In 1997, Barthlott and Neinhuis published a groundbreaking article entitled "Purity of the sacred lotus, or escape from contamination in biological surfaces" that caused a true paradigm shift in surface science. In this article, they explained the water-repellent and self-cleaning properties of plants, attributing the superhydrophobicity to nano- and micrometric wax textures on the surface of the leaves. This became known as the "Lotus Effect". In the late 1980s, Barthlott already demonstrated the microtexture of plant surfaces and its effect on wetting. However, this knowledge remained confined to botany until the 1997 article popularized it. The dissemination of this knowledge to the materials science community led to the development of countless synthetic superhydrophobic surfaces and a better understanding of wetting mechanisms. The story of this discovery and its consequences demonstrates the relevance of atypical approaches and emphasizes the urgency of respecting biodiversity.

Among grain legumes, faba bean is reputed to be relatively sensitive to drought stress. Epicuticular wax (ECW) quantity is considered as an important drought adaptation strategy in plant species. This study aimed to define variation in leaf ECW concentration as a drought-adaptive trait in 197 faba bean accessions under well-watered conditions. The relationship between ECW and stomatal characteristics was also investigated. Highly significant differences were found in the ECW concentration, which ranged from 0.680 to 2.104 mg/dm2. No relationships were found between ECW and any measure of stomatal morphology and function. This study provides evidence of the wide variation in ECW in faba bean germplasm, which is independent of stomatal characteristics and leaf water content. This variation may allow the genetic improvement of ECW as a drought-adaptive character in faba bean breeding programs aiming at the economical use of water.

Removing the epicuticular wax from mature pads (cladophylls) of Lindheimer pricklypear increased picloram absorption by four- to sixfold in the laboratory, while the addition of surfactant had little effect on absorption. Absorption decreased with increasing pH of the picloram solution, indicating that picloram diffused through the cuticle as the undissociated molecule. Picloram entered detached pads at the areoles more readily than through the surrounding cuticle. In the glasshouse, whole plants consisting of an old, mature pad supporting a young, growing pad absorbed picloram very slowly whether picloam was applied as a spray to old or young pads or to the soil. About 90 and 80% of the applied picloram remained on the waxy surface of old and new pads, respectively, and about 2% of the applied picloram was recovered from within the epicuticular wax after 30 days. Picloram concentrations within pads treated in the glasshouse were greater when the herbicide was applied to new pads (4.6 μg/g) than old pads (1.9 μg/g) after 30 days. More picloram was translocated basipetally from treated new pads to untreated old pads than in the opposite direction, but concentrations in untreated pads were low (<1 μg/g). Little picloram was absorbed by roots, compared to pads, and little was translocated into or out of roots. These results conflict with the view that the effectiveness of picloram for pricklypear control is attributable to extensive root uptake and acropetal transport. However, observations of plants 6 months after treatment indicated that soil applications were more effective than sprays in the glasshouse.

The influence of ultraviolet-B (UV-B) radiation on seedling growth and leaf surface characteristics of important rangeland weeds Cynoglossum officinale L. (houndstongue), Centaurea diffusa Lam. (diffuse knapweed), and Tragopogon pratensis L. (meadow salsify) was investigated in a greenhouse by exposing seedlings to 0, 7, or 11 kJ m−2 d−1 of biologically effective UV-B radiation. UV-B radiation reduced leaf, stem, and root fresh weights, leaf area, and leaf: shoot ratio and increased shoot dry matter content, specific leaf weight, and leaf greenness of C. officinale seedlings. Leaf, stem, and root fresh weight, and leaf area of C. diffusa seedlings decreased, whereas shoot dry matter content, specific leaf weight, leaf: shoot ratio, and leaf greenness were unaffected. T. pratensis seedlings exposed to UV-B radiation had diminished leaf greenness, but no change was observed in leaf or stem fresh weight, leaf area, or leaf: shoot ratio. Uniseriate trichome abundance in C. officinale seedlings increased and trichome orientation changed in response to UV-B exposure. UV-B treatments decreased uniseriate trichome abundance in C. diffusa; glandular trichome abundance and the ratio of glandular: uniseriate trichomes were not affected. T. pratensis seedlings showed no change in the amount of epicuticular wax on the adaxial leaf surface in response to UV-B irradiation. Shoot dry weight was not influenced by removal of epicuticular wax prior to UV-B exposure. Results suggest that epicuticular wax is not an important factor in acclimation of T. pratensis seedlings to UV-B radiation. Susceptibility to UV-B–induced damage was greatest for C. officinale seedlings and least for T. pratensis seedlings. Modification of plant morphology or reduction in growth induced by enhanced UV-B radiation may influence competitive relationships between rangeland weeds and their associated forage species.

