Diversity of essential oil glands of clary sage (Salvia sclarea L., Lamiaceae)

The Lamiaceae is rich in aromatic plant species. Most of these species produce and store essential oils in specialised epidermal oil glands, which are responsible for their specific flavour. Two types of glands producing essential oil and possessing different morphological structure can be found in Salvia sclarea : peltate and capitate glands. The content of single oil glands from different positions on the plant (corolla, calyx and leaf) were sampled using an SPME fibre and analysed by gas chromatography in order to study variability of the essential oil composition. It was found that the composition of terpenoids is quite variable within an individual plant. Capitate oil glands mainly produce three essential oil compounds: the monoterpenes linalool and linalyl acetate, and the diterpene sclareol. Peltate oil glands, however, accumulate noticeable concentrations of sesquiterpenes and an unknown compound (m/z = 354). Furthermore, the oil composition varies within each gland type according to the plant organ. Linalool and linalyl acetate are characteristic substances of flowers, whereas the sesquiterpenes occur in higher proportions in leaves. Even within one gland type on a single leaf, the chemical variability is exceedingly high.     

Essential Oil Gland Number and Ultrastructure During Mentha arvensis Leaf Ontogeny

Alterations in essential oil gland number, distribution and fine structure, and the oil content in the leaf of Mentha arvensis L. were examined during its growth and senescence. Accumulation of essential oil occurred predominantly during the rapid leaf expansion phase followed by a similar decline. The oil gland (trichome) number increased upto leaf maturation and declined thereafter. Initially, cuticle remains tightly apposed to the secretory head of oil glands but progressively a sub-cuticular space appears to be created for the oil. Considerable enlargement of vacuole with ageing is witnessed, whereas cytoplasm gradually decreases to a thin peripheral layer. Some secretory cells from senescing leaf were found almost empty, having only a few remnant oil droplets. This revised version was published online in June 2006 with corrections to the Cover Date.     

Short-term responses of leaf growth rate to water deficit scale up to whole-plant and crop levels: an integrated modelling approach in maize

Physiological and genetic studies of leaf growth often focus on short-term responses, leaving a gap to whole-plant models that predict biomass accumulation, transpiration and yield at crop scale. To bridge this gap, we developed a model that combines an existing model of leaf 6 expansion in response to short-term environmental variations with a model coordinating the development of all leaves of a plant. The latter was based on: (1) rates of leaf initiation, appearance and end of elongation measured in field experiments; and (2) the hypothesis of an independence of the growth between leaves. The resulting whole-plant leaf model was integrated into the generic crop model APSIM which provided dynamic feedback of environmental conditions to the leaf model and allowed simulation of crop growth at canopy level. The model was tested in 12 field situations with contrasting temperature, evaporative demand and soil water status. In observed and simulated data, high evaporative demand reduced leaf area at the whole-plant level, and short water deficits affected only leaves developing during the stress, either visible or still hidden in the whorl. The model adequately simulated whole-plant profiles of leaf area with a single set of parameters that applied to the same hybrid in all experiments. It was also suitable to predict biomass accumulation and yield of a similar hybrid grown in different conditions. This model extends to field conditions existing knowledge of the environmental controls of leaf elongation, and can be used to simulate how their genetic controls flow through to yield.     

Specificity of constitutive and induced resistance: pigment glands influence mites and caterpillars on cotton plants

Cotton plants contain suites of phytochemicals thought to be important in defense against herbivores, some of which are localized in pigment glands which contain gossypol and other terpenoid aldehydes. The simple genetic basis for the expression of these glands has led to the development of near-isogenic glanded and glandless genotypes. Glands may also be phenotypically induced by herbivory. We determined the consequences of constitutive and induced gland expression on two types of herbivores, spider mites (cell content feeders) and noctuid caterpillars (leaf chewers).Induction of glands was strongly dependent on the density of attackers. Spider mite herbivory on cotyledons (1) increased the density (but not total number) of glands on cotyledons linearly, (2) increased the density and total number of glands on the first true leaf linearly, and (3) affected the density and total number of glands on the second true leaf non-linearly, compared to controls. Neither constitutive nor induced expression of glands affected mite population growth. An equal reduction of mite population size on induced glanded and glandless plants (50%) relative to uninduced controls indicated that factors other than glands were associated with induced resistance to mites. Constitutive gland expression had a strong negative impact on caterpillar performance, reducing growth by 45%. Induced resistance to caterpillars was three times stronger in glanded genotypes than in glandless genotypes, indicating that factors associated with induced resistance to caterpillars are strongly associated with glands. Three cotton varieties were highly variable in their constitutive and induced resistance to mites and caterpillars.Thus, defense of cotton plants against herbivores can be roughly categorized as constitutive and inducible factors associated with terpenoid aldehyde containing pigment glands that are effective against caterpillars, and factors not associated with glands that are effective against mites.     

