Populus Canescens Research Articles

High Temperature-Induced Spindle Destabilization Results in Aborted Pollen Production in Populus

High temperature can induce the production of 2n gametes and aborted pollen during microsporogenesis in Populus canescens. However, the mechanism by which high temperature induces pollen abortion remains unknown. Here, pollen abortion was induced by exposing male flower buds of P. canescens to 38 and 41 °C; pollen morphology, meiotic abnormalities, defects of the meiotic microtubular cytoskeleton, and tapetum development were characterized. We found that the dominant meiotic stage, temperature, and duration of treatment significantly affected the percentage of high temperature-induced aborted pollen. Damaged spindle microtubules and depolymerized microtubular cytoskeletons were observed, which resulted in many lagging chromosomes at anaphase I and II as well as aneuploid male gametes and micronuclei, thereby generating aborted pollen grains. Tapetum disintegration was also delayed. The anther dehisced normally, and some viable pollen grains were released. However, no sufficient evidence showed that the delayed degradation of the tapetum was responsible for pollen abortion.

Salicaceae as potential host plants of Xylella fastidiosa in European temperate regions

The discovery of several strains belonging to three subspecies of Xylella fastidiosa in Europe has triggered major attention to the potential spread up north of the bacteria. It is essential to assess the susceptibility of the previously unexposed European flora to this pathogen. Under biosafety facility, we evaluated the susceptibility of Salicaceae such as Populus tremula, Populus canescens, Salix alba and Salix caprea by mechanically inoculating the KLN59.3 GFP-labelled X. fastidiosa at 22 °C and at 28 °C. Bacterial movement and multiplication in plants were investigated by PCR, real-time PCR, confocal or scanning electron microscopy. Nine months post-inoculation, 100% of the plants tested positive for X. fastidiosa, with the exception of 57% for P. canescens under the 22 °C-growing conditions. Bacteria were detected up to 120 cm from the inoculation point for S. alba. They were detected in the roots of all species and were successfully isolated for S. alba and P. tremula. Estimates of average CFU/g of plant tissue per species ranged from 1.5E + 03 to 3.5E + 06, with the lowest figures for P. canescens and the highest for P. tremula together with high number of totally obstructed vessels observed by confocal microscopy. The possibility of insect transmission was also evaluated using an experimental set up based on Majorca Island. There, transmission by P. spumarius of both X. fastidiosa ST1 and ST81 was proven on S. alba. We thus demonstrated that indigenous European Salicaceae such as S. alba or P. tremula are new potential hosts for X. fastidiosa.

Heat shock-induced failure of meiosis I to meiosis II transition leads to 2n pollen formation in a woody plant.

The formation of diploid gametes through chromosome doubling is a major mechanism of polyploidization, diversification, and speciation in plants. Unfavorable climate conditions can induce or stimulate the production of diploid gametes during meiosis. Here, we demonstrated that heat shock stress (38°C for 3 or 6 h) induced 2n pollen formation, and we generated 42 triploids derived from heat shock-induced 2n pollen of Populus canescens. Meiotic analysis of treated pollen mother cells revealed that induced 2n pollen originated from the complete loss of meiosis II (MII). Among the 42 triploids, 38 triploids derived from second division restitution (SDR)-type 2n pollen and 4 triploids derived from first division restitution-type 2n pollen were verified using simple sequence repeats(SSR) molecular markers. Twenty-two differentially expressed genes related to the cell cycle were identified and characterized by expression profile analysis. Among them was POPTR_0002s08020g (PtCYCA1;2), which encodes a type A Cyclin CYCA1;2 that is required for the meiosis I (MI) to MII transition. After male flower buds were exposed to heat shock, a significant reduction was detected in PtCYCA1;2 expression. We inferred that the failure of MI-to-MII transitions might be associated with downregulated expression of PtCYCA1;2, leading to the formation of SDR-type 2n pollen. Our findings provide insights into mechanisms of heat shock-induced 2n pollen formation in a woody plant and verify that sensitivity to environmental stress has evolutionary importance in terms of polyploidization.

