Silicon-mediated growth promotion in maize (Zea mays L.) occurs via a mechanism that does not involve activation of the plasma membrane H+-ATPase.

Silicon (Si)-mediated growth promotion of various grasses is well documented. In the present study, Si-induced changes in maize shoot growth and its underlying mechanisms were studied. Maize plants were grown with various concentrations of Si (0-3 mM) in the nutrient solution. Silicon nutrition improved plant expansion growth. Silicon-supplied maize plants (0.8 and 1.2 mM) showed higher plant height and leaf area compared to no-Si amended plants. It was assumed that Si-induced expansion growth was due to positive Si effects on plasma membrane (PM) H+-ATPase. In this context, western blot analysis revealed an increase in PM H+-ATPase abundance by 77% under Si nutrition. However, in vitro measurements of enzyme activities showed no significant effect on apoplast pH, proton pumping, passive H+ efflux and enzyme kinetics such as Km, Vmax, and activation energy. Further, these results were confirmed by in vivo ratiometric analysis of apoplastic pH, which showed non-significant changes upon Si supply. In contrast, 1 mM Si altered the relative transcripts of specific PM H+-ATPase isoforms. Silicon application resulted in a significant decrease of MHA3, and this decrease in transcription seems to be compensated by an increased concentration of H+-ATPase protein. From these results, it can be concluded that changes in cell wall composition and PM H+-ATPase may be responsible for Si-mediated growth improvement in maize.

Ethephon Activates the Transcription of Senescence-Associated Genes and Nitrogen Mobilization in Grapevine Leaves (Vitis vinifera cv. Riesling).

Nitrogen (N) remobilization in the context of leaf senescence is of considerable importance for the viability of perennial plants. In late-ripening crops, such as Vitis vinifera, it may also affect berry ripening and fruit quality. Numerous studies on the model plant Arabidopsis thaliana have confirmed an involvement of the plant hormone ethylene in the regulation of senescence. However, ethylene research on grapevine was mostly focused on its involvement in berry ripening and stress tolerance until now. To investigate the effect of ethylene on the initiation, regulation, and progress of senescence-dependent N mobilization in grapevine leaves, we treated field-grown Vitis vinifera cv. Riesling vines with 25 mM ethephon at the end of berry ripening. Ethephon induced premature chlorophyll degradation and caused a shift of the leaf transcriptome equivalent to developmental leaf senescence. The upregulated metabolic processes covered the entire N remobilization process chain, altered the amino acid composition in the leaves, and resulted in an average 60% decrease in leaf N. Our findings increase the fundamental knowledge about the initiation and manipulation of leaf N remobilization in perennial woody plants by ethephon. This offers a methodological approach to the targeted induction of senescence and thus to an improvement in the N supply of grapes.

Transcription profile analysis identifies marker genes to distinguish salt shock and salt stress after stepwise acclimation in Arabidopsis thaliana and Zea mays.

Many physiological and molecular responses to salt stress have been investigated after a salt shock. However, salt shock rarely happens in agricultural practice. In the field, salts accumulate gradually due to poor agricultural management. Thus in salinity research, it is more reasonable to investigate plant reaction after stepwise acclimation to salt stress. Previous studies demonstrate that salt shock induces Phase 0, a short-term effect that shows transient water loss and rapid turgor decrease; salt stress after stepwise acclimation avoids Phase 0 effects and induces Phase 1. During Phase 1, plants show maintenance of turgor. In this study, salt shock and stepwise acclimation to salt stress were separated at physiological and transcriptional levels. Four major experiments were conducted: 1) leaf turgor changes were monitored in real time after salt application to separate Phase 0 and Phase 1 effects at the physiological level, 2) RNA-sequence analysis was conducted in Arabidopsis thaliana L. to identify potential marker genes that are involved in plant water relations to distinguish Phase 0 and Phase 1 at transcript level, 3) these selected marker gene candidates were identified in Arabidopsis at different Phase 0 and Phase 1 time points via qRT-PCR, 4) these candidates were further evaluated in Zea mays L. (a model plant for applied research in plant physiology and an important crop plant) via qRT-PCR. In future salinity research, marker genes that are both applicable in Arabidopsis and maize have the potential to differentiate salt shock and stepwise acclimation to salt stress.

