A unified framework of plant adaptive strategies to drought: Crossing scales and disciplines

Plant adaptation to drought has been extensively studied at many scales from ecology to molecular biology across a large range of model species. However, the conceptual frameworks underpinning the definition of plant strategies, and the terminology used across the different disciplines and scales are not analogous. ‘Drought resistance’ for instance refers to plant responses as different as the maintenance of growth and productivity in crops, to the survival and recovery in perennial woody or grassland species. Therefore, this paper aims to propose a unified conceptual framework of plant adaptive strategies to drought based on a revised terminology in order to enhance comparative studies. Ecological strategies encapsulate plant adaptation to multidimensional variation in resource variability but cannot account for the dynamic and short‐term responses to fluctuations in water availability. Conversely, several plant physiological strategies have been identified along the mono‐dimensional gradient of water availability in a given environment. According to a revised terminology, dehydration escape, dehydration avoidance, dehydration tolerance, dormancy, and desiccation tolerance are clearly distinguishable. Their sequential expression is expressed as water deficit increases while cavitation tolerance is proposed here to be a major hydraulic strategy underpinning adaptive responses to drought of vascular plants. This continuum of physiological strategies can be interpreted in the context of the ecological trade‐off between water‐acquisition vs. water‐conservation, since growth maintenance is associated with fast water use under moderate drought while plant survival after growth cessation is associated with slow water use under severe drought. Consequently, the distinction between ‘drought resistance’ and ‘drought survival’, is emphasized as crucial to ensure a correct interpretation of plant strategies since ‘knowing when not to grow’ does not confer ‘drought resistance’ but may well enhance ‘drought survival’. This framework proposal should improve cross‐fertilization between disciplines to help tackle the increasing worldwide challenges that drought poses to plant adaptation.     

siRNA release from gold nanoparticles by nanosecond pulsed laser irradiation and analysis of the involved temperature increase

Nanosecond pulsed laser irradiation can trigger a release of nucleic acids from gold nanoparticles, but the involved nanoeffects are not fully understood yet. Here we investigate the release of coumarin labeled siRNA from 15 to 30 nm gold particles after nanosecond pulsed laser irradiation. Temperatures in the particle and near the surface were calculated for the different radiant exposures. Upon irradiation with laser pulses of 4 nanosecond duration release started for both particle sizes at a calculated temperature increase of approximately 500 K. Maximum coumarin release was observed for 15 nm particles after irradiation with radiant exposure of 80 mJ cm^?2 and with 32 mJ cm^?2 for 30 nm particles. This corresponds to a temperature increase of 815 and 900 K, respectively. Our results show that the molecular release by nanosecond pulsed irradiation is based on a different mechanism compared to continuous or femtosecond irradiation. Local temperatures are considerably higher and it is expected that bubble formation plays a crucial role in release and damage to cellular structures.      

Tree hydraulic traits are coordinated and strongly linked to climate‐of‐origin across a rainfall gradient

Plant hydraulic traits capture the impacts of drought stress on plant function, yet vegetation models lack sufficient information regarding trait coordination and variation with climate‐of‐origin across species. Here, we investigated key hydraulic and carbon economy traits of 12 woody species in Australia from a broad climatic gradient, with the aim of identifying the coordination among these traits and the role of climate in shaping cross‐species trait variation. The influence of environmental variation was minimized by a common garden approach, allowing us to factor out the influence of environment on phenotypic variation across species. We found that hydraulic traits (leaf turgor loss point, stomatal sensitivity to drought [P_gs], xylem vulnerability to cavitation [P_x], and branch capacitance [C_branch]) were highly coordinated across species and strongly related to rainfall and aridity in the species native distributional range. In addition, trade‐offs between drought tolerance and plant growth rate were observed across species. Collectively, these results provide critical insight into the coordination among hydraulic traits in modulating drought adaptation and will significantly advance our ability to predict drought vulnerability in these dominant trees species.     

Transport constraints on water use by the Great Basin shrub, Artemisia tridentata

As soil and plant water status decline, decreases in hydraulic conductance can limit a plant's ability to maintain gas exchange. We investigated hydraulic limitations for Artemisia tridentata during summer drought. Water use was quantified by measurements of soil and plant water potential ( Ψ ), transpiration and leaf area. Hydraulic transport capacity was quantified by vulnerability to water stress-induced cavitation for root and stem xylem, and moisture release characteristics for soil. These data were used to predict the maximum possible steady-state transpiration rate ( E _crit) and minimum leaf xylem pressure ( Ψ _crit). Transpiration and leaf area declined by ~ 80 and 50%, respectively, as soil Ψ decreased to –2·6 MPa during drought. Leaf-specific hydraulic conductance also decreased by 70%, with most of the decline predicted in the rhizosphere and root system. Root conductance was projected to be the most limiting, decreasing to zero to cause hydraulic failure if E _crit was exceeded. The basis for this prediction was that roots were more vulnerable to xylem cavitation than stems (99% cavitation at –4·0 versus –7·8 MPa, respectively). The decline in water use during drought was necessary to maintain E and Ψ within the limits defined by E _crit and Ψ _crit.     