Effects of Colchicine on Populus canescens Ectexine Structure and 2n Pollen Production.

Triploid breeding is a central way to improve growth traits, timber quality, and stress resistance in Populus. In the present study, the morphology and viability of colchicine-induced 2n pollen, triploid production by crossing induced 2n pollen, and identification of genetic constitution of colchicine-induced 2n pollen were conducted in Populus canescens based on optimizing technology for inducing chromosome doubling in pollen. We found that the meiotic stage, injection time, and the interaction between the meiotic stage and injection time had highly significant effects on the 2n pollen production rate. The most effective treatment for inducing 2n pollen was to give 11 injections of 0.5% colchicine solution when pollen mother cells (PMCs) were at the pachytene stage. The highest 2n pollen production rate was 30.27 ± 8.69%. Colchicine occasionally affected ectexine deposition, and some narrow furrows were detected in the ectexine structure. However, no significant difference was observed in the pollen germination rate between natural 2n pollen and colchicine-induced 2n pollen. Moreover, 5 triploids derived from FDR-type 2n pollen were generated by crossing induced 2n pollen, suggesting that colchicine does not eliminate the function of colchicine-induced 2n pollen. However, slower growth of 2n pollen tubes was responsible for a lower triploid production rate.

Increased water use efficiency and water productivity of arabidopsis by abscisic acid receptors from Populus canescens.

Water deficit is the single most important factor limiting plant productivity in the field. Poplar is a crop used for second-generation bioenergy production that can be cultivated on marginal land without competing for land use in food production. Poplar has a high demand for water, which makes improving its water use efficiency (WUE) an attractive goal. Recently, we showed that enhanced expression of specific receptors of arabidopsis for the phytohormone abscisic acid (ABA) can improve WUE in arabidopsis and water productivity, i.e. more biomass is formed per unit of water over time. In this study, we examined whether ABA receptors from poplar can enhance WUE and water productivity in arabidopsis. ABA receptors from poplar were stably introduced into arabidopsis for analysis of their effect on water use efficiency. Physiological analysis included growth assessment and gas exchange measurements. The data presented here are in agreement with the functionality of poplar ABA receptors in arabidopsis, which led to ABA-hypersensitive seed germination and root growth. In addition, arabidopsis lines expressing poplar RCAR10, but not RCAR9, showed increased WUE by up to 26 % compared with the wild type with few trade-offs in growth that also resulted in higher water productivity during drought. The improved WUE was mediated by reduced stomatal conductance, a steeper CO2 gradient at the leaf boundary and sustained photosynthesis resulting in an increased intrinsic WUE (iWUE). The analysis is a case study supporting the use of poplar ABA receptors for improving WUE and showing the feasibility of using a heterologous expression strategy for generating plants with improved water productivity.

Forty-five-year monitoring of selection stands of white (Populus alba L.), gray (Populus canescens Sm.), black poplar (Populus nigra L.) and willow (Salix alba L.) in Khoper State Natural Reserve

This paper presents an analysis of forty-five-year dynamics of the main characteristics of white (Populus alba L.), gray (Populus canescens Sm.), black poplar (Populus nigra L.) and willow (Salix alba L.) stands on the territory of the Khoper State Natural Reserve on the basis of the materials of permanent test plots restored and newly established by A I Sivolapov in 1972 for the purpose of selection of the most productive and stable clone micropopulations of these species. The annual changes taking place in the sample plots, and considerable statistical material, make it possible to carry out quantitative and qualitative analysis of the behavior of the existing associations of white, gray, black poplar and willow with great certainty. Selected highly productive genotypes have been uterine trees to create varieties and are recommended for plantation cultivation.

