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Aluminum-Dependent Root-Growth Inhibition in Arabidopsis Results from AtATR-Regulated Cell-Cycle Arrest

Aluminum induced malate transporter (ALMT1) is regulating the Aluminum stress tolerance responses of mungbean seedlings

The aim of this research was to test the utilization of arbuscular mycorrhizal fungus (AMF) to improve adaptation ability of chili to aluminum (Al) stress based on growth and yield response in four genotypes of chili ( Capsicum annuum L.). The research was carried out at University Farm of IPB in Cikabayan from September 2006 to Maret 2007. The media was Ultisol from Gajrug (Lebak, Banten) in polybag. Four genotypes of chili, PBC 619 and Jatilaba (Al tolerant genotypes), and Cilibangi 3 and Helm (Al sensitive genotypes) were treated with and without inoculation of Gigaspora margarita , and planted further in media without Al stress (Al saturation 0.77%) and Al stress (Al saturation 60.85%). Variables observed were degree of AMF infection, root length, plant height, shoot dry weight, number of harvested fruits, fruit length, fruit weight and weight of harvested fruits. The results showed that inoculation of G . margarita effectively decreased negative influence of Al stress by increasing plant height, shoot dry weight, number of harvested fruit, fruit length, weight per fruit and weight of harvested fruits. Inoculation of G . margarita to Al sensitive genotypes was more advantageous than to tolerant genotypes. The Al sensitive genotypes were adapted to Al stress if they were inoculated with G . margarita . In Al stress condition, inoculation of G . margarita to Al sensitive genotypes increased weight of harvested fruits up to 94.49% in Cilibangi 3 and 80.37% in Helm. Key words: Adaptation, aluminum stress, arbuscular mycorrhizal fungus, Capsicum annuum L., Ultisol

Although NH4+ fertilization is known to acidify rhizosphere and enhance nutrient uptake, the effects on a nutrient-sufficient acidic soil amended with lime are not demonstrated. Thus, the influence of NH4+ fertilization of an unlimed and limed (3 g calcium carbonate per kg soil) acidic soil on the nutrient uptake and growth of maize was studied in comparison to NH4NO3 fertilization. The pH of limed rhizosphere soil was about two units higher than that of the unlimed soil. The maize plants were grown in pots under greenhouse conditions for about two months. The results showed that the pH of the NH4+-fertilized unlimed and limed soil was 0.54 and 0.15 units lower than the NH4NO3-fertilized soil. Liming negatively affected shoot and root dry matter production, whereas the NH4+-fertilized plants produced higher dry matter than the NH4NO3-fertilized plants, with significant difference of 28% in the limed soil only. Liming decreased Fe concentration in rhizosphere soil from 99 to 69 mg kg−1 and decreased plant-available Mn the most (71%), whereas the NH4+-fertilized unlimed and limed soil had 48% and 21% higher Mn concentration than the respective NH4NO3-fertilized soils. Similarly limed rhizosphere soil had 50% lower plant-available Zn concentration than the unlimed soil, and the NH4+-fertilized soil had an 8% higher Zn concentration than the NH4NO3-fertilized unlimed soil. The liming negatively affected P, K, Mn, and Zn concentrations and contents in maize shoot to a lower degree in the NH4+-fertilized soil, whereas the positive effect of NH4+ on the nutrient concentration and contents was vigorous in the unlimed soil than the limed soil. It is concluded that NH4+ fertilization could be beneficial in enhancing nutrient uptake and growth of maize in both acidic and alkaline soils, despite the higher inherent plant-available concentrations of the nutrient in soil.