Differences in susceptibility of sugarbeet (Beta vulgaris L.) to preemergence application of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate], pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], and TCA (trichloroacetic acid) were evaluated in several combination treatments. Exposure of plants to ethofumesate severely decreased epicuticular wax deposition on leaf surfaces. Separation of epicuticular wax into major components by gas-liquid chromatography indicated that ethofumesate decreased deposition of alkanes and sec-ketones, but increased the percentage of long-chain waxy esters. TCA also decreased deposition of alkane and ketone components, but not of waxy esters. Waxes were unaffected by pyrazon. Greater foliar absorption of 14C-ethofumesate, 14C-desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)], and 14C-ethofumesate + 14C-desmedipham was observed in plants that received preemergence treatments of ethofumesate plus TCA compared to pyrazon or a control.

Wax filaments > 100 μm long on the epidermis of johnsongrass leaves and culms occurred only around the edge of costal cork-silica cell pairs and intercostal silica cells. Silica cells alternating with cork cells occurred in rows over veins. Solitary or occasionally paired cork-silica cells occurred between veins. The high silicon content of silica cells was verified with X-ray mapping of silicon. X-ray analysis also indicated that wax filaments contained silicon. Scanning electron micrographs (SEM) of dislodged intercostal silica cells showed that wax filaments emerged from an integument that surrounded the silica cell. It is theorized that at high ambient temperatures the silica gel in silica cells provides the localized cooling necessary to solidify liquid wax constituents as they are extruded onto the surface of the plant.

Absorption of 14C-bentazon from the leaf surfaces of common cocklebur and velvetleaf was rapid and most occurred within 4 h after foliar application. Greater 14C in the epicuticular wax (ECW) did not correlate with higher radioactivity in the leaf tissue. There was significantly less ECW on the “mature” leaves of common cocklebur and “juvenile” leaves of velvetleaf. However, the “mature” leaves exhibited greater 14C absorption for both species. The use of 28% urea ammonium nitrate increased 14C-absorption when compared with crop oil concentrate and with no adjuvant.

Absorption of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} by tanoak [Lithocarpus densiflorus (Hook. & Am.) Rehd.] leaves was investigated. Greater amounts of 14C-triclopyr were absorbed by immature leaves than mature leaves and by abaxial than adaxial surfaces. Both surfaces of immature and mature tanoak leaves were characterized. Stomata were present only on the abaxial surface and were more numerous on immature leaves than mature leaves. Immature leaves had less epicuticular wax and thinner, more permeable cuticular membranes than mature leaves. Stellate trichome densities were greater on abaxial surfaces than adaxial surfaces and on immature than mature leaves. Absorption of 14C-triclopyr was influenced by each of the leaf surface features studied.

More than 70% of all 14C-bentazon absorption occurred within 4 h after herbicide application regardless of adjuvant Moisture stress reduced 14C-bentazon absorption by common cocklebur and velvetleaf. Mature (second true leaf) and moisture-stressed leaves of velvetleaf had 50 and 17 μg cm−1 more epicuticular wax (ECW) than did juvenile and unstressed leaves, respectively. Common cocklebur had less 14C in the ECW and lower total 14C in treated mature leaves compared to juvenile leaves. The use of 28% urea ammonium nitrate (UAN) or crop oil concentrate (COC) increased 14C in ECW samples of both plant species, regardless of leaf age or moisture stress. More 14C in the ECW did not always correlate with more 14C in the leaf tissue. Adjuvants increased 14C-bentazon absorption into leaves of plants that had been stressed.

The leaves of tall morningglory, giant duckweed, and common purslane were treated with nine surfactants at a concentration of 0.1% and examined after 24 hr using cryo-scanning electron microscopy for phytotoxicity as evidenced by tissue damage and epicuticular wax morphology changes. In some instances, tissue damage could be discerned; however, the effects of a particular surfactant were not uniform across the three species. Morphological alteration of epicuticular waxes was not observed. Gas chromatographic analyses of the epicuticular waxes of the species used in the study reveal component differences and may, in part, explain the lack of uniform response across species for a particular surfactant.