Characterising the water use and hydraulic properties of riparian tree invasions: A case study of Populus canescens in South Africa

Invasive alien plants (IAPs) pose a serious threat to the already limited water resources in dry countries like South Africa which are facing increasing water shortages. Much of South Africa is expected to get drier in future due to climate change. In addition, the future climatic conditions are also predicted to accelerate the rate at which IAPs will spread, due to favourable growing conditions, further disrupting the provision of goods and services. Previous studies on tree water use in South Africa focused on commercial forests of introduced genera mainly Pinus, Eucalyptus, and Acacia. This study sought to expand these observations by quantifying water use and its drivers in riparian Grey Poplar (Populus canescens) invasions in the Berg River catchment of South Africa. Whole tree hydraulic resistance ranged from ~ 1.4 MPa·h·g-1 for large trees to ~14.3 MPa·h·g-1 for the small ones. These resistances are higher than those found for poplars in temperate climates, suggesting substantial hydraulic constraints to transpiration. Daily peak transpiration varied from 5 to 6 L·tree-1 in small trees (~9.2 cm DBH) to between 35 and 40 L·tree-1 for large trees (~24 cm DBH). Stand-level transpiration peaked at ~4 mm·d-1 in summer (Jan–Feb). However, the annual total transpiration was only 338 mm due to the deciduous nature of the species and also the high hydraulic resistance in the transpiration stream. Daily transpiration was strongly correlated to solar radiation (R2 > 0.81) while the air vapour pressure deficit (VPD) constrained transpiration at high VPD values. We conclude that the water use of the poplar invasions is significantly lower than that of other riparian invasions. The impact of these invasions on the water resources is therefore likely quite low, warranting less priority in alien plant clearing operations aimed at salvaging water.

High temperature exposure did not affect induced 2n pollen viability in Populus.

High temperature exposure is widely used as a physical mutagenic agent to induce 2n gametes in Populus. However, whether high temperature exposure affects induced 2n pollen viability remains unknown. To clarify whether high temperature exposure affected the induced 2n pollen viability, 2n pollen induced by 38 and 41°C temperatures, pollen morphology, 2n pollen germination in vitro, and crossing induced 2n pollen with normal gametes to produce a triploid was, based on observations of meiosis, conducted in Populus canescens. We found that the dominant meiotic stages (F=56.6, p<.001) and the treatment duration (F=21.4, p<.001) significantly affected the occurrence rate of induced 2n pollen. A significant decrease in pollen production and an increase in aborted pollen were observed (p<.001). High temperature sometimes affected in ectexine deposition and some narrow furrows were also analysed via details of ectexine structure. However, no significant difference in 2n pollen germination rate was observed between natural 2n pollen (26.7%) and high-temperature-induced 2n pollen (26.2%), and 42 triploids were created by crossing high-temperature-induced 2n pollen, suggesting that 38 and 41°C temperatures exposure will not result in dysfunctional induced 2n pollen.

Investigation of gas exchange and biometric parameters in isogenic lines of poplar differing in ploidy

Abstract Three poplar clones of section Populus (Brauna 11 [Populus tremula], L447 [Populus canescens] and Esch 5 [Populus tremula × Populus tremuloides]) were used to analyse the effects of ploidy levels on primary productivity and water use efficiency. The clones were established in tissue culture (2N) and lines with different ploidy levels (2N/4N and 4N) were generated via colchicine treatment. Light response curves were modelled based on gas exchange measurements carried out three times during the growing season on the 1st fully developed leaf under controlled conditions. The plants were harvested in September to analyse biometric parameters. The photosynthetic capacity was greatest in May, decreased throughout the season and increased slightly again in September. The decrease in Brauna 11 and Esch 5 varied from 20-50% compared with values in May and it was not as pronounced in L 447. Photosynthesis and intrinsic water use efficiency differed between clones, but not among the single isogenic lines within each clone. The seasons in which the experiments were conducted influenced the rankings of the 9 variants in physiological measurements, but these rankings were not uniform during the growing period. Differences in biometric parameters were detected between the clones and variants, e.g.; leaf masses were greater in all of the polyploid variants and lowest in the diploid variants. All of the L 447 lines showed the highest wood densities, which were higher in the mixoploid and lower in the tetraploid variants within each clone. A compact wood structure could prevent damage to the water-conducting system under drought stress.