Seasonal, populational and ontogenic variation in the volatile oil content and composition of individuals of Origanum vulgare subsp. Hirtum, assessed by GC headspace analysis and by SPME sampling of individual oil glands

Small-scale GC headspace analyses combined with SPME sampling of individual oil glands have been used to measure the variation in volatile content and composition in and within different oregano plants as affected by age, season and developmental state. The main monoterpenes found were p-cymene, carvacrol and their precursor gamma-terpinene. The early season preponderance of p-cymene over carvacrol was reversed as the season progressed and this pattern could also be seen at any time within the plant, from the latest leaves to be produced (low in cymene) to the earliest (high in cymene). Seedlings from the same mother plant developed this pattern at different rates. Within individual leaves the pattern was not observed, even within the youngest developing leaves. However it was found that the oil composition of individual glands within a single leaf varied considerably, most notably in respect of the production of carvacrol and its isomer thymol.     

Dynamic Scaling in the Growth of a Non-Branching Plant,Cardiocrinum cordatum

We investigated whole-plant leaf area in relation to ontogenetic variation in leaf-size for a forest perennial herb, Cardiocrinum cordatum. The 200-fold ontogenetic variability in C. cordatum leaf area followed a power-law dependence on total leaf number, a measure of developmental stage. When we normalized for plant size, the function describing the size of single leaves along the stem was similar among different-sized plants, implying that the different-sized canopies observed at different times in the growth trajectory were fundamentally similar to each other. We conclude that the growth trajectory of a population of C. cordatum plant leaves obeyed a dynamic scaling law, the first reported for a growth trajectory at the whole-plant level.     

Elevated CO2 concentration has independent effects on expansion rates and thickness of soybean leaves across light and nitrogen gradients

The rate and extent of leaf thickness and area development are important determinants of whole plant photosynthetic capacity. The interactive effects of photon flux density (PFD), nitrogen supply and CO2 concentration on leaf expansion rate were measured as well as final leaf size and thickness of soybean. Leaf thickness and final area were not correlated with leaf relative expansion rate (RER) suggesting that these parameters are controlled by different mechanisms and that final leaf dimensions are determined by the duration rather than the rate of leaf expansion. Carbohydrate supply did not explain the variation in leaf RER since RER increased with increasing CO2 concentration, but decreased with increasing PFD. Leaf thickness and final area were related to resource supply but not in a simple fashion. Both positive and negative correlations between leaf thickness and carbohydrate and nitrogen concentrations were obtained depending on the environmental variable responsible for the variation. In contrast, there was a simple proportional relationship between whole plant relative growth rate and a correlate of leaf thickness (leaf water content per unit area), suggesting that leaf thickness responds to the balanced supply of all resources, in the same fashion as RGR, rather than to any individual resource.     

A direct liquid, non-equilibrium solid-phase micro-extraction application for analysing chemical variation of single peltate trichomes on leaves of Salvia officinalis

A non-equilibrium solid phase micro-extraction application was tested for the rapid extraction of essential oil from single oil glands of sage and the oil components compared with those determined by solvent extract and distillation. Oil glands were directly ruptured with a polydimethylsiloxane-coated fused silica fibre and the essential oil was sorbed. Three insertion levels of an individual plant of Salvia officinalis involving an immature apical young leaf, an expanding and a fully developed leaf, respectively, were used to determine the applicability of this method. Thirty-eight components in the oil could be identified by GC-MS. The method only showed small semi-quantitative differences compared with conventional methods. Chemical variation of single oil glands within the immature and premature leaf was higher than within the homogeneous mature leaf. The intermediary, still-expanding leaf was used to carry out a detailed study of the glands. The basal region of the intermediary leaf contained compounds in high conformity with the young leaf trichomes. The remaining oil glands of this leaf showed inconsistent accumulation patterns.     