Growth chamber experiments were conducted to elucidate the morphological and physiological responses of rice to postemergence application of fenoxaprop. Two rice cultivars, ‘Newbonnet’ and ‘Mars’, and barnyardgrass were treated with 0.17 kg ai ha−1 fenoxaprop at the five-leaf stage. Within 2 days of fenoxaprop application, rice cultivars developed a white chlorotic band across leaves that were in direct contact with spray droplets. Leaf elongation rates for the two rice cultivars were inhibited by 40% after 4 days and by over 50% after 14 days. Inhibition of leaf elongation by fenoxaprop contributed to an overall decrease in leaf area and shoot dry weight. Net photosynthesis was reduced by 35% in fenoxaprop-treated plants 11 days after application, although stomatal conductance was not affected. Nitrogen fertilization prior to fenoxaprop application increased foliar injury of both rice cultivars. Visible injury symptoms showed the following order of susceptibility to foliar-applied fenoxaprop: barnyardgrass > Mars rice > Newbonnet rice.

Laboratory studies were conducted to examine the leaf surface, epicuticular wax content, and spray droplet behavior on common lambsquarters, common purslane, and velvetleaf. Adaxial and abaxial leaf surfaces were examined using scanning electron microscopy, and leaf wax was extracted and quantified for all three weed species. The spread of 1-μl droplets of distilled water, primisulfuron solution (without surfactant), primisulfuron solution with a nonionic low foam wetter/spreader adjuvant (0.25% v/v), and with an organosilicone wetting agent (0.1% v/v) was determined on the adaxial leaf surfaces of each of the weed species. Glands and trichomes were present on both the adaxial and abaxial leaf surfaces of velvetleaf. Common purslane had neither glands nor trichomes on either side of the leaf. Common lambsquarters did not have any glands or trichomes, but it had globular bladder hairs on both adaxial and abaxial leaf surfaces. Stomata were present on both adaxial and abaxial leaf surfaces in all three weed species. Common purslane had a much lower number of stomata per unit area of leaf as compared with velvetleaf or common lambsquarters. Common lambsquarters had the highest epicuticular wax content on the leaf surface (274.5 μg cm−2), followed by common purslane (153.4 μg cm−2) and velvetleaf (7.4 μg cm−2). There were no significant variations in the spread of the 1-μl droplet of distilled water and primisulfuron (without adjuvant) among the species. Spread of primisulfuron droplets with surfactant was highest on the leaf surface of velvetleaf that had the lowest wax content. Droplet spread was greatest with organosilicone surfactant followed by the nonionic surfactant.

Laboratory studies were conducted to examine the leaf surface, epicuticular wax content, and spread area of primisulfuron spray droplet with and without surfactant on leaf surface of barnyardgrass and green foxtail. Adaxial and abaxial leaf surfaces were examined using scanning electron microscopy and leaf wax was extracted and quantified. The spread of 1-μl droplets of distilled water, primisulfuron solution (without surfactant), primisulfuron solution with a nonionic low foam wetter/spreader adjuvant (0.25% v/v), and with an organosilicone wetting agent (0.1% v/v) was determined on the adaxial leaf surfaces of each of the weed species. Stomata and trichomes were present on adaxial and abaxial leaf surfaces in both species. Green foxtail had more stomata per unit area on the adaxial as compared to the abaxial leaf surface. Barnyardgrass had more stomata on the abaxial than on the adaxial leaf surface. There was no significant variation in the number of trichomes per unit leaf area of green foxtail, and the number of prickles per unit area of leaf was significantly higher in adaxial than the abaxial leaf surface, in both young and old leaves. In barnyardgrass, there were more trichomes on abaxial than adaxial leaf surface. The mean value of the wax content per unit of leaf area in barnyardgrass and green foxtail was 35.9 μg cm−2 and 19.1 μg cm−2, respectively. On both species primisulfuron with a nonionic surfactant had more spread area than that without a surfactant, and the spread was even greater with organosilicone wetting agent. The spread area of primisulfuron droplet was higher on the leaf surface of barnyardgrass than on green foxtail when surfactant was added.

