Main conclusion So far, considerable advances have been achieved in understanding the mechanisms of Si uptake and transport in vascular plants. This review presents a comprehensive update about this ...issue, but also provides the new insights into the role of Si against mineral stresses that occur in acid soils. Such information could be helpful to understand both the differential Si uptake ability as well as the benefits of this mineral element on plants grown under acidic conditions. Silicon (Si) has been widely recognized as a beneficial element for many plant species, especially under stress conditions. In the last few years, great efforts have been made to elucidate the mechanisms involved in uptake and transport of Si by vascular plants and recently, different Si transporters have been identified. Several researches indicate that Si can alleviate various mineral stresses in plants growing under acidic conditions, including aluminium (A1) and manganese (Mn) toxicities as well as phosphorus (P) deficiency all of which are highly detrimental to crop production. This review presents recent findings concerning the influence of uptake and transport of Si on mineral stress under acidic conditions because a knowledge of this interaction provides the basis for understanding the role of Si in mitigating mineral stress in acid soils. Currently, only four Si transporters have been identified and there is little information concerning the response of Si transporters under stress conditions. More investigations are therefore needed to establish whether there is a relationship between Si transporters and the benefits of Si to plants subjected to mineral stress. Evidence presented suggests that Si supply and its subsequent accumulation in plant tissues could be exploited as a strategy to improve crop productivity on acid soils.
Silicon (Si) has been well documented to alleviate aluminum (Al) toxicity in vascular plants. However, the mechanisms underlying these responses remain poorly understood. Here, we assessed the effect ...of Si on the modulation of Si/Al uptake and the antioxidant performance of ryegrass plants hydroponically cultivated with Al (0 and 0.2 mM) in combination with Si (0, 0.5, and 2.0 mM). Exposure to Al significantly increased Al concentration, mainly in the roots, with a consequent reduction in root growth. However, Si applied to the culture media steadily diminished the Al concentration in ryegrass, which was accompanied by an enhancement in root dry matter production. A reduced concentration of Si in plant tissues was also observed when plants were simultaneously supplied with Al and Si. Interestingly, Si transporter genes (
and
) were down-regulated in roots after Si or Al was applied alone; however, both
and
were up-regulated as a consequence of Si application to Al-treated plants, denoting that there is an increase in Si requirement in order to cope with Al stress in ryegrass. Whereas Al addition triggered lipid peroxidation, Si contributed to an attenuation of Al-induced oxidative stress by increasing phenols concentration and modulating the activities of superoxide dismutase (SOD), catalase, peroxidase, and ascorbate peroxidase antioxidant enzymes. Differential changes in gene expression of SOD isoforms (
, and
) and the profile of peroxide (H
O
) generation were also induced by Si in Al-stressed plants. This, to the best of our knowledge, is the first study to present biochemical and molecular evidence supporting the effect of Si on the alleviation of Al toxicity in ryegrass plants.
Aluminum (Al) toxicity is one of the main growth and yield limiting factors for barley grown on acid soils. Silicon (Si) ameliorates Al toxicity as well as it promotes the phenolic compounds ...production that have antioxidant or structural role. We evaluated the time-dependent kinetics of Al and Si uptake and the impact of Si on the production of antioxidant- or structural- phenols in barley cultivars at the short-term. Two barley cultivars with contrasting Al tolerance (Hordeum vulgare ‘Sebastian’, Al tolerant; and H. vulgare ‘Scarlett’, Al sensitive), exposed to either −Al (0 mM) or +Al (0.2 mM) nutrient solutions without Si (−Si) or with 2 mM (+Si) were cultured for 48 h. Aluminum and Si concentration decreased in plants at all harvest times when Al and Si were simultaneously supplied; this effect was more noticeable in ‘Scarlett’. Nevertheless, Si influenced the antioxidant system of barley irrespective of the Al tolerance of the cultivar, decreasing oxidative damage and enhancing radical scavenging activity, the production of phenolic compounds, and lignin accumulation in barley with short-term exposure to Al.
