A bifunctional dermaseptin–thanatin dipeptide functionalizes the crop surface for sustainable pest management

To reduce pesticide use while preserving crop productivity, alternative pest and disease control measures are needed. We thought of an alternative way of functionalizing leaves of soybean to fight its most severe disease, Asian soybean rust (Phakopsora pachyrhizi). To do so, we produced bifunctional peptides that adhere to the soybean leaf surface and prevent the germination of P. pachyrhizi spores. In detail, amphiphilic peptides liquid chromatography peak I (LCI), thanatin (THA), tachystatin A2 (TA2), and lactoferricin B (LFB) were all fused to enhanced green fluorescent protein (eGFP). Of these fusion peptides, eGFP–LCI and eGFP–THA bound strongly and in a rainfast manner to the surface of soybean, barley, and corn leaves. eGFP–THA binding to soybean also withstood high temperature, sunlight and biotic degradation for at least 17 days. The dipeptides seem to bind mainly to the surface wax layer of leaves because eGFP–THA and eGFP–LCI did not stick to the wax-depleted cer-j59 mutant of barley or to corn leaves with their surface wax removed. A fusion of the antimicrobial peptide dermaseptin 01 and THA (DS01–THA) inhibits the germination of P. pachyrhizi spores in vitro and reduces Asian soybean rust disease in a rainfast manner. Therefore, this study reveals that bifunctional peptides can be used to functionalize the crop surface for sustainable disease management

Camouflaged as degraded wax: hygroscopic aerosols contribute to leaf desiccation, tree mortality, and forest decline

Some 40 years ago, air pollution caused widespread forest decline in Central Europe and eastern North America. More recently, high levels of tree mortality worldwide are thought to be driven by rising temperatures and increasing atmospheric drought. A neglected factor, possibly contributing to both phenomena, is the foliar accumulation of hygroscopic aerosols. Recent experiments with experimentally added aerosols revealed that foliar aerosol accumulation can (i) create the microscopic impression of 'wax degradation', considered an important proxy of forest decline associated with air pollution, though the mechanism remains unexplained; and (ii) increase epidermal minimum conductance (g min), a measure of cuticular permeability and completeness of stomatal closure—both could lead to reduced drought tolerance. Here, those studies with applied aerosol are extended by addressing plant responses to reduction of ambient aerosol. Scots pine, silver fir, and common oak seedlings were grown for 2 years in greenhouses ventilated with ambient air (AA) or air filtered to remove nearly all aerosol particles (FA). Removal of ambient aerosol prevented the development of amorphous structures viewed in the electron microscope that have typically been interpreted as degraded waxes. Lower g min values suggested that FA plants had better stomatal control and therefore greater drought tolerance than AA plants. The co-occurrence of apparent wax degradation and reduced drought tolerance in AA plants suggests a common cause. This may be mediated by the deliquescence and spreading of hygroscopic aerosols across the leaf surface. The liquid film produced may penetrate the stomata and facilitate unproductive stomatal transpiration. In this way, aerosol pollution may enhance the impacts of atmospheric drought, and may damage trees and forests on large spatial scales

ECLAIRE third periodic report

The ÉCLAIRE project (Effects of Climate Change on Air Pollution Impacts and Response Strategies for European Ecosystems) is a four year (2011-2015) project funded by the EU's Seventh Framework Programme for Research and Technological Development (FP7)

ECLAIRE: Effects of Climate Change on Air Pollution Impacts and Response Strategies for European Ecosystems. Project final report

