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1.
The effects of polydisperse ethoxylated fatty alcohol (EFA) surfactants on the penetration of six organic compounds varying in size (molar volumes, 107–282 cm3 mol-1) and lipophilicity (log Kow 0·8–6·5) were investigated using astomatous isolated cuticular membranes (CM) of Citrus and pear leaves. Mobilities of model compounds in CM were measured by unilateral desorption from the outer surface (UDOS). Rate constants (k*) obtained in these experiments are directly proportional to diffusion coefficients and, in the absence of EFA, k* values decreased by a factor of 52 when molar volumes increased only 2·64-fold. Under UDOS conditions using micellar surfactant solutions as desorption media, surfactants are sorbed in the CM and the volume fractions sorbed were found to decrease from approximately 0·062 to 0·018 when the average number of ethoxy groups (nE) increased from 5 to 17. In the presence of the EFA surfactants in the CM, solute mobilities increased markedly though this effect diminished with increasing nE. Surfactants with nE=17 affected solute mobilities only marginally. Surfactant effects on solute mobility increased with the size of the solutes leading to almost identical mobilities of the model compounds. With the current range of our model compounds, lipophilicity increased with increasing molar volumes, though evidence is presented showing that the mobilities of solutes depend on their molar volumes while lipophilicity has no effect. Effects of micellar aqueous solutions of polydisperse surfactants on solute mobilities followed the pattern observed with monodisperse ones. © 1997 SCI 相似文献
2.
Effects of monodisperse alcohol ethoxylates on mobilities of 14C-labelled pentachlorophenol (PCP) and tetracosanoic acid (C24AC) in reconstituted cuticular wax of barley leaves were measured. Depending on the respective alcohol ethoxylate investigated, the diffusion coefficient (D) of PCP in barley wax was increased by factors ranging from 3·3 to 19·6, whereas D of C24AC, was increased by factors varying between 22 and 315. In order to analyse the relationship between the concentration of surfactants in the wax and their effects on D, the amounts of alcohol ethoxylates dissolved in the wax at equilibrium with external concentrations well above the critical micelle concentration (CMC) were determined. Wax/water partition coefficients (Kww) of the alcohol ethoxylates were about one order of magnitude lower than cuticle/water partition coefficients (Kcw), which is a consequence of the semi-crystalline structure of the wax compared with amorphous cutin. Correlations between effects on D and maximum amounts of alcohol ethoxylates dissolved in the wax were obtained indicating an unspecific wax/surfactant interaction. This was solely dependent on the amount of surfactant sorbed to the wax, leading to increased mobilities of pesticides in the wax. Applying ESR-spectroscopy, which gave an insight into the molecular structure of the wax, supported this interpretation of an unspecific plasticising effect of the alcohol ethoxylates on the molecular structure of the wax. The results obtained in this study are in good accordance with the results obtained in a recent study investigating the effects of the same group of alcohol ethoxylates on mobilities of pesticides in isolated, but intact, cuticular membranes of Citrus. This demonstrates that the investigation of isolated and subsequently reconstituted cuticular wax is a useful model system analysing the mechanisms of the surfactant interaction with the transport-limiting barrier of plant cuticles. 相似文献
3.
A finite dose diffusion system was employed to study cuticular penetration of 2‐(1‐naphthyl) [1−14C]acetic acid (NAA) from simulated spray droplets through enzymatically isolated tomato fruit cuticles (Lycopersicon esculentum Mill cv Pik Red). Isolated cuticles were mounted on diffusion half‐cells with the cell wall surfaces facing a 20 mM citric acid receiver solution (pH 3.2, volume 2.9 ml, prepared with deionized water). A 5‐µl donor droplet containing NAA at 100 µM in 20 mM citric acid buffer (pH 3.2) was applied to the outer surface. Penetration was monitored by repeated sampling of the receiver solution. NAA penetration was characterized by (1) an initial lag phase of about 2.3 h, (2) a phase of nearly constant maximum rate of penetration averaging 6.3% of applied NAA h−1 (equivalent to 0.032 nmol h−1) and (3) a plateau phase approaching an asymptote at 81.2% of applied NAA (equivalent to 0.406 nmol) at 120 h. Within 1 h after application droplets appeared dry on visual inspection. Immediately after droplet drying, 7.0% of the applied NAA was sorbed to the cuticle, but only 0.5% penetrated into the receiver solution, indicating that penetration occurred almost exclusively from the apparently dry deposit. At 120 h, 5.2% of the NAA applied was associated with the deposit and 4.3% with the cuticle. The distribution of maximum rates of penetration was log‐normal, but penetration at 120 h followed a normal distribution. Cuticle thickness (estimated 5–25 µm) had no significant effect on NAA penetration. Maximum rates of penetration through pepper fruit and citrus and ficus leaf cuticles were 4.9‐, 2.6‐ and 0.1‐times that through tomato fruit cuticles. At 120 h, penetration averaged 85.5, 79.5 and 34.7% for pepper, citrus and ficus cuticles, respectively. Extracting epicuticular and embedded waxes increased NAA penetration rates through tomato fruit cuticle more than three‐fold, but had little effect on penetration at 120 h (71.0 vs 87.7% for cuticular vs dewaxed cuticular membranes). The maximum penetration rate and total penetration were found to be useful parameters in describing the penetration time‐course. © 2000 Society of Chemical Industry 相似文献
4.
