Aluminum Stress Research Articles

Morphological characterization of sorghum lines with aluminium stress and phosphorus deficiency tolerance

Sorghum has a good adaptation in marginal land, such as acid soil. The development of acid soil tolerant variety was directed to combine with Al stress and P deficiency adaptation. Characterization of the qualitative and quantitative traits was necessary to obtain the line performance information. The traits were expected to have a distinct, uniform, and stable traits as a requirement for variety registration. The purpose of this research was to obtain information about the quantitative and qualitative character of F9 sorghum lines. The study was conducted from March to July 2019 at Cikabayan Bawah Experimental Field, Plant Breeding Laboratory, and Micro technical Laboratory, Department of Agronomy and Horticulture, IPB University. Randomized complete block design with genotype as a treatment factor was carried out in this experiment. Analysis of variance showed significant differences in quantitative and qualitative traits in sorghum lines. There were variations in the qualitative and quantitative traits observed. Based on cluster analysis, Sorghum lines and check varieties formed three groups. group 1 (Super 2), group 2 (170-9, 151-8, dan 114-7) and group 3 (67-9, 104-7, 115-9, 286-6, 331-8, and Numbu). Three promising sorghum lines were identified for varietal release, i.e., 114-7, 115-9, and 331-8.

Gas exchange and antioxidant activity accessions of Jatropha curcas L. under aluminium (Al) stress

The aluminium at toxic levels causes biochemical and physiological damage that inhibits plant growth and limits productivity. Root growth, chlorophyll a fluorescence, and enzyme activity of four accessions of Jatropha curcas were evaluated under cultivation conditions with different levels of aluminium. The experimental design was completely randomized with a split-split-plot design, in which the plots included four levels of aluminium in the soil (0.0, 8.2, 16.5, and 24.0 mmolc dm-3), the split-plot were the four accessions of J. curcas seeds (P1 = Dourados, MS; P2 = Montes Claros, MG; P3 = Alta Floresta, MT; P4 = Petrolina, PE), and split-split-plot in all four times of evaluation (25, 50, 75, and 100 days after emergence - DAE) with four replications. At 100 DAE were evaluated the curve of transient chlorophyll a fluorescence (OJIP) and enzyme activity, the treatments were arranged in split-plot, being four levels of aluminium in the soil and the four accesses of J. curcas. Six readings for the OJIP curve and three repetitions for enzymatic analysis were conducted. The characteristics of gas exchange and chlorophyll a fluorescence indicated that doses above 8.2 accentuated aluminium stress on plants from all accessions. The reduced efficiency of carboxylation of Rubisco and the results of the OJIP test indicated that photochemical efficiency of all varieties was decreased. The activity of the enzymes catalase, peroxidase, and superoxide dismutase was higher in the presence of aluminium for the accessions P3-Alta Floresta and P4-Petrolina. Our results indicate the greater tolerance of these accesses to aluminium stress conditions.

GsMAS1 Encoding a MADS-box Transcription Factor Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana.

The MADS-box transcription factors (TFs) are essential in regulating plant growth and development, and conferring abiotic and metal stress resistance. This study aims to investigate GsMAS1 function in conferring tolerance to aluminum stress in Arabidopsis. The GsMAS1 from the wild soybean BW69 line encodes a MADS-box transcription factor in Glycine soja by bioinformatics analysis. The putative GsMAS1 protein was localized in the nucleus. The GsMAS1 gene was rich in soybean roots presenting a constitutive expression pattern and induced by aluminum stress with a concentration-time specific pattern. The analysis of phenotypic observation demonstrated that overexpression of GsMAS1 enhanced the tolerance of Arabidopsis plants to aluminum (Al) stress with larger values of relative root length and higher proline accumulation compared to those of wild type at the AlCl3 treatments. The genes and/or pathways regulated by GsMAS1 were further investigated under Al stress by qRT-PCR. The results indicated that six genes resistant to Al stress were upregulated, whereas AtALMT1 and STOP2 were significantly activated by Al stress and GsMAS1 overexpression. After treatment of 50 μM AlCl3, the RNA abundance of AtALMT1 and STOP2 went up to 17-fold and 37-fold than those in wild type, respectively. Whereas the RNA transcripts of AtALMT1 and STOP2 were much higher than those in wild type with over 82% and 67% of relative expression in GsMAS1 transgenic plants, respectively. In short, the results suggest that GsMAS1 may increase resistance to Al toxicity through certain pathways related to Al stress in Arabidopsis.

