Si Plants Research Articles

Differential gene expression in soybean infected by Phakopsora pachyrhizi in response to acibenzolar‐S‐methyl, jasmonic acid and silicon

AbstractAsian soybean rust (ASR), caused by Phakopsora pachyrhizi, has negatively impacted soybean production worldwide. This study evaluated the effect of foliar spray of acibenzolar‐S‐methyl (ASM) and jasmonic acid (JA) as well as silicon (Si) supplied, either by soil amendment using calcium silicate or through a nutrient solution, on ASR control as well as on the expression of some defence‐related genes (phenylalanine ammonia‐lyase (PAL), chitinase (CHI), chalcone isomerase (CHAL), lipoxygenase (LOX), pathogenesis‐related protein 1 (PR‐1) and metalloproteinase (MET)) in soybean plants infected or not by P. pachyrhizi. Foliar Si concentration ranged from 2.6 to 8.7 dag/kg for Si supply by soil application or through a nutrient solution in comparison with the control treatment (no Si supply). Higher foliar Si concentration contributed to reducing ASR severity greater than 30%, mainly if supplied through nutrient solution. The ASR severity was significantly reduced by 36% with the ASM spray in comparison with the control treatment without any expressive effect on the expression of the analysed genes. The JA spray did not result in reduction on ASR severity in comparison with the control treatment even though with higher transcript levels of PAL at 12 hai. The transcripts levels of MET and PAL were significantly higher for inoculated plants taking up Si from the soil in comparison to non‐inoculated plants of this treatment at 72 hai. For Si supply through the nutrient solution (+Si plants), the transcripts levels of LOX and CHAL were significantly higher for inoculated plants in comparison to inoculated ‐Si ones at 12 hai. At 141 hai, the transcript level of PAL was significantly higher for inoculated + Si plants in comparison to inoculated ‐Si ones. In conclusion, Si supply contributed decisively to reduce ASR severity through the potentiation of some defence‐related genes mainly PAL and CHAL involved, respectively, in the biosynthesis of phenolics and flavonoids.

Silicon alleviates mesophyll limitations of photosynthesis on rice leaves infected by Monographella albescens

Leaf scald, caused by Monographella albescens, is a key disease affecting rice production worldwide. Alternative methods for leaf scald management are demanded by the growers and silicon (Si) application emerges as a promising way to decrease severity not only of leaf scald but also of other relevant rice diseases. Some evidence suggests that Si may preserve the photosynthetic performance of plants upon pathogen infection but the mechanistic basis for this remain unresolved. In the present study, mesophyll conductance (gm) was calculated to suitably parameterize the responses of net carbon assimilation rate (A) to chloroplastidic CO2 concentration (Cc) and to resolve the relative contributions of stomatal, mesophyll, and biochemical drawbacks to photosynthesis in rice plants challenged with M. albescens and how all of these facts may be influenced by Si application. Rice plants (cultivar “Primavera”) were hydroponically grown with 0 or 2 mM Si (− Si and + Si plants) and inoculated with M. albescens. Leaf scald-induced decreases in A were associated with roughly proportional decreases in CO2 diffusion (lower stomatal conductance and gm) and impaired photochemistry (e.g. reduced maximum electron transport rate) and biochemistry (e.g. RuBisCO activity) regardless of Si supply. The magnitude of these decreases were, overall, greater in − Si plants than in their + Si counterparts, and therefore a mitigating effect of Si on the preservation of the photosynthetic activity on diseased plants is evident. On infected leaves, gm was not scaled with maximum carboxylation rate (Vcmax) − Cc and, as a consequence, Cc increased accordingly, but only in + Si plants. In conclusion, the supply of Si to rice plants played a central role in decreasing leaf scald symptoms and, as such, preserving to a certain extent their photosynthetic performance. This preservation was not linked to differential impairments on the stomatal function or biochemical steps of photosynthesis but rather with increased CO2 diffusion throughout the mesophyll. This ultimately led to a lower photorespiration-to-gross photosynthesis ratio and less mesophyll limitations of photosynthesis in + Si plants than in their − Si counterparts during the infection process of M. albescens on rice leaves.

Silicon application affects cadmium translocation and physiological traits of Lallemantia royleana under cadmium stress

To study the interaction of different concentrations of cadmium and silicon on physiological traits of Lallemantia royleana a factorial experiment was conducted based on a completely randomized design. Experimental treatments were different concentrations of cadmium (0, 2.5, 5 and 10 mg L−1) in the absence (-Si) or presence (+Si) of silicon with a concentration of 1 mmol L−1. Based on results the highest amount of shoot Cd content (84.1 mg kg−1 DW) measured in -Si treatments was measured when the highest concentration of Cd (10 mg Cd L−1) was utilized. In all of the + Si treatments shoot Cd content decreased. The highest translocation factor (0.195) was observed in 2.5 mg Cd L−1 treatment without Si application and as a result of increasing Cd concentration in plant growth medium, the translocation factor decreased significantly. In + Si treated plants the translocation factor of Cd compared with –Si treated plants significantly decreased. Increasing the cadmium concentration up to 2.5 mg.L−1 did not have a significant effect on relative water content, leaf area, Chlorophyll a, and catalase activity. At the highest concentration of cadmium, the activity of peroxidase, catalase and superoxide dismutase in + Si plants compared with -Si plants increased about 23%, 55% and 30%, respectively. Silicon reduced the negative effects of cadmium on plant growth either by increasing the activity of antioxidant enzymes or decreasing Cd translocation to shoot. Therefore, application of silicon for increasing growth and to produce healthier plants under cadmium stress with a concentration of 5 mg L−1 is recommended.