Acidic soils with high aluminum (Al) toxicity are a major constraint to upland rice productivity in many tropical regions, including Kalimantan. Local rice cultivars often possess adaptive traits that can be utilized for breeding tolerant varieties. This study aimed to investigate the genetic diversity of Kalimantan local upland rice cultivars using SSR markers and their adaptation to aluminum toxicity stress. A total of 93 rice accessions obtained from the Agricultural Gene Bank of IAARD were subjected to both genetic diversity and Al stress adaptation analyses. The genetic diversity analysis used 11 SSR markers, while the adaptation study employed a hydroponic method with 45 ppm Al in Yoshida nutrient solution. Root and shoot growth were observed after 21 days of stress treatment. The SSR markers were highly polymorphic, grouping the accessions into four clusters at a 35% similarity level. Most accessions showed tolerance to Al stress based on relative root and shoot growth parameters. Accessions P. Pulut Timai, Padai Cina, Raya, Parai Paliping, and P. Pulut Ayang/Pang were the most adaptive. Root length, shoot length, and shoot fresh weight exhibited moderate heritability. These findings provide valuable insights for breeding Al-tolerant upland rice adapted to acidic soils. Keywords: adaptability; aluminum stress; molecular marker; SSR; upland rice

This study tested the hypothesis that lucerne (Medicago sativa L.) populations selected in solution culture high in aluminium (Al) would increase seedling root growth when grown in an acid soil high in exchangeable Al. Root growth of six elite populations (Aurora C2, UQL-1 C2, T02-011 C1, T02-011 C2, A513 C3 and Sardi 7 C2) selected in high-Al solution culture (SHASC) was compared with that of corresponding parent as well as the Georgia acid soil-tolerant populations in an acid soil in pots grown for 8 days under controlled environmental conditions. Lime was added to the soil to provide contrasts in the severity of stress imposed by low pH and high Al. Averaged across six SHASC populations, total root length increased 19% at pH 4.34 in CaCl2 (35% exchangeable Al) and 26% at pH 5.26 (<1% exchangeable Al) compared with the control populations. At all pH levels SHASC populations showed increased tap root length, total root length (includes lateral roots), root weight and root surface area, but decreased average root diameter compared with the six control populations. A large amount of variability was observed both between and within lucerne populations with three SHASC populations (Aurora C2, UQL-1 C2 and Sardi 7 C2) exhibiting increased root growth at lower pH levels, but little increase in root length at higher pH, consistent with increased tolerance to Al toxicity. This was in contrast to three other SHASC populations (T02-011 C1, T02-011 C2 and A513 C3), which exhibited increased root length at all pH levels, consistent with increased seedling vigour. The Sardi 7 C2 population exhibited the greatest increase in tap root growth with tap root length increasing by 40 and 30% at pH 4.34 and 4.48, respectively, compared with its parent population Sardi 7. This study provides evidence that seedlings of lucerne populations selected in high-Al solution culture can confer significantly improved root and shoot growth in acid soil. It is recommended that such screening be incorporated into lucerne breeding programs to reduce costs in space and time.

Formate dehydrogenase (FDH; EC 1.2.1.2.) has been implicated in plant responses to a variety of stresses, including aluminum (Al) stress in acidic soils. However, the role of this enzyme in Al tolerance is not yet fully understood, and how FDH gene expression is regulated is unknown. Here, we report the identification and functional characterization of the tomato (Solanum lycopersicum) SlFDH gene. SlFDH encodes a mitochondria-localized FDH with Km values of 2.087mm formate and 29.1μm NAD+ . Al induced the expression of SlFDH in tomato root tips, but other metals did not, as determined by quantitative reverse transcriptase-polymerase chain reaction. CRISPR/Cas9-generated SlFDH knockout lines were more sensitive to Al stress and formate than wild-type plants. Formate failed to induce SlFDH expression in the tomato root apex, but NAD+ accumulated in response to Al stress. Co-expression network analysis and interaction analysis between genomic DNA and transcription factors (TFs) using PlantRegMap identified seven TFs that might regulate SlFDH expression. One of these TFs, SlSTOP1, positively regulated SlFDH expression by directly binding to its promoter, as demonstrated by a dual-luciferase reporter assay and electrophoretic mobility shift assay. The Al-induced expression of SlFDH was completely abolished in Slstop1 mutants, indicating that SlSTOP1 is a core regulator of SlFDH expression under Al stress. Taken together, our findings demonstrate that SlFDH plays a role in Al tolerance and reveal the transcriptional regulatory mechanism of SlFDH expression in response to Al stress in tomato.

