Real-Time Imaging of Leaf Apoplastic pH Dynamics in Response to NaCl Stress

Knowledge concerning apoplastic ion concentrations is important for the understanding of many processes in plant physiology. Ion-sensitive fluorescent probes in combination with quantitative imaging techniques offer opportunities to localize, visualize, and quantify apoplastic ion dynamics in situ. The application of this technique to the leaf apoplast is complicated because of problems associated with dye loading. We demonstrate a more sophisticated dye loading procedure that enables the mapping of spatial apoplastic ion gradients over a period of 3 h. The new technique has been used for the real-time monitoring of pH dynamics within the leaf apoplast in response to NaCl stress encountered by the roots

Biofortification and subcellular localization of minerals in faba bean as influenced by Mg foliar application

Foliar application of Mg is a measure for the correction of Mg deficiency in crop plants. Foliar applied nutrients need to access the symplastic side where majority of physiological processes take place. To achieve an adequate uptake of the Mg ions through the leaf surface, high concentrations of of 100-200 mM MgSO4 are usually supplied. This can cause antagonistic perturbations on the subcellular distribution of Caand K cations. To test for such unintended side effects, we used the infiltration-centrifugation method to extract ions from the apoplastic and symplastic side of Vicia faba leaves and quantified concentrations of Mg, Ca and K in dependency to the dose of the foliar fertilized Mg. Results show that a large fraction of Mg accesses the symplast whereas the apoplastic fraction shows a concomitant increase. Symplastic and apoplastic K and Ca relations were only affected under conditions of high exogenous leaf supply of Mg (200 mM) but did not change upon moderate Mg supply (50; 100 mM). Overall, results reveal the suitability of leaf fertilization to biofortify plant-based products with magnesium. With respect to human nutrition, care must be taken that K and Ca do not become impoverished based on antagonistic effects

Feeding the world sustainably - efficient nitrogen use

Globally, overuse of nitrogen (N) fertilizers in croplands is causing severe environmental pollution. In this context, Gu et al. suggest environmentally friendly and cost-effective N management practices and Hamani et al. highlight the use of microbial inoculants to improve crop yields, while reducing N-associated environmental pollution and N-fertilizer use

Einfluss von NaCl-Stress auf die Expression von Expansinen sowie den apoplastischen pH-Wert in expandierenden Blättern

Soil salinity poses a major threat to agriculture, because during the osmotic stress phase, salt-sensitive crops such as maize (Zea mays L.) exhibit a strong growth reduction. A modified capacity of cell walls to expand irreversibly has been suggested to be the major growth-limiting factor during the salinity-induced osmotic stress phase. Elucidation of the way that salinity affects shoot growth is thus of great importance for a better understanding of processes that contribute to salt resistance. For this purpose, shoot growth and shoot growth-related factors have been compared between a salt-sensitive and a salt-resistant maize hybrid under saline condition. The 100 mM NaCl treatment of maize plants that differ in their degree of salt-resistance over a period of 8–days has revealed genotype-specific differences regarding the ability of the young shoots to maintain growth. The salt-sensitive hybrid Lector exhibited a strong reduction in growth, as is known to occur in the first phase of salt stress. In contrast, the shoots of the salt-resistant hybrid SR03 were only marginally affected and maintained growth. The up-regulation of the mRNA of wall-loosening factors (ZmXTH1, ZmXET1, ZmEXPA1, ZmEXPB2, ZmEXPB6, and ZmEXPB8) within the expanding shoots of the salt-resistant hybrid might contribute to a mechanism for improving wall extensibility under stress and thus might counteract growth reduction as occurs, for example, in the salt-sensitive hybrid. In favour of this assumption, transcripts of these wall-loosening factors were down-regulated in the size-reduced leaves of the salt-sensitive Lector hybrid. These genotypic differences are indicative of a role for these wall-loosening agents in processes related to salt-resistance. Genotypic-specific effects were also confirmed to occur on the proteome level: salinity did not affect the abundance of the vegetatively expressed β-expansins in the shoots of the salt-resistant SR03. However, β-expansin proteins were down-regulated in size-reduced shoots of the salt-sensitive cultivar. 2D-Western blotting revealed that one out of four isoform was down-regulated in size-reduced leaves of the salt-sensitive Lector. Growth might be reduced because salinity possibly impairs the synthesis of this growth-mediating enzyme. These genotypic differences are indicative of a role for the β-expansins in maintaining growth and thus of their contribution to salt resistance. After salt treatment, the apoplastic pH seemed to be differentially regulated between both hybrids. The leaf apoplast of the salt-resistant SR03 was acidified in response to salinity. The findings that (i) acidification of the leaf apoplast is a major requirement for increasing wall extensibility and that (ii) expansins are activated by an acidic pH, are both indicative that the observed acidification represents a mechanism possibly related to the maintenance of growth under saline conditions. In favour of this hypothesis, the leaf apoplast of the salt-sensitive Lector does not acidify but exhibits a strong reduction in its shoot growth. A comparative study of plants that differ in their degree of salt resistance revealed contrasting physiological features in terms of cell wall-associated agents that mediate growth. Wall-loosening agents were impaired in size-reduced leaves of the salt-sensitive hybrid but not in leaves of the salt-resistant hybrid that maintained growth. This physiological difference is indicative for a role of these wall-loosening agents for salt-resistance and thus may be used for screening for salt-resistant plants