Silicon is an inducible and effective herbivore defence against Helicoverpa punctigera (Lepidoptera: Noctuidae) in soybean.

The role of silicon (Si) in alleviating the effects of biotic and abiotic stresses, including defence against insect herbivores, in plants is widely reported. Si defence against insect herbivores is overwhelmingly studied in grasses (especially the cereals), many of which are hyper-accumulators of Si. Despite being neglected, legumes such as soybean (Glycine max) have the capacity to control Si accumulation and benefit from increased Si supply. We tested how Si supplementation via potassium, sodium or calcium silicate affected a soybean pest, the native budworm Helicoverpa punctigera Wallengren (Lepidoptera: Noctuidae). Herbivory reduced leaf biomass similarly in Si-supplemented (+Si) and non-supplemented (-Si) plants (c. 29 and 23%, respectively) relative to herbivore-free plants. Both Si supplementation and herbivory increased leaf Si concentrations. In relative terms, herbivores induced Si uptake by c. 19% in both +Si and -Si plants. All Si treatments reduced H. punctigera relative growth rates (RGR) to a similar extent for potassium (-41%), sodium (-49%) and calcium (-48%) silicate. Moreover, there was a strong negative correlation between Si accumulation in leaves and herbivore RGR. To our knowledge, this is only the second report of Si-based herbivore defence in soybean; the rapid increase in leaf Si following herbivory being indicative of an induced defence. Taken together with the other benefits of Si supplementation of legumes, Si could prove an effective herbivore defence in legumes as well as grasses.

Nutritional status of rice plants supplied with silicon in response to Pyricularia oryzae infection

ABSTRACT Considering the importance of silicon (Si) to increase rice resistance to blast, this study investigated the nutritional status of rice plants supplied with this element in response to Pyricularia oryzae infection. Plants were grown in nutrient solutions containing 0 and 2 mmol·L-1 of Si (referred to -Si and +Si plants, respectively). The area under blast progress curve decreased for +Si plants due to a significant increase of 714% on the foliar Si concentration in contrast to -Si plants. For +Si plants, the foliar N, P, K, Ca, Mg, Cu, and B concentrations were significantly lower in comparison to -Si plants. On infected plants, the foliar N, K, and Cu concentrations were significantly lower in comparison to noninfected ones. The foliar Zn, Fe, and Mn concentrations were significantly lower for -Si inoculated plants in comparison to -Si noninoculated ones. The foliar Mn and S concentrations were significantly lower for +Si inoculated plants in comparison to +Si noninoculated ones. The foliar Fe concentration was significantly lower for +Si inoculated plants in comparison to +Si noninoculated ones. Foliar Zn and Mn concentrations were significantly lower for +Si plants in comparison to -Si plants regardless of their inoculation with P. oryzae. Foliar Fe and S concentrations were significantly lower for +Si plants in comparison to -Si plants, respectively, for noninoculated and inoculated plants. Taken together, Si stood for itself in reducing blast symptoms without the need of high foliar concentrations of either macro or micronutrients that could affect plantgrowth.

IbINH positively regulates drought stress tolerance in sweetpotato

Invertase inhibitor (INH) post-translationally regulates the activity of invertase, which hydrolyzes sucrose into glucose and fructose, and plays essential roles in plant growth and development. However, little is known about the role of INH in growth and responses to environmental challenges in sweetpotato. Here, we identified and characterized an INH-like gene (IbINH) from sweetpotato. IbINH belongs to the pectin methylesterase inhibitor super family. IbINH transcript was the most abundant in storage roots. IbINH mRNA levels were significantly up-regulated in response to drought, abscisic acid (ABA), salicyclic acid (SA) and jasmonic acid (JA) treatments. Overexpressing IbINH in sweetpotato (SI plants) led to the decrease of plant growth and the increase of drought tolerance, while down-regulation of IbINH (RI plants) by RNAi technology resulted in vigorous growth and drought sensitivity. Furthermore, sucrose was increased and hexoses was decreased in SI plants, but the opposite results were observed in RI plants. Moreover, higher levels of sugars were accumulated in SI plants in comparison to non-transgenic plants (NT plants) and RI plants during water deficit. In addition, ABA biosynthesis-involved and abiotic stress response-involved genes were prominently up-regulated in SI plants under drought stress. Taken together, these results indicate that IbINH mediates plant growth and drought stress tolerance in sweetpotato via induction of source-sink strength and ABA-regulated pathway.

The Role of Silicon in Antiherbivore Phytohormonal Signalling.

The role of plant silicon (Si) in the