Para-crystalline membrane structures resembling prolamellar bodies in the invasion zones of indeterminate root nodules of Vicia faba L.

Novel para-crystalline structures resembling prolamellar bodies in etioplasts were found in the invasion zones of indeterminate root nodules of Vicia faba, which possess persistent meristems and exhibit sequential developmental stages. The para-crystalline structures existed in most cells in the area of the invasion zone and a hexagonal arrangement of tubular membranes was recognized. Extensive membranes, apparently procured from the structures, were often in contact with the bacteria in young infected cells. We propose that the para-crystalline structures serve as a reservoir of membranes for the formation of the numerous symbiosomes that propagate and fill the infected cells, and suggest naming them pro-symbiosome membrane bodies.

High­magnesium waters and soils: Emerging environmental and food security constraints.

Food insecurity and declining availability of freshwater and new productive land in water-scarce areas and countries necessitate effective use of marginal-quality waters and underperforming soils. High­magnesium waters and soils are emerging examples of water quality deterioration and land degradation leading to environmental and food security constraints in several irrigation schemes. A ratio of magnesium-to-calcium > 1 in irrigation waters and an exchangeable magnesium percentage > 25% in soils are considered high enough to result in soil degradation and impact crop yields negatively. These soil and water resources occur in the Aral Sea Basin in Central Asian countries, the Cauca River Valley in Colombia, the Central Plateau Basin in Iran, the Indus Basin in Pakistan, the Indo-Gangetic Plains in India, the Murray-Darling Basin in Australia, and the Coastal Mountain Range in California, among others. With limited and scattered information, their occurrence remains hidden or unnoticed in many cases due to the lack of criteria in water quality assessment and soil classification systems. Managing high­magnesium waters and soils requires a source of calcium to mitigate magnesium effects, in addition to an effective drainage system for safe disposal of excess magnesium salts. There is a need to put high­magnesium waters and soils on the public policy agenda. Pertinent policies can catalyze stakeholders' involvement in supporting water and land quality monitoring systems and introducing innovative financial mechanisms to facilitate provision of calcium-supplying amendments in affected areas. Equally important would be strengthening institutional and professionals' capacity, enhancing institutional collaboration, encouraging private sector involvement in at-risk areas, and engaging local communities and farmers. These efforts will support the 2030 Sustainable Development Agenda. Eradicating extreme poverty and meeting the Sustainable Development Goals in water-scarce areas without adequately addressing underperforming land and water resources is highly unlikely.

Multiple functions of caprylic acid-induced impurity precipitation for process intensification in monoclonal antibody purification.

New emerging technologies delivering benefits in terms of process robustness and economy are an inevitable prerequisite for monoclonal antibody purification processes intensification. Caprylic acid was proven as an effective precipitating agent enabling efficient precipitaton of product- and process-related impurities while leaving the antibody in solution. This purification step at mild acidic pH was therefore introduced in generic antibody platform approaches after Protein A capture and evaluated for its impact regarding process robustness and antibody stability. Comparison of 13 different monoclonal antibodies showed significant differences in antibody recovery between 65-95% during caprylic acid-induced impurity precipitation. Among six compared physicochemical properties, isoelectric point of the antibody domains was figured out to correlate with yield. Antibodies with mild acidic pI of the light chain were significantly susceptible to caprylic acid-induced precipitation resulting in lower yields. Virus clearance studies revealed that caprylic acid provided complete virus inactivation of an enveloped virus. Multiple process relevant factors such as pH range, caprylic acid concentration and antibody stability were investigated in this study to enable an intensified purification process including caprylic acid precipitation for HCP removal of up to 2 log10 reduction values at mAb yields >90% while also contributing to the virus safety of the process.

Potato plants (Solanum tuberosum L.) are chloride-sensitive: Is this dogma valid?