Combined effects of long-term salinity and soil drying on growth, water relations, nutrient status and proline accumulation of Sesuvium portulacastrum

The interaction between soil drying and salinity was studied in the perennial halophyte, Sesuvium portulacastrum. Rooted cuttings were individually cultivated for three months in silty-sandy soil under two irrigation modes: 100 and 25% of field capacity (FC). The amount of the evapotranspirated water was replaced by a nutrient solution containing either 0 or 100 mM NaCl. Whole-plant growth, leaf water content, leaf water potential (Psi(w)), and Na+, K+, and proline concentrations in the tissues were measured. When individually applied, both drought and salinity significantly restricted whole-plant growth, with a more marked effect of the former stress. However, the effects of the two stresses were not additive on whole-plant biomass or on leaf expansion. Root growth was more sensitive to salt than to soil drying, the latter being even magnified by the adverse impact of salinity. Leaf water content was significantly reduced following exposure to water-deficit stress, but was less affected in salt-treated plants. When simultaneously submitted to water-deficit stress and salinity, plants displayed higher values of water and potassium use efficiencies, leaf proline and Na+ concentrations, associated with lower leaf water potential (-1.87 MPa), suggesting the ability of S. portulacastrum to use Na+ and proline for osmotic adjustment.     

Bracelet salt glands of the recretohalophyte Limonium bicolor: Distribution,morphology, and induction

Halophytes complete their life cycles in saline environments. The recretohalophyte Limonium bicolor has evolved a specialized salt secretory structure,the salt gland, which excretes Na⁺to avoid salt damage. Typical L. bicolor salt glands consist of 16 cells with four fluorescent foci and four secretory pores. Here, we describe a special type of salt gland at the base of the L. bicolor leaf petiole named bracelet salt glands due to their beaded-bracelet-like shape of blue auto-fluoresc...     

Leaf expansion – an integrating plant behaviour

Leaves expand to intercept light for photosynthesis, to take up carbon dioxide, and to transpire water for cooling and circulation. The extent to which they expand is determined partly by genetic constraints, and partly by environmental conditions signalling the plant to expand more or less leaf surface area. Leaves have evolved sophisticated sensory mechanisms for detecting these cues and responding with their own growth and function as well as influencing a variety of whole-plant behaviours. Leaf expansion itself is an integrating behaviour that ultimately determines canopy development and function, allocation of materials determining relative shoot : root volume, and the onset of reproduction. To understand leaf development, and in particular, how leaf expansion is regulated, we must know at the molecular level which biochemical processes accomplish cell growth. Physiological experimentation focusing on ion fluxes across the plasmamembrane is providing new molecular information on how light stimulates cell expansion in some dicotyledonous species. Genetic analyses in Arabidopsis, corn, and other species are rapidly generating a list of mutations and enzyme activities associated with leaf development and expansion. Combination of these approaches, using informed physiological interpretations of phenotypic variation will allow us in the future to identify genes encoding both the processes causing cell expansion, and the regulators of these events.     

Growth and N Allocation in Rice Plants under CO2 Enrichment

The effects of CO2 enrichment on growth and N allocation of rice (Oryza sativa L.) were examined. The plants were grown hydroponically in growth chambers with a 14-h photoperiod (1000 [mu]mol quanta m-2 s-1) and a day/night temperature of 25/20[deg]C. From the 28th to 70th d after germination, the plants were exposed to two CO2 partial pressures, namely 36 and 100 Pa. The CO2 enrichment increased the final biomass, but this was caused by a stimulation of the growth rate during the first week of the exposure to elevated CO2 partial pressures. The disappearance of the initial stimulation of the growth rate was associated with a decreased leaf area ratio. Furthermore, CO2 enrichment decreased the investment of N in the leaf blades, whereas the N allocation into the leaf sheaths and roots increased. Thus, the decrease in leaf N content by CO2 enrichment was not due to dilution of N caused by a relative increase in the plant biomass but was due to the change in N allocation at the whole-plant level. We conclude that the growth responses of rice to CO2 enrichment are mainly controlled by leaf area expansion and N allocation into leaf blades at the whole-plant level.     

