Hans-Werner Koyro

Compartmental nitrate concentrations in barley root cells measured with nitrate-selective microelectrodes and by single-cell sap sampling

Nitrate-selective microelectrodes were used to measure intracellular nitrate concentrations (as activities) in epidermal and cortical cells of roots of 5-d-old barley (Hordeum vulgare L.) seedlings grown in nutrient solution containing 10 mol · m−3 nitrate. Measurements in each cell type grouped into two populations with mean (±SE) values of 5.4 ± 0.5 mol · m−3 (n=19) and 41.8 ± 2.6 mol · m−3 (n = 35) in epidermal cells, and 3.2 ± 1.2 mol · m−3 (n = 4) and 72.8 ± 8.4 mol · m−3 (n = 13) in cortical cells. These could represent the cytoplasmic and vacuolar nitrate concentrations, respectively, in each cell type. To test this hypothesis, a single-cell sampling procedure was used to withdraw a vacuolar sap sample from individual epidermal and cortical cells. Measurement of the nitrate concentration in these samples by a fluorometric nitrate-reductase assay confirmed a mean vacuolar nitrate concentration of 52.6 ± 5.3 mol · m−3 (n = 10) in epidermal cells and 101.2 ± 4.8 mol · m−3 (n = 44) in cortical cells. The nitrate-reductase assay gave only a single population of measurements in each cell type, supporting the hypothesis that the higher of the two populations of electrode measurements in each cell type are vacuolar in origin. Differences in the absolute values obtained by these methods are probably related to the fact that the nitrate electrodes were calibrated against nitrate activity but the enzymic assay against concentration. Furthermore, a 28-h time course for the accumulation of nitrate measured with electrodes in epidermal cells showed the apparent cytoplasmic measurements remained constant at 5.0 ± 0.7 mol · m−3, while the vacuole accumulated nitrate to 30–50 mol · m−3. The implications of the data for mechanisms of nitrate transport at the plasma membrane and tonoplast are discussed.

Plant growth improvement mediated by nitrate capture in co-composted biochar

Soil amendment with pyrogenic carbon (biochar) is discussed as strategy to improve soil fertility to enable economic plus environmental benefits. In temperate soils, however, the use of pure biochar mostly has moderately-negative to -positive yield effects. Here we demonstrate that co-composting considerably promoted biochars’ positive effects, largely by nitrate (nutrient) capture and delivery. In a full-factorial growth study with Chenopodium quinoa, biomass yield increased up to 305% in a sandy-poor soil amended with 2% (w/w) co-composted biochar (BCcomp). Conversely, addition of 2% (w/w) untreated biochar (BCpure) decreased the biomass to 60% of the control. Growth-promoting (BCcomp) as well as growth-reducing (BCpure) effects were more pronounced at lower nutrient-supply levels. Electro-ultra filtration and sequential biochar-particle washing revealed that co-composted biochar was nutrient-enriched, particularly with the anions nitrate and phosphate. The captured nitrate in BCcomp was (1) only partly detectable with standard methods, (2) largely protected against leaching, (3) partly plant-available, and (4) did not stimulate N2O emissions. We hypothesize that surface ageing plus non-conventional ion-water bonding in micro- and nano-pores promoted nitrate capture in biochar particles. Amending (N-rich) bio-waste with biochar may enhance its agronomic value and reduce nutrient losses from bio-wastes and agricultural soils.

Elevated atmospheric CO2 concentration ameliorates effects of NaCl salinity on photosynthesis and leaf structure of Aster tripolium L.

This study investigated the interaction of NaCl-salinity and elevated atmospheric CO2 concentration on gas exchange, leaf pigment composition, and leaf ultrastructure of the potential cash crop halophyte Aster tripolium. The plants were irrigated with five different salinity levels (0, 25, 50, 75, 100% seawater salinity) under ambient and elevated (520 ppm) CO2. Under saline conditions (ambient CO2) stomatal and mesophyll resistance increased, leading to a significant decrease in photosynthesis and water use efficiency (WUE) and to an increase in oxidative stress. The latter was indicated by dilations of the thylakoid membranes and an increase in superoxide dismutase (SOD) activity. Oxidative stress could be counteracted by thicker epidermal cell walls of the leaves, a thicker cuticle, a reduced chlorophyll content, an increase in the chlorophyll a/b ratio and a transient decline of the photosynthetic efficiency. Elevated CO2 led to a significant increase in photosynthesis and WUE. The improved water and energy supply was used to increase the investment in mechanisms reducing water loss and oxidative stress (thicker cell walls and cuticles, a higher chlorophyll and carotenoid content, higher SOD activity), resulting in more intact thylakoids. As these mechanisms can improve survival under salinity, A. tripolium seems to be a promising cash crop halophyte which can help in desalinizing and reclaiming degraded land.