BACKGROUND: Chloride sensitivity of the potato (Solanum tuberosum L.) cultivars Marabel and Désirée was investigated in two pot experiments (soil/sand mixture and hydroponics). It was tested whether there are differential effects of KCl and K2 SO4 application on tuber yield and tuber quality, and whether both potato cultivars differ in their chloride sensitivity. RESULTS: Tuber yield, dry matter percentage of the tubers, starch concentration and starch yield were not significantly affected by potassium source (K2 SO4 or KCl). After exposure to salt stress in hydroponics (100 mmol L-1 NaCl, 50 mmol L-1 Na2 SO4 , 50 mmol L-1 CaCl2 ) for 5 days, 3-week-old potato plants had significantly reduced shoot dry mass after NaCl and Na2 SO4 application. However, CaCl2 treatment did not significantly affect shoot growth, although the chloride concentration reached 65 to 74 mg Cl- mg-1 dry matter, similar to the NaCl treatment. In contrast, growth reductions were closely related to sodium concentrations, thus plants suffered sodium toxicity and not chloride toxicity. CONCLUSION: Both potato cultivars are chloride-resistant and can be fertilised with KCl instead of K2 SO4 without the risk of depression in tuber yield or tuber quality. The statement that potatoes are chloride-sensitive and that chloride has negative effects on yield performance needs reconsideration. © 2017 Society of Chemical Industry.

Preisach models of hysteresis driven by Markovian input processes.

We study the response of Preisach models of hysteresis to stochastically fluctuating external fields. We perform numerical simulations, which indicate that analytical expressions derived previously for the autocorrelation functions and power spectral densities of the Preisach model with uncorrelated input, hold asymptotically also if the external field shows exponentially decaying correlations. As a consequence, the mechanisms causing long-term memory and 1/f noise in Preisach models with uncorrelated inputs still apply in the presence of fast decaying input correlations. We collect additional evidence for the importance of the effective Preisach density previously introduced even for Preisach models with correlated inputs. Additionally, we present some results for the output of the Preisach model with uncorrelated input using analytical methods. It is found, for instance, that in order to produce the same long-time tails in the output, the elementary hysteresis loops of large width need to have a higher weight for the generic Preisach model than for the symmetric Preisach model. Further, we find autocorrelation functions and power spectral densities to be monotonically decreasing independently of the choice of input and Preisach density.

In vitro protein synthesis of sugar beet (Beta vulgaris) and maize (Zea mays) is differentially inhibited when potassium is substituted by sodium.

The substitution of potassium ions (K+) by sodium ions (Na+) in the nutrition of plants is restricted. It was shown earlier that net protein synthesis is the process which is most sensitive to the substitution of K+ by Na+ in young sugar beet. We hypothesized that the activity of ribosomes is inhibited by the substitution. This hypothesis was tested in an in vitro approach. Cytosolic polysomes were isolated from growing leaves of sugar beet and maize by means of differential centrifugation. In vitro systems of both plant species were tested for functionality and comparability. Translation was quantified by the 35S-methionine incorporation in TCA-precipitable products. The effect of different substitution levels (0%, 20%, 40%, 60%, and 80% substitution of K+ by Na+) on in vitro translation was measured. Translation by polysomes of both plant species was significantly inhibited by the substitution. However, the translation by maize polysomes was more negatively affected by the substitution. A significant decrease in the translation by maize polysomes was observed already when 20% of K+ were replaced by Na+, whereas in the case of sugar beet, the translation was inhibited firstly at the substitution level of 40%. The in vitro results show that the process of translation itself is disturbed by the substitution and indicate a higher tolerance of sugar beet polysomes to increased Na+ concentrations and Na+/K+ ratios compared to polysomes of maize. We propose that this tolerance contributes to the salt resistance of sugar beet.

Salt stress reduces kernel number of corn by inhibiting plasma membrane H+-ATPase activity.