Susceptibility of Riparian Wetland Plants to Perfluorooctanoic Acid (PFOA) Accumulation

As plants have been shown to accumulate organic compounds from contaminated sediments, there is a potential for long-lasting ecological impact as a result of contaminant accumulation in riparian areas of wetlands, particularly the accumulation of non-biodegradable contaminants such as perfluorooctanoic acid (PFOA). In this study, commonly found riparian wetland plants including reeds, i.e., Xanthium strumarium, Phragmites australis, Schoenoplectus corymbosus, Ruppia maritime; Populus canescens, Polygonum salicifolium, Cyperus congestus; Persicaria amphibian, Ficus carica, Artemisia schmidtiana, Eichhornia crassipes, were studied to determine their susceptibility to PFOA accumulation from PFOA contaminated riparian sediment with a known PFOA concentration, using liquid chromatography/tandem mass spectrometry (LC/MS/MS). The bioconcentration factor (BCF) indicated that the plants affinity to PFOA accumulation was; E. crassipes, > P. salicifolium, > C. congestus, > P. x canescens, > P. amphibian, > F. carica, > A. schmidtiana, > X. strumarium, > P. australis, > R. maritime, > S. corymbosus. The concentration of PFOA in the plants and/or reeds was in the range 11.7 to 38 ng/g, with a BCF range of 0.05 to 0.37. The highest BCF was observed in sediment for which its core water had a high salinity, total organic carbon and a pH which was near neutral. As the studied plants had a higher affinity for PFOA, the resultant effect is that riparian plants such as E. crassipes, X. strumarium, and P. salicifolium, typified by a fibrous rooting system, which grow closer to the water edge, exacerbate the accumulation of PFOA in riparian wetlands.

Assessing the Influence of a Range of Spring Meteorological Parameters on Tree Phenology

The timing of phenological phases, such as leaf unfolding of trees, is partly driven by the weather. The impact of weather on the spring phenology of a selection of tree species in the phenological garden at Valentia Observatory, Caherciveen, County Kerry, Ireland, for the period 1967-2004 was assessed. In particular, the beginning of the growing season (BGS), as determined by the date of leaf unfolding, was considered. The impact on BGS of a range of meteorological parameters and derived parameters, including minimum, maximum and mean air temperature (°C), soil temperature (°C), rainfall (mm), sunshine (hours), number of air frost days and number of rain days was investigated. These parameters were averaged or summed over the months of February, March and April and linear regression analysis with BGS was carried out for several tree species. The results showed that the regression coefficients of BGS on minimum air and soil temperature were highest, with Populus canescens and Populus tremula showing the strongest relationships. Temperature parameters were found to be more important in driving advancing phenology than any other meteorological parameter tested.

Clonal reproduction and natural variation of Populus canescens patches

Trees growing in their natural habitat represent a valuable resource for elucidating mechanisms of adaptation to environmental constraints. Along the Erqis river, there are various Populus forests, which provide 'natural laboratories' for studying tree ecophysiological responses to their habitat. Reproduction strategies and natural variation of the 'mosaic' distributed Populus canescens patches were studied using a proteomic approach and nuclear microsatellite markers. Clonal reproduction was the primary reproduction strategy of these P. canescens patches. Forty-eight percent of the locations represented in one or two P. canescens patches were identified. In total, 83 different proteins were identified in 118 of 119 protein spots, most of them involved in metabolism. Distinct proteomes and post-translational modifications were found in different P. canescens patches. The differences in the proteomes originate both from the expression of different protein isoforms with the same function and from the differential expression of proteins with different functions, suggesting that different patches might have a functional basis for their adaptation to their environments. Our studies provide a good example of applying proteomics to measure natural variation between patches and will provide a basis for understanding how trees survive through their responses to natural conditions.