Manganese (Mn) toxicity limits plant growth in acid soils. Although Mn toxicity induces oxidative stress, the role of superoxide dismutase (SOD, EC.1.15.1.1) isoforms in conferring Mn tolerance ...remains unclear. Seedlings of ryegrass cultivars Nui (Mn-sensitive) and Kingston (Mn-tolerant) were hydroponically grown at 2.4 (optimal) or 750 μM Mn (toxic) concentration, and harvested from 2 to 48 h. Kingston showed higher shoot Mn than Nui at 2.4 μM Mn. At toxic supply, shoot Mn concentration steadily increased in both cultivars, with Kingston having the highest accumulation at 48 h. An early (2 h) increase in lipid peroxidation under Mn excess occurred, but it returned (after 6 h) to the basal level in Kingston only. Kingston exhibited higher SOD activity than Nui, and that difference increased due to toxic Mn. In general, Mn-induced gene expression of Mn- and Cu/Zn-SOD isoforms was higher in Nui than Kingston. Nevertheless, under Mn excess, we found a greater Fe-SOD up-regulation (up to 5-fold) in Kingston compared to Nui. Thus, Fe-SOD induction in Kingston might explain, at least partly, its high tolerance to Mn toxicity. This is the first evidence that Mn toxicity causes differential gene expression of SOD isoforms in ryegrass cultivars in the short-term.
•Gene expression of SOD isoforms in ryegrass under Mn excess was studied during 48 h.•Differential SOD gene expression between cultivars was found at optimal and toxic Mn.•Mn-induced gene expression of Mn- and Cu/Zn-SOD isoforms was the highest in Nui.•Fe-SOD up-regulation and low oxidative stress were found in Kingston.•Fe-SOD induction might partially explain the high Mn-toxicity tolerance of Kingston.
Aluminum (Al) toxicity and phosphorus (P) deficiency are widely recognized as major constraints to agricultural productivity in acidic soils. Under this scenario, the development of ryegrass plants ...with enhanced P use efficiency and Al resistance is a promising approach by which to maintain pasture production. In this study, we assessed the contribution of growth traits, P efficiency, organic acid anion (OA) exudation, and the expression of Al-responsive genes in improving tolerance to concurrent low-P and Al stress in ryegrass (
L.). Ryegrass plants were hydroponically grown under optimal (0.1 mM) or low-P (0.01 mM) conditions for 21 days, and further supplied with Al (0 and 0.2 mM) for 3 h, 24 h and 7 days. Accordingly, higher Al accumulation in the roots and lower Al translocation to the shoots were found in ryegrass exposed to both stresses. Aluminum toxicity and P limitation did not change the OA exudation pattern exhibited by roots. However, an improvement in the root growth traits and P accumulation was found, suggesting an enhancement in Al tolerance and P efficiency under combined Al and low-P stress. Al-responsive genes were highly upregulated by Al stress and P limitation, and also closely related to P utilization efficiency. Overall, our results provide evidence of the specific strategies used by ryegrass to co-adapt to multiple stresses in acid soils.
Silicon (Si) exerts beneficial effects in mitigating aluminum (Al) toxicity in different plant species. These include attenuating oxidative damage and improving structural strengthening as a result ...of the increased production of secondary metabolites such as phenols. The aim of this research was to evaluate the effect of Si on phenol production and composition in two barley cultivars under Al stress. Our conceptual approach included a hydroponic experiment with an Al-tolerant (Sebastian) and an Al-sensitive (Scarlett) barley cultivar treated with two Al doses (0 or 0.2 mM of Al) and two Si doses (0 or 2 mM) for 21 days. Chemical, biochemical and growth parameters were assayed after harvest. Our results indicated that the Al and Si concentration decreased in both cultivars when Al and Si were added in combination. Silicon increased the antioxidant activity and soluble phenol concentration, but reduced lipid peroxidation irrespective of the Al dose. Both barley cultivars showed changes in culm creep rate, flavonoids and flavones concentration, lignin accumulation and altered lignin composition in Si and Al treatments. We concluded that Si fertilization could increase the resistance of barley to Al toxicity by regulating the metabolism of phenolic compounds with antioxidant and structural functions.
The relationship between phosphorus (P) availability and water restriction was explored in this study, focusing on its impact on phosphorus use efficiency (PUE) and water use efficiency (WUE) in ...various bromegrass (Bromus spp.) genotypes. Under controlled conditions, five bromegrass genotypes, as well as one ryegrass (Lolium perenne) cultivar, were compared by subjecting them to two P levels and two watering regimes. It was determined that combining water and phosphorus limitations led to reduced plant productivity. Initially, the ryegrass outperformed the bromegrass, but this result declined over time, while bromegrass exhibited consistent stability. Notably, under P and water stress, enhanced root development was observed in bromegrass compared to that in ryegrass. Distinct patterns of PUE and WUE allowed for the categorization of bromegrass genotypes into three groups. Genotype 3457 emerged as the most efficient, scoring 20 out of 24, while Pro 94-49 A achieved a score of only 10 out of 24. This study suggests that the drought resilience of bromegrass may be linked to increased root growth during the early vegetative stages, which potentially facilitates improved P acquisition. However, further validation through long-term field experiments is needed. The insights from this study are potentially valuable for use in shaping plant breeding programs by revealing the plant adaptation mechanisms for both P and water absorption.