Anatomical Responses of Rice (Oryza Sativa L.) to Aluminium Toxicity

Anatomical response of rice (Oryza sativa L.) to aluminium toxicity grown in sand culture and half strength Hoagland solution revealed that aluminium stress caused a decrease in diameter of the root and the shoot. Aluminium toxicity reduced the number of metaxylem vessels in the root of rice. Number of sclerenchyma cells was more in aluminium-treated rice root. Under Al stress, smaller sized vascular bundles were found in the leaf of rice. Size and frequency of bulliform cells were increased in the leaf of Al-treated plants than that in control plants. Al treatment caused closure of stomata in rice leaves.
 Journal of Bangladesh Academy of Sciences, Vol. 43, No. 2, 123-131, 2019

Function of NHX-type transporters in improving rice tolerance to aluminum stress and soil acidity.

In this study, we show that ectopic expression of either HtNHX1 or HtNHX2, from Helianthus tuberosus plant (located at vacuolar and endosome membranes, respectively), in rice plants could enhance its tolerance to aluminum (Al3+) stress and soil acidity. Plant sodium (potassium)/proton (Na+(K+)/H+ antiporters of the NHX family have been extensively characterized as they are related to the enhancement of salt tolerance. However, no previous study has reported NHX transporter functions in plant tolerance to Al3+ toxicity. In this study, we demonstrate their role as a component of the Al3+ stress tolerance mechanism. We show that the ectopic expression of either HtNHX1 or HtNHX2 , from Helianthus tuberosus plant, in rice (located at vacuole and endosome, respectively) could also enhance rice tolerance to Al3+ stress and soil acidity. Expression of either HtNHX1 or HtNHX2 reduced the inhibitory effect of Al3+ on the rice root elongation rate; both genes were reported to be equally effective in improvement of stress conditions. Expression of HtNHX1 enhanced Al3+-trigged-secretion of citrate acids, rhizosphere acidification, and also reduced K+ efflux from root tissues. In contrast, expression of HtNHX2 prevented Al3+-trigged-decrease of H+ influx into root tissues. Al3+-induced damage of the cell wall extensibility at the root tips was impaired by either HtNHX1 or HtNHX2. Co-expression of HtNHX1 and HtNHX2 further improved rice growth, particularly under the Al3+ stress conditions. The results demonstrate that HtNHX1 and HtNHX2 improved rice tolerance to Al3+ via different mechanisms by altering the K+ and H+ fluxes and the cell wall structure.

Genetic dissection of spike-related traits in wheat (Triticum aestivum L.) under aluminum stress

Wheat (Triticum aestivum L.) is one of the most important cereals and is a major staple food in developing countries. However, in acid soils, its productivity is limited by aluminum (Al) toxicity. Wheat yield can be enhanced by modifying the spike-related traits. In order to identify quantitative trait loci (QTL) associated with Al tolerance, 167 recombinant inbred lines (RILs) derived from a cross between SeriM82 and Babax were evaluated under normal and Al stress conditions for two consecutive crop seasons. Using Composite Interval Mapping (CIM) method, 64 QTLs including 13 putative and 51 suggestive QTLs were detected for all traits. These QTLs explained 3.58–14.39% of the total variations during both the crop seasons. Using mixed model-based composite interval mapping (MCIM) method, 58 QTLs were determined to have significant additive effects, of which 21 also showed epistatic effects. Twenty-three additive QTLs had significant interaction with environment, and 35 QTLs with no additive × environment interactions (AEI) were suggested as stable. Seven pairs of 12 pairs epistatic QTLs exhibited significant interactions with environment. 16.00% of additive QTL × environment interactions (QEIs) and 71.43% of epistatic QEIs were related to Al stress with significant genetic effects increasing phenotypic values. In both method, nine QTL clusters on six LGs 2A-d, 2D, 3B, 4B, 6A-a, and 7D-a, indicated pleiotropy or gene linkage in the inheritance of spike-related traits. These results will be of great value for marker-assisted selection and QTL pyramiding in wheat breeding programs for Al tolerance, following validation in different environments and genetic backgrounds and will accelerate the understanding of the genetic relationships among spike-related traits at the molecular level.