Plant-environment interactions: Accumulation of hypericin in dark glands of Hypericum perforatum

BACKGROUND AND AIMS: Hypericum perforatum is a perennial herbaceous plant and an extract from this plant has a significant antidepressant effect when administered to humans. The plant is characterized by its secretory glands, also known as dark glands, which are mainly visible on leaves and flowers. The current study evaluates the influence of several environmental factors and developmental stages of the plant on the accumulation and synthesis of hypericin and pseudohypericin (Hy-G), the major bioactive constituents, in H. perforatum plants. METHODS: The appearance of dark glands on different parts of the plant, under several environmental conditions, was monitored by microscopy. Hy-G concentrations were quantified by high-performance liquid chromatography. KEY RESULTS: A significant presence of dark glands accompanying the highest concentrations of Hy-G was observed in the stamen tissues more than in any other organ of H. perforatum. A linear relationship between the number of dark glands and net photosynthetic rate of the leaf and Hy-G concentration in the leaf tissue was also established. A very high concentration of Hy-G was measured in the dark-gland tissues, but in the tissues without any dark glands it was almost absent. The presence of emodin, a precursor of Hy-G, at a high concentration in the dark-gland tissues, and its absence in the surrounding tissues was also observed, suggesting that the site of biosynthesis of Hy-G is in the dark-gland cells. A significantly low concentration of Hy-G (occasionally non-detectable) was measured in the xylem sap of the stem tissues. The dark-gland tissues collected from leaves, stems or flowers contained similar concentrations of Hy-G. CONCLUSIONS: The concentration of Hy-G in various organs of H. perforatum plants is dependent on the number of dark glands, their size or area, not on the location of the dark glands on the plant. The study provides the first experimental evidence that Hy-G is synthesized and accumulates in dark glands.     

A hierarchical analysis of the interactive effects of elevated CO<Subscript>2</Subscript> and water availability on the nitrogen and transpiration productivities of velvet mesquite seedlings

In this study we apply new extensions of classical growth analysis to assess the interactive effects of elevated CO₂ and differences in water availability on the leaf-nitrogen and transpiration productivities of velvet mesquite (Prosopis velutina Woot.) seedlings. The models relate transpiration productivity (biomass gained per mass of water transpired per day) and leaf-nitrogen productivity (biomass gain per unit leaf N per day) to whole-plant relative growth rate (RGR) and to each other, allowing a comprehensive hierarchical analysis of how physiological and morphological responses to the treatments interact with each other to affect plant growth. Elevated CO₂ led to highly significant increases in N and transpiration productivities but reduced leaf N per unit leaf area and transpiration per unit leaf area, resulting in no net effect of CO₂ on the RGR of seedlings. In contrast, higher water availability led to an increase in leaf-tissue thickness or density without affecting leaf N concentration, resulting in a higher leaf N per unit leaf area and consequently a higher assimilatory capacity per unit leaf area. The net effect was a marginal increase in seedling RGR. Perhaps most important from an ecological perspective was a 41% reduction in whole-plant water use due to elevated CO₂. These results demonstrate that even in the absence of CO₂ effects on integrative measures of plant growth such as RGR, highly significant effects may be observed at the physiological and morphological level that effectively cancel each other out. The quantitative framework presented here enables some of these tradeoffs to be identified and related directly to each other and to plant growth.     

Leaf glands act as nectaries in Diplopterys pubipetala (Malpighiaceae)

Leaf glands of Diplopterys pubipetala were studied with light and electron microscopy. Aspects of their secretion, visitors and phenology were also recorded. Glands occur along the margin, at the apex and at the base of the leaf blade. All the glands begin secretion when the leaf is still very young, and secretion continues during leaf expansion. The highest proportion of young leaves coincides with the beginning of flowering. The glucose‐rich secretion is collected by Camponotus ants, which patrol the newly formed vegetative and reproductive branches. All the glands are sessile, partially set into the mesophyll, and present uniseriate epidermis subtended by nonvascularised parenchyma. The glands at the apex and base are larger and also consist of vascularised subjacent parenchyma. The cytoplasm of epidermal and parenchyma cells has abundant mitochondria, polymorphic plastids filled with oil droplets and a few starch grains. Golgi bodies and endoplasmic reticulum are more abundant in the epidermal cells. The parenchyma cells of the subjacent region contain chloroplasts and large vacuoles. Plasmodesmata connect all the nectary cells. The zinc iodide–osmium tetroxide (ZIO) method revealed differences in the population of organelles between epidermal cells, as well as between epidermal cells and parenchyma cells. Ultrastructural results indicate that leaf glands of D. pubipetala can be classified as mixed secretory glands. However, the secretion released by these glands is basically hydrophilic and composed primarily of sugars, hence these glands function as nectaries.     