Salt stress affects yield formation of corn (Zea mays L.) at various physiological levels resulting in an overall grain yield decrease. In this study we investigated how salt stress affects kernel development of two corn cultivars (cvs. Pioneer 3906 and Fabregas) at and shortly after pollination. In an earlier study, we found an accumulation of hexoses in the kernel tissue. Therefore, it was hypothesized that hexose uptake into developing endosperm and embryo might be inhibited. Hexoses are transported into the developing endosperm by carriers localized in the plasma membrane (PM). The transport is driven by the pH gradient which is built up by the PM H+-ATPase. It was investigated whether the PM H+-ATPase activity in developing corn kernels was inhibited by salt stress, which would cause a lower pH gradient resulting in impaired hexose import and finally in kernel abortion. Corn grown under control and salt stress conditions was harvested 0 and 2 days after pollination (DAP). Under salt stress sucrose and hexose concentrations in kernel tissue were higher 0 and 2 DAP. Kernel PM H+-ATPase activity was not affected at 0 DAP, but it was reduced at 2 DAP. This is in agreement with the finding, that kernel growth and thus kernel setting was not affected in the salt stress treatment at pollination, but it was reduced 2 days later. It is concluded that inhibition of PM H+-ATPase under salt stress impaired the energization of hexose transporters into the cells, resulting in lower kernel growth and finally in kernel abortion.

Protein synthesis is the most sensitive process when potassium is substituted by sodium in the nutrition of sugar beet (Beta vulgaris).

Potassium ions (K(+)) and sodium ions (Na(+)) share many physical and chemical similarities. However, their interchangeability in plant nutrition is restricted. Substitution studies showed that K(+) can be replaced by Na(+) to a large extent in the nutrition of Beta vulgaris L. However, the extent of substitution without negative impacts is not unlimited. The aim of the present study was to identify the process which is most sensitive during the substitution of K(+) by Na(+) in nutrition of young sugar beet plants. We focused on transpiration, growth, and net protein synthesis. Plants were grown under controlled environmental conditions. With transfer of seedlings into nutrient solution, plants were cultivated in different substitution treatments. For all treatments the sum of K(+) and Na(+) (applied as chloride) was fixed to 4 mM. The extent of substitution of K(+) by Na(+) in the nutrient solution was varied from low (0.25% substitution: 3.99 mM K(+), 0.01 mM Na(+)) to almost complete substitution (99.75% substitution: 0.01 mM K(+), 3.99 mM Na(+)). The supply of 3.99 mM K(+) in 0.25% substitution treatment guaranteed the absence of K(+) deficiency. Transpiration was not affected by the substitution. Growth was inhibited at a substitution level of 99.75%. Net protein synthesis was already affected at a substitution level of 97.50% (0.10 mM K(+), 3.90 mM Na(+)). Hence, net protein synthesis was most sensitive to the substitution and limited the extent of substitution of K(+) by Na(+) in the nutrition of young sugar beet plants.

Accumulation potentials of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) in maize (Zea mays).

Uptake of perfluoroalkyl acids (PFAAs) by maize represents a potential source of exposure for humans, either directly or indirectly via feed for animals raised for human consumption. The aim of the following study was, therefore, to determine the accumulation potential of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) in maize (Zea mays). Two different concentrations of PFAAs were applied as aqueous solution to the soil to attain target concentrations of 0.25 mg or 1.00 mg of PFAA per kg of soil. Maize was grown in pots, and after harvesting, PFAA concentrations were measured in the straw and kernels of maize. PFCA and PFSA concentrations of straw decreased significantly with increasing chain length. In maize kernels, only PFCAs with a chain length ≤ C8 as well as perfluorobutanesulfonic acid (PFBS) were detected. The highest soil-to-plant transfer for both straw and kernels was determined for short-chained PFCAs and PFSAs.

Diferulic acids in the cell wall may contribute to the suppression of shoot growth in the first phase of salt stress in maize.

