Role of silicon in Plasmalemma H+-ATPase hydrolytic and pumping activity in maize (Zea mays L.)

Silicon is the second most abundant element in the earth crust and all plants grown in soil contain some amount of Si in their body. Despite of the ubiquitous nature of Si in soil-plant systems the essentiality of Si is not yet proven for higher plants. The beneficial effects of Si are more pronounced in plants grown under various biotic and abiotic stresses. Unfortunately, there is little evidence that Si application takes part in some of the physiological and biochemical processes in plants. Some earlier studies suggested that Si can increase the expansion growth in various plant species by changing the cell-wall extensibility in young growing shoot and root tissues. Moreover, some studies also suggested that Si uptake and translocation are energy requiring processes and may require a proton gradient. Plasma membrane H+-ATPase is a master enzyme and it extrudes H+ out of the cytosol and creates an electrochemical H+ gradient. The plasma membrane H+-ATPase generated H+ gradient is responsible for cell wall extensibility and expansion growth. Moreover, the electrochemical H+ gradient energizes various proteins involved in nutrient and solute uptake and translocation. Although few attempts have been made to elucidate the role of Si in plant growth and cell-wall extensibility, mechanisms lying behind are not fully understood. Therefore, it was assumed that Si-enhanced plant growth and uptake and translocation of Si from nutrient solution may require increased plasma membrane H+-ATPase activity. To determine the effect of Si nutrition on maize growth and its relationship with the plasma membrane H+-ATPase regulation the following hypotheses were tested: (1) Exogenously supplied Si in nutrient solution improves maize (Zea mays L cv. Amadeo) growth under normal growth conditions (2) Changes in plasma membrane H+-ATPase are responsible for the Si-induced maize growth (3) Silicon-nutrition increases maize shoot growth by inducing the apoplast acidification. The results are summarized as: 1. Silicon application in nutrient solution increased maize growth at all concentrations. The maximum increase in plant growth attributes was observed at 0.8 - 1.2 mM Si in nutrient solution. Furthermore, the results showed that Si nutrition had a balancing effect on other mineral nutrients in maize plants. Silicon application in nutrient solution changed the concentrations of different cations in maize roots and shoots tissues especially Ca, Zn, Mn, and Fe. 2. Silicon nutrition changed the plasma membrane H+-ATPase characteristics that were: (I) Plasma membrane vesicles isolated from Si-treated shoots had 77% more enzyme protein. (II) The plasma membrane H+-ATPase isolated from Si-treated maize shoots showed inhibited hydrolytic and pumping activities by Si addition in the assay medium in comparison to the vesicles isolated from plants grown without Si. (III) Silicon nutrition induced differential transcription of plasma membrane H+-ATPase isforms. The plants supplied with Si had reduced MHA3 and MHAfam transcription. (IV) Similar to the shoots, Si nutrition brought some changes in the characteristics of plasma membrane H+-ATPase in roots as well. The addition of 1 mM Si in the assay medium significantly reduced the hydrolytic activity of plasma membrane H+-ATPase isolated from plants supplied with Si in nutrient solution. 