Root growth in Nicotiana attenuata is transiently reduced after application of oral secretions (OS) of Manduca sexta larvae to wounds in leaves. Feeding of M. sexta or OS elicitation is known to result in jasmonic acid (JA) and ethylene bursts, and activates a suite of defence responses. Because both plant hormones are known to strongly reduce root growth, their activation might account for the observed reduction of root growth following herbivory. To test this hypothesis, we measured primary root growth with digital image sequence processing at high temporal resolution in antisense-lipoxygenase 3 (asLOX3) and inverted repeat-coronatin-insensitive 1 (irCOI1) seedlings which are impaired in JA biosynthesis and perception, respectively, and wild-type (WT) seedlings. Higher root growth rates in irCOI1 compared with WT were observed after OS elicitation. The dynamics of wound-induced root growth reduction coincide with the dynamics of root growth reduction induced by external application of methyl JA. In an experiment with 1-methylcyclopropen (1-MCP), a potent ethylene receptor blocker, no wounding-specific difference between growth of 1-MCP-treated plants and non-treated plants was observed, suggesting that wound-induced endogenous JA and not ethylene mediates the wounding-specific reduction in root growth. Yet, inhibiting the ethylene response by applying 1-MCP led to markedly increased root growth compared with that of control plants, indicating that ethylene normally suppresses plant growth in N. attenuata seedlings.

Aluminum and water stress effects on growth and proline of sorghum

An ATP binding cassette transporter HvABCB25 confers aluminum detoxification in wild barley

BackgroundIonic aluminum (mainly Al3+) is rhizotoxic and can be present in acid soils at concentrations high enough to inhibit root growth. Many forest tree species grow naturally in acid soils and often tolerate high concentrations of Al. Previously, we have shown that aspen (Populus tremula) releases citrate and oxalate from roots in response to Al exposure. To obtain further insights into the root responses of aspen to Al, we investigated root gene expression at Al conditions that inhibit root growth.ResultsTreatment of the aspen roots with 500 μM Al induced a strong inhibition of root growth within 6 h of exposure time. The root growth subsequently recovered, reaching growth rates comparable to that of control plants. Changes in gene expression were determined after 6 h, 2 d, and 10 d of Al exposure. Replicated transcriptome analyses using the Affymetrix poplar genome array revealed a total of 175 significantly up-regulated and 69 down-regulated genes, of which 70% could be annotated based on Arabidopsis genome resources. Between 6 h and 2 d, the number of responsive genes strongly decreased from 202 to 26, and then the number of changes remained low. The responses after 6 h were characterized by genes involved in cell wall modification, ion transport, and oxidative stress. Two genes with prolonged induction were closely related to the Arabidopsis Al tolerance genes ALS3 (for Al sensitive 3) and MATE (for multidrug and toxin efflux protein, mediating citrate efflux). Patterns of expression in different plant organs and in response to Al indicated that the two aspen genes are homologs of the Arabidopsis ALS3 and MATE.ConclusionExposure of aspen roots to Al results in a rapid inhibition of root growth and a large change in root gene expression. The subsequent root growth recovery and the concomitant reduction in the number of responsive genes presumably reflect the success of the roots in activating Al tolerance mechanisms. The aspen genes ALS3 and MATE may be important components of these mechanisms.

