Gravimetric Determination of Acid Detergent Fiber and Lignin in Feed: Interlaboratory Study

On the basis of AOAC Official Method 973.18, a collaborative study was performed to determine fractions of acid detergent fiber (ADF) and lignin (ADL) in animal feed. The study used 6 animal feed and forage samples as blind duplicates and involved 22 participants from 7 countries. The samples analyzed covered a range from 3.5 to 70 ADF and from <1 to 20 ADL. Repeatability standard deviations ranged from 0.27 to 0.95 for ADF and from 0.08 to 0.59 for ADL. The reproducibility standard deviations ranged from 0.56 to 2.44 for ADF and from 0.52 to 2.09 for ADL. Analyzed samples comprised clover and grass silages, soy meal, cattle feed, wheat, and sawdust. The studied method has been published as the EN ISO 13906:2008 standard.

[Systemic sclerosis and pregnancy. A review of the current literature]

Pregnancy in women diagnosed with systemic sclerosis generally has a favorable outcome according to most recent studies. Women with systemic sclerosis who wish to become pregnant should achieve low disease activity for at least 6 months prior to conception. Regular follow-up of pregnant scleroderma patients by an interdisciplinary medical team including gynaecologists and rheumatologists is necessary to control disease activity and avoid possible complications. Severe organ involvement, early diffuse systemic sclerosis with rapid onset, and pulmonary hypertension ought to discourage patients from pregnancy, as these situations are at high risk of complications for both mother and fetus during pregnancy.

Transformation of apple ( Malus domestica Borkh.) with the stilbene synthase gene from grapevine ( Vitis vinifera L.) and a PGIP gene from kiwi ( Actinidia deliciosa)

The objective of the present research was to introduce genes with antifungal potential into the commercially important apple cvs. Elstar and Holsteiner Cox in order to establish resistance against fungal diseases. The gene encoding the stilbene synthase (Vst1) from Vitis vinifera L., responsible for the synthesis of the phytoalexin resveratrol in grapevine, and the gene for a polygalacturonase-inhibiting protein (PGIP) from kiwi ( Actinidia deliciosa) were transferred into Holsteiner Cox and Elstar via Agrobacterium tumefaciens-mediated transformation. A total of nine transgenic Holsteiner Cox clones and one transgenic E clone carrying the stilbene-synthase gene as well as three transgenic Holsteiner Cox lines harbouring the polygalacturonase-inhibiting protein from Kiwi were identified via polymerase chain reaction and Southern blot analysis. High performance liquid chromatography analysis revealed the accumulation of a resveratrol-derivate, a glycoside, in transgenic Vst1 plants.

Effects of temperature and concentration of the accelerators ethoxylated alcohols, diethyl suberate and tributyl phosphate on the mobility of [14C]2,4-dichlorophenoxy butyric acid in plant cuticles

Intrinsic activities of monodisperse ethoxylated dodecanols (MEDs), diethyl suberate (DESU) and tributyl phosphate (TBP) were investigated using Stephanotis floribunda leaf cuticular membranes (CMs) and [14C]2,4-dichlorophenoxy butyric acid (2,4-DB) as a model solute. When sorbed in cuticular membranes, MEDs, DESU and TBP increase solute mobility and are called accelerators for this reason. With MEDs, dose-effect curves (log mobility vs accelerator concentration) were linear but, with DESU and TBP, curves convex to the x axes were obtained that approached a maximum at 90 and 150 g kg-1, respectively. Accelerators increased the mobility of 2,4-DB in the CMs by 9- to 48-fold, and effects were larger at lower temperatures (range 15-30 degrees C). Activation energy for diffusion of 2,4-DB was 105 kJ mol-1, decreasing with increasing accelerator concentrations to 26 kJ mol-1 with DESU at 90 g kg-1 and 64 kJ mol-1 with TBP at 150 g kg-1. Thus, the intrinsic activity of DESU was much higher than that of TBP, which implies that, for a given effect, less DESU than TBP would be needed. MEDs were also very effective accelerators, lowering activation energies to 36 kJ mol-1. Data are discussed in relation to increasing rates of foliar penetration of active ingredients at low temperatures.