Effect of salinity on composition, viability and germination of seeds of Chenopodium quinoa Willd

Salinity influences plant growth, seed yield and seed quality even of halophytic crops such as Chenopodium quinoa. Plant growth, total seed yield, number of seeds, fresh weight and dry weight of seeds, were all significantly reduced in the presence of salinity. Only at high salinity did the content of proteins (as well as total N) increase significantly in the seeds whereas the content of total carbohydrates (as well as total C) decrease. Aside from that the capacity for germination was diminished by a reduced seed size and a disproportionate reduction of the volume of the perisperm. However, the reduced capacity seemed to be compensated by an accelerated germination owing to high Na and Cl concentrations leading to a low water potential in the walls of the plant ovary. At high salinity the passage of NaCl to the seed interior was hindered by the seed cover. There was an obvious gradient between potentially toxic (Na and Cl) and essentially needed elements (K, Mg, Ca, P and S) across the seed coat of salt treated plants and also a significant change of the distribution of elements in the embryo. The results indicate a highly protected seed interior leading to a high salinity resistance of quinoa seeds.

Abiotic Stress Responses in Plants: An Overview

Plants are more and more affected by environmental stresses, especially by the devastating consequences of desertification and water scarcity which can be seen and felt all over the world. About 3.6 billion of the world’s 5.2 billion hectares of dryland used for agriculture have already suffered erosion, soil degradation, and salinization. Desertification can hinder efforts for sustainable development and introduces new threats to human health, ecosystems, and national economies. This problem is catalyzed by global climate change which exacerbates desertification and salinization. Therefore, solutions are desperately needed, such as the improvement of drought and salinity tolerance of crops, which in turn requires a detailed knowledge about tolerance mechanisms in plants. These mechanisms comprise a wide range of responses on molecular, cellular, and whole plant levels, which include amongst others the synthesis of compatible solutes/osmolytes and radical scavenging mechanisms. Regarding global change, elevated atmospheric CO2 concentrations can enhance salt and drought tolerance because oxidative stress is alleviated and more energy can be provided for energy-dependent tolerance mechanisms such as the synthesis of compatible solutes and antioxidants, thus increasing the suitability of plants as crops in future. A detailed knowledge of the physiological and biochemical basis of drought and salt tolerance and its interaction with elevated CO2 concentration can provide a basis for the cultivation of suitable plants in regions threatened by desertification and water scarcity under sustainable culture conditions. Even the drylands could offer tangible economic and ecological opportunities.

Relationship between the photosynthetic activity and the performance of Cakile maritima after long‐term salt treatment

Cakile maritima is a halophyte with potential for ecological, economical and medicinal uses. We address here the impact of salinity on its growth, photosynthesis and seed quality. Whole plant growth rate and shoot development were stimulated at moderate salinity (100-200 mM NaCl) and inhibited at higher salt concentrations. Although diminished in the presence of salt, potassium and calcium uptake per unit of root biomass was maintained at relatively high value, while nutrient-use efficiency (NUE) was improved in salt-treated plants. Chl and carotenoid concentrations decreased at extreme salinities, but anthocyanin concentration continuously grew with salinity. Net photosynthetic rate (A), stomatal conductance, maximum quantum efficiency of PSII and quantum yield were stimulated in the 100-200 mM NaCl range. Higher salinity adversely affected gas exchange and changed PSII functional characteristics, resulting in a reduction of A per leaf area unit. This phenomenon was associated with increased non-photochemical quenching. Harvest index, silique number and seeds per fruit valve were maximal at 100 mM NaCl. Despite the decreasing salt accumulation gradient from the vegetative to the reproductive organs, high salinities were detrimental for the seed viability and increased the proportion of empty siliques. Overall, the salt-induced changes in the plant photosynthetic activity resulted into analogous responses at the vegetative and reproductive stages. The enhancement of NUE, the absence of pigment degradation, the reduction of water loss and the concomitant PSII protection from photodamage through thermal dissipation of excess excitation significantly accounted for Cakile survival capacity at high salinity.

Phytodesalination of a salt-affected soil with the halophyte Sesuvium portulacastrum L. to arrange in advance the requirements for the successful growth of a glycophytic crop.