3. Silicon-induced expansion growth in maize shoot showed no correlation with apoplastic pH. The plants grown with and without 1 mM Si supply in nutrient solution had a comparable value for their in vivo-measured apoplastic pH. Therefore, it is assumed that the Si-mediated increased shoot growth was due to unknown factors other than apoplastic pH.Silicium ist das zweithäufigste chemische Element der Erdkruste und somit ubiquitär im Boden vorhanden. Obwohl sich in allen im Boden wachsenden Pflanzen Si wiederfindet, konnte bisher nicht nachgewiesen werden, inwieweit Si als Nährstoff für die Pflanze essentiell ist. Vor allem unter biotischem und abiotischem Stress aber wird ein positiver Effekt einer Si-Ernährung auf das Pflanzenwachstum festgestellt. Leider gibt es aber bis heute kaum Belege dafür, dass Si an physiologischen und biochemischen Prozessen in der Pflanze beteiligt ist. Jedoch wurde in früheren Studien vorgeschlagen, dass Si das Streckungswachstum verschiedener Pflanzenarten verbessern kann, indem es die Zellwandextensibilität des jungen Spross- und Wurzelgewebes verändert. Darüber hinaus wird angenommen, dass sowohl die Aufnahme als auch die Translokation von Si Energie benötigt und durch einen Protonengradient angetrieben wird. Das Masterenzym, welches Protonen aus dem Cytosol der Zelle in die Zellwand pumpt und auf diese Weise einen elektrochemischen Protonengradient aufbaut, ist die Plasmalemma-H+-ATPase. Der durch dieses Enzym generierte Protonengradient ist verantwortlich für die Zellwandextensibilität und das Streckungswachstum bei Pflanzen. Des Weiteren werden durch den Aufbau des elektrochemischen Protonengradienten verschiedene Proteine aktiviert, welche beispielsweise für die Aufnahme und Translokation von Pflanzennährstoffen notwendig sind. Obwohl über die Jahre bereits zahlreiche Versuche unternommen wurden, die Rolle von Si bei Pflanzenwachstum und Zellwandextensibilität zu beschreiben, sind die zugrunde liegenden Mechanismen bis heute nicht aufgeklärt. Vor diesem Hintergrund wurde in dieser Arbeit angenommen, dass das durch Si-verbesserte Pflanzenwachstum, sowie die Aufnahme und Translokation von Si aus dem Nährmedium in die Pflanze auf eine erhöhte Aktivität der Plasmalemma-H+-ATPase zurückgeht. Um den Einfluss von Si auf das Wachstum von Mais unter Berücksichtigung einer möglichen Regulation der Plasmalemma-H+-ATPase zu untersuchen, wurden folgende Hypothesen aufgestellt: (1) Exogen appliziertes Si in der Nährlösung verbessert das Wachstum von Mais (Zea mays L.) unter normalen Wachstumsbedingungen. (2) Änderungen in der Aktivität der Plasmalemma-H+-ATPase sind verantwortlich für das durch Si-induzierte Wachstum von Mais. (3) Si-Ernährung verbessert das Sprosswachstum von Mais durch eine gesteigerte Zellwandansäuerung. Die aus dieser Arbeit gewonnenen Ergebnisse lassen sich wie folgt zusammenfassen: 1. Die Applikation von Si zur Nährlösung verbessert das Wachstum von Mais unter allen angebotenen Si-Konzentrationen. Hierbei wurde der größte Wachstumszuwachs bei Si-Konzentrationen in der Nährlösung von 0,8 bis 1,2 mM festgestellt. Darüber hinaus zeigte sich, dass in Mais eine Si-Ernährung förderlich für das Gleichgewicht anderer Pflanzennährstoffe ist. So wurden durch die Zugabe von Si die Konzentrationen verschiedener Kationen wie Ca, Zn, Mn und Fe in Spross und Wurzel von Mais verändert. 2. Die Ernährung der Pflanze mit zusätzlichem Si veränderte auch die Eigenschaften der Plasmalemma-H+-ATPase: (I) Aus dem Spross Si-ernährter Pflanzen isolierte Plasmamembran-Vesikel zeigten eine um 77% gesteigerte Proteinmenge. (II) Die Plasmalemma-H+-ATPase Si-behandelter Pflanzen zeigte im Vergleich zu unbehandelten Pflanzen eine gehemmte hydrolytische und Pumpaktivität nach Zugabe von Si zum Analysemedium. (III) Die Zugabe von Si zum Nährmedium führte zu einer veränderten Transkription verschiedener Plasmalemma-H+-ATPase-Isoformen. Insbesondere die Transkription der Isoformen MHA3 und MHAfam war unter Si-Einfluss reduziert. (IV) Ähnlich wie im Spross, resultierte die Zugabe von 1 mM Si zum Analysemedium in einer signifikanten Abnahme der hydrolytischen Aktivität der Plasmalemma-H+-ATPase in der Wurzel Si-behandelter Maispflanzen. 3. Das durch Si verbesserte Streckungswachstum des Maissprosses ist nicht auf eine verbesserte Zellwandansäuerung zurückzuführen. Sowohl Si-behandelte als auch unbehandelte Maispflanzen zeigten nach in vivo-Messung einen vergleichbaren apoplastischen pH. Hieraus kann abgeleitet werden, dass das durch Si verbesserte Sprosswachstum durch andere, noch unbekannte Faktoren bedingt wird