Thermodynamic analysis of diffusion of non-electrolytes across plant cuticles in the presence and absence of the plasticiser tributyl phosphate

Solute mobility in cuticular membranes (CMs) of 14 plant species (Citrus aurantiumn L., Citrus grandis L., Hedera helix L., Ilex aquifolium L., Ilex paraguariensis St.-Hil., Malus domestica Borkh. cv. Golden Delicious, Populus alba L., Prunus laurocerasus L., Pyrus communis L. cv. Bartlett, Conference and Gellerts Butterbirne, Pyrus pyrifolia (Burm. f.) Nakai, Schefflera actinophylla (Endl.) Harms and Strophanthus gratus Baill.) was measured over the temperature range 25-55 degrees C. The five organic model compounds differed in size (130-349 cm3 mol(-1)) and cuticle/water partition coefficient (18-10(8)). For all individual CMs (n = 297), the data were plotted according to the thermodynamic relationship between the preexponential factor (which is proportional to entropy) of the Arrhenius equation and the activation energy (enthalpy) of diffusion (ED). A strict linear correlation was obtained, providing evidence that the five compounds diffused along the same lipophilic diffusion path in all plant species tested. Extracting cuticular waxes from CMs of four plant species (Hedera, Pyrus, Schefflera and Strophanthus) had no effect on the slope of the plot but a parallel displacement towards higher entropy was observed with these polymer matrix (MX) membranes. This displacement is interpreted as a temperature-independent tortuosity factor directly related to entropy. The influence of the plasticiser tributyl phosphate on solute mobility at various temperatures was measured for CM and MX membranes. The plasticiser increased solute mobility and ED was reduced drastically for both membrane types. This plasticiser effect was almost completely reversible, when tributyl phosphate was desorbed from the membranes. For both, plasticised CM and MX, the thermodynamic correlation exists whereby all data points lie on the same line. The data are used to characterise the lipophilic pathway across plant cuticles in terms of the free-volume theory.

Calcium chloride penetrates plant cuticles via aqueous pores

Penetration of calcium chloride across astomatous cuticular membranes (CMs) isolated from leaves of Pyrus communis L. has been studied. Penetration was a first-order process when calcium chloride concentrations ranged from 2 gl(-1) to 10 gl(-1). Rate constants were increased 10-fold by adding wetting agents but they did not depend on temperature. The accelerators tributyl phosphate and diethyl sebacate had no effect on rates of penetration. Increasing humidity over the salt residue on the CMs from 50 to 90% increased rate constants by about 2-fold. Extracting cuticular waxes from pear leaf CMs increased rate constants by factors of 2 to 3, depending on humidity. Leaf CMs from Malus domestica Borkh., Populus aelha L., Stephanotis floribunda Brongn. and Schefflera actinophylla (Endl.) Harms were also permeable to CaCl2. Highest rate constants were observed with poplar CMs while Schefflera CMs exhibited the lowest permeability. By comparing these results with the well established transport properties of the lipophilic pathway it is concluded that calcium chloride hexahydrate penetrated cuticular membranes via aqueous pores.

Phase transitions and thermal expansion coefficients of plant cuticles : The effects of temperature on structure and function

The temperature-induced volume expansion of enzymatically isolated cuticular membranes of twelve plant species was measured. All cuticular membranes exhibited distinct second-order phase transitions in the temperature range of about 40 to 50° C. Increases in the volumes of fruit cuticles (Lycopersicon, Cucumis, Capsicum, Solanum and Malus) were fully reversible, while leaf cuticular membranes (Ficus, Hedera, Nerium, Olea, Pyrus, Picea and Citrus) underwent irreversible structural changes. Below the phase-transition temperature, volumetric expansion coefficients ranged from 0.39·10(-6) m(3)·kg(-1)·K(-1) to 0.62·10(-6) m(3)·kg(-1)·K(-1), and above from 0.60·10(6) m(3)·kg(-1)·K(\-1) to 1.41· 10(-6) m(3)·kg(-1)·K(-1). Densities of cuticles at 25° C ranged from 1020 kg·m(-3) to 1370 kg·m(-3). Expansion coefficients and phase transitions were characteristic properties of the polymer matrix as a composite material, rather than of cutin alone. It is argued that the sudden increase of water permeability above the transition temperature, is caused by an increase of disorder at the interface between the polymer matrix and the soluble cuticular lipids. Possible ecological and physiological consequences of these results for living plants are discussed.

The effect of the environment on the permeability and composition of Citrus leaf cuticles : I. Water permeability of isolated cuticular membranes

The water permeabilities of 3174 astomatous, isolated cuticular membranes from Citrus aurantium L. leaves were studied. Trees were grown in environmental chambers at temperatures ranging from 15 to 35° C and humidities of 50% and 90%. Photosynthetically active radiation was 500-1000 μmol photons·m(-2)· s(-1). The different growing conditions had no effect on the water permeability of the membranes. However, storing isolated cuticular membranes at 8° C for up to 112 weeks decreased their water permeability, and it is argued that this is a consequence of the healing of defects between wax crystallites, and also indicates the dynamic nature of cuticular waxes.