In the first phase of salt stress the elongation growth of maize shoots is severely affected. The fixation of shape at the end of the elongation phase in Poaceae leaves has frequently been attributed to the formation of phenolic cross-links in the cell wall. In the present work it was investigated whether this process is accelerated under salt stress in different maize hybrids. Plants were grown in nutrient solution in a growth chamber. Reduction of shoot fresh mass was 50% for two hybrids which have recently been developed for improved salt resistance (SR 03, SR 12) and 60% for their parental genotype (Pioneer 3906). For SR 12 and Pioneer 3906, the upper three leaves were divided into elongated and elongating tissue and cell walls were isolated from which phenolic substances and neutral sugars were determined. Furthermore, for the newly developed hybrids the activity of phenolic peroxidase in the cell wall was analysed in apoplastic washing fluids and after sequential extraction of cell-wall material with CaCl2 and LiCl. The concentration of ferulic acid, the predominant phenolic cross-linker in the grass cell wall, was about 5mgg(-1) dry cell wall in elongating and in elongated tissue. The concentration of diferulic acids (DFA) was 2-3mgg(-1) dry cell wall in both tissues. Salt stress increased the concentration of ferulic acid (FA) and DFA in the parental genotype Pioneer 3906, but not in SR 12. Both genotypes showed an increase in arabinose, which is the molecule at which FA and DFA are coupled to interlocking arabinoxylan polymers. In SR 12, the activity of phenolic peroxidase was not influenced by salt stress. However, in SR 03 salt stress clearly increased the phenolic peroxidase activity. Results are consistent with the hypothesis that accelerated oxidative fixation of shape contributes to growth suppression in the first phase of salt stress in a genotype-specific manner.

Effects of chain length and pH on the uptake and distribution of perfluoroalkyl substances in maize (Zea mays).

Maize is the most important grain crop grown for human nutrition, animal fodder and biogas production worldwide. Nonetheless, no systematic studies have been undertaken on these plants to examine the uptake mechanisms for perfluoroalkyl substances (PFASs) dependent upon chain length and pH value. The aim of the present study was therefore to determine the influence of chain length (C4 to C10) and pH value (pH 5, pH 6, pH 7) on the uptake and distribution of seven perfluoroalkyl carboxylic acids (PFCAs) and three perfluoroalkane sulfonic acids (PFSAs) by maize in nutrient solution experiments under controlled conditions in a climate chamber. A pH-dependent uptake was observed for perfluorodecanoic acid (PFDA) with an uptake rate of 2.51 µg g(-1) at pH 5 compared to 1.52 µg g(-1) root dry weight (DW) per day (d) at pH 7. Perfluorobutanoic acid (PFBA) had the highest uptake rate within the group of PFCAs with an average of 2.46 µg g(-1) root DWd(-1) and perfluorooctane sulfonic acid (PFOS) had the highest uptake rate (3.63 µg g(-1) root DWd(-1)) within the group of PFSAs. The shoot:root ratio for shorter-chain PFCAs (≤ C7) and PFBS (C4) was >2.0, which indicates that shorter-chain PFASs are transferred predominantly and at higher concentrations to the shoot. In contrast, long-chain PFCAs such as perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) as well as the PFASs perfluorohexane sulfonic acid (PFHxS) and perfluorooctane sulfonic acid (PFOS) accumulated at higher concentrations in the roots of maize plants with a shoot:root ratio of <1.0.

Modulatory ATP binding to the E2 state of maize plasma membrane H+-ATPase indicated by the kinetics of vanadate inhibition.

