( Holloway, 1984 ), and retention times of the authentic standards. Leaf cuticular wax analysis. The hexane-soluble cuticular waxes extracted from rose terminal leaflets of known area were evaporated to dryness and derivatized with BSTFA, like in
Abstract
Water loss in relation to the wax associated with the surface of leaves of Brassica oleracea was investigated. Varieties of Brussels sprouts, broccoli, cauliflower and collards were found to possess highly significant differences in regard to stomatal transpiration, cuticular transpiration and quantity of wax per unit area of leaf surface. Rubbing away the waxy bloom increased the cuticular transpiration rate. There was little correlation between the quantity of wax and the water loss per unit area of leaf surface either during the daytime or nighttime experiments. It appears inadvisable to attempt to breed for drought resistance in Brassica oleracea by selecting for the presence of a heavy waxy bloom or high levels of wax per unit area of leaf surface.
Abstract
Leaves of nonglaucous cotton and tomato absorbed Mn whether or not a surfactant was added to a MnSO4 spray solution, whereas the leaves of glaucous cabbage and onion absorbed Mn only when a surfactant was added. Manganese was absorbed by cabbage leaves only when a surfactant was added or when leaf surface wax formation was inhibited by ethyl N,N-dipropylthiolcarbamate (EPTC). Non-glaucous and glaucous pea mutants did not significantly absorb Mn unless surfactant was added to a MnSO4 spray, after which both mutants equally absorbed Mn.
Surfactants increased the concn of 59fe penetrating into a wax paraffin model to a 0.5 mm depth by 8- to 30-fold over a no-surfactant treatment. Both the rate and depth of penetration were increased by surfactant. No Fe was absorbed by cabbage leaves unless surfactant was present in the spray solution or the leaf wax was disturbed by brushing.
Thus, surfactant efficiently overcame an external leaf wax layer as a barrier to the absorption of foliar applied ions and thereby increased ion movement into the leaf.
Chlorotic bands across sugarcane leaves were first described as symptoms of cold chlorosis in 1926 and later described in sorghum and maize. The injury develops after exposure of seedlings to temperatures in the 0°C to 12°C range. The severity of injury in maize seedlings may be reduced by high relative humidity during the post-chilling period suggesting a temperature induced water stress. An early visible chilling response is the appearance of a glazed area in the region in which the chlorotic band will develop. This area of the young expanding maize leaf was studied with scanning electron microscopy(SEM). Maize seedlings were grown for 6 days at 24°C with a 15/9 h light/dark cycle. Plants were chilled at 10°C for 9 h during the 7th dark period and leaves sampled 39 h after the end of chilling. SEM photomicrographs revealed a gradient of epicuticular wax deposition from the tip to the base of the leaf. In the region of chill-induced chlorotic band formation, the control leaves exhibited a greater amount of wax deposition than the chilled leaves. It is suggested that the reduced epicuticular wax in a band across the chilled leaves might lead to a water stress resulting in chlorosis and eventually developing into the typical necrotic band.
Abstract
Long-chain alkanes present in epicuticular wax of citrus leaves changed in composition as the leaves matured. From 89 to 95% of the hydrocarbons in the mature leaves were linear, saturated, and C29 to C33 compounds. Alkane profiles changed during the year but were not influenced by the period of leaf flush (spring or fall). The alkane profiles for 67 citrus cultivars, representing 11 citrus biotypes, were determined by gas liquid chromatography (GLC). The mean alkane profile of 9 of the bio types were distinct from the others as determined by Duncan's multiple range test, Twelve other citrus and related taxa were examined, and the profile of each showed possible inheritance patterns.
Cuticular waxes were analyzed on abaxial and adaxial leaf surfaces of three Hosta genotypes differing in leaf surface glaucousness; the glossy-leaved Hosta plantaginea, the glossy-leaved Hosta lancifolia, and the glaucous-leaved Hosta `Krossa Regal'. All three hosta had their highest total leaf wax quantity in the spring soon after full leaf expansion. The major wax constituent class on these hosta was primary alcohols, comprising up to 84.6% of the total wax. Many hosta leaves had unusually high C24 length primary alcohols, especially in the spring. However, the dominant chain length in this alcohol class varied with development and genotype. A unique class of ß-diketones were present on the glaucous `Krossa Regal', comprising as much as 28.7% of the total waxes on abaxial leaf surfaces in the summer. Interestingly, these ß-diketones were only 0.9% of total waxes on adaxial leaf surfaces of `Krossa Regal' in the summer. Studies are under way to determine whether the dramatic seasonal changes in the waxy leaf coatings described in this report are associated with biotic and abiotic stress resistance in hosta.