Biosorption potential of natural, pyrolysed and acid-assisted pyrolysed sugarcane bagasse for the removal of lead from contaminated water

Lead (Pb) is a ubiquitous pollutant which poses serious threats to plants, animals and humans once entered into the food chain via contaminated industrial effluents on their discharge into the surface of water bodies and/or geological materials. This study aimed to examine and compare the biosorption potential of natural sugarcane bagasse (NB), pyrolysed sugarcane bagasse (PB) and acid assisted pyrolysed sugarcane bagasse (APB) for the removal of Pb from contaminated water. To explore this objective, a series of batch experiments were conducted at various adsorbent mass (0.25, 0.5, 0.75, 1.0 g per 100 ml contaminated water), initial Pb concentration (7, 15, 30, 60 and 120 ppm), and contact time (7, 15, 30, 60 and 120 min). Results revealed that all the tested bio-sorbents have potential to adsorb and remove Pb ions from the contaminated water. In this regard, APB proved more effective since it removed 98% of Pb from aqueous solution at initial Pb concentration of 7 ppm and mass of 0.25 g per 100 ml of aqueous solution. The respective values in case of NB and PB were 90 and 95%. For a given adsorbent type, Pb adsorption decreased by increasing the mass from 0.25 to 1.0 g per 100 ml of aqueous solution. However, the greatest Pb removal occurred at adsorbent mass of 1.0 g per 100 ml of aqueous solution. Initial Pb concentration had a great impact on Pb adsorption and removal by adsorbent. The former increased and the latter decreased with the increase in initial Pb concentration from seven to 120 ppm. At seven ppm Pb concentration, maximum Pb removal took place irrespective to the adsorbent type. Out of the total Pb adsorption and removal, maximum contribution occurred within 15 min of contact time between the adsorbate and adsorbent, which slightly increased till 30 min, thereafter, it reached to equilibrium. Application of equilibrium isotherm models revealed that our results were better fitted with Freundlich adsorption isotherm model. Overall, and for the reasons detailed above, it is concluded that sugarcane bagasse has capabilities to adsorb and remove Pb ions from contaminated water. Its bio-sorption potential was considerably increased after pyrolysis and acid treatment

Optimal level of silicon for maize (Zea mays L. c.v. AMADEO) growth in nutrient solution under controlled conditions.

Silicon (Si) is the second most abundant element in the earth's crust and plants vary in their response to Si. In order to investigate the effect of Si as Na2SiO3 fertilization on maize hybrid AMADEO growth in hydroponics, two experiments were conducted. In the first experiment, plants were supplied with two levels of Si; control (0 mM Si) and +Si (3 mM Si). In the second experiment, plants were supplied with a wide range of Si concentrations in nutrient solution in seven treatments (0, 0.4, 0.8, 1.2, 1.6, 2.0 and 3.0 mM Si). In the first experiment, no significant differences were observed in shoot and root biomass but reduced leaf area was observed after Si application. In the second experiment, plants supplied with 0.8 and 1.2 mM Si produced a significantly higher amount of fresh and dry biomass and also increased plant height and leaf area of youngest and fully developed young leaf. It is concluded that 1 mM Si represents an optimum concentration for maize nutrition in hydroponics

Optimal level of silicon for maize (Zea mays L. c.v. AMADEO) growth in nutrient solution under controlled conditions.

Silicon (Si) is the second most abundant element in the earth's crust and plants vary in their response to Si. In order to investigate the effect of Si as Na2SiO3 fertilization on maize hybrid AMADEO growth in hydroponics, two experiments were conducted. In the first experiment, plants were supplied with two levels of Si; control (0 mM Si) and +Si (3 mM Si). In the second experiment, plants were supplied with a wide range of Si concentrations in nutrient solution in seven treatments (0, 0.4, 0.8, 1.2, 1.6, 2.0 and 3.0 mM Si). In the first experiment, no significant differences were observed in shoot and root biomass but reduced leaf area was observed after Si application. In the second experiment, plants supplied with 0.8 and 1.2 mM Si produced a significantly higher amount of fresh and dry biomass and also increased plant height and leaf area of youngest and fully developed young leaf. It is concluded that 1 mM Si represents an optimum concentration for maize nutrition in hydroponics

Protective Role of Silicon (Si) Against Combined Stress of Salinity and Boron (B) Toxicity by Improving Antioxidant Enzymes Activity in Rice

Farooq MA, Saqib ZA, Akhtar J, Bakhat HF, Pasala R-K, Dietz K-J. Protective Role of Silicon (Si) Against Combined Stress of Salinity and Boron (B) Toxicity by Improving Antioxidant Enzymes Activity in Rice. SILICON. 2019;11(4):2193-2197.The beneficial element silicon (Si) is known to enhance plant tolerance against various kinds of biotic and abiotic stresses. However, little is known about its protective role for plants facing multiple stresses such as salinity and boron (B) toxicity. Therefore, the current study was planned in pots to evaluate the beneficial role of exogenous applied Si (150 mg kg(-1)) nutrition against salinity stress (10 dS m(-1)), and B toxicity (2.5 mg kg(-1)) alone or in combinations. Results showed that both salinity and B toxicity reduced plant growth and biomass of rice, with maximum damage under their combined stress due to increased uptake of toxic ions such as sodium (Na+) and B. Contrarily, Si application helped the plants to overcome negative effects of these toxic ions by increasing silica and K+ uptake and decreasing Na+ and B entry in plants that ultimately lead to improvement in plant biomass. High silica uptake ability of rice significantly improved the efficiency of antioxidant mechanism, as indicated by reduced catalase (CAT) activity and improvement in guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activity by Si application under stress, resulting in reduced oxidative damage. From this study, we conclude that Si fertilization can enhance crop production in salt affected soils by helping plant defenses against salts as well as associated B toxicities; however, field trials should be carried out before setting any recommendations for farmers