The importance of xylem constraints in the distribution of conifer species

Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (φ₅₀) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi-arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides . Mean φ₅₀ was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of φ₅₀ was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO₂ concentration (c_i) in the leaves of these species during artificial drought was strongly correlated with φ₅₀ suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade-off between xylem conductivity and xylem vulnerability was tested in a sub-sample of four species, but no evidence of an inverse relationship between φ₅₀ and either stem-area specific (K_a) or leaf-area specific conductivity (K₁) was found.     

周期性土壤干旱和叶片水势对气孔响应木质部ABA灵敏度的影响

研究了周期性土壤干旱期间气孔对木质部ＡＢＡ响应的灵敏度的变化以及叶片水势对灵敏度的影响。实验结果证明了木质部ＡＢＡ浓度是反映根系周围土壤水分状况的一个指标的结论。土壤周期性干旱不影响木质部ＡＢＡ浓度对土壤水分状况的依赖关系,但显著地提高了气孔对木质部ＡＢＡ 响应的灵敏度。根据对实测数据的数学模拟结果显示,引起气孔导度下降５０％ 所需的木质部ＡＢＡ浓度从第一轮土壤干旱的７５０ ｎｍｏｌ／Ｌ降至第二轮土壤干旱的５５０ ｎｍｏｌ／Ｌ。分根实验的结果表明,叶片水分亏缺显著提高了气孔对木质部ＡＢＡ 的响应的灵敏程度,全根干旱中引起气孔导度下降５０ ％ 所需的木质部ＡＢＡ 浓度比半根干旱的小２ ～４ 倍。这表明,气孔对木质部ＡＢＡ响应的灵敏度不是一个固定的特性,可随植物生长环境及许多其他因素的变化而表现出很大的差异     

The effect of ultrasound cavitation on endothelial cells

Acoustic cavitation has been widely explored for both diagnostic and therapeutic purposes. Ultrasound-induced cavitation, including inertial cavitation and non-inertial cavitation, can cause microstreaming, microjet, and free radical formation. The acoustic cavitation effects on endothelial cells have been studied for drug delivery, gene therapy, and cancer therapy. Studies have demonstrated that the ultrasound-induced cavitation effect can treat cancer, ischaemia, diabetes, and cardiovascular diseases. In this minireview, we will review the impact of ultrasound-induced cavitation on the endothelial cells such as cell permeability, cell proliferation, gene expression regulation, cell viability, hemostasis interaction, oxygenation, and variation in the level of calcium ions, ceramide, nitric oxide (NO) and nitric oxide synthase (NOS) activity. The applications of these effects and the cavitation mechanism involved will be summarized, demonstrating the important role of acoustic cavitation in non-invasive ultrasound treatment of various physiological conditions.     

Analysis of Growth and Water Relations of Tomato Fruits in Relation to Air Vapor Pressure Deficit and Plant Fruit Load

The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.     

Xylem function of arid-land shrubs from California, USA: an ecological and evolutionary analysis

Xylem traits were examined among 22 arid-land shrub species, including measures of vessel dimensions and pit area. These structural measures were compared with the xylem functional traits of transport efficiency and safety from cavitation. The influence of evolution on trait relationships was examined using phylogenetic independent contrasts (PICs). A trade-off between xylem safety and efficiency was supported by a negative correlation between vessel dimensions and cavitation resistance. Pit area was correlated with cavitation resistance when cross species data were examined, but PICs suggest that these traits have evolved independently of one another. Differences in cavitation resistance that are not explained by pit area may be related to differences in pit membrane properties or the prevalence of tracheids, the latter of which may alter pit area through the addition of vessel-to-tracheid pits or through changes in xylem conduit connectivity. Some trait relationships were robust regardless of species ecology or evolutionary history. These trait relationships are likely to be the most valuable in predictive models that seek to examine anatomical and functional trait relationships among extant and fossil woods and include the relationship among hydraulic conductivity and vessel diameter, between vessel diameter and vessel length, and between hydraulic conductivity and wood density.