Building a Barrier: The Influence of Different Wax Fractions on the Water Transpiration Barrier of Leaf Cuticles

Waxes are critical in limiting non-stomatal water loss in higher terrestrial plants by making up the limiting barrier for water diffusion across cuticles. Using a differential extraction protocol, we investigated the influence of various wax fractions on the cuticular transpiration barrier. Triterpenoids (TRPs) and very long-chain aliphatics (VLCAs) were selectively extracted from isolated adaxial leaf cuticles using methanol (MeOH) followed by chloroform (TCM). The water permeabilities of the native and the solvent-treated cuticles were measured gravimetrically. Seven plant species (Camellia sinensis, Ficus elastica, Hedera helix, Ilex aquifolium, Nerium oleander, Vinca minor, and Zamioculcas zamiifolia) with highly varying wax compositions ranging from nearly pure VLCA- to TRP-dominated waxes were selected. After TRP removal with MeOH, water permeability did not or only slightly increase. The subsequent VLCA extraction with TCM led to increases in cuticular water permeabilities by up to two orders of magnitude. These effects were consistent across all species investigated, providing direct evidence that the cuticular transpiration barrier is mainly composed of VLCA. In contrast, TRPs play no or only a minor role in controlling water loss.

Structural and Functional Insights into the Role of Guard Cell Ion Channels in Abiotic Stress-Induced Stomatal Closure

A stomatal pore is formed by a pair of specialized guard cells and serves as a major gateway for water transpiration and atmospheric CO2 influx for photosynthesis in plants. These pores must be tightly controlled, as inadequate CO2 intake and excessive water loss are devastating for plants. When the plants are exposed to extreme weather conditions such as high CO2 levels, O3, low air humidity, and drought, the turgor pressure of the guard cells exhibits an appropriate response against these stresses, which leads to stomatal closure. This phenomenon involves a complex network of ion channels and their regulation. It is well-established that the turgor pressure of guard cells is regulated by ions transportation across the membrane, such as anions and potassium ions. In this review, the guard cell ion channels are discussed, highlighting the structure and functions of key ion channels; the SLAC1 anion channel and KAT1 potassium channel, and their regulatory components, emphasizing their significance in guard cell response to various stimuli.

Leaf Cuticular Transpiration Barrier Organization in Tea Tree Under Normal Growth Conditions

The cuticle plays a major role in restricting nonstomatal water transpiration in plants. There is therefore a long-standing interest to understand the structure and function of the plant cuticle. Although many efforts have been devoted, it remains controversial to what degree the various cuticular parameters contribute to the water transpiration barrier. In this study, eight tea germplasms were grown under normal conditions; cuticle thickness, wax coverage, and compositions were analyzed from the epicuticular waxes and the intracuticular waxes of both leaf surfaces. The cuticular transpiration rates were measured from the individual leaf surface as well as the intracuticular wax layer. Epicuticular wax resistances were also calculated from both leaf surfaces. The correlation analysis between the cuticular transpiration rates (or resistances) and various cuticle parameters was conducted. We found that the abaxial cuticular transpiration rates accounted for 64–78% of total cuticular transpiration and were the dominant factor in the variations for the total cuticular transpiration. On the adaxial surface, the major cuticular transpiration barrier was located on the intracuticular waxes; however, on the abaxial surface, the major cuticular transpiration barrier was located on the epicuticular waxes. Cuticle thickness was not a factor affecting cuticular transpiration. However, the abaxial epicuticular wax coverage was found to be significantly and positively correlated with the abaxial epicuticular resistance. Correlation analysis suggested that the very-long-chain aliphatic compounds and glycol esters play major roles in the cuticular transpiration barrier in tea trees grown under normal conditions. Our results provided novel insights about the complex structure–functional relationships in the tea cuticle.

Power Generation by Water Transpiration from Microporous Alumina

The authors have requested that this preprint be withdrawn due to erroneous posting.

Power Generation by Water Transpiration from Microporous Alumina

Hydropower generation has been the most developed sustainable energy source that is based on the electromagnetic transduction of the gravitational potential energy but is only realized through elaborate construction of water dam and not yet suitable for small-scale energy harvesters. Here, we report that wetting and evaporation of water from a small block of porous alumina can generate electrical current in the direction of water transpiration. This induced current in microporous alumina is associated with the mass transport of water accompanying the accumulated charge near the negatively charged surface of the alumina pore. Without any pre-treatment or additives, once water evaporation commences, a 3×3 cm2 piece of alumina generates an open-circuit voltage of up to 0.27 V. Possible influence on power generation of the water-insulator interface and naturally available protons in water are discussed with respect to experimental results. Total output of this novel microporous ceramic electric generator can be scaled up and could be used for stand-alone energy harvesters or power generators in self-powered off-grid agricultural/ industrial sensors.