Transgenic hybrid aspen overexpressing the Atwbc19 gene encoding an ATP-binding cassette transporter confers resistance to four aminoglycoside antibiotics

Antibiotic-resistance genes of bacterial origin are invaluable markers for plant genetic engineering. However, these genes are feared to pose possible risk to human health by horizontal gene transfer from transgenic plants to bacteria, potentially resulting in antibiotic-resistant pathogenic bacteria; this is a considerable regulatory concern in some countries. The Atwbc19 gene, encoding an Arabidopsis thaliana ATP-binding cassette transporter, has been reported to confer resistance to kanamycin specifically as an alternative to bacterial antibiotic-resistance genes. In this report, we transformed hybrid aspen (Populus canescens x P. grandidentata) with the Atwbc19 gene. Unlike Atwbc19-transgenic tobacco that was only resistant to kanamycin, the transgenic Populus plants also showed resistance to three other aminoglycoside antibiotics (neomycin, geneticin, and paromomycin) at comparable levels to plants containing a CaMV35S-nptII cassette. Although it is unknown why the transgenic Populus with the Atwbc19 gene is resistant to all aminoglycoside antibiotics tested, the broad utility of the Atwbc19 gene as a reporter gene is confirmed here in a second dicot species. Because the Atwbc19 gene is plant-ubiquitous, it might serve as an alternative selectable marker to current bacterial antibiotic-resistance marker genes and alleviate the potential risk for horizontal transfer of bacterial-resistance genes in transgenic plants.

Zinc accumulation potential and toxicity threshold determined for a metal-accumulating Populus canescens clone in a dose–response study

The effect of increasing soil Zn concentrations on growth and Zn tissue concentrations of a metal-accumulating aspen clone was examined in a dose–response study. Plants were grown in a soil with a low native Zn content which was spiked with Zn salt solutions and subsequently aged. Plant growth was not affected by NH 4NO 3-extractable soil Zn concentrations up to 60 μg Zn g −1 soil, but it was completely inhibited at extractable concentrations above 90 μg Zn g −1 soil. From these data an effective concentration of 68.5 μg extractable Zn g −1 soil was calculated at which plant growth was reduced by 50%. The obtained information on toxicity threshold concentrations, and the relation between plant Zn accumulation and extractable soil Zn concentrations may be used to assess the suitability of the investigated Populus canescens clone for various phytoremediation strategies. The potential risk of metal transfer into food webs associated with P. canescens stands on Zn-polluted sites may also be estimated.

Bottom-up down from the top: Honeydew as a carbon source for soil organisms

Honeydew produced by aphids is a well-studied food source for mutualistic ants. Although considerable amounts drop onto the soil surface there are hardly any studies dealing with the potential effects of this additional C source for soil organisms, particularly those living at the soil surface. We studied this question by simulating honeydew and investigating plots under Populus canescens formerly infested with aphids on two ruderal sites differing in soil organic matter content and vegetation cover. The simulated honeydew input increased microbial biomass with some delay in week 10. Both natural and simulated honeydew raised the activity densities of an epigeic Collembola taxon, the Bourletiellidae, but not of the dominant Hemisotoma thermophila. The honeydew effect varied over time and with the site, and was more pronounced at the nutrient-poor site for Collembola, but not for microbial biomass. Ant consumption reduced the amount of honeydew reaching the soil surface by 50%. The activity density of H. thermophila was negatively related to ants and spiders, hinting at a top-down control. Honeydew clearly acts as a bottom-up force for soil organisms, which is however only part of the complex network connecting the food webs of primary producers and decomposers.