Greenhouse and laboratory experiments were conducted to investigate mechanisms of glyphosate resistance in horseweed populations from Mississippi, Arkansas, Delaware, and Tennessee. A nondestructive leaf-dip bioassay was developed to confirm resistance and susceptibility in individual test plants. A single leaf was excised from each plant, and the petiole and bottom one-fourth of leaf was dipped in a 600 mg ae L−1 glyphosate solution for 2 d followed by visually estimating the injury on a scale of 0 to 10. Plants were classified as resistant (R) if the score was 2 to 3 and susceptible (S) if the score was 5 to 6. 14C-glyphosate solution was applied on the adaxial surface of a fully expanded leaf of the second whorl of four-whorl rosette plants. Plants were harvested 48 h after treatment and radioactivity was determined in treated leaf, other leaves, crown, and roots. Absorption of 14C-glyphosate was similar (47 to 54%) between R and S plants from within and among the four states, suggesting absorption is not involved in glyphosate resistance. The amount of radioactivity translocated from the treated leaf was reduced in R plants compared with S plants. The reduction in translocation of 14C-glyphosate ranged from 28% in Mississippi-R biotype to 48% in Delaware-R biotype compared with their respective S biotypes. Epicuticular wax mass ranged from 6 to 80 μg cm−2 among horseweed biotypes, with no differences between R and S biotypes within each state. Treating two leaves with glyphosate solution at the field use rate (0.84 kg ae ha−1) killed S plants but not R plants (38 to 58% control) regardless of state origin. These results suggest that a simple bioassay can be used to screen biotypes for suspected resistance and that reduced translocation of glyphosate plays a major role in glyphosate resistance in R biotypes of horseweed.

Two-yr-old Norway (Picea abies (L.) Karst.), red (P. rubens Sarg.), black (P. mariana (Mill.) B.S.P.) and white (P. glauca (Moench.) Voss) spruce seedlings were exposed from bud break for 35 or 63 d (4·5 h irradiance d−1) to a gradient of biologically effective u.v.-B radiation (λ=280–315 nm) ranging from 0·61 kJ m−2 d−1 to 5·99 kJ m−2 d−1. No visible symptoms of u.v.-B injury were observed. Epicuticular wax production was not affected by needle exposure to increasing u.v.-B irradiance. Seven constituent classes were resolved by GC and confirmed by GC–MS in wax recovered from needles of the four species. Wax composition of Norway, black and red spruce was altered following needle exposure to increasing u.v.-B dose. White spruce wax composition was unaffected. Direction and magnitude of wax composition response was species-dependent. The proportion of nonacosane diols on Norway spruce needles increased (P<0·05) whereas that of alkyl esters decreased with increasing u.v.-B dose. The proportion of fatty acids in black spruce needle wax increased (P<0·05), and that of estolides (GC-identified) in red spruce needle wax increased (P<0·05) with increasing u.v.-B dose. Changes in wax chemical composition reported were induced following to daily, 4-h duration exposures of needles to u.v.-B centred on 1200 hours. Affected variables exhibited a continuum of response. The highest dose applied was within the range of measured or predicted increases in mid-northern latitudes. Such changes in conifer needle epicuticular wax chemical composition might result in increased seedling sensitivity to the changing atmospheric environment, especially from co-exposure to tropospheric ozone in mid-northern latitudes where much of Canada's productive forest is located.

The response of epicuticular wax of Scots pine (Pinus sylvestris L.) needles to dry- and wet- deposited sulphur and heavy metals was investigated at six sites located 10–110 km from the Monchegorsk Cu-Ni smelter on the Kola Peninsula, North-West Russia, and in a long-term irrigation experiment where pines were exposed over four growing seasons (1991–1994) to either acid rain treatment at pH 3·1 (H2SO4), metal treatment at pH 5·7 (Cu and Ni) or a combination of these at pH 3·1. Needle wettability exhibited a closer relationship with epistomatal wax tube distribution (WTD) than with chemical composition of epicuticular wax. Water droplet contact angles (DCA) decreased towards the smelter, and significant differences due to site were noted for 26-month-old and 38-month-old needles. Significant differences due to site were determined for secondary alcohols, dehydroabietic acid and hydroxy fatty acids, the proportions of which ranged from 22·5 to 48·9%, 6·2 to 22·4% and 0·6 to 2·6% respectively, depending on site and needle age class. The proportion of dehydroabietic acid increased towards the smelter, but no gradient was observed in the proportion of secondary alcohols or hydroxy fatty acids. No major effect of experimentally applied pollutants on the chemical composition or structure of the epicuticular wax was observed. The effect of treatment on DCA was significant in 1993 and 1994 due to a 6·5–13·2 degree greater wettability of the 37–49-month-old acid-treated needles relative to the irrigated or dry controls. Sulphuric acid at pH 3·1 did not increase needle wettability when combined with copper and nickel sulphate in similar concentrations. These data indicate that S deposition, especially H2SO4, plays a more important role in needle surface deterioration than Cu and Ni. Pollutant-induced changes in epicuticular wax structure and needle wettability mimic natural wax ageing, but at an accelerated rate. Changes in wax chemical composition might also be caused by pollutant-induced metabolic changes in elongating needles.