A theory of cuticular penetration of crop protection agents (CPAs) is presented, which incorporates properties of cuticles and cuticular waxes as well as properties of active ingredients and adjuvants. Based on this theory, two models are developed which are analytical in the sense that they help to quantify and understand (i) differences in permeability among cuticles from different species, (ii) effects of properties of CPAs on permeabilities of cuticles and rates of uptake and (iii) the effects of adjuvants on properties of cuticles and rates of uptake of CPAs. The models can be used to predict rates of uptake of CPAs as affected by properties of cuticular waxes, active ingredients and adjuvants. However, before this can be done, a constant, two parameters and at least two variables must be estimated. Properties of cuticles are accounted for by the constant D0/Δx and the parameter β′. The former, the ratio of the mobility of a hypothetical molecule having zero molar volume (D0x) divided by the path length (Δx) across the cuticle, has the dimension of velocity (ms?1) and is independent of the solubility of the CPA. The latter is a measure of size selectivity of the cuticle. Differences in permeabilities of cuticles from different species increase with increasing size of active ingredients due to size selectivity (β′). Removing cuticular waxes from Citrus cuticles increased D0/Δx by a factor of 2042, while β was not affected. Differential solubility of CPAs is considered part of the driving force and at least two different partition coefficients are needed to account for differences in solubilities in cuticular waxes, cutin, water and the formulation residue on the surface of the cuticles. Adjuvants are solvents in the formulation residue on the leaf surface once the carriers (water and other volatile solvents) have evaporated and certain adjuvants also act as accelerators; they penetrate the cuticle and increase D0/Δx. Thus, accelerators increase rates of uptake and this effect depends on two factors, (i) the intrinsic activity of the accelerator and (ii) rate of penetration into the cuticle, because the active ingredients follow the accelerator front across the cuticle. Since accelerators penetrate from the formulation residue into the cuticle, the volume of the formulation residue decreases with time. This maintains high concentrations of CPAs in the formulation residue and, thus, maximum driving forces and rates of penetration. To utilise fully this dual accelerator effect, it is necessary to match velocities of penetration of accelerators and active ingredients accurately. 相似文献
5.
Impacts of pH and sorption-desorption of ‘Pegosperse’ 100-O (PEG. 100-O; diethylene glycol monooleate, containing 15% diester) surfactant by apple (Malus pumila M.) leaf cuticles on surfactant-enhanced cuticular penetration of 2,4-D [(2,4-dichlorophenoxy)acetic acid] were studied. Glass cylinders were affixed to enzymatically isolated adaxial apple leaf cuticles after the cuticle segments had been soaked in 10 ml liter?1 PEG 100-O solution and washed for 20 and 120 min, respectively. Quantities of [14C]2,4-D in the glass-cuticle chambers passing through the cuticles at pH values from 1 to 6 5 were determined. PEG 100-O significantly increased cuticular penetration of dissociated 2,4-D at pH 4–5; the surfactant had no effect on penetration of undissociated 2,4-D at pH 10. Surfactant-enhanced penetration of 2,4-D occurred only when the surfactant was in the cuticles, while the process of surfactant sorption-desorption alone had no effect on penetration. These results support a ‘hydrophilic channel’ hypothesis, i.e. that surfactants may create hydrophilic channels or increase the area of the channels in the cuticle and, consequently, enhance the passing of polar molecules like dissociated 2,4-D through the cuticle. 相似文献
6.