Interaction of nitrogen nutrition and salinity in Grey poplar (Populus tremula × alba)

Salinity represents an increasing environmental problem in managed ecosystems. Populus spp. is widely used for wood production by short-rotation forestry in fertilized plantations and can be grown on saline soil. Because N fertilization plays an important role in salt tolerance, we analysed Grey poplar (Populus tremula x alba, syn. Populus canescens) grown with either 1 mM nitrate or ammonium subjected to moderate 75 mM NaCl. The impact of N nutrition on amelioration of salt tolerance was analysed on different levels of N metabolism such as N uptake, assimilation and N (total N, proteins and amino compounds) accumulation. Na concentration increased in all tissues over time of salt exposure. The N nutrition-dependent effects of salt exposure were more intensive in roots than in leaves. Application of salt reduced root increment as well as stem height increase and, at the same time, increased the concentration of total amino compounds more intensively in roots of ammonium-fed plants. In leaves, salt treatment increased concentrations of total N more intensively in nitrate-fed plants and concentrations of amino compounds independently of N nutrition. The major changes in N metabolism of Grey poplar exposed to moderate salt concentrations were detected in the significant increase of amino acid concentrations. The present results indicate that N metabolism of Grey poplar exposed to salt performed better when the plants were fed with nitrate instead of ammonium as sole N source. Therefore, nitrate fertilization of poplar plantations grown on saline soil should be preferred.

Caratterizzazione energetica di biomasse agro-forestali presenti in aree collinari e montane della Basilicata

Abstract: An evaluation of energetic characteristics such as high calorific value (on ash-free dry weight basis), ash, carbon, nitrogen, and moisture content of 12 indigenous tree and shrub species of Southern Italy (Basilicata Region) was carried out. The studied species are the most abundant in this area: Quercus cerris L., Quercus pubescens Willd., Fraxinus ornus L., Populus canescens (Aiton) Smith, Salix alba L., Alnus cordata L., Robinia pseudoacacia L., Olea europaea L., Spartium junceum L., Rubus hirtus W., Onopordum illirium L., Arundo donax L. For Q. cerris, Q. pubescens and O. europaea L., the energetic characteristics were measured by separating the wood components from the leaves. Q. cerris leaves contained the greatest high calorific value. F. ornus leaves had a greater ash content than the other samples while the lowest values were measured for S. junceum, Q. pubescens and R. pseudoacacia. The highest content of Carbon was in O. europaea leaves. A. donax and O. illirium had the lower level of high calorific value and Carbon than all the other species. The highest Nitrogen content was measured in Q. cerris leaves and the lowest one in F. ornus wood components.

Some cesium and potassium salts increase the water permeability of astomatous isolated plant cuticles

AbstractSalts were applied as aqueous solution to the outer surfaces of astomatous isolated cuticles, and the water was allowed to evaporate. Effects of salt residues on the surfaces of cuticles on water permeability of cuticles were measured at 25°C. A surface dose of 0.2 mol m–2 Cs2CO3 and K2CO3 increased the water permeability of pear leaf cuticles by factors of 9.9 and 3.9, respectively. Na2CO3 was barely effective, and Li2CO3 as well as (NH4)2CO3 had no influence on water permeability. Potassium applied as sulfate, nitrate, or chloride had no effect on the water permeability of pear leaf cuticles, while K+ salts of weak acids (0.2 mol m–2) were effective, as they increased water permeability by factors of 5.4 (K+‐acetate), 3.9 (K2CO3), and 2.0 (K2HPO4), respectively. Sensitivity of Idesia polycarpa leaf cuticles to treatment with K2CO3 at 0.2 mol m–2 was greatest as water permeability was increased 35‐fold, while the water permeability of cuticles from other species tested (astomatous leaf cuticles from Hedera helix, Citrus aurantium, Prunus laurocerasus, Pyrus communis, and Populus canescens; fruit cuticles from Capsicum annuum and Lycopersicon esculentum) increased only by factors ranging from 1.7 to 3.9. Data are discussed in relation to swelling and ion‐exchange properties of cuticles.