The central goal of ECLAIRE is to assess how climate change will alter the extent to which air pollutants threaten terrestrial ecosystems. Particular attention has been given to nitrogen compounds, especially nitrogen oxides (NOx) and ammonia (NH3), as well as Biogenic Volatile Organic Compounds (BVOCs) in relation to tropospheric ozone (O3) formation, including their interactions with aerosol components. ECLAIRE has combined a broad program of field and laboratory experimentation and modelling of pollution fluxes and ecosystem impacts, advancing both mechanistic understanding and providing support to European policy makers. The central finding of ECLAIRE is that future climate change is expected to worsen the threat of air pollutants on Europe’s ecosystems. Firstly, climate warming is expected to increase the emissions of many trace gases, such as agricultural NH3, the soil component of NOx emissions and key BVOCs. Experimental data and numerical models show how these effects will tend to increase atmospheric N deposition in future. By contrast, the net effect on tropospheric O3 is less clear. This is because parallel increases in atmospheric CO2 concentrations will offset the temperature-driven increase for some BVOCs, such as isoprene. By contrast, there is currently insufficient evidence to be confident that CO2 will offset anticipated climate increases in monoterpene emissions. Secondly, climate warming is found to be likely to increase the vulnerability of ecosystems towards air pollutant exposure or atmospheric deposition. Such effects may occur as a consequence of combined perturbation, as well as through specific interactions, such as between drought, O3, N and aerosol exposure. These combined effects of climate change are expected to offset part of the benefit of current emissions control policies. Unless decisive mitigation actions are taken, it is anticipated that ongoing climate warming will increase agricultural and other biogenic emissions, posing a challenge for national emissions ceilings and air quality objectives related to nitrogen and ozone pollution. The O3 effects will be further worsened if progress is not made to curb increases in methane (CH4) emissions in the northern hemisphere. Other key findings of ECLAIRE are that: 1) N deposition and O3 have adverse synergistic effects. Exposure to ambient O3 concentrations was shown to reduce the Nitrogen Use Efficiency of plants, both decreasing agricultural production and posing an increased risk of other forms of nitrogen pollution, such as nitrate leaching (NO3-) and the greenhouse gas nitrous oxide (N2O); 2) within-canopy dynamics for volatile aerosol can increase dry deposition and shorten atmospheric lifetimes; 3) ambient aerosol levels reduce the ability of plants to conserve water under drought conditions; 4) low-resolution mapping studies tend to underestimate the extent of local critical loads exceedance; 5) new dose-response functions can be used to improve the assessment of costs, including estimation of the value of damage due to air pollution effects on ecosystems, 6) scenarios can be constructed that combine technical mitigation measures with dietary change options (reducing livestock products in food down to recommended levels for health criteria), with the balance between the two strategies being a matter for future societal discussion. ECLAIRE has supported the revision process for the National Emissions Ceilings Directive and will continue to deliver scientific underpinning into the future for the UNECE Convention on Long-range Transboundary Air Pollution

Progressive wetting of initially hydrophobic plant surfaces by salts – a prerequisite for hydraulic activation of stomata?

Nutrient input by atmospheric particles is important or even essential for forest ecosystems. Many particles will first deposit to leaf surfaces. Competition is avoided by direct foliar uptake, compared to uptake via the soil. While there is meanwhile clear evidence for foliar uptake to happen via the stomata under natural conditions, this requires the establishment of a liquid water connection along the hydrophobic stomatal walls, called ‘hydraulic activation of stomata’ (HAS). Several possibilities for HAS to establish have been suggested including fungal hyphae, bacteria, and salts. Here we show for the first time the spreading of different salts on hydrophobic cuticles by repeated drying/wetting cycles, a plausible model for HAS.NaCl, K2HPO4, and NaClO3 were placed on hydrophobic leaf surfaces or isolated cuticles. Gas exchange and water use efficiency were recorded for several days after the application of droplets on bean (Vicia faba) and on apple (Malus domesticus) leaves. Repeated drying/wetting cycles for the different salts were observed with an environmental scanning electron microscope (ESEM).Apple leaves treated with NaClO3 on the astomatous adaxial surface were unaffected while treatment on stomatous abaxial surfaces caused photosynthesis and water use efficiency to decrease. Transpiration of bean leaves increased after K2HPO4 application, while water use efficiency decreased. Salts changed their appearance by drying wetting cycles, after some time spreading out in dentritic growth.The study shows the crucial influence of stomata for the transport of ionic substances, the interaction of hygroscopic salts with plant water relations, and a possible mechanism for HAS establishment

Progressive wetting of initially hydrophobic plant surfaces by salts – a prerequisite for hydraulic activation of stomata?

Nutrient input by atmospheric particles is important or even essential for forest ecosystems. Many particles will first deposit to leaf surfaces. Competition is avoided by direct foliar uptake, compared to uptake via the soil. While there is meanwhile clear evidence for foliar uptake to happen via the stomata under natural conditions, this requires the establishment of a liquid water connection along the hydrophobic stomatal walls, called ‘hydraulic activation of stomata’ (HAS). Several possibilities for HAS to establish have been suggested including fungal hyphae, bacteria, and salts. Here we show for the first time the spreading of different salts on hydrophobic cuticles by repeated drying/wetting cycles, a plausible model for HAS.NaCl, K2HPO4, and NaClO3 were placed on hydrophobic leaf surfaces or isolated cuticles. Gas exchange and water use efficiency were recorded for several days after the application of droplets on bean (Vicia faba) and on apple (Malus domesticus) leaves. Repeated drying/wetting cycles for the different salts were observed with an environmental scanning electron microscope (ESEM).Apple leaves treated with NaClO3 on the astomatous adaxial surface were unaffected while treatment on stomatous abaxial surfaces caused photosynthesis and water use efficiency to decrease. Transpiration of bean leaves increased after K2HPO4 application, while water use efficiency decreased. Salts changed their appearance by drying wetting cycles, after some time spreading out in dentritic growth.The study shows the crucial influence of stomata for the transport of ionic substances, the interaction of hygroscopic salts with plant water relations, and a possible mechanism for HAS establishment