Additions of micromolar concentrations of magnesium (Mg) to hydroponics enhance aluminum (Al) tolerance of soybean by increasing citrate secretion from roots and external complexation of toxic Al species. The objective of this study was to assess the ameliorative effect of Mg additions on soybean root elongation into mineralogically different acid soils. Roots of soybean seedlings grew for 28 days into acid soils treated with three Mg levels in their soil solution (Control, 150 and 300 μM) and lime. Root growth in the acid soils and aboveground dry matter responses to the Mg treatments were less than for the lime treatments. Citrate fate in the acid soils revealed that 66–99% of added citrate was either adsorbed or biodegraded, suggesting that root secreting citrate in the soil abundant with Al and iron (Fe) hydroxides potentially reduces the availability to complex rhizotoxic Al. A calcium (Ca) deficiency may have constrained root growth response to the Mg-treated soils.

Interplay of phosphorus and Piriformospora indica in attenuating aluminium stress in barley and other plants: Recent developments and phytoremediation strategies.

Aluminum (Al) toxicity is a major barrier to rice yield in acidic soils, yet the hormonal mechanisms underlying Al tolerance remain incompletely understood. Strigolactones (SLs) have recently been identified as key regulators of plant adaptation to abiotic stress, but their involvement in Al tolerance has not been clearly defined. Using rice (Oryza sativa L.) seedlings, we investigated Al-induced changes in endogenous SL accumulation and examined the effects of pharmacological activation of SL signaling with the synthetic analog GR24 on root growth, Al accumulation, cell wall composition, gene expression and nitric oxide (NO) production under Al stress. Al exposure rapidly stimulated endogenous SL accumulation in rice roots by approximately 10%. Activation of SL signaling by GR24 significantly alleviated Al-induced inhibition of root elongation by 20% and decreased Al content in root tips by 29%, respectively. GR24 treatment under Al stress altered root cell wall properties by decreasing hemicellulose- and pectin-associated Al sequestration and attenuated the transcriptional activation of key Al-responsive genes, including OsART1 (Oryza sativa ALUMINUM RESISTANCE TRANSCRIPTION FACTOR 1), citrate transporter genes OsFRDL2 and OsFRDL4 (Oryza sativa FRD3-LIKE PROTEIN 2/4) and the Al transporter gene OsNRAT1 (NRAMP ALUMINUM TRANSPORTER 1). Notably, GR24-enhanced Al tolerance was accompanied by elevated accumulation of NO in root tips, and disruption of NO signaling abolished the protective effects of GR24. These research confirm that strigolactone signaling plays a previously unrecognized role in rice Al tolerance by coordinating NO-dependent regulation of cell wall Al sequestration and Al-responsive gene expression. This study provides new insight into the hormonal control of plant adaptation to acidic soils.

Lipid peroxide-derived reactive carbonyl species (RCS), generated downstream of reactive oxygen species (ROS), are critical damage-inducing species in plant aluminum (Al) toxicity. In mammals, RCS are scavenged primarily by glutathione (reduced form of glutathione, GSH), but in plant Al stress, contribution of GSH to RCS detoxification has not been evaluated. In this study, Arabidopsis plants overexpressing the gene AtGR1 (accession code At3g24170), encoding glutathione reductase (GR), were generated, and their performance under Al stress was examined. These transgenic plants (GR-OE plants) showed higher GSH levels and GSH/GSSG (oxidized form of GSH) ratio, and an improved Al tolerance as they suffered less inhibition of root growth than wild-type under Al stress. Exogenous application of 4-hydroxy-2-nonenal, an RCS responsible for Al toxicity in roots, markedly inhibited root growth in wild-type plants. GR-OE plants suffered significantly smaller inhibition, indicating that the enhanced GSH level increased the capacity of RCS detoxification. The generation of H2 O2 due to Al stress in GR-OE plants was lower by 26% than in wild-type. Levels of various RCS, such as malondialdehyde, butyraldehyde, phenylacetaldehyde, (E)-2-heptenal and n-octanal, were suppressed by more than 50%. These results indicate that high levels of GSH and GSH/GSSG ratio by GR overexpression contributed to the suppression of not only ROS, but also RCS. Thus, the maintenance of GSH level by overexpressing GR reinforces dual detoxification functions in plants and is an efficient approach to enhance Al tolerance.