Polydisperse ethoxylated fatty alcohol (EFA) surfactants can improve the performance of crop protection agents. At the cuticular level they act as accelerators of penetration by increasing the mobility of active ingredients in the cuticle, the barrier properties of which are mainly caused by cuticular waxes. Polydisperse Genapol C-050 (GP C-050, average formula C12.5E5.8) was also found to increase mobility in wax-extracted polymer matrix membranes (MX) of bitter orange and pear, indicating that sorption of surfactants increased segmental mobility of polymethylene chains in cutin and wax. Sorption into MX of the active fraction of GP C-050 from 5g litre−1 micellar solutions was in equilibrium in less than 1 h after establishing contact. This is almost 100-fold faster than with cuticular membranes (CM). Temperature dependence of solute mobilities in CM was studied in order to measure activation energies (ED) of diffusion in the presence and absence of aqueous surfactant solutions. Monodisperse fatty alcohol ethoxylates C8E3, C8E4 and C12E6, and (non-surface-active) tributylphosphate decreased ED of the model compounds WL 110547 and bifenox in Citrus, Pyrus and Stephanotis CM by more than 100 kJ mol−1. This corresponds to 50 to 275-fold increases of mobilities at 15 °C. Our data suggest that the decrease in activation energies with the concomitant accelerating effect on mobility contributes considerably to the effects of so-called activator surfactants. High temperature and accelerators act similarly on barrier properties of CM. It is shown that effects of both monodisperse and polydisperse EFA surfactants on solute mobility are reversible and that radiolabelled C12E8 penetrated pear CM rapidly. However, rates of penetration were lowered by excess amounts of WL 110547 and especially phenylurea. Partition coefficients of seven organic solutes between Capsicum fruit cuticles and GP C-050 were very low and, with the exception of methylglucose, smaller than 1. They decreased with lipophilicity and differed about 100-fold. Especially for the lipophilic compounds they were orders of magnitude lower than octanol/water or cuticle/water partition coefficients, which indicates the limited usefulness of these values for an understanding of penetration of active ingredients from formulation residues. © 1999 Society of Chemical Industry 相似文献
7.
Jrg Schnherr 《Pest management science》1993,39(3):213-223
Effects of n-alcohols, ethoxylated alcohols and glycols on mobility of 2,4-dichlorophenoxy acetic acid (2,4-D) in cuticular membranes (CM) isolated from bitter orange (Citrus aurantium L.) leaves were studied. 1-Heptanol, 1-octanol and 1-nonanol had the highest effects, as they increased solute (2,4-D) mobility by 25- to 30-fold. Increasing the number of carbon atoms in the alcohols decreased their effectiveness. Ethoxylation of alcohols did not increase 2,4-D mobility and effectiveness decreased with increasing ethoxylation. Free glycols had no effect on solute mobility in isolated cuticles. The results show that ethoxylation is not required for increasing solute mobility in cuticles. It is suggested that alcohols and ethoxylated alcohols are sorbed in cuticular waxes and plasticize them. The data show that alcohols and ethoxylated alcohols having between seven and ten carbon atoms are powerful accelerator adjuvants, as long as the degree of ethoxylation is not too high. Free short-chain alcohols synthesized by leaves may act as endogenous plasticizers and modulate permeabilities of cuticles, depending on environmental and growing conditions. 相似文献
8.
Surfactants increase the uptake of some foliar-applied chemicals to a greater extent than would be expected from their effects on surface tension and spray coverage. This study of the uptake of 2, 4-D [(2, 4-dichlorophenoxy)acetic acid] evaluated the effect of surfactants on penetration through and sorption by isolated cuticles of apple leaves. [14C]2, 4-D was placed in glass chambers affixed to enzymatically isolated adaxial apple leaf cuticles after the cuticle segments had been treated with various surfactants. The same surfactant pretreatments were included in sorption studies in which cuticle segments were immersed in [14C]2, 4-D for 96 h. Quantities of 2, 4-D passing through or sorbed by the cuticle were determined. Similar experiments were conducted with unaltered cuticles and cuticles dewaxed with chloroform. The hydrophile-lipophile balance (HLB) of polyethylene-glycol-based surfactants was inversely related to the sorption of those surfactants by the cuticles and penetration of 2, 4-D. Sorption of 2, 4-D by apple leaf cuticles was unaffected by surfactant pretreatment. Dewaxed cuticle membranes showed a similar response to 2, 4-D penetration and sorption following the surfactant pretreatment. 相似文献
9.
Removal of waxes from the upper pear leaf cuticle by chloroform extraction greatly increased sorption of naphthaleneacetic acid (NAA) into the cuticle. Penetration of NAA through isolated upper pear leaf cuticle was likewise increased following wax removal by chloroform extraction. Plating pear leaf wax back onto dewaxed cuticle surfaces reduced sorption and penetration. 相似文献
10.
