. Stopped-flow spectroscopy was employed to elucidate the transient intermediates as well as the catalytic cycle involving wild-type (wt) and mutant TcDyPs. Although residues Asp²²⁰ and Arg³²⁷ are found necessary for compound I formation, His³¹² is proposed to play roles in compound II reduction. Transient kinetics of hydroquinone (HQ) oxidation by wt-TcDyP showed that conversion of the compound II to resting state is a rate-limiting step, which will explain the contradictory observation made with the aspartate mutants of A-type DyPs. Moreover, replacement of His³¹² and Arg³²⁷ has significant effects on the oligomerization and redox potential (E°′) of the enzyme. Both mutants were found to promote the formation of dimeric state and to shift E°′ to a more negative potential. Not only do these results reveal the unique catalytic property of the A-type DyPs, but they will also facilitate the development of these enzymes as lignin degraders.     

Modeling Occupancy of Hosts by Mistletoe Seeds after Accounting for Imperfect Detectability

The detection of an organism in a given site is widely used as a state variable in many metapopulation and epidemiological studies. However, failure to detect the species does not necessarily mean that it is absent. Assessing detectability is important for occupancy (presence—absence) surveys; and identifying the factors reducing detectability may help improve survey precision and efficiency. A method was used to estimate the occupancy status of host trees colonized by mistletoe seeds of Psittacanthus plagiophyllus as a function of host covariates: host size and presence of mistletoe infections on the same or on the nearest neighboring host (the cashew tree Anacardium occidentale). The technique also evaluated the effect of taking detectability into account for estimating host occupancy by mistletoe seeds. Individual host trees were surveyed for presence of mistletoe seeds with the aid of two or three observers to estimate detectability and occupancy. Detectability was, on average, 17% higher in focal-host trees with infected neighbors, while decreased about 23 to 50% from smallest to largest hosts. The presence of mistletoe plants in the sample tree had negligible effect on detectability. Failure to detect hosts as occupied decreased occupancy by 2.5% on average, with maximum of 10% for large and isolated hosts. The method presented in this study has potential for use with metapopulation studies of mistletoes, especially those focusing on the seed stage, but also as improvement of accuracy in occupancy models estimates often used for metapopulation dynamics of tree-dwelling plants in general.     

Downregulation of caffeoyl-CoA O-methyltransferase (CCoAOMT) by RNA interference leads to reduced lignin production in maize straw

Lignin is a major cell wall component of vascular plants that provides mechanical strength and hydrophobicity to vascular vessels. However, the presence of lignin limits the effective use of crop straw in many agroindustrial processes. Here, we generated transgenic maize plants in which the expression of a lignin biosynthetic gene encoding CCoAOMT, a key enzyme involved in the lignin biosynthesis pathway was downregulated by RNA interference (RNAi). RNAi of CCoAOMT led to significantly downregulated expression of this gene in transgenic maize compared with WT plants. These transgenic plants exhibited a 22.4% decrease in Klason lignin content and a 23.3% increase in cellulose content compared with WT plants, which may reflect compensatory regulation of lignin and cellulose deposition. We also measured the lignin monomer composition of the RNAi plants by GC-MS and determined that transgenic plants had a 57.08% higher S/G ratio than WT plants. In addition, histological staining of lignin with Wiesner reagent produced slightly more coloration in the xylem and sclerenchyma than WT plants. These results provide a foundation for breeding maize with low-lignin content and reveal novel insights about lignin regulation via genetic manipulation of CCoAOMT expression.     

Purification and characterization of lignin peroxidases from <Emphasis Type="Italic">Penicillium decumbens</Emphasis> P6