Cholesterol derivatives make large part of the lipids from epidermal molts of the desert-adapted Gila monster lizard (Heloderma suspectum)

In order to understand the cutaneous water loss in the desert-adapted and venomous lizard Heloderma suspectum, the microscopic structure and lipid composition of epidermal molts have been examined using microscopic, spectroscopic and chemical analysis techniques. The molt is formed by a variably thick, superficial beta-layer, an extensive mesos-region and few alpha-cells in its lowermost layers. The beta-layer contains most corneous beta proteins while the mesos-region is much richer in lipids. The proteins in the mesos-region are more unstructured than those located in the beta-layer. Most interestingly, among other lipids, high contents of cholesteryl-β-glucoside and cholesteryl sulfate were detected, molecules absent or present in traces in other species of squamates. These cholesterol derivatives may be involved in the stabilization and compaction of the mesos-region, but present a limited permeability to water movements. The modest resistance to cutaneous water-loss of this species is compensated by adopting other physiological strategies to limit thermal damage and water transpiration as previous eco-physiological studies have indicated. The increase of steroid derivatives may also be implicated in the heat shock response, influencing the relative behavior in this desert-adapted lizard.

Abscisic acid homeostasis is mediated by feedback regulation of MdMYB88 and MdMYB124

The phytohormone abscisic acid (ABA) is involved in various plant processes. In response to drought stress, plants quickly accumulate ABA, but the regulatory mechanism of ABA accumulation is largely unknown, especially in woody plants. In this study, we report that MdMYB88 and MdMYB124 are myeloblastosis (MYB) transcription factors critical for ABA accumulation in apple trees (Malus x domestica) following drought, and this regulation is negatively controlled by ABA. MdMYB88 and MdMYB124 positively regulate leaf water transpiration, photosynthetic capacity, and stress endurance in apple trees under drought conditions. MdMYB88 and MdMYB124 regulate the expression of biosynthetic and catabolic genes of ABA, as well as drought- and ABA- responsive genes. MdMYB88 associates with promoter regions of the ABA biosynthetic gene 9-cis-epoxycarotenoid dioxygenase 3 (NCED3). Finally, expression of MdMYB88 and MdMYB124 is repressed by ABA. Our results identify a feedback regulation of MdMYB88 and MdMYB124 in modulating ABA homeostasis in apple trees.

Improving the water transpiration in a solar steam generation device

Solar steam generation (SSG) has been proposed as one of the most advanced techniques to trigger solar energy desalination of sea water. Although many efforts have been dedicated to develop SSG devices, the efficiency remains relatively low. Previous work was mainly focused on thermal insulation film and light absorption. Attention has seldom been concentrated on device structure. Inspired by the manner of water transportation within flowers, we designed an artificial SSG unit which can effectively speed up the water transpiration from the bulk to the surface. Another advantage of such a device is that steam generation is separated from the bulk salty solution and thereby the solar thermal evaporation can be improved greatly. As demonstrated via the desalination experiment, the mass change and evaporation rate under 1 solar irradiation can reach as high as 2.51 kg/m2 and 1.26 kg/m2·h−1, respectively. Meanwhile, the evaporation efficiency is 74%. These values are much higher than those of traditional SSG devices and bulk water.

Far infrared imaging, an effective way to screen maize seedling mutants for drought stress response

Water shortage is a global challenge and affects crop growth and development seriously. Stoma is the main channel of plant water transpiration. Water transpiration through stomata is an endothermic process and affects temperature of plants, especially leaf surface. In this study, we established a method for screening maize seedling mutant with abnormal leaf temperature by far infrared imaging. We found that seedling mutants with abnormal leaf temperature manifested different drought tolerance. Mutants with lower leaf temperature demonstrated faster moisture loss rate, poorer drought tolerance, higher osmotic potential, lower leaf relative water content, more accumulation of hydrogen peroxide, more serious cell membrane damage and more robust root systems and biomass under drought treatment, which are opposite in maize seedling mutants with higher leaf surface temperature compared with the corresponding control. Taken together, the method we established is an effective way to screen maize mutants with abnormal drought response.