Isolated cuticular wax, obtained from barley leaves, was mixed with 14Clabelled organic chemicals including aromatic pesticides and long-chain linear alkanes, alcohols and acids. These mixtures were reconstituted from the melt and labelled chemicals were desorbed from the wax by immersing the wax samples in aqueous phospholipid suspensions. Diffusion coefficients (D) of radiolabelled test compounds in the wax were derived from desorption kinetics. Diffusion coefficients ranged from 10?17 to 10?22 m2 s?1 and decreased rapidly with increasing molar volumes of solutes. However, size selectivity of D was much more pronounced with the linear, long-chain molecules than with the aromatic compounds. It is argued that the two different groups of chemicals (compounds occurring naturally in cuticular waxes vs pesticide molecules) were trapped in different fractions of wax during crystallization from the melt. The normal long-chain aliphatic compounds appear to be incorporated into the crystalline fraction of the wax, while the cyclic pesticide molecules are confined to the solid amorphous regions. Our data indicate that constituents of cuticular waxes are not immobile. In fact, relatively small linear aliphatic molecules have mobilities that do not differ too much from those of cyclic pesticides. However, the pronounced size selectivity of diffusivities of long-chain aliphatic compounds causes a rapid decrease in D with increasing chain length. The value of D of hexadecanoic acid was 3.81 × 10?18 m2 s?1 while that of dotriacontane was only 4.07 × 10?22 m2 s?1. Thus, increasing the carbon number by a factor of two resulted in a decrease in mobility by almost four orders of magnitude. Diffusivities of selected pesticide molecules in reconstituted wax were compared with permeances measured using intact barley leaves and were found to be in satisfactory agreement. 相似文献
11.
Nuray Özer Temine Şabudak Cengiz Özer Katia Gindro Sylvain Schnee Erhan Solak 《Journal of General Plant Pathology》2017,83(5):316-328
Cuticular wax on the plant epidermis inhibits or enhances prepenetration events of powdery mildew (Erysiphe necator Schwein). We examined the role of cuticular leaf and berry waxes as a resistance mechanism in four grapevine genotypes (Italia?×?Mercan-174, Gürcü, Isabella, Özer Karas?) resistant to powdery mildew after natural infection and inoculation. To understand cuticular wax properties, we determined the amount of wax and antifungal effects of thin layer chromatography (TLC) fractions from cuticular leaf and berry waxes, then assessed the chemical composition of fractions with different antifungal activities using gas chromatography/mass spectrometry (GC/MS). Susceptible genotypes Cabernet Sauvignon and Italia were used for comparison. Resistant and sensitive genotypes did not differ significantly in the total amount of wax on leaves and berries; however, 27 fatty acids, 26 alkanes, 6 terpenes, 4 indole derivatives and 4 ketones, and 3 amides, 3 phenols and 3 steroids were detected in fractions with high antifungal activity (≥75% inhibition of germination) in leaf and/or berry cuticular waxes of resistant genotypes only. These compounds may be evaluated as markers for powdery mildew resistance during genotype selection in a grapevine breeding program. 相似文献
12.
Uptake of pesticides into barley leaves was measured under controlled conditions. Leaves detached from plants were submerged in aqueous solutions of 14C-labelled (2,4-dichlorophenoxy)acetic acid, triadimenol, bitertanol and pentachlorophenol. Uptake was biphasic. A short (30-min) period with high rates of uptake was followed by uptake that proceeded more slowly and was steady over hours. Compartmentation of pesticides was studied by desorbing pentachlorophenol from leaves previously loaded with [14C]pentachlorophenol. From the uptake and desorption kinetics it was concluded that penetration of pesticides proceeds as follows: the compounds are first sorbed at the surface of epicuticular wax aggregates where they are in contact with the donor solutions. Solutes then diffuse through the surface wax aggregates into the cuticle. Equilibrium between donor solutions, surface wax and cuticle is established in about 30 min. After this time the amounts of solutes in these compartments no longer increase. Uptake after this time represents penetration into the leaf cells. This fraction of the pentachlorophenol is retained irreversibly, while that sorbed in wax and cutin can be desorbed again. All compounds were sorbed in cuticular waxes and partition coefficients wax/water were determined. On a mass basis only 5 to 10% of the amounts sorbed in cutin are sorbed in wax. This comparatively low solubility in wax contributes to the barrier properties of cuticular waxes. The other determinant of permeability is the very low mobility of solutes in cuticular waxes. 相似文献
13.