Enhancement of polyphenolic metabolism as an adaptive response of lettuce (Lactuca sativa) roots to aluminum stress

Polyphenols, pivotal secondary metabolites, are involved in plant adaption to abiotic stresses. Here, we investigated the role and metabolism profile of polyphenols under aluminum (Al) stress in different lettuce genotypes grown in 0.5 mM CaCl2 solution with AlCl3 (pH = 4.5). The complementary use of high-resolution mass spectrometry and quantitative biochemical approaches allowed the characterization of total and unique phenols, as well as their roles in Al tolerance. By comparing the most tolerant and sensitive genotype, 8 polyphenols, including 4 phenolic acids, 2 flavonoids, 1 xanthone and 1 unknown compound, were identified in the roots of the tolerant genotype. The total phenolic and flavonoid contents significantly increased in the tolerant genotype under Al stress. Seedlings with more phenolic accumulation usually performed greater Al tolerance. Meanwhile, principal enzymes related to phenolic biosynthesis significantly increased in roots of the tolerance genotype after Al treatment, with phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase, and 4-coumarate coenzyme A ligase increased by 16, 18 and 30%, respectively. The elevated total phenolics were significantly suppressed by AIP, a highly specific PAL inhibitor. Consequently, the antioxidant capacity was inhibited, leading to lettuce sensitivity to Al stress. These results clearly suggested the enhancement of unique polyphenolic biosynthesis as an adaptive strategy of lettuce to Al stress by protecting plants from oxidative stress.

QTL mapping of seed germination-related traits in <italic>Brassica napus</italic> L. under aluminum toxicity stress

<p indent=0mm>With the aggravation of soil acidification, aluminum toxicity has become one of the important stress factors that affect crop seed germination quality and crop yield. There have been many reports on QTL mapping and candidate gene screening for aluminum tolerance related traits in crops, but few reports on QTL mapping for aluminum tolerance during germination in <italic>Brassica napus</italic> L. The seed germination test was conducted on the recombinant inbred line population treated with <sc>80 µg mL^-1</sc> aluminum solution and with distilled water as control. Germination potential was investigated at <sc>3 d,</sc> germination rate was investigated at <sc>7 d,</sc> root length, bud length and dry weight were measured, and the relative values of various characters were calculated. Based on 6K SNP chip and combined with high density genetic linkage map, we detected 23 QTLs for five traits in rape germination period. QTLs for relative germination potential, relative germination rate, relative root length, relative bud length and relative dry weight were 9, 1, 4, 5, and 4 respectively, covering A and C genomes, with LOD values from 3.00 to 5.26, and interpretable phenotypic variation from 7.70% to 13.10%. According to the confidence interval sequence of each QTL, 30 candidate genes related to aluminum stress were screened. <italic>ALMT1</italic> gene and <italic>MATE</italic> gene are related to the synthesis and secretion of organic acids, which mainly enhance the aluminum tolerance of plants through the secretion of organic acids such as malic acid, citric acid and oxalic acid. <italic>STOP1</italic> gene, <italic>NAC </italic>gene and <italic>RAP2.4 </italic>gene all belong to transcription activation factors, which enhance the resistance of plants by inducing the expression of aluminum tolerance genes. ABC transporter, membrane protein transporter, GDSL lipase enhance aluminum tolerance of plants by reducing accumulation of toxic substances on plasma membrane or discharging toxic substances out of body. Peroxidase and cytochrome P450 are genes related to oxidative stress, which have the functions of preventing oxidative damage of plant cells and resisting stress. At the same time, many genes encoding stress proteins were found, which play an important role in various stress reactions. The results of this study provide a theoretical basis for the cultivation of aluminum-tolerant rape varieties and the functional research of subsequent genes.