Managing Tillage Operation and Manure to Restore Soil Carbon Stocks in Wheat-Maize Cropping System

Increasing soil organic matter (SOM) contents improve the resilience of productive soil for future sustainability particularly in poor soil (<1% SOM). This study sought to elucidate how tillage and N fertilizer sources affect soil bulk density, soil organic carbon (SOC) and soil total N (TN) in 0- to 20-cm soil depth. Treatments included minimum till (MT), conventional till (CT), deep till (DT), and twelve N treatments (60 and 120 kg urea N ha(-1), 10 and 20 Mg farmyard manure [FYM] ha(-1), 10 Mg soybean residue [SR] ha(-1) and their combinations along with a control). The experiment was designed in randomized complete block design with split plot arrangement. Soil bulk density increased for DT toward the end of the experiment than CT or MT. The sequestration rates of SOC of MT was 22% higher than DT. The FYM retuned more SOC than SR, however SR returned more TN than FYM. Application of FYM as well as SR sequestered more C than urea or control. Conclusively, SOC returned was increased with 10 Mg FYM ha(-1) along with 30 kg urea N ha(-1) but TN with 10 Mg SR ha(-1) in CT plots. This practice can therefore increase soil quality and productivity, and thus is considered a sustainable approach for soils deficient in organic matter

Zinc in soil-plant-human system: A data-analysis review

Zinc (Zn) plays an important role in the physiology and biochemistry of plants due to its established essentiality and toxicity for living beings at certain Zn concentration i.e., deficient or toxic over the optimum range. Being a vital cofactor of important enzymes, Zn participates in plant metabolic processes therefore, alters the biophysicochemical processes mediated by Zn-related enzymes/proteins. Excess Zn can provoke oxidative damage by enhancing the levels of reactive radicals. Hence, it is imperative to monitor Zn levels and associated biophysicochemical roles, essential or toxic, in the soil-plant interactions. This data-analysis review has critically summarized the recent literature of (i) Zn mobility/phytoavailability in soil (ii) molecular understanding of Zn phytouptake, (iii) uptake and distribution in the plants, (iv) essential roles in plants, (v) phyto-deficiency and phytotoxicity, (vi) detoxification processes to scavenge Zn phytotoxicity inside plants, and (vii) associated health hazards. The review especially compares the essential, deficient and toxic roles of Zn in biophysicochemical and detoxification processes inside the plants. To conclude, this review recommends some Zn-related research perspectives. Overall, this review reveals a thorough representation of Zn bio-geo-physicochemical interactions in soil-plant system using recent data

Evaluation and analysis of temperature for historical (1996-2015) and projected (2030-2060) climates in Pakistan using SimCLIM climate model: ensemble application

Climate change is a global issue that's affecting food security. An increase and decrease in temperature due to climate change is expected across many regions of the world. Analysis of 39 weather stations (Pakistan) trend for maximum and minimum temperatures was done on monthly, seasonal and annual observations. Two statistical tests (Sen's slope and Mann-Kendall) were applied to find out the slopes and magnitude of climate change trend. This statistical analysis was carried out to study the possible variations for maximum and minimum temperature trend. A statistical downscaling climate projection model (SimCLIM) was used to predict magnitude of maximum and minimum temperature for 2030 and 2060. Ensemble of 40 General Circulation Models (GCMs) was used with median Representative Concentration Pathway (RCP-6.0) for future projections in SimCLIM. This study showed more number of positive trends for maximum temperature over all the weather stations. Significantly positive temperature trend was observed in February and March for maximum temperature for all sites ranges from 0.06 to 0.51 degrees C. Mostly, statistically significant negative trend (-0.06 to -0.30 degrees C) was found in Balochistan province and northern areas of Pakistan. In future, minimum temperature projected by model showed negative trends for 60% of weather sites for December where, the negative trend also increased for monthly and seasonal analysis. Minimum temperature trend reveal that December has large number of sites with negative trends with high magnitude, which further decreased for annual followed by seasonal analysis. Minimum temperature projections showed similar trends with past December results but negative trends decreased for seasonal and annual resolution. Future projections also reveal that annual maximum and minimum temperature will be increased for 2060 as compared to 2030. These results may have significant effect on agriculture of northern and high mountain areas of Pakistan, which could be managed by sustainable agricultural activities