Summary Peroxidases are essential enzymes in biodegradation of lignin and lignite which have been investigated intensively in the white-rot fungi. This is the first report of purification and characterization of lignin peroxidase from Penicillium sp. P6 as lignite degradation fungus. The results indicated that the lignin peroxidase of Penicillium decumbens P6 had physical and chemical properties and a N-terminal amino acid sequence different from the lignin peroxidases of white-rot fungi. The lignin peroxidase was isolated from a liquid culture of P. decumbens P6. This enzyme had a molecular weight of 46.3 KDa in SDS-PAGE and exhibited greater activity, temperature stability and wider pH range than those previously reported. The isolation procedure involved (NH₄)₂SO₄ precipitation, ion-exchange chromatography on DEAE-cellulose and CM-cellulose, gel filtration on Sephadex G-100, and non-denaturing, discontinuous polyacrylamide gel electrophoresis. The K _m and V _max values of this enzyme using veratryl alcohol as substrate were 0.565 mmol L ⁻¹ and 0.088 mmol (mg protein) ⁻¹ min ⁻¹ respectively. The optimum pH of P6 lignin peroxidase was 4.0, and 70.6 of the relative activity was remained at pH 9.0. The optimum temperature of the enzyme was 45 °C.     

Effect of sulfonated lignin on enzymatic activity of the ligninolytic enzymes Cα-dehydrogenase LigD and β-etherase LigF

NAD⁺-dependent Cα-dehydrogenase LigD and glutathione-dependent β-etherase LigF which selectively cleave the β-O-4 aryl ether linkage present in lignin, are key-enzymes for the biocatalytic depolymerization of lignin. However, the catalytic efficiency of the two enzymes is low when they are used to break down the β-aryl ether linkage in natural lignin. When sulfonated lignin was added to LigF hydrolysis reactions, the conversion rate of MPHPV decreased significantly from 99.5% to 32.6%. On the contrary, sulfonated lignin has little affection on LigD, which the conversion rate of GGE only decreased from 41.7% to 41%. The strong nonspecific interactions of enzymes onto sulfonated lignin detected by surface plasmon resonance (SPR) and isothermal titration calorimetric (ITC) was obvious and universal, which can reduce enzyme activity of many enzymes, including ligninolytic enzyme β-etherase LigF. To elucidate the exact mechanisms by which β-etherase LigF interact with lignin, molecular modeling was applied. Finally, analysis on catalytic efficiency of LigD and LigF in different concentrations and molecular weights of sulfonated lignin, solution ionic strength, pH, temperature and concentration of Tween 80 revealed that electrostatic interactions and hydrophobic interactions play important roles in absorption between LigF and sulfonated lignin.     

氮钾对慈竹纤维素和木质素动态积累的调控效应

以慈竹为材料,通过施用不同比例的氮、钾肥,研究其对慈竹木质素和纤维素分布和动态积累的调控效应,为慈竹优质栽培提供理论依据。研究结果表明,氮钾肥处理并没有改变木质素和纤维素动态积累趋势,不同处理的慈竹木质素的动态积累呈先上升后下降的趋势,而纤维素的动态积累呈上升的趋势;慈竹不同部位木质素和纤维素的分布呈下部＞中部＞上部的趋势。施用氮、钾肥可以降低慈竹木质素含量,降低幅度为1.05%~3.97%,提高纤维素含量,提高幅度为1.25%～3.36%。N、K肥和时间对慈竹木质素和纤维素含量总变异的贡献都是N×K＞N＞TIME＞K＞N×K×TIME＞N×TIME＞K×TIME。慈竹纤维素和木质素含量之间呈不明显的正相关关系（r=0.020 4）。     

Evaluating conditions for producing spray-dried formulations of Anagrapha falcifera nucleopolyhedroviruses (AfMNPV)

We investigated how altering parameters during the production of spray-dried lignin formulations affected the insecticidal activity of a baculovirus (AfMNPV), which was originally isolated from celery looper, Anagrapha falcifera (Kirby). Exposure to high temperature, varied pH of the dryer feedstock, substitution of formulation ingredients, and different commercial production lots of virus were evaluated for their effect on the insecticidal activity of AfMNPV. Insecticidal activities of treatments were determined by droplet-feeding assays using neonate Trichoplusia ni (Hübner) for dosage response or single-dosage comparisons. Unformulated virus exposed to 68^oC for 2 h showed no loss of insecticidal activity, whereas exposure to 90^oC for 30 min caused >20% loss of activity. Thus, residence at higher temperatures in drying systems could adversely affect virus activity. Spray-dried formulations made with Indulin AT lignin (pH 8.5, 9.5, and 10.5) lost insecticidal activity with increasing alkalinity of the dryer feedstock. In contrast to Indulin AT, the same formulations made with PC-1307 lignin did not lose insecticidal activity with increased alkalinity. Adding corn flour to spray-dried Indulin AT-based formulations improved insecticidal activity of the virus. These experiments demonstrated the importance of carefully selecting feed-stock ingredients and processing conditions when spray drying AfMNPV.     