Genome-Wide Identification of Aluminum-Activated Malate Transporter (ALMT) Gene Family in Rubber Trees (Hevea brasiliensis) Highlights Their Involvement in Aluminum Detoxification

The rubber tree (Hevea brasiliensis) is a widely cultivated crop in tropical acidic soil that is tolerant to high concentration of aluminum and the aluminum-activated malate transporter (ALMT) plays an important role in plant aluminum detoxification. However, the effects of ALMT on rubber tree aluminum tolerance, growth performance, and latex production are unclear. In this study, 17 HbALMT genes were identified from the genome of rubber trees. The physiological and biochemical characteristics, phylogenetic relationships, gene structures, conserved motifs, cis-elements of promoter, and expression patterns of the identified HbALMT genes were studied. Phylogenetic relationships indicated that these genes were divided into four clusters and genes in the same cluster have similar gene structures and conserved motifs. The promoters of HbALMT genes contain many cis-elements associated with biotic stress and abiotic stress. Quantitative real-time PCR analysis revealed HbALMTs showed various expression patterns in different tissues, indicating the functional diversity of HbALMT genes in different tissues of rubber trees. Transcriptome analysis and qRT-PCR assay showed that most of the HbALMT genes responded to aluminum stress, and among the 17 HbALMTs, HbALMT1, HbALMT2, HbALMT13, and HbALMT15 displayed higher expression levels in roots after two or five days of Al treatments, indicating their potential involvement in aluminum detoxification. Taken together, this study laid a foundation for further understanding the molecular evolution of the ALMT genes and their involvement in rubber tree aluminum adaption.

Effects of temperature on the flow stress of aluminum in shock waves and rarefaction waves

Elastic–plastic waves of shock compression and unloading in annealed AD1 aluminum were recorded at room temperature, 508 °C, and 610 °C. Using measurements of the parameters of the plastic shock waves and quasi-elastic rarefaction waves at the peak shock stresses from about 1.5 to 4.2 GPa, the strain rate dependences on the stress, the temperatures, and the loading histories were obtained in the range of 105–107 s−1. The initial resistance to high-rate deformation was found to increase anomalously with increasing temperature, but even a small deformation in the shock wave and the accompanying multiplication of dislocations changed the sign of the temperature dependence of the flow stress.

Characterization of the Soybean GmIREG Family Genes and the Function of GmIREG3 in Conferring Tolerance to Aluminum Stress.

The IREG (IRON REGULATED/ferroportin) family of genes plays vital roles in regulating the homeostasis of iron and conferring metal stress. This study aims to identify soybean IREG family genes and characterize the function of GmIREG3 in conferring tolerance to aluminum stress. Bioinformatics and expression analyses were conducted to identify six soybean IREG family genes. One GmIREG, whose expression was significantly enhanced by aluminum stress, GmIREG3, was studied in more detail to determine its possible role in conferring tolerance to such stress. In total, six potential IREG-encoding genes with the domain of Ferroportin1 (PF06963) were characterized in the soybean genome. Analysis of the GmIREG3 root tissue expression patterns, subcellular localizations, and root relative elongation and aluminum content of transgenic Arabidopsis overexpressing GmIREG3 demonstrated that GmIREG3 is a tonoplast localization protein that increases transgenic Arabidopsis aluminum resistance but does not alter tolerance to Co and Ni. The systematic analysis of the GmIREG gene family reported herein provides valuable information for further studies on the biological roles of GmIREGs in conferring tolerance to metal stress. GmIREG3 contributes to aluminum resistance and plays a role similar to that of FeIREG3. The functions of other GmIREG genes need to be further clarified in terms of whether they confer tolerance to metal stress or other biological functions.

Effects of aluminium toxicity on some biochemical components of rice (Oryza sativa L.)

An experiment was conducted to investigate the effect of aluminium (Al) toxicity on reducing and total sugar, proline, total amino acid and protein in rice seedlings grown in solution culture and phenolic compounds, chlorophyll and carotenoids in rice plants grown in sand culture. Exposure of rice seedlings to different concentrations of aluminium (10 - 150 μM) led to a stimulation of reducing and total sugar in the root and the shoot. Similarly, Al stress increased proline and total amino acid contents in different parts of rice seedlings. Aluminium toxicity caused a significant increase in phenolic compounds in rice plants. On the other hand, aluminium stress resulted in a reduction of chlorophyll-a, chlorophyll-b and carotenoid contents in the leaves of rice plants.&#x0D; Dhaka Univ. J. Biol. Sci. 29(1): 125-132, 2020 (January)

Mapping QTLs associated with grain yield and yield-related traits under aluminum stress in bread wheat