Development of plant cuticles: fine structure and cutin composition of Clivia miniata Reg. leaves

The fine structure and monomeric composition of the ester-cutin fraction (susceptible to BF3/CH3OH transesterification) of the adaxial leaf cuticle of Clivia miniata Reg. were studied in relation to leaf and cuticle development. Clivia leaves grow at their base such that cuticle and tissues increase in age from the base to the tip. The zone of maximum growth (cell expansion) was located between 1 and 4 cm from the base. During cell expansion, the projected surface area of the upper epidermal cells increased by a factor of nine. In the growth region the cuticle consists mainly of a polylamellate cuticle proper of 100-250 nm thickness. After cell expansion has ceased both the outer epidermal wall and the cuticle increase in thickness. Thickening of the cuticle is accomplished by interposition of a cuticular layer between the cuticle proper and the cell wall. The cuticular layer exhibits a reticulate fine structure and contributes most of the total mass of the cuticle at positions above 6 cm from the leaf base. The composition of ester cutin changed with the age of cuticles. In depolymerisates from young cuticles, 26 different monomers could be detected whereas in older ones their number decreased to 13. At all developmental stages, 9,16-/10,16-dihydroxyhexadecanoic acid (positional isomers not separated), 18-hydroxy-9-octadecenoic acid, 9,10,18-trihydroxyoctadecanoic acid and 9,10-epoxy-18-hydroxyoctadecanoic acid were most frequent with the epoxy alkanoic acid clearly predominating (47% at 16 cm). The results are discussed as to (i) the age dependence of cutin composition, (ii) the relationship between fine structure and composition, (iii) the composition of the cuticle proper, the cuticular layer and the non-depolymerizable cutin fraction, and (iv) the polymeric structure of cutin.

Thermodynamic analysis of nonelectrolyte sorption in plant cuticles: The effects of concentration and temperature on sorption of 4-nitrophenol

The sorption of 4-nitrophenol (4-NP) in enzymatically isolated cuticles ofLycopersicon esculentum fruits andFicus elastica leaves was studied as a function of temperature and solute concentration. Plots of the concentrations of 4-NP sorbed in the cuticle versus the equilibrium concentrations in the aqueous phase gave linear isotherms at low concentrations that tended to approach plateaus at higher sorbate concentrations (≥ 10 mmol·kg(-1)). At low concentrations of sorbed 4-NP, cuticles have sorptive properties similar to those of organic solvents which are able to form intermolecular hydrogen bonds, while at higher concentrations their solid nature becomes apparent. During sorption of 4-NP the cutin matrix swells and new sorption sites are successively formed. The partition coefficients of 4-NP in the system cuticle/buffer are functions of temperature and concentration. At high sorbate concentrations (approx. 1 mol·kg(-1)) they approach a value of 1. Different sorptive properties were observed for the cutin regions normally encrusted with soluble cuticular lipids (SCL) and those without SCL. Increasing temperature augmented the number of sorption sites in the cutin ofLycopersicon while no effect was observed withFicus. The changes of partial molar free energy (ΔG (o) tr), enthalpy (ΔH (o) tr), and entropy (ΔS (o) tr) for the phase transfer of 4-NP also depended on sorbate concentration: ΔH (o) tr and ΔS (o) tr were negative and steeply decreased at high sorbate concentrations. This is due to solute-solute interactions replacing solute-cutin interactions at high concentrations resulting in solid precipitates of solute within the cutin matrix. This formation of ordered solid domaines starting from a small number of nonelectrolyte molecules interacting with the cutin is proposed as a model for the intracuticular deposition of SCL.

Accumulation and transport of (2,4-dichlorophenoxy)acetic acid in plant cuticles. II. Permeability of the cuticular membrane

Diffusion of (2,4-dichlorophenoxy)acetic acid (2,4-D) across plant cuticles from 10 species was investigated at 25 degrees C using enzymatically isolated cuticles. Permeance coefficients (P) and extrapolated holdup times (te) were measured and permeability (P), diffusion (D), and partition coefficients (K) were calculated. Permeance coefficients ranged from 2.72 X 10(-8) (Capsicum fruit) to 1.00 X 10(-10) m/sec (Ficus leaf). Extraction of soluble cuticular lipids from cuticular membranes increased permeances by up to four orders of magnitude. This demonstrates that permeance is determined by the soluble cuticular lipids associated with the cutin, rather than by cutin alone. Mean diffusion coefficients calculated from holdup times were 4.0 X 10(-15) (fruit cuticular membranes) and 1.71 X 10(-16) m2/sec (leaf cuticular membranes), respectively. Since a common diffusion coefficient exists for both leaf and fruit cuticles, differences in permeability coefficients between species can be attributed to differences in the partition coefficients. However, partition coefficients calculated from transmembrane diffusion are lower than those determined directly in a sorption experiment by a factor of from 6 to 200. Thus, the high resistance of plant cuticles to transport of 2,4-D can be attributed to both low diffusion and partition coefficients in the transport-limiting layer made up of cutin and soluble lipids which are densely packed and highly ordered. A linear equation is derived and permits the prediction of permeability coefficients of plant cuticles from partition coefficients determined in a simple sorption experiment.