Biosynthesis of p-hydroxybenzoic acid in poplar lignin

Biosynthetic pathways to p-hydroxybenzoic acid in polar lignin were examined by tracer experiments. High incorporation of radioactivity to the acid was observed when shikimic acid-[1-¹⁴C], phenylalanine-[3-¹⁴C], trans-cinnamic acid-[3-¹⁴C], p-coumaric acid-[3-¹⁴C] and p-hydroxybenzoic acid-[COOH-¹⁴C] were administered, while incorporation was low from shikimic acid-[COOH-¹⁴C], phenylalanine-[1-¹⁴C], phenylalanine-[2-¹⁴C], tyrosine-[3-¹⁴C], benzoic acid-[COOH-¹⁴C], sodium acetate-[1-¹⁴C] and d-glucose-[U-¹⁴C]. Thus p-hydroxybenzoic acid in poplar lignin is formed mainly via the pathway: shikimic acid → phenylalanine → trans-cinnamic acid → p-coumaric acid → p-hydroxybenzoic acid.     

Biochemical changes assessed by 13C-CPMAS NMR spectroscopy control fungal growth on water extracts of decaying plant litter

The mechanistic bases of saprotrophic fungal dynamics in soil are not fully clarified. By assessing hyphal density and radial expansion of Aspergillus niger on extracts 45 plant litter types (15 species at 3 decomposition stages), encompassing a broad range of organic quality, we investigated how changes in litter biochemistry affected fungal growth. Plant litter were characterized by classic proximate chemical analyses (total C and N, labile C, cellulose and lignin content, C/N and lignin/N ratios) and, at molecular level, by solid-state ¹³C-CPMAS NMR. The growth of A. niger decreased during the decomposition process over all organic matter types, consistently with the well-known disappearance of this species during the early successional stages. The litter suitability as a substrate to A. niger progressively decreased during decomposition, both considering proximate parameters and C types corresponding to spectral regions, with the latter being also invariably predictive of fungal growth over the 45 substrates. A. niger growth was positively associated with the content of labile C, and with di-O-alkyl C and O-alkyl C spectral regions, but negatively with lignin content and with methoxyl C region. Our results suggest that organic matter quality may control saprotrophic fungal dynamics, at least for the tested species.     

Mistletoes and mutant albino shoots on woody plants as mineral nutrient traps

Background and Aims

Potassium, sulphur and zinc contents of mistletoe leaves are generally higher than in their hosts. This is attributed to the fact that chemical elements which are cycled between xylem and phloem in the process of phloem loading of sugars are trapped in the mistletoe, because these parasites do not feed their hosts. Here it is hypothesized that mutant albino shoots on otherwise green plants should behave similarly, because they lack photosynthesis and thus cannot recycle elements involved in sugar loading.

Methods

The mineral nutrition of the mistletoe Scurrula elata was compared with that of albino shoots on Citrus sinensis and Nerium oleander. The potential for selective nutrient uptake by the mistletoe was studied by comparing element contents of host leaves on infected and uninfected branches and by manipulation of the haustorium–shoot ratio in mistletoes. Phloem anatomy of albino leaves was compared with that of green leaves.

Key Results

Both mistletoes and albino leaves had higher contents of potassium, sulphur and zinc than hosts or green leaves, respectively. Hypothetical discrimination of nutrient elements during the uptake by the haustorium is not supported by our data. Anatomical studies of albino leaves showed characteristics of release phloem.

Conclusions

Both albino shoots and mistletoes are traps for elements normally recycled between xylem and phloem, because retranslocation of phloem mobile elements into the mother plant or the host is low or absent. It can be assumed that the lack of photosynthetic activity in albino shoots and thus of sugars needed in phloem loading is responsible for the accumulation of elements. The absence of phloem loading is reflected in phloem anatomy of these abnormal shoots. In mistletoes the evolution of a parasitic lifestyle has obviously eliminated substantial feeding of the host with photosynthates produced by the mistletoe.