The effects of different external nitrate concentrations on growth of Avena sativa cv. Amuri treated with diclofop-methyl

Avena sativa cv. Amuri fed either low or high nitrate was sprayed with diclofop-methyl (1 kg a.i. ha^-1) at the three leaf stage. The short term effects of the herbicide on chlorophyll concentration of leaves (laminae) and short and long term effects on d.wt of the component plant parts were determined by comparison with unsprayed plants. For unsprayed and sprayed plants, total leaf d.wt approximately doubled during the first twelve days after commencing treatments. Growth was substantially greater at high nitrate than low nitrate. For unsprayed plants, the increase in total leaf d.wt was due primarily to growth of leaf 3 but for sprayed plants it was due to growth of leaves 1 and 2. Twelve days after commencing treatments, d.wt of leaves 1 and 2 was substantially greater for sprayed plants than for unsprayed plants given similar nitrate, while chlorophyll concentration was substantially less. Leaf 3 d.wt and chlorophyll concentration were substantially greater in unsprayed plants than in sprayed plants given similar nitrate. For unsprayed plants, values were greater at high nitrate than low nitrate, for sprayed plants the converse was the case. Forty nine days after commencing treatments, unsprayed plants had a greater total plant d.wt than sprayed plants given similar nitrate. Total plant d.wt for unsprayed plants was greater at high nitrate than low nitrate, the opposite was the case for sprayed plants. Unsprayed plants at both nitrate levels and sprayed plants given low nitrate produced seed heads but sprayed plants given high nitrate did not. Diclofop-methyl at a rate of 0.3 kg a.i. ha^-' stopped seed head production at high nitrate. Retention and uptake of diclofop-methyl were not significantly different at low and high nitrate. At 1 kg a.i. ha-^l diclofop-methyl, plants switched from low to high nitrate at spraying showed damage similar to that shown by plants given high nitrate throughout. Addition of 200 μg GA into the leaf sheaths two days prior to spraying increased the efficacy of diclofop-methyl at low nitrate. It is proposed that increased efficiency of diclofop-methyl at high nitrate is due to increased leaf damage caused by a greater rate of leaf expansion.     

Correlations of stomatal conductance with hydraulic and chemical factors in several deciduous tree species in a natural habitat

Recent research in whole-plant stomatal physiology, conducted largely with potted plants in controlled environments, suggests that stomatal conductance ( g _s) might be more closely linked to plant chemical variables than to hydraulic variables. To test this in a field situation, seasonal g _s was examined in relation to a number of plant and environmental variables in 11 temperate, deciduous forest tree species. Stomatal conductance was generally better correlated with environmental variables (air temperature, vapor pressure deficit, PPFD) than with plant variables, and slightly better correlated with plant hydraulic variables (shoot water and osmotic potentials) than with plant chemical variables (xylem sap ABA concentration, xylem sap pH). We examined a model, developed previously for maize, which describes regulation of g _s by xylem sap ABA concentration with leaf water status acting to modify stomatal sensitivity to the ABA signal. This model explained slightly more variation in seasonal g _s in the forest trees than did single plant variables but not more variation than most single environmental variables. Response surface models, especially those incorporating environmental variables, were more consistently successful at explaining g _s across species.     

Mechanized techniques for the selective extraction of enzymes from plant epidermal glands

Many plant products are biosynthesized and accumulated in epidermal glands. For investigations on the metabolism of these compounds it is most convenient to obtain cell-free preparations enriched in gland contents. Two simple mechanized procedures have been developed for gently abrading the plant surface in order to efficiently extract glandular enzymes in high purity. These methods allow rapid processing of large quantities of plant material and yield extracts largely uncontaminated with materials from underlying tissue. The use of these procedures for isolating several enzymes of terpenoid metabolism is described. These techniques work especially well for microsomal enzymes and may be useful not only for enzymes found in epidermal glands but also for other enzymes localized in or near the epidermis. With simple modification, these procedures can be adapted for use with a variety of different types of plant tissues.