In the present work, we studied the potential of the obligate halophyte, Sesuvium portulacastrum L., to desalinize an experimentally-salinized soil after the following criteria: (i) decrease in soil salinity and sodicity, (ii) plant biomass capacity to accumulate sodium ions, and (iii) phytodesalinized soil quality (equivalent to growth of a glycophytic test culture of Hordeum vulgare L.). The cultivation of the halophyte on the salinized soil (phytodesalination culture) led to a marked absorption of Na(+) ions by S. portulacastrum roots and their accumulation in the above-ground biomass up to 872 mg plant(-1) and 4.36 g pot(-1) (about 1 tha(-1)). The decrease in salinity and sodicity of the phytodesalinized soil significantly reduced the negative effects on growth of the test culture of H. vulgare. Furthermore, the phytodesalination enabled H. vulgare plants to keep a high water content and to develop a higher biomass with relatively high K and low Na contents.

Biochar reduces copper toxicity in Chenopodium quinoa Willd. In a sandy soil.

Mining, smelting, land applications of sewage sludge, the use of fungicides containing copper (Cu), and other human activities have led to widespread soil enrichment and contamination with Cu and potentially toxic conditions. Biochar (BC) can adsorb several substances, ranging from herbicides to plant-inhibiting allelochemicals. However, the range of potential beneficial effects on early-stage plant growth with regard to heavy metal toxicity is largely unexplored. We investigated the ameliorating properties of a forestry-residue BC under Cu toxicity conditions on early plant growth. Young quinoa plants () were grown in the greenhouse in the presence of 0, 2, and 4% BC application (w/w) added to a sandy soil with 0, 50, or 200 μg g Cu supplied. The plants without BC showed severe stress symptoms and reduced growth shortly after Cu application of 50 μg g and died at 200 μg Cu g. Increasing BC concentrations in the growth medium significantly increased the plant performance without Cu toxicity or under Cu stress. At the 4% BC application rate, the plants with 200 μg g Cu almost reached the same biomass as in the control treatment. In the presence of BC, less Cu entered the plant tissues, which had reduced Cu concentrations in the order roots, shoots, leaves. The amelioration effect also was reflected in the plant-soil system CO gas exchange, which showed clear signs of improvement with BC presence. The most likely ameliorating mechanisms were adsorption of Cu to negatively charged BC surfaces and an improvement of the water supply. Overall, BC seems to be a beneficial amendment with the potential to ameliorate Cu toxicity in sandy soils. Further research with a broad spectrum of different soil types, BCs, and crop plants is required.

Functional structure of the indeterminate Vicia faba L. root nodule: implications for metabolite transport

Summary The structure of N 2 -fixing nodules of faba bean ( Vicia faba L.) was investigated by means of light and electron microscopy to determine possible pathways for metabolite movement. The central infected zone is enclosed by a cortex, which is composed of a loosely arranged outer part and a densely packed inner part. Both are separated by the nodule endodermis, which borders on the root endodermis and continuously envelopes the entire nodule interior, with the exception of the apical meristematic region. Vascular bundles, located peripherally within the inner cortex, are surrounded by another endodermal layer. Radial cell walls of both nodule and vascular endodermis are incrusted and form Casparian bands. Additionally, all endodermal cells are coated by suberin lamellae. These modifications may prevent an apoplastic loss of solutes from the enclosed tissues, and require a symplastic metabolite passage. This is supported by high plasmodesmatal frequencies found between vascular endodermis and inner cortex. Within vascular bundles, transfer cells adjacent to xylem elements may play a role in xylem loading. The central infected tissue contains uninfected cells, possibly representing a symplastic continuity. These cells may form a preferred metabolite pathway since plasmodesmata are extremely sparse between infected cells. The low number of uninfected cells in the central tissue of V. faba nodules favors an additional apoplastic pathway.

Proteomic and physiological responses of the halophyte Cakile maritima to moderate salinity at the germinative and vegetative stages.

Responses of the halophyte Cakile maritima to moderate salinity were addressed at germination and vegetative stages by bringing together proteomics and eco-physiological approaches. 75 mM NaCl-salinity delayed significantly the germination process and decreased slightly the seed germination percentage compared to salt-free conditions. Monitoring the proteome profile between 0 h and 120 h after seed sowing revealed a delay in the degradation of seed storage proteins when germination took place under salinity, which may explain the slower germination rate observed. Of the sixty-seven proteins identified by mass spectrometry, several proteins involved in glycolysis, amino acid metabolism, photosynthesis, and protein folding showed significantly increased abundance during germination. This pattern was less pronounced under salinity. At the vegetative stage, 100mM NaCl-salinity stimulated significantly the plant growth, which was sustained by enhanced leaf expansion, water content, and photosynthetic activity. Comparative proteome analyses of leaf tissue revealed 44 proteins with different abundance changes, most of which being involved in energy metabolism. A specific set of proteins predominantly involved in photosynthesis and respiration showed significantly higher abundance in salt-treated plants. Altogether, combining proteomics with eco-physiological tools provides valuable information, which contributes to improve our understanding in the salt-response of this halophyte during its life cycle.