Accumulation and transport of (2,4-dichlorophenoxy)acetic acid in plant cuticles: I. Sorption in the cuticular membrane and its components

Partition coefficients (K) of (2,4-dichlorophenoxy)acetic acid (2,4-D) have been determined for the system plant cuticle/aqueous buffer. Cuticles isolated enzymatically from leaves (Clivia miniata, Ficus elastica, Citrus aurantium, Hedera helix, Pyrus communis cv. Conférence and cv. Williams, Olea europaea) and fruits (Lycopersicon esculentum, Capsicum annuum, Solanum melongena, Cucumis sativus) were utilized. Only the nondissociated species of 2,4-D was sorbed by cuticles and their lipophilic components. The average partition coefficient for leaf cuticles was 316 (range, 240-470) and for fruit cuticles 476 (range, 424-579). The dependence of sorption upon 2,4-D concentration was tested using tomato fruit cuticle. The sorption isotherm was linear from 2.0 to 5.0 X 10(-4) mol m-3. With increasing 2,4-D concentrations partition coefficients decreased slightly. Extraction of soluble cuticular lipids (SCL) increased the partition coefficients and these relative increases were correlated to relative amounts of SCL. In most species the hydrolytic removal of polar cuticular components resulted in a further increase of partition coefficients. No single cuticle was found to be representative for the sorption characteristics of all plant species investigated. The amounts of cuticle present in plant communities can be estimated from the data presented in conjunction with leaf area indices.

Water permeability of periderm membranes isolated enzymatically from potato tubers (Solanum tuberosum L.)

The fine structure and water permeability of potato tuber periderm have been studied. Periderm membranes (PM) were isolated enzymatically using pectinase and cellulase. They were composed of, about six layers of phellem cells arranged in radial rows. The walls of phellem cells consist of cellulosic primary and tertiary walls and suberized secondary walls which are lamellated. Middle lamellae and primary walls contain lignin. Since the PM did not disintegrate during enzymatic isolation it appears that lignin also extends into the secondary suberized walls. The water permeability of PM was low, ranging from 1-3·10(-10) m s(-1). This low water permeability developed only during storage of tubers in air. Periderm membranes from freshly harvested tubers had a relatively high permeability. The low permeability of PM from stored tubers is attributed to soluble lipids associated with suberin since: (1) extraction of soluble lipids from PM increased permeability by more than 100-fold, (2) a phase transition of soluble lipids was observed between 46 and 51° C, and (3) only the permeability of PM decreased during storage while the permeability of extracted PM remained unchanged. Evidence is presented that two pathways for water movement exist in parallel. Pathway 1 is represented by middle lamellae and primary walls extending in radial direction across the membranes. This pathway has a relatively high specific permeability. Pathway 2 is represented by a polylaminated structure made up of tangential walls of phellem cells which are orientated normal to the direction of water flow. This pathway has a low specific permeability because of the properties of secondary walls incrusted with soluble lipids. It is calculated that about 10% of the water flows across pathway 1 and 90% across pathway 2 which has a volume fraction of 0.995.

In-vivo study of cutin synthesis in leaves of Clivia miniata Reg

Cutin synthesis of Clivia miniata Reg. was studied by using intact leaves. Tritium-labelled hexadecanoic acid was used as precursor and was administered as droplets of micellar solutions to the upper surface of expanding leaves. Radiolabel was incorporated rapidly. Within 2 h, up to 10% of the label administered had been incorporated into cutin. Rates of (3)H-cutin synthesis depended on the position of the site of precursor donation to the leaf. Highest rates were observed between 3 to 4 cm from the leaf base. From zero to 3 cm, rates increased by about one order of magnitude every centimeter. Above 4 cm, the decrease in rates of (3)H-cutin synthesis was again logarithmic, such that at 10 cm from leaf base only 1%, and at 15 cm from leaf base only 0.1% of the maximum rates were observed. Rates of cutin synthesis depended on the hexadecanoic acid concentration of the droplets, according to the Michaelis-Menten equation. The maximum rate was 0.71 μg cm(-2) h(-1). The half-maximum rate was observed at a hexadecanoic acid concentration of 42.4 mg l(-1). Maximal cutin synthesis coincided with maximal cell elongation. Microautoradiography indicated that most of the label was incorporated into the internal cuticular layer.

Development of plant cuticles: occurrence and role of non-ester bonds in cutin of Clivia miniata Reg. leaves

The effect of BF3-methanol treatment on the mass and fine structure of isolated Clivia leaf cuticles at different stages of development has been investigated. BF3-methanol cleaves ester linkages in cutin; however, the cuticles are not completely depolymerized. With increasing age, the residue left after BF3-methanol treatment increases in mass. In very young cuticles, 10% of the total cutin resisted BF3-methanol and the fraction of nonester cutin increased up to 62% in mature leaves. Transmission electron microscopy shows that fine structure of the cuticle proper is severely distorted but not destroyed. The internal cuticular layer, which exhibits a heavy contrast when fixed with KMnO4, is completely depolymerized, while the external cuticular layer is hardly affected. The results are discussed in relation to cuticle development and to the function of cuticles as transpiration resistances.