Aluminum (Al) toxicity is one of the major environmental constraints to crop production in acidic soils. The objective of this study was to map quantitative trait loci (QTLs) of yield-related traits associated with tolerance to Al in wheat (Triticum aestivum L.). A recombinant inbred line population of wheat was evaluated under conditions of 800 µm aluminum chloride hexahydrate (AlCL3.6H2O) at tillering, stem-elongation and flowering stages. Single-locus analysis showed that 22 of 79 QTLs identified were putative. These QTLs explained 4.38–12.24% of the total variation of traits in two growing seasons. Based on two-locus analysis, 71 additive and 11 epistatic QTLs were identified, of which 34 additive and three epistatic QTLs had significant interaction with environmental effects. The greatest number of stable QTLs was related to the A genome. Stable QTLs associated with days to heading and grain yield, with no additive × environment interactions, were co-located with Al concentration (on the 2D linkage group) and 1000-grain weight (on the 6B linkage group). The markers linked to major and stable QTLs identified in the present study can be further assessed in other genetic backgrounds and environmental conditions in order to improve marker-assisted selection and Al tolerance in wheat.

Effect of aluminum stress on the absorption and transportation of aluminum and macronutrients in roots and leaves of Aleurites montana

Aluminum toxicity is common in subtropical acidic soils, and the effect of Al stress on Aleurites montana is unknown. This study determined the growth and Al and macronutrient contents (C, N, P, K, Ca, and Mg) in leaves and roots of 1-year-old A. montana seedings to reveal the effects of Al stress on growth and elements of A. montana seedings and the difference of growth and content of elements in potted seedlings and hydroponic seedlings under Al addition. The content of Al in the leaves of potted A. montana seedlings was greater than 1000 mg kg−1 under Al stress, so it can be judged that A. montana is likely an Al accumulator and has a high Al tolerance in potted soil. The changes of macronutrient contents in the seedlings varied with Al concentration. For potted seedlings, Al stress had a significant effect on Mg and K contents in roots and Mg and C contents in leaves, but it had no effect on other macronutrients, such as N, P and Ca. For hydroponic seedlings, Al content in roots and N, P, and K contents in roots and leaves increased significantly, and C and Ca contents in roots decreased significantly when the Al concentration exceeded 0.290 mmol L−1. The Al stress affected the distribution and transportation of macronutrients between roots and leaves. The Al and K contents in the roots were higher than those in leaves in both cultivation methods, while the C, N, and Ca contents were smaller than those in leaves. The transportation of N, P and Ca from root to leaf in potted seedlings changed with the increase of Al concentration. There were major differences in the growth and the absorption and transportation of elements between potted and hydroponic seedlings under Al stress. In this study, Al promoted or had no significant effect on the growth of potted seedlings, while the growth of hydroponic seedlings was significantly inhibited when the Al concentration was relatively high. Moreover, the effect of Al concentration on Al and macronutrients of potted seedlings was less than that of hydroponic seedlings. Therefore, the effects of the primary environment should be considered in future stress experiments. This study revealed the effect of Al concentration on A. montana seedlings from the perspective of growth and nutrition, which are crucial in ecological restoration function of mixed tree species in acid rain area. Comparison of the effects of Al concentration on A. montana seedlings under two cultivation methods provides new perspectives for future stress test research.

Genetic control of some plant growth characteristics of bread wheat (Triticum aestivum L.) under aluminum stress.

Biomass yield is an important trait for wheat breeding programs. Enhancing the yield of the aerial components of wheat cultivars will be an integral part of future wheat improvement. Aluminum (Al) toxicity is one of the main factors limiting wheat growth and production in acid soils, which occur on up to 50% of the arable lands of the world especially in tropical and subtropical regions. Our objective was to identify quantitative trait loci (QTL) of plant growth characteristics and yield in wheat. A recombinant inbred line (RIL) population consisting of 167 lines, derived from a cross between SeriM82 and Babax were evaluated under two Al treatments (+ Al, 800 µM of Al; -Al, 0 µM of Al) in the field based on an alpha lattice design with two replications for two consecutive crop seasons. A total of 40 QTLs including nine putative and 31 suggestive QTLs were found for all traits using the composite interval mapping (CIM) method. By mixed model-based composite interval mapping (MCIM) method, 42 additive QTLs and nine pairs of epistatic effects were detected for studied traits, of which 20 additive and six pairs of epistatic QTLs showed significant QTL × environment interactions. Most of the detected QTLs across environments were stable, and the highest number of stable QTLs was related to A genome. Co-localization of QTL was found on linkage groups (LGs) 2B, 4B, 6A-a, and 7A (CIM method) and 2A-d, and 6A-a (MCIM method). These results have implications for selection strategies in biomassyield and for increasing the yield of the aerial part of wheatfollowing further evaluations in various genetic backgrounds and environments.