P-type ATPases, as major consumers of cellular ATP in eukaryotic cells, are characterized by the formation of a phosphorylated enzyme intermediate (E2P), a process that is allosterically coupled to translocation of cations against an electrochemical gradient. The catalytic cycle comprises binding of Mg-ATP at the nucleotide-binding domain, phosphorylation of the E1 state (E1), conformational transition to the E2P state, and dephosphorylation through the actuator domain and re-establishment of the E1 state. Recently, it has been suggested that, for several P-type ATPases, Mg-ATP binds to the phosphorylated enzyme, thereby accelerating the transition to the E1 state, before then becoming the enzyme's catalytic substrate. Here, we provide evidence supporting this viewpoint. We employed kinetic models based on steady-state kinetics in the presence and absence of the reversible inhibitor orthovanadate. Vanadate is generally considered to be a conformational probe that specifically binds to the E2 state, arresting the enzyme in a state analogous to the E2P state. Hydrolytic H(+) -ATPase activities were measured in inside-out plasma membrane vesicles isolated from roots and shoots of maize plants. For root enzymes, kinetic models of vanadate inhibition that allow simultaneous binding of Mg-ATP and vanadate to the same enzyme state were most plausible. For shoot enzymes, application of the competitive inhibitor Mg-free ATP attenuated vanadate inhibition, which is consistent with a model in which either Mg-free ATP or Mg-ATP is bound to the enzyme when vanadate binds. Therefore, data from roots and shoots indicate that binding of ATP species before transition to the E1 state plays an important role in the catalytic cycle of plant plasma membrane H(+) -ATPase.

Kinetics of carbon mineralization of biochars compared with wheat straw in three soils.

Application of biochars to soils may stabilize soil organic matter and sequester carbon (C). The objectives of our research were to study in vitro C mineralization kinetics of various biochars in comparison with wheat straw in three soils and to study their contribution to C stabilization. Three soils (Oxisol, Alfisol topsoil, and Alfisol subsoil) were incubated at 25°C with wheat straw, charcoal, hydrothermal carbonization coal (HTC), low-temperature conversion coal (LTC), and a control (natural organic matter). Carbon mineralization was analyzed by alkali absorption of CO released at regular intervals over 365 d. Soil samples taken after 5 and 365 d of incubation were analyzed for soluble organic C and inorganic N. Chemical characterization of biochars and straw for C and N bonds was performed with Fourier transformation spectroscopy and with the N fractionation method, respectively. The LTC treatment contained more N in the heterocyclic-bound N fraction as compared with the biochars and straw. Charcoal was highly carbonized when compared with the HTC and LTC. The results show higher C mineralization and a lower half-life of straw-C compared with biochars. Among biochars, HTC showed some C mineralization when compared with charcoal and LTC over 365 d. Carbon mineralization rates were different in the three soils. The half-life of charcoal-C was higher in the Oxisol than in the Alfisol topsoil and subsoil, possibly due to high Fe-oxides in the Oxisol. The LTC-C had a higher half-life, possibly due to N unavailability. We conclude that biochar stabilization can be influenced by soil type.

In vitro effect of different Na+/K+ ratios on plasma membrane H+ -ATPase activity in maize and sugar beet shoot.

Plant growth is impaired primarily by osmotic stress in the first phase of salt stress, whereas Na+ toxicity affects the plant growth mainly in the second phase. Salinity leads to increased Na+/K+ ratio and thus displacement of K+ by Na+ in the plant cell. Relatively higher cytosolic Na+ concentrations may have an effect on the activity of plasma membrane (PM) H+ -ATPase. A decreased PM-H+ -ATPase activity could increase the apoplastic pH. This process could limit the cell-wall extensibility and thus reduce growth according to the acid growth theory. To compare the effect of Na+ on PM H+ -ATPase activity in salt-sensitive maize (Zea mays L.) and salt-resistant sugar beet (Beta vulgaris L.) shoot, PM vesicles were isolated from growing shoots of both species and ATPase activity was determined by assaying the P(i) released by hydrolysis of ATP. The H+ pumping activity was measured as the quenching of acridine-orange absorbance. An increased Na+/K+ ratio decreased the PM H+ -ATPase activity in vesicles of maize as well as of sugar beet shoots. Nevertheless, the detrimental effect of increased Na+/K+ ratio was more severe in salt-sensitive maize compared to salt-resistant sugar beet. At 25 mM Na+ concentration, hydrolytic activity was not affected in sugar beet. However, a significant decrease in hydrolytic activity was observed in maize at pH 7. In maize and sugar beet, reduction in active H+ flux was 20% and 5% at 25 mM Na+ concentration in the assay, respectively. The active H+ flux was decreased to 80% and 60%, when 100 mM K+ were substituted by 100mM Na+. We conclude that PM H+ -ATPases of salt-resistant sugar beet and maize shoot are sensitive to higher concentration of Na+. However, sugar beet PM-H+ -ATPases are relatively efficient and may have constitutive resistance against lower concentration (25 mM) of Na+ as compared to that of salt-sensitive maize.