Fine structure of isolated and non-isolated potato tuber periderm

Cell walls of the periderm of native potato tuber (Solanum tuberosum L. cv. Primura) consist of a primary wall, a suberized secondary wall and a tertiary wall. With a mixture of pectinase and cellulase intact periderm membranes can be isolated. Isolation does not affect fine structure. It is suggested that the lignin in the middle lamellae and primary walls prevents the enzymes from digesting pectinaceous materials and cellulose. In specimens fixed with OsO4, the suberized walls appear as alternating electrondense and electron-lucent lamellae. This lamellar architecture is not altered by extraction with chloroform. Therefore, the current view that the electronlucent lamellae consist of soluble lipids (waxes) can no longer be maintained. It is argued that the lamellation is a property of the suberin itself, and the suberized wall consists of alternating layers of suberins differing in polarity. A hypothesis of suberin assembly from sub-units is advanced and the subunits are shown for the first time.

Fine structure of plant cuticles in relation to water permeability: The fine structure of the cuticle of Clivia miniata reg. leaves

The fine structure of the upper cuticular membrane (CM) of Clivia miniata leaves was investigated using electron microscopy. The CM is made up of a thin (130 nm) lamellated cuticle proper (CP) and a thick (up to 7 μm over periclinal walls) cuticular layer (CL) of marbled appearance. Evidence is presented to show that the electron lucent lamellae of the CP do not simply represent layers of soluble cuticular lipids (SCL). Instead, the lamellation is probably due to layers of cutin differing in polarity. It is argued that the SCL in the Cp are the main barrier to water. Thickening of the CM during leaf development takes place by interposition of cutin between the CM and the cellin wall. The cutin of young, expanding leaves has a high affinity for KMnO4 and is therefore relatively polar. As leaves mature, the external CL underneath the CP becomes non-polar, as only little contrast can be obtained with permanganate as the post fixative.

Water permeability of Betula periderm

The water permeability of periderm membranes stripped from mature trees of Betula pendula Roth was investigated. The diffusion of water was studied using the system water/membrane/water, and transpiration was measured using the system water/membrane/water vapor. Betula periderm consists of successive periderm layers each made up of about 5 heavily suberized cell layers and a varying number of cell layers that are little suberized, if at all. It is shown that these layers act as resistances in series. The permeability coefficient of the diffusion of water (P d) can be predicted with 79% accuracy from the reciprocal of the membrane weight (x in mg cm(-2)) by means of the linear equation P d=14.69·10(-7) x-0.73·10(-7). For example, the P d of a periderm membrane having a weight of 10 mg cm(-2) (approx. 250 μm thick) is 7.4·10(-8) cm s(-1), which is comparable to the permeability of cuticles. This comparison shows that on a basis of unit thickness, Betula periderm is quite permeable to water as cuticles have the same resistance with a thickness of only 0.5 to 3 μm. It is argued that this comparatively high water permeability of birch periderm is due to the fact that middle lamellae and the primary walls of periderm cells are not at all, or only incompletely suberized and, therefore, form a hydrophilic network within which the water can flow. This conclusion is based on the following observations: (1) Middle lamellae and primary walls stain strongly with toluidine blue, which shows them to be polar. (2) If silver ions are added as tracer for the flow of water, they are found only in the middle lamellae, primary walls, and in plasmodesmata, while no silver can be detected in the suberized walls. (3) Permeability coefficients of transpiration strongly depend on water activity. This shows conclusively that water flows across Betula periderm via a polar pathway. It is further argued that liquid continuity is likely to be maintained under all physiological conditions in the network formed by middle lamellae and primary walls. On the other hand, the lumina of periderm cells, intercellular air spaces in the lenticels, and even the pores in the suberized walls (remainders of plasmodesmata) will drain at a humidity of 95% and below. Due to the presence of intercellulars the permeability coefficient of lenticels is much greater than that of the periderm. A substantial amount of the total water, therefore, flows as vapor through lenticels even though they cover only 3% of the surface.

Water permeability of plant cuticles: The effect of temperature on diffusion of water

The effect of temperature on water permeability of plant cuticles (astomatous Citrus leaf cuticles) has been investigated. The Arrhenius plot (logarithm of the permeability coefficient vs. 1/temperature) has two linear portions that intersect at 44° C. Evidence is presented to show that this intersection represents the solid/liquid phase transition of cuticular lipids. As the Arrhenius plot has only one phase transition in the temperature range of 5 to 80° C, it appears that all soluble cuticular lipids in the cuticle are present as a homogeneous mixture rather than as individual layers differing in composition. This view is supported by electron spin resonance evidence showing homogenous distribution of spin label fatty acids. The original distribution of soluble cuticular lipids is irreversibly altered by heating cuticular membranes above the transition temperature. This is accompanied by an irreversible increase in water peremeability, demonstrating the importance of the structure of cuticular lipids with regard to cuticular permeability.