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 °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. © 2001 Society of Chemical Industry 相似文献
14.
Penetration of four herbicides (atrazine, diclofop-methyl, dinoseb and glyphosate-mono(isopropylammonium) salt) was followed through isolated pear leaf cuticles into agar and across intact cuticles of Argenteum (ARG) mutant pea leaves from monosized droplets (300 μ diam.) during 48 h following application. Penetration into pea leaves ranged from low for glyphosatemono(isopropylammonium) (5% of amount applied) and atrazine (14%) to rapid for dinoseb (91%) and diclofop-methyl (82%). A major proportion (90%) of the dinoseb retained in the tissues underlying the site of droplet application migrated across the cuticle and the epidermal layer of cells. In contrast, only a small proportion (13%) of the dinoseb entering the leaf was transported to the tissues surrounding the treatment zone. Corresponding values for diclofop-methyl were 61% and 4% respectively. Initially, dinoseb also penetrated rapidly through isolated pear leaf cuticles, 36% of the applied dose being recovered in an agar receiver disc 4 h after treatment, but subsequent uptake was slower. Penetration of glyphosate-mono(isopropylammonium) also decreased after 4 h whereas atrazine and diclofop-methyl diffused steadily through isolated cuticles up to 216 h after treatment. The incorporation of ‘Tween 20’ or ‘Agral 90’ (1 g litre?1) into the formulation reduced the penetration of glyphosate-mono(isopropylammonium) through isolated pear leaf cuticles. 相似文献
15.
Sorption and desorption of ‘Pegosperse’ 100-O(PEG 100-O; diethylene glycol monooleate, containing 15% diester) surfactant by unaltered (CM) and dewaxed (DCM) adaxial cuticle membranes isolated from apple (Malus pumila M.) leaves were studied. The aim of this study was to understand interactions between surfactants and cuticles. Enzymatically isolated cuticles were soaked in buffer or PEG 100-O solution (pH 7–0). and the weight changes of cuticles were measured to determine the amount of surfactant sorbed or desorbed by the cuticles. For very low surfactant concentrations, sorption was measured by changes in the surface tension of the solutions. PEG 100-O sorption by both the CMs and the DCMs occurred mainly in the first three hours and was concentration-dependent. The DCMs always sorbed more surfactant than the CMs. Desorption of PEG 100-O from both CMs and DCMs was rapid in the first few hours and then decreased to a relatively low rate until the surfactant was totally desorbed from the cuticles after about two months. The sorption and complete desorption of the surfactant by both CMs and DCMs show that PEG 100-O interacts with both cutins and waxes of the cuticles and the interactions are reversible. 相似文献
16.
Radiolabelling of isolated cuticles from foliar discs used as a test of cuticle biosynthesis 总被引：1，自引：0，他引：1
The radiolabelling of isolaled Hedera helix L, (ivy) leaf cutieles was investigated after incorporation of [14 C]acetate in foliar discs Cuticle radioactivity greatly decreased as leaf age inereased. The percentage of radioactivity incorporated in the upper cuticles decreased from 0.5% to 0.08% of the total radioactivity of foliar dises from young to old leaves. Cuticle radioactivity was recovered in waxes, cutin and polar components. It was considerably greater for waxes when expressed in terms of cuticle mass. The methodology was validated using S-ethyl-dipropylthiocarbamate (EPTC). The radioactivity incorporation in cuticles was significanly reduced when 1 m m EPTC was deposited as a 20-μL droplet on lo foliar dises 6 h before the incorporation of radiolabelled acetate. EPTC inhibited radioiabelling of wax and cutin fractions in the upper and lower cuticles. Some acetylenic fatty acid analogues inactivating lauric and oleic acid ω-hydroxylases, used as acid and sulphonate forms in the same experimental conditions as EPTC, induced no reduction in cuticle radiolabelling. An inhibitory effect was observed only for the acetylenic and the saturated C12 fatty acid analogues, used as tetrabu-tylammonium sulphonates, when applied directly in the liquid medium supporting foliar dises. Several assumptions are considered to explain the results of the present investigation. 相似文献
17.