Changes in cytosolic Mg2+ levels can regulate the activity of the plasma membrane H+-ATPase in maize.

Plant PM (plasma membrane) H+-ATPase, a major consumer of cellular ATP, is driven by the MgATP complex which may dissociate at low cytosolic Mg2+ activity. We investigated whether hydrolytic activity of PM H+-ATPase is inhibited at ATP concentrations exceeding the Mg2+ concentration. Activity in isolated maize PMs was measured at pH 6.5 in the presence of 5 mM Mg2+ (high) or 2 mM Mg2+ (low), whereas K+ was applied at concentrations of 155 mM (high) or 55 mM (low). In all experiments, with membrane vesicles either from roots or leaves, the enzyme activity decreased in the presence of Mg2+-free ATP. At inhibitory ATP concentrations, the activity was not influenced by the K+ concentration. The activity was restored after increasing the Mg2+ concentration. ATP inhibition also occurred at pH 7.5. Kinetic modelling shows that Mg2+-free ATP acted as a competitive inhibitor with a Ki in the range of the Km. Ki decreased by 75% at low K+ concentration. Ki was one order of magnitude lower at pH 7.5 compared with pH 6.5. The observed inhibition is consistent with a concept in which down-regulation of the cytosolic Mg2+ activity is involved in (phyto)hormonal stress responses.

Proteome analysis of sugar beet (Beta vulgaris L.) elucidates constitutive adaptation during the first phase of salt stress.

Salinity is one of the major stress factors responsible for growth reduction of most of the higher plants. In this study, the effect of salt stress on protein pattern in shoots and roots of sugar beet (Beta vulgaris L.) was examined. Sugar beet plants were grown in hydroponics under control and 125 mM salt treatments. A significant growth reduction of shoots and roots was observed. The changes in protein expression, caused by salinity, were monitored using two-dimensional gel-electrophoresis. Most of the detected proteins in sugar beet showed stability under salt stress. The statistical analysis of detected proteins showed that the expression of only six proteins from shoots and three proteins from roots were significantly altered. At this stage, the significantly changed protein expressions we detected could not be attributed to sugar beet adaptation under salt stress. However, unchanged membrane bound proteins under salt stress did reveal the constitutive adaptation of sugar beet to salt stress at the plasma membrane level.

Hydrolytic and pumping activity of H+-ATPase from leaves of sugar beet (Beta vulgaris L.) as affected by salt stress.

Cell wall extensibility plays an important role in plant growth. According to the acid-growth theory, lower apoplastic pH allows extension growth by affecting cell wall extensibility. A lowered apoplastic pH is presumed to activate wall-loosening enzymes that control plant growth. Plasma membrane (PM) H(+)-ATPases play a major role in the apoplastic acidification by H(+) transport from cytosol to the apoplast. A salt-induced decrease in H(+)-pumping activity of plasma membrane H(+)-ATPases in salt-sensitive maize plants has previously been found. This led us to formulate the hypothesis that salt-resistant plant species such as sugar beet (Beta vulgaris L.) may have a mechanism to eliminate the effect of higher salt concentrations on plasma membrane H(+)-ATPase activity. In the present study, sugar beet plants were grown in 1mM NaCl (control) or 150 mM NaCl in hydroponics. H(+)-ATPase hydrolytic and pumping activities were measured in plasma membrane vesicles isolated from sugar beet shoots. We found that plasma membrane H(+)-ATPase hydrolytic and pumping activities were not affected by application of 150 mM NaCl. Moreover, apoplastic pH was also not affected under salt stress. However, a decrease in plant growth was observed. We assume that growth reduction was not due to a decrease in PM-H(+)-ATPase activity, but that other factors may be responsible for growth inhibition of sugar beet plants under salt stress.