Composition of soluble cuticular lipids and water permeability of cuticular membranes from Citrus leaves

Water permeability and composition of soluble cuticular lipids of isolated cuticular membranes from leaves of Citrus aurantium L. were investigated for 3 successive years. The average water permeability coefficient determined using 169 cuticular membranes was 1.09·10(-7) cm s(-1) with a standard deviation of 0.78·10(-7) cm s(-1). There were no significant differences in water permeability between years. Cuticular membranes are characterized by a great variability in water permeability both within and between years. Both water permeability of individual membranes and variability between membranes are shown to be determined by soluble cuticular lipids contained within the cuticular membranes. The soluble cuticular lipids of Citrus leaves are composed of fatty acids, primary alcohols, esters, and hydrocarbons. They occur in amounts of 9.84 μg cm(-2), which represents approx. 3% of the total mass of isolated cuticular membranes. The specific weight of cuticular membranes (365.4 μg cm(-1)) and total amount of soluble cuticular lipids did not vary significantly between years. Significant differences were observed for the amounts and composition of the constituent classes of lipids. Six homologues comprise 86% of the fatty acids (C16; C18; C19; C21; C24; C26), 83% of the primary alcohols (C24; C26; C28; C30; C32; C34) and 88% of the esters (C36; C38; C40; C41; C42; C44). Eleven major homologues amount only to 62% of the total hydrocarbons (C16; C17; C18; C20; C26; C27; C29; C30; C31; C32; C33). Variability in the composition of soluble cuticular lipids between years was much smaller than variability of water permeability and, therefore, no relation between composition of soluble cuticular lipids and water permeability could be found. It is suggested that this may be due to the fact that the lipid composition observed represents the averages of 20 to 30 membranes analyzed so that differences between individual membranes may have been leveled out.

Water permeability of plant cuticles : Dependence of permeability coefficients of cuticular transpiration on vapor pressure saturation deficit

Using the system vapor/membrane/liquid, permeability coefficients of cuticular transpiration (P ct) were determined as functions of water activity in the vapor (a wv). Enzymatically isolated cuticular membranes (CM) of Citrus aurantium L. and nonisolated CM of onion bulb scales and eggplant fruits were investigated. P ct of Citrus and eggplant CM decreased with decreasing a wv, while permeability coefficients of CM of onion were independent of a wv. Extraction of soluble cuticular lipids (SCL) from the CM of Citrus increased permeability coefficients by a factor of approximately 500. This extraction had no effect on the dependence of P ct on a wv.Treating cuticular membranes as a resistance network consisting of SCL and the polymer matrix, it is shown that the permeability of onion CM is determined by the resistance of the SCL arranged in series with the polymer matrix. In this type of CM liquid and vapor are separated by a continuous, nonporous layer of SCL, and the driving force of transpiration is the gradient of partial pressure of water vapor across the SCL layer. In the CM of Citrus and eggplant, the SCL layer is traversed by polar pores that swell or shrink depending on a wv. However, liquid continuity is maintained across these membranes down to a wv=0.22, the lowest value used. In this type of membrane the driving force of transpiration is the water potential gradient across the membrane.

Plant Cuticles Are Polyelectrolytes with Isoelectric Points around Three

The isoelectric points of isolated cuticles from Citrus aurantium L. (3.15), Prunus armeniaca L. (3.45), and Pyrus communis L. (2.90) leaves were determined from membrane potentials. At pH values below the isoelectric point, cuticular membranes carry a net positive charge and are permselective to anions (determined using (82)Br(-)). Above the isoelectric point, they carry a net negative charge and are permselective to cations (determined using (24)Na(+)). There are no gradients of fixed charges across the cuticular membranes as indicated by the absence of asymmetry potentials. Positive charges in the membranes originate from residues of basic amino acids of proteins or polypeptides contained in a nonextractable form within the cuticle. The exchange capacity of basic fixed groups in the cuticles of six species (Lycopersicon esculentum Mill., Capsicum annuum L. fruit cuticles, and Brassaia spec. leaf cuticles in addition to the above species) varied between 0.010 and 0.025 meq g(-1) cuticle. Fixed acidic groups were donated by residues of acidic amino acids, polygalacturonic acid, and nonesterified -COOH groups of the cutin polymer. At pH 8, total cation exchange capacity as determined using (45)Ca(2+) varied between 0.26 (Citrus) and 0.30 (apricot) meq g(-1).