Post-release deformation and curvature correction of an electrothermally actuated MEMS bilayer platform

Surface micromachined devices are known to have residual stress-induced deformation. This paper presents the effects of residual stress on the flatness of an electrothermally actuated large aperture MEMS bilayer platform. The platform consists of a SiO2–Al composite plate of area 500 × 500 μm2 suspended over a cavity through bimorph actuators. The bilayer platform consists of 0.95 μm thick aluminum film on a thermally grown 0.75 μm thick silicon dioxide on a silicon substrate. Bimorph actuators also consist of laminated layers of silicon dioxide and aluminum of thicknesses the same as on the platform. The ensuing compressive stress in silicon dioxide (240 MPa) & tensile stress in aluminum (35 MPa) manifests itself in significant post-release curling of the bilayer platform. Finite Element Simulation is done in Coventorware® to analyze the room temperature post-release deformation behavior of the platform.In order to correct the platform curvature, two methods of stress counterbalancing i.e. (i) metal reinforcement framing, and (ii) deposition of a stress compensation layer are proposed and their effectiveness is investigated using FEM simulations. The simulation results show that a 1 μm thick gold reinforcement frame results in a 13 μm peak-to-valley height difference between center and corner of the platform, which improves to 6 μm for a gold reinforcement thickness of 3 μm. The maximum height difference reduces to 1 μm for silicon dioxide of thickness 0.75 μm. According to FEM results, the presence of a stress compensation layer at the top is more effective in curvature correction compared to metal reinforcement framing; however, the post-release elevation of the stress-compensated platform is 5 μm below the post-release elevation of the reinforced platform and 25 μm below the zero reference plane. To verify the simulation results, the platform is fabricated with a deposition of 1 μm thick silicon dioxide layer at the top. The fabricated platform exhibit significant improvement in post-release deformation with a stress compensation layer compared to an unbalanced platform.

Biochemical characterization of phospholipases C from Coffea arabica in response to aluminium stress

Signal transduction in plants determines their successful adaptation to diverse stress factors. Our group employed suspension cells to study the phosphoinositide pathway, which is triggered by aluminium stress. We investigated about members of the PI-specific phospholipase C (PLC) family and evaluated their transcription profiles in Coffea arabica (Ca) suspension cells after 14days of culture when treated or not with 100μM AlCl3. The four CaPLC1-4 members showed changes in their transcript abundance upon AlCl3 treatment. The expression profiles of CaPLC1/2 exhibited a rapid and transitory increase in abundance. In contrast, CaPLC3 and CaPLC4 showed that transcript levels were up-regulated in short times (at 30s), while only CaPLC4 kept high levels and CaPLC3 was reduced to basal after 3h of treatment. CaPLC proteins were heterologously expressed, and CaPLC2 and CaPLC4 were tested for in vitro activity in the presence or absence of AlCl3 and compared to Arabidopsis PLC2 (AtPLC2). A crude extract was isolated from coffee cells. CaPLC2 showed a similar inhibition (30%) as in AtPLC2 and in the crude extract, while in CaPLC4, the activity was enhanced by AlCl3. Additionally, we visualized the yellow fluorescent protein PH domain of human PLCδ1 (YFP-PHPLCδ1) subcellular localization in cells that were treated or not with AlCl3. In non-treated cells, we observed a polar fluorescence signal towards the fused membrane. However, when cells were treated with AlCl3, these signals were disrupted. Finally, this is the first time that PLC activity has been shown to be stimulated in vitro by AlCl3.

Loss of function of Arabidopsis NADP-malic enzyme 1 results in enhanced tolerance to aluminum stress.