Improving plant ability to acquire and efficiently utilize phosphorus (P) is a promising approach for developing sustainable pasture production. This study aimed to identify ryegrass cultivars with ...contrasting P use efficiency, and to assess their associated biochemical and molecular responses. Nine ryegrass cultivars were hydroponically grown under optimal (0.1 mM) or P-deficient (0.01 mM) conditions, and P uptake, dry biomass, phosphorus acquisition efficiency (PAE) and phosphorus utilization efficiency (PUE) were evaluated. Accordingly, two cultivars with high PAE but low PUE (Ansa and Stellar), and two cultivars with low PAE and high PUE (24Seven and Extreme) were selected to analyze the activity and gene expression of acid phosphatases (APases), as well as the transcript levels of P transporters. Our results showed that ryegrass cultivars with high PAE were mainly influenced by root-related responses, including the expression of genes codifying for the P transporter
, purple acid phosphatase
and APase activity. Moreover, the traits that contributed greatly to enhanced PUE were the expression of
and
, and the APase activity in shoots. These outcomes could be useful to evaluate and develop cultivars with high P-use efficiency, thus contributing to improve the management of P in grassland systems.
Volcanic ash-derived soils are characterized by low pH (pH ≤ 5.5) with increased concentrations of aluminum (Al
) and manganese (Mn
), which decreases plant growth, fruit quality, and yield. Methyl ...jasmonate (MeJA) improves abiotic stress tolerance. Our work aimed to evaluate the application of MeJA's impact on the growth, antioxidant defense, and fruit quality of highbush blueberry grown under Al and Mn toxicity. A field assay was conducted with four-year-old bushes of highbush blueberry cultivar Legacy under eight treatments (Control, Al (87% of Al saturation), Mn (240 mg kg
), and Al-Mn with and without MeJA application). Physiological, biochemical, and fruit quality parameters were measured. Growth rate significantly decreased with Al (20%), Mn (45%), and Al-Mn (40%). MeJA application recovered the growth rate. Photosynthetic parameters were not affected. Antioxidant activity increased under all treatments compared with controls, being higher with MeJA application. Total phenols (TP) were decreased in plants under Al (43%) and Mn (20%) compared with controls. MeJA application increased TP in all treatments. Fruits of bushes under Al and Mn toxicity with MeJA applications exhibited an increase in fruit firmness and weight, maintaining suitable contents of soluble solids. Our results provide insights about the beneficial effect of MeJA application on growth, antioxidant properties, and fruit quality of highbush blueberry plants grown in acid soils under Al and Mn toxicity.
Selenium (Se) is regarded as an antioxidant in animal and human nutrition, but its biological role in plants needs to be clarified. Plants vary considerably in their ability to tolerate Se, and their ...biochemical response to Se may be affected by liming or P fertilization. Two greenhouse experiments were conducted with white clover (Trifolium repens L.) to evaluate Se accumulation, tolerance, and the antioxidant response at increasing selenite supply levels (from 0 to 60 g Se ha-¹) and the effect of lime and P on both the Se uptake and the antioxidant activity of plants treated with 0, 20 and 40 g Se ha-¹. Selenium concentration in plant tissues was increased by Se applications, and plant growth was reduced at Se supply levels above 20 g ha-¹. At shoot concentration up to 200 μg kg-¹ DW, Se promoted antioxidant ability by increasing the free radical scavenging activity and by inhibiting lipid peroxidation (TBARS), whereas above this level TBARS accumulation increased. Significant changes in the activities of peroxidase (POD) and ascorbate peroxidase (APX) enzymes were also observed as a consequence of the increase in shoot Se concentration. The application of lime and P improved the plant nutrition, which increased the dry matter yield and enhanced the plant's antioxidative system. Under different combinations of soil acidity and P fertilization a differential uptake of Se by the plant occurred. These factors appear to be responsible for beneficial or detrimental effects of Se in terms of lipid peroxidation of biological membranes and the activation of POD and APX in white clover.
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