Water permeability of isolated cuticular membranes: The effect of cuticular waxes on diffusion of water

The water permeability of astomatous cuticular membranes isolated from Citrus aurantium L. leaves, pear (Pyrus communis L.) leaves and onion (Allium cepa L.) bulb scales was determined before and after extraction of cuticular waxes with lipid solvents. In pear, the permeability coefficients for diffusion of tritiated water across cuticular membranes (CM) prior to extraction [P d(CM)] decreased by a factor of four during leaf expansion. In all three species investigated P d(CM) values of cuticular membranes from fully expanded leaves varied between 1 to 2×10(-7) cm(-3) s(-1)·P d(CM) values were not affected by pH. Extraction of cuticular waxes from the membranes increased their water permeability by a factor of 300 to 500. Permeability coefficients for diffusion of THO across the cutin matrix (MX) after extraction [P d(MX)] increased with increasing pH. P dvalues were not inversely proportional to the thickness of cuticular membranes. By treating the cutin matrix and cuticular waxes as two resistances acting in series it was shown that the water permeability of cuticles is completely determined by the waxes. The lack of the P d(CM) values to respond to pH appeared to be due to structural effects of waxes in the cutin matrix. Cuticular membranes from the submerse leaves of the aquatic plant Potamogeton lucens L. were three orders of magnitude more permeable to water than the cuticular membranes of the terrestrial species investigated.

Water permeability of isolated cuticular membranes: The effect of pH and cations on diffusion, hydrodynamic permeability and size of polar pores in the cutin matrix

The upper astomatous cuticle of Citrus aurantium L. leaves was isolated enzymatically or chemically, extracted with lipid solvents and used for the determination of water diffusion (P d ) and osmotic water permeability (P f ). The water permeability was strongly dependent on the pH value and the cations of the buffer solutions. In presence of monovalent alkali metal ions P d increased almost five fold between pH 3 and 11. The shape of the plot P d vs. pH suggests the presence of 3 different dissociable groups fixed to the membrane matrix. They are tentatively identified as two carboxyl groups dissociating between pH 3 to 6 and 6 to 9, respectively, and as phenolic hydroxyl groups dissociating above pH 9. The carboxyl group dissociating between pH 6 and 9 discriminated between alkali metal ions according to their ionic radius. Water permeability was lowest in the Li(+) from and increased in the order Li(+)<Na(+)<K(+)<Rb(+). The water permeability of membranes in Ca(2+) form was only slightly higher than that of membranes in H(+) form and little dependent on pH. The energy of activation which amounted to 13 kcal mol(-1) was constant over the temperature range of 5 to 40°C and pH independent. Since P f was greater than P d it was concluded that the cutin matrix contained polar pores and that water transport caused by a chemical potential gradient was both by diffusion and by viscous flow. The porous nature of the membranes was also confirmed by the fact that they are permselective according to size of the permeating molecule. Using the empirical equations of Paganelli and Solomon (1957) and Nevis (1958) the equivalent radius of the pores was estimated to be 0.46 and 0.45 nm, respectively. This estimate is in good agreement with the observations that (a) [(14)C]urea (molecular radius r s =0.264 nm) and [(3)H]glucose (r s =0.444 nm) penetrated the membranes and (b) the reflection coefficient was equal to one for raffinose (r s =0.654 nm) and sucrose (r s =0.555 nm) but 0.95 for glucose and 0.78 for urea. Both, the reflection coefficient and the pore radius estimates were pH independent, hence the increase in water permeability with increasing pH was due to an increase in the number of pores per unit area (1 cm(2)) from 5x10(10) at pH 3 to 15.8x10(10) at pH 9.

Hydrophobic cuticular ledges prevent water entering the air pores of liverwort thalli

Air pore geometry of 14 liverwort species was investigated using light, scanning and transmission electron microscopy to assess their ability to prevent water entering into the air pore and the intercellular space of the thallus. The air pores of 12 species [Marchantia polymorpha L., M. paleacea Bertol., M. nitida Lindenberg & Lehmann in Lehmann, Conocephalum conicum (L.) Wiggers, C. supradecompositum (S.O. Lindberg) Stephani, Grimaldia capensis Stephani, Targionia hypophylla L., Lunularia cruciata (L.) Dum., Reboulia hemisphaerica (L.) Raddi, Oxymitra paleacea Bischoff, Exormotheca bullata (Link) K. Müller (Tüb.), Plagiochasma elongatum Lindenberg & Gottsche] are equipped with hydrophobic ledges which constrict the air pore entrance after the fashion of an iris shutter. As a consequence only liquids having a contact angle of zero degree with the ledges are able to penetrate the air pore. The ledge of Marchantia paleacea was found to have a surface composed of methyl and methylene groups as indicated by the critical surface tension of less than 30.4 dyne cm(-1). Evidence is presented that the ledge is covered with a layer of cutin. It is shown that from the standpoint of protection against water entry these air pores must be considered perfect structures. Plagiochasma rupestre (Forster) Stephani and P. peruvianum Nees & Montagne are exceptional as they do not have ledges around their air pores. As a consequence liquids having a finite contact angle are able to enter through the pores into the thallus. Thus, they are imperfect and must be considered primitive.

