Cloning and expression analysis of candidate genes involved in wax deposition along the growing barley (Hordeum vulgare) leaf.

The aim of the present study was to isolate clones of genes which are likely to be involved in wax deposition on barley leaves. Of particular interest were those genes which encode proteins that take part in the synthesis and further modification of very long chain fatty acids (VLCFAs), the precursors of waxes. Previously, it had been shown that wax deposition commences within a spatially well-defined developmental zone along the growing barley leaf (Richardson et al.

Cuticular permeance in relation to wax and cutin development along the growing barley (Hordeum vulgare) leaf.

The developing leaf three of barley provides an excellent model system for the direct determination of relationships between amounts of waxes and cutin and cuticular permeance. Permeance of the cuticle was assessed via the time-course of uptake of either toluidine blue or (14)C-labelled benzoic acid ([(14)C] BA) along the length of the developing leaf. Toluidine blue uptake only occurred within the region 0-25 mm from the point of leaf insertion (POLI).

Water transport in plant cuticles: an update.

The scale, mechanism, and physiological importance of cuticular transpiration were last reviewed in this journal 5 and 10 years ago. Progress in our basic understanding of the underlying processes and their physiological and structural determinants has remained frustratingly slow ever since. There have been major advances in the quantification of cuticular water permeability of stomata-bearing leaf and fruit surfaces and its dependence on leaf temperature in astomatous surfaces, as well as in our understanding of the respective roles of epicuticular and intracuticular waxes and molecular-scale aqueous pores in its physical control.

Parameterization, comparison, and validation of models quantifying relative change of cuticular permeability with physicochemical properties of diffusants.

Predictions from two previously published models and a new model for the relative change in cuticular permeability with boiling point, octanol/air partition coefficient, and/or molar volume of a wide range of diffusants (not including ions and large hydrophilic compounds) are compared with each other and to experimental data sets not used for model parameterization. While the models work in a similar way for all cuticles for which data are available, it is not yet possible to predict in absolute terms the permeability of any cuticles for which no data are available-that is, while the slope of a plot representing the change in permeability with diffusant properties is predictable, the position of the linear relationship along the ordinate needs to be determined experimentally for each type of cuticle at or near the relevant temperature(s).

Quantification of cuticular permeability in genetically modified plants.

More and more studies on genetically modified plants are identifying parts of the genetic code with putative involvement in creating the cuticular barrier. Unfortunately, many of these studies suffer from the inadequacy of the chosen methods to quantify, in a reasonably unambiguous way, if and how the efficacy of the cuticular barrier is affected by the genetic change. A short overview of relevant findings is given and a more stringent experimental approach to quantifying effects on cuticular permeability in genetically modified plants proposed.

Rising atmospheric CO2 reduces sequestration of root-derived soil carbon.

Forests have a key role as carbon sinks, which could potentially mitigate the continuing increase in atmospheric carbon dioxide concentration and associated climate change. We show that carbon dioxide enrichment, although causing short-term growth stimulation in a range of European tree species, also leads to an increase in soil microbial respiration and a marked decline in sequestration of root-derived carbon in the soil. These findings indicate that, should similar processes operate in forest ecosystems, the size of the annual terrestrial carbon sink may be substantially reduced, resulting in a positive feedback on the rate of increase in atmospheric carbon dioxide concentration.

Cuticular wax deposition in growing barley (Hordeum vulgare) leaves commences in relation to the point of emergence of epidermal cells from the sheaths of older leaves.

In grasses, leaf cells divide and expand within the sheaths of older leaves, where the micro-environment differs from the open atmosphere. By the time epidermal cells are displaced into the atmosphere, they must have a functional cuticle to minimize uncontrolled water loss. In the present study, gas chromatography and scanning electron microscopy were used to follow cuticular wax deposition along the growing leaf three of barley (Hordeum vulgare L.

Exchange of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) between air and a mixed pasture sward.

To improve understanding of air-to-vegetation transfer of persistent organic pollutants (POPs), uptake and depuration of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) between grass sward and air was investigated. Pasture swards were placed in fanned (2 m s(-1) wind speed) and unfanned conditions for a period of 20 days and sampled at intervals. Depuration was carried out after a short (4 days) and a long (14 days) exposure period.

Current issues and uncertainties in the measurement and modelling of air-vegetation exchange and within-plant processing of POPs.

Air-vegetation exchange of POPs is an important process controlling the entry of POPs into terrestrial food chains, and may also have a significant effect on the global movement of these compounds. Many factors affect the air-vegetation transfer including: the physicochemical properties of the compounds of interest; environmental factors such as temperature, wind speed, humidity and light conditions; and plant characteristics such as functional type, leaf surface area, cuticular structure, and leaf longevity. The purpose of this review is to quantify the effects these differences might have on air/plant exchange of POPs, and to point out the major gaps in the knowledge of this subject that require further research.

Study of plant-air transfer of PCBs from an evergreen shrub: implications for mechanisms and modeling.

The depuration of gas-phase polychlorinated biphenyls (PCBs) from a slow-growing evergreen shrub, Skimmia japonica Thunb., was studied to investigate the reversibility of uptake and the compartmentalization of PCB congeners within leaves with respect to air-plant exchange processes. Depuration of PCBs was monitored over periods of hours, days, and weeks.

Investigation into the importance of the stomatal pathway in the exchange of PCBs between air and plants.

The transfer of persistent organic pollutants (POPs) from air to vegetation is an important air-surface exchange process that affects global cycling and can result in human and wildlife exposure via the terrestrial food chain. To improve understanding of this process, the role of stomata in uptake of gas-phase polychlorinated biphenyls (PCBs) was investigated using Hemerocallis x hybrida "Black Eyed Stella", a plant with a high stomatal density. Uptake of PCBs was monitored over a 72-h period in the presence and absence of light.

Air-side and plant-side resistances influence the uptake of airborne PCBs by evergreen plants.

The transfer of persistent organic pollutants (POPs) from airto vegetation is an important air-surface exchange process that affects global cycling and can result in human and wildlife exposure via the terrestrial food chain. To improve understanding of this process, the uptake of gas-phase polychlorinated biphenyls (PCBs) by two slow-growing evergreen shrubs, Skimmia japonicaThunb. and Hebe"Great Orme", was studied to investigate the influence of air-side and plant-side resistances.

Sodium-related partial stomatal closure and salt tolerance of Aster tripolium.

•  When Aster tripolium is grown at high salinity, stomatal closure is induced by the presence of sodium ions in the apoplast surrounding the guard cells. The occurrence of this system in Aster tripolium and not in the closely related glycophyte Aster amellus suggests that it could be an important factor in the network of physiological attributes required for salt tolerance. •  Gas exchange and growth parameters were measured in Aster tripolium plants grown at different levels of salinity.

In vivo manipulation of cuticular water permeance and its effect on stomatal response to air humidity.

Cuticular water permeance was manipulated in Corylus avellana L., Hypericum androsaemum L. and Populus tremula L.