Treating the outer surfaces of isolated cuticles of Seville orange (Citrus aurantium L.) and pear (Pyrus communis L. cv. Bartlett) leaves with a number of nonionic (polyoxyethylene) surfactants increased their permeability to water by factors ranging from 4.1 to 14.7 and from 7.2 to 152.4, respectively. However, sodium dodecylsulphate, an anionic surfactant, had little effect on water permeability. In both species the major aliphatic constituents were n-alkanes, 1-alkanols and n-alkyl esters. None of the surfactant treatments altered the amounts or composition of waxes in the cuticles used for transport measurements. The reasons for the apparent absence of solubilization or dissolution of cuticular waxes by nonionic surfactants are discussed and a hypothesis is presented for the mechanism by which activator adjuvants may increase the permeability of plant cuticles. 相似文献
18.
In addition to the molecular structure of a pesticide, environmental conditions may influence its persistence through their effect on the growth and activity of pesticide-degrading micro-organisms. As a result, transformation rates may decrease rapidly when a compound is leached into subsoil. Metamitron sorption isotherms were determined and incubation series were set up for a sandy loam soil, simulating single and combination effects that occur during transport of metamitron into subsoils. KOC values increased with increasing depth from 185 to 700 litre kg−1. A combination of conditions that are unfavourable for microbial activity, such as low temperature (5°C), low concentrations (0·5 mg kg−1) and a large sorbed fraction (KOC = 700) resulted in half-lives of over one year. Oxygen inhibition decreased the transformation rate of metamitron from 0·058 to 0·019 day−1. In order of significance, the transformation of metamitron appears to be a function of temperature, oxygen availability and sorption to organic carbon. Increasing doses did not change transformation rates significantly, although different transformation pathways were observed. 相似文献
19.
The effects of NAA [2‐(1‐naphthyl)acetic acid] concentration and pH on penetration of NAA from aqueous droplets (5 µl) through isolated tomato (Lycopersicon esculentum) fruit cuticles were studied using a finite dose diffusion system. Penetration time‐courses were characterized by a lag phase, which generally extended beyond the time of droplet drying. Initially penetration rates increased, reached a maximum penetration rate, remained constant for several hours, and then decreased with time. Penetration approached a plateau within 120 h after droplet application. Increasing NAA concentration in the donor droplet increased NAA penetration in both the presence and absence of the citric acid buffer (20 mM , pH 3.2). Maximum rates of penetration and the total amount of NAA that penetrated at 120 h were both linearly related to the initial concentration of the donor droplet (ranging from 0.001 to 0.1 mM NAA). The apparent first‐order rate constants for the concentration dependence of NAA penetration rates were greater with buffer than without (0.94 × 10−8 vs 0.50 × 10−8 m s−1, respectively). While pH of the receiver solution (pH 6.2 vs 2.2) did not affect penetration, decreasing donor pH from 6.2 to 2.2 increased NAA penetration at 120 h. © 2000 Society of Chemical Industry 相似文献
20.
Experiments were conducted on olive plants in controlled environments to determine the effect of conidial concentration, leaf age, temperature, continuous and interrupted leaf wetness periods, and relative humidity (RH) during the drier periods that interrupted wet periods, on olive leaf spot (OLS) severity. As inoculum concentration increased from 1·0 × 102 to 2·5 × 105 conidia mL?1, the severity of OLS increased at all five temperatures (5, 10, 15, 20 and 25°C). A simple polynomial model satisfactorily described the relationship between the inoculum concentration at the upper asymptote (maximum number of lesions) and temperature. The results showed that for the three leaf age groups tested (2–4, 6–8 and 10–12 weeks old) OLS severity decreased significantly (P < 0·001) with increasing leaf age at the time of inoculation. Overall, temperature also affected (P < 0·001) OLS severity, with the lesion numbers increasing gradually from 5°C to a maximum at 15°C, and then declining to a minimum at 25°C. When nine leaf wetness periods (0, 6, 12, 18, 24, 36, 48, 72 and 96 h) were tested at the same temperatures, the numbers of lesions increased with increasing leaf wetness period at all temperatures tested. The minimum leaf wetness periods for infection at 5, 10, 15, 20 and 25°C were 18, 12, 12, 12 and 24 h, respectively. The wet periods during early infection processes were interrupted with drying periods (0, 3, 6, 12, 18 and 24 h) at two levels of RH (70 and 100%). The length of drying period had a significant (P < 0·001) effect on disease severity, the effect depending on the RH during the interruption. High RH (100%) resulted in greater disease severity than low RH (70%). A polynomial equation with linear and quadratic terms of temperature, wetness and leaf age was developed to describe the effects of temperature, wetness and leaf age on OLS infection, which could be incorporated as a forecasting component of an integrated system for the control of OLS. 相似文献