Ion exchange properties of isolated tomato fruit cuticular membrane: Exchange capacity, nature of fixed charges and cation selectivity

Isolated tomato fruit cuticular membrane, free of extractable materials, was titrated potentiometrically using various bases. Three dissociable groups were observed in the pH ranges 3-6 (0.2 meq g(-1)), 6-9 (0.3 meq g(-1)) and 9-12 (0.55 meq g(-1)). The first group was tentatively assigned to-COOH groups of pectic materials and protein embedded in the membrane, the second to nonesterified-COOH groups of the cutin polymer and the third to phenolic-OH groups, such as non-extractable flavenoids present in the membrane, and to a small amount of-NH 3 (+) groups of proteins. The cuticular membrane exhibited a behavior typical of highly cross-linked, high-capacity ion exchange resins of the weak-acid type. Ion exchange capacity increased with increasing pH and neutral salt concentration. At constant pH and salt concentration, the exchange capacity increased with increasing counter ion valence and decreasing crystal radius, e.g. [tris (ethylenediamine) Co](3+)≥Ca(2+)>Ba(2+)>Li(+)>Na(+)>Rb(+)>N(CH3) 4 (+) . The cutin polymer exhibited a pronounced selectivity for Ca(2+) over Na(+) which increased with increasing neutralization of fixed charges. The large trivalent [Co(en)3](3+) was preferred only at low equivalent ionic fractions in the polymer. These results are discussed in relation to the structure and function of cuticular membranes.

Penetration of stomata by liquids: dependence on surface tension, wettability, and stomatal morphology

Wettability of the leaf surface, surface tension of the liquid, and stomatal morphology control penetration of stomata by liquids. The critical surface tension of the lower leaf surface of Zebrina purpusii Brückn. was estimated to be 25 to 30 dyne cm(-1). Liquids having a surface tension less than 30 dyne cm(-1) gave zero contact angle on the leaf surface and infiltrated stomata spontaneously while liquids having a surface tension greater than 30 dyne cm(-1) did not wet the leaf surface and failed to infiltrate stomata. Considering stomata as conical capillaries, we were able to show that with liquids giving a finite contact angle, infiltration depended solely on the relationship between the magnitude of the contact angle and the wall angle of the aperture. Generally, spontaneous infiltration of stomata will take place when the contact angle is smaller than the wall angle of the aperture wall. The degree of stomatal opening (4, 6, 8, or 10 mum) was of little importance. Cuticular ledges present at the entrance to the outer vestibule and between the inner vestibule and substomatal chamber resulted in very small if not zero wall angles, and thus played a major role in excluding water from the intercellular space of leaves. We show why the degree of stomatal opening cannot be assessed by observing spontaneous infiltration of stomata by organic liquids of low surface tension.

Preferential polar pathways in the cuticle and their relationship to ectodesmata

Ectodesmata-like structures, referred to here as mercurous or mercury precipitates (MP) and considered to be identical to precipitates observed after treatment of leaf tissue with Gilson solution for demonstration of ectodesmata, were demonstrated with cuticle enzymatically isolated from Allium bulb scales and leaves mounted on ascorbic acid-enriched agar or gelatin. The MP distribution patterns obtained with isolated cuticle, in the absence of a cell wall, were identical to those observed with living tissue. Since the distribution in either the presence or absence of the cell wall was similar, the distribution pattern must be determined by the cuticle and not by the cell wall. Disruption of the physical arrangement of epicuticular wax by brushing or removal with chloroform altered the distribution pattern and increased the frequency of MP. This was interpreted to mean that epicuticular wax plays an important role and also that the necessary reductant was not localized in specific structures in the cell wall. Based on this evidence, it appears that ectodesmata, as demonstrated with Gilson solution, are not specific cell-wall structures, whether plasmic or not plasmic. More likely, the MP observed in the cell wall reflect areas in the cuticle permeable to mercuric chloride and undoubtedly to other polar compounds. The presence of such pathways in the cuticle, long established as the prime barrier to penetration of polar compounds, has marked implications in foliar uptake and excretion.

The nature of precipitates formed in the outer cell wall following fixation of leaf tissue with Gilson solution

The nature of precipitates formed in the outer cell walls of leaf tissue fixed in Gilson solution, used extensively to demonstrate ectodesmata, is described. Electron-microbe X-ray analysis established that the crystalline precipitates contained both mercury and chlorine. Based on solubility in water and ethanol, birefringence and ratio of mercury to chlorine, the chemical form is probably mercurous chloride. Further treatment of the leaf tissue with potassium iodide caused the crystalline precipitate to turn black and lose birefringence when viewed with plane-polarized light. Analysis of this precipitate showed the presence of only mercury, chlorine having been lost.