Hosta variants for epicuticular waxes were selected based on variation in surface glaucousness, from highly glaucous to highly glossy. In an effort to determine seasonal variation in hosta waxes, gas-chromatography mass-spectrometry was used to perform detailed chemical analysis of the adaxial and abaxial leaf blade waxes four times points during the growing season, early spring, mid-spring, mid-summer, and autumn. These studies revealed that in all variants, the total wax loads increased dramatically during the period of leaf expansion in the spring, dropped roughly five fold by midsummer, and then accumulated slightly above summer levels into the fall season. The dominant wax constituent class on all hosta cultivars was primary alcohols. Changes in these alcohols were primarily responsible for seasonal changes in total wax load. In some variants, the shorter chain length alcohols were unusually high compared with alcohol distributions normally found on other plants. Besides primary alcohols, significant amounts of acids, aldehydes, and alkanes, were also found and shown to vary during the growing season. A possible association between these seasonal changes in wax profiles and hosta resistance to slugs is discussed.
Abstract
The influence of environmental conditions on tree growth and cuticular covering of leaves of apple (Malus domestica Borkh.) was investigated in relation to spary uptake. Various interactions between environmental factors influenced growth responses. Under cooler temperatures (20°C), 75% shade reduced shoot growth and leaf number; however, under warmer temperatures (25°), shading had no effect. High soil water potential (−13 KPa) and 75% shade significantly reduced total leaf area per tree, while under low soil water potential (−33 KPa), shading had little effect. The dry weight of total leaves per tree decreased 46% as soil water potential decreased under full-sun conditions. Under shade, a decrease in soil water potential resulted in a 20% decrease in dry weight. Total stem dry weight decreased as temperature increased under full-sun conditions; however, temperature had little effect on stem dry weight in plants grown under shade. Under 75% shade, an increase in temperature decreased total specific leaf weight (SLW), while under full sun there was no temperature effect. SLW of newly formed leaves was not influenced by environmental interactions. Leaf epicuticular wax quantity increased as soil water potential decreased. A decrease in soil water potential increased the proportion of alkanes and wax esters in extracted leaf waxes. Alkane content also increased as temperature increased. The different environmental growing conditions influenced the photosynthetic mechanism and masked the effect of prometryn, a triazine herbicide, thereby rendering it unreliable as a method for determining foliar absorption.
Azaleas (Ericales: Ericaceae: Rhododendron L.) are a staple plant in many landscapes of the United States and are largely resistant to predation by insects, with the exception of azalea lace bug [ALB (Heteroptera: Tingidae: Stephanitis pyrioides)]. Within deciduous azalea (Rhododendron: section Pentanthera G. Don) varying levels of resistance to ALB are observed with a continuous distribution from susceptible to highly resistant. In this study, epicuticular leaf wax from two ALB-resistant [R. canescens Michaux and R. periclymenoides (Michaux) Shinners] and two ALB-susceptible (`Buttercup' and `My Mary') deciduous azalea genotypes was extracted and re-applied to fresh azalea foliage. Leaf wax extracted from ALB-resistant genotypes and applied to ALB-susceptible genotypes conferred a high level of resistance to both ALB feeding and oviposition in the treated ALB-susceptible genotypes. Conversely, leaf wax extracted from ALB-susceptible genotypes and applied to ALB-resistant genotypes conferred susceptibility to the treated ALB-resistant genotypes. However, the effect was much less substantial than the effect of resistant wax extracts on susceptible genotypes and confined to ALB oviposition. When applied to the same genotype from which the extract was collected, leaf wax extract from ALB-susceptible genotypes had no effect on susceptibility, whereas resistant wax extract had a moderate effect on ALB oviposition rate. The results indicate that leaf wax serves as a primary mechanism of resistance of deciduous azalea to ALB.
Scanning electron microscopic (SEM) studies and gravimetric analysis of in vitro cultured leaf surfaces showed reduced epicuticular wax (EW) structurally and quantitatively as compared to greenhouse plants. However, leaves of in vitro plantlets subjected to polyethylene glycol-treatment (PEG) showed an increase in quantitative and structural EW which was similar to that of greenhouse plants. Furthermore, leaves initiated during in vitro culture and which persisted, when transferred to the greenhouse, showed an increase in structural wax as well as in amount, 30 days after transplanting in the greenhouse. Similarly, leaves newly-formed in the greenhouse from in vitro cultured plants developed more dense crystalline structure and greater levels of wax than those leaves observed immediately after removal from culture. A correlation between density of structural EW and amount of EW were observed in in vitro cultured, PEG-treated in vitro cultured and greenhouse grown leaves.