In acidic soils, aluminum (Al) toxicity is a significant limitation to crop production worldwide. Given its Al-binding capacity, malate allows internal as well as external detoxification strategies to cope with Al stress, but little is known about the metabolic processes involved in this response. Here, we analyzed the relevance of NADP-dependent malic enzyme (NADP-ME), which catalyzes the oxidative decarboxylation of malate, in Al tolerance. Plants lacking NADP-ME1 (nadp-me1) display reduced inhibition of root elongation along Al treatment compared with the wild type (wt). Moreover, wt roots exposed to Al show a drastic decrease in NADP-ME1 transcript levels. Although malate levels in seedlings and root exudates are similar in nadp-me1 and wt, a significant increase in intracellular malate is observed in roots of nadp-me1 after long exposure to Al. The nadp-me1 plants also show a lower H2 O2 content in root apices treated with Al and no inhibition of root elongation when exposed to glutamate, an amino acid implicated in Al signaling. Proteomic studies showed several differentially expressed proteins involved in signal transduction, primary metabolism and protection against biotic and other abiotic stimuli and redox processes in nadp-me1, which may participate directly or indirectly in Al tolerance. The results indicate that NADP-ME1 is involved in adjusting the malate levels in the root apex, and its loss results in an increased content of this organic acid. Furthermore, the results suggest that NADP-ME1 affects signaling processes, such as the generation of reactive oxygen species and those that involve glutamate, which could lead to inhibition of root growth.

Microtranscriptome analysis of sugarcane cultivars in response to aluminum stress.

Although several metallic elements are required for plant growth, excessive amounts of aluminum ions (Al3+) can result in the inhibition of root growth, thus triggering water and nutrient deficiencies. Plants under stress undergo gene expression changes in specific genes or post-transcriptional gene regulators, such as miRNAs, that can lead to stress tolerance. In this study, we investigated the miRNAs involved in the response of sugarcane to aluminum stress. Four miRNA libraries were generated using sugarcane roots of one tolerant and one sensitive sugarcane cultivar grown under aluminum stress and used to identify the miRNAs involved in the sugarcane aluminum toxicity response. The contrast in field phenotypes of sugarcane cultivars in the field during aluminum stress was reflected in the micro-transcriptome expression profiles. We identified 394 differentially expressed miRNAs in both cultivars, 104 of which were tolerant cultivar-specific, 116 were sensitive cultivar-specific, and 87 of which were common among cultivars. In addition, 52% of differentially expressed miRNAs were upregulated in the tolerant cultivar while the majority of differentially expressed miRNAs in the sensitive cultivar were downregulated. Real-time quantitative polymerase chain reaction was used to validate the expression levels of differentially expressed miRNAs. We also attempted to identify target genes of miRNAs of interest. Our results show that selected differentially expressed miRNAs of aluminum-stressed sugarcane cultivars play roles in signaling, root development, and lateral root formation. These genes thus may be important for aluminum tolerance in sugarcane and could be used in breeding programs to develop tolerant cultivars.

ATR-IR and EPR spectroscopy for detecting the alterations in cortical synaptosomes induced by aluminium stress.

Aluminium (Al) is reported to promote free radical production, decrease the antioxidant enzyme status and disturb the enzyme activity involved in acetylcholine metabolism leading to cognitive dysfunction that are strongly associated with Alzheimer's disease (AD) pathogenesis. This work aimed at investigating the effect of Al-toxicity on synaptosomal membrane biophysical properties and lipid peroxidation during 65 days. We utilized ATR-IR spectroscopy to study the changes in membrane biochemical structure and biophysical properties of isolated rat cortical synaptosomes, and EPR spin trapping and labeling to follow NADPH oxidase activity and changes of membrane order parameter, respectively. The results showed increase in membrane fluidity and disorder in early 21d of AlCl3 treatment, while after 42d the membrane rigidity, packing, and order increased. The late (65d) an increase in the amount of unsaturated fatty acids, the accumulation of lipid peroxide end products, and ROS production were detected in rat cortex synaptosomes mediated by Al toxicity and oxidative stress (OS). A dramatic increase was also detected in Ca2+ level, synaptic membrane polarity, and EPR-detected order S-parameter. These outcomes strongly suggest that the synaptosomal membrane phospholipids underwent free radical attacks mediated by AlCl3 due to greater NOX activity, and the release of synaptic vesicles into synaptic cleft might be hindered. The adopted spectroscopic techniques have shed light on the biomolecular structure and membrane biophysical changes of isolated cortical synaptosomes for the first time, allowing researchers to move closer to a complete understanding of pathological tissues.