Chemical products from temperate forest tree species—Developing strategies for exploitation

Forest trees are integral to the landscape and rural economy. Unfortunately, the economic returns from timber production have declined significantly across Europe. Only 25% of felled wood is converted to timber, the remaining material is a rich composite of primary and secondary metabolites and plant fibres, a relatively unexplored and unexploited resource for potentially novel products that could compliment revenue from traditional market outlets. Wood from temperate forest trees has traditionally been used as a source of tannins, terpenes, rosins and aromatic phenolic compounds. Existing information on such chemical groups, and other secondary metabolites was collated for a range of temperate forest tree species including, alder ( Alnus glutinosa L. Gaertn.), ash ( Fraxinus excelsior L.), aspen ( Populus tremula L.), beech ( Fagus sylvatica L.), birch ( Betula pendula Roth., Betula pubescens Ehrh.), cherry ( Prunus avium L .), Corsican pine ( Pinus nigra Arnold), Douglas fir ( Pseudotsuga menziesii Mirib. Franco), larch ( Larix deciduas Mill., Larix kaempferi Sarg.), oak ( Quercus robur L., Quercus petraea Mattuschka, Liebl), poplar ( Populus nigra L., Populus gileadensis Rouleau, Populus alba L., Populus canescens Ait. Sm.), Scots pine ( Pinus sylvestris L.), sitka spruce ( Picea sitchensis Bong. Carr .) and willow ( Salix alba L., Salix fragilis L.). Over 37,000 records were extracted from phytochemical databases, research papers, conference proceedings, books, unpublished reports and company literature, covering identified metabolites, the tissues from which they were extracted (e.g., bark, leaves, heartwood, roots), reported yields, properties and hazards. Very little data exists on the yield or variability of individual metabolites limiting the ability to assess economic potential. The information sourced is collated in a database, available to view at http://tree-chemicals.csl.gov.uk. Traditional and new markets for exploitation of tree metabolites are reviewed along with possible methods of extraction. Computer-aided Quantitative-Structure Activity Relationship Modelling (QSAR) augmented the search for novel applications for the tree metabolites. By this method, monoterpenes with useful anti-microbial properties were identified. Application of green chemical technologies also show promise in adding value to tree metabolites including the modification of cellulose and the benign extraction of valuable chemical products. Opportunities for possible future routes of exploitation of wood biomass are presented and discussed.

Characterization of aqueous pores in plant cuticles and permeation of ionic solutes

Plant cuticles are lipid membranes with separate diffusion paths for lipophilic non-electrolytes and hydrated ionic compounds. Ions are lipid insoluble and require an aqueous pathway across cuticles. Based on experimental data, the aqueous pathway in cuticles has been characterized. Aqueous pores arise by hydration of permanent dipoles and ionic functional groups. They can be localized using ionic fluorescent dyes, silver nitrate, and mercuric chloride. Aqueous pores preferentially occur in cuticular ledges, at the base of trichomes, and in cuticles over anticlinal walls. Average pore radii ranged from 0.45 to 1.18 nm. Penetration of ions was a first order process as the fraction of the salt remaining on the cuticle surface decreased exponentially with time. Permeability of cuticles to ions depended on humidity and was highest at 100% humidity. Wetting agents increased rate constants by factors of up to 12, which indicates that the pore openings are surrounded by waxes. The pores in cuticular ledges of Helxine soleirolii allowed passage of berberine sulphate, which has a molecular weight of 769 g mol(-1). Increasing the molecular weight of solutes from 100 to 500 g mol(-1) decreased the rate constants of penetration by factors of 7 (Vicia faba) and 13 (Populus canescens), respectively. Half-times of penetration of inorganic salts and organic ions across Populus cuticles and Vicia leaf surfaces varied between 1 and 12 h. This shows that penetration of ionic compounds can be fairly rapid, and ions with molecular weights of up to 800 g mol(-1) can penetrate cuticles that possess aqueous pores.