Saving CO2 Emissions by Reusing Organic Growing Media from Hydroponic Tomato Production as a Source of Nutrients to Produce Ethiopian Kale (Brassica carinata)

Large quantities of growing media residues that are rich in nutrients are disposed of after their use in hydroponics. The objective of this study was to investigate the benefits of different organic growing media (wood fibers, hemp fibers, sphagnum moss) residues from hydroponic tomato production as a nutrient source to produce Ethiopian kale. The amount of nutrients that can be reused as fertilizer and the associated CO2 savings have been calculated. Kale was cultivated in sand-residue mixtures, either with 25 or 50 vol% of the mentioned growing media residues. Control treatments with sand with or without nutrient addition were cultivated too. The incorporation of all growing media residues to sand increased the field capacity and growth. Plants that were supplemented with hemp fiber residues showed the strongest growth and highest yields. However, the hemp fiber residues that are used are not suitable for use in the open field due to its excessive content of certain nutrients, which restrict the output quantity. Regarding the fertilization effect of growing media residues, it was calculated that 11–300 kg nutrients ha−1 (N, P, K, Mg, Ca, S), with an average primary energy demand of 90–3435 MJ and 6–317 kg CO2 eq, could potentially be saved when different crops were considered.Peer Reviewe

Inorganic carbon dynamics in coastal arctic sea ice and related air-ice CO2 exchanges

Arctic Ocean contributes to the global oceanic uptake of CO2 by about 5% to 14% in taking up from 66 to 199 TgC yr-1. However, the role of the marine cryosphere was ignored because it is considered as an impermeable barrier, impeding the gas exchanges between the ocean and the atmosphere [Bathes and Mathis, 2009]. However, a growing body of evidence suggests that gases exchange could occur between sea ice and the atmosphere. In this context, two arctic surveys were carried out in the framework of the International Polar Year (IPY). From there, we present a snapshot of the partial pressure of CO2 (pCO2) dynamics firstly during the initial sea ice growth and secondly from early spring to the beginning of the summer. We confirmed previous laboratory measurement findings that growing young sea ice acts as a source of CO2 to the atmosphere by measuring CO2 efflux from the ice (4 to 10 mmol m-2 d-1). We also confirmed the precipitation of calcium carbonate as ikaite in the frost flowers and throughout the ice and its negligible role on the effluxes of CO2. In early spring, supersaturations in CO2 up to 1834 µatm) were observed in sea ice as consequence of concentration of solutes in brines, CaCO3 precipitation and microbial respiration. As the summer draw near, brine shifts to a marked undersaturation (down to almost 0 µatm) because of the brine dilution by ice meltwater, dissolution of CaCO3 and photosynthesis during the sympagic algal bloom. Out of the winter, soon as the ice becomes permeable, CO2 fluxes were observed: (i) from the ice to the atmosphere, as the brine were supersaturated, (ii) from the atmosphere to the ice, as brine shift to an undersaturation. Temperature appears to be the main driver of the pCO2 dynamics within sea ice. It mainly controls the saturation state of the brine (where other processes may be added, e.g. CaCO3 precipitation, primary production) and thus, the concentration gradient of CO2 between sea ice and the atmosphere. It also controls the brine volume and so the brine connectivity, allowing the gas exchanges between sea ice and the atmosphere. We also present a new analytical method to measure the pCO2 of the bulk sea ice. This method, based on equilibration between an ice sample and a standard gas, was successfully applied on both artificial and natural sea ice. However, this method is only applicable for permeable sea ice (i.e., brine volume > 5% [Golden et al., 1998; 2007]) to allow the equilibration between the ice and the standard gas

Measuring CO2 in sea ice: caveats and improvements

info:eu-repo/semantics/publishe

CO2 and CH4 in sea ice from a subarctic fjord under influence of riverine input

We present the CH4 concentration [CH4], the partial pressure of CO2 (pCO2) and the total gas content in bulk sea ice from subarctic, land-fast sea ice in the Kapisillit fjord, Greenland. Fjord systems are characterized by freshwater runoff and riverine input and based on dδ18O data, we show that > 30% of the surface water originated from periodic river input during ice growth. This resulted in fresher sea-ice layers with higher gas content than is typical from marine sea ice. The bulk ice [CH4] ranged from 1.8 to 12.1 nmol Lg-1, which corresponds to a partial pressure ranging from 3 to 28 ppmv. This is markedly higher than the average atmospheric methane content of 1.9 ppmv. Evidently most of the trapped methane within the ice was contained inside bubbles, and only a minor portion was dissolved in the brines. The bulk ice pCO2 ranged from 60 to 330 ppmv indicating that sea ice at temperatures above -4 °C is undersaturated compared to the atmosphere (390 ppmv). This study adds to the few existing studies of CH4 and CO2 in sea ice, and we conclude that subarctic seawater can be a sink for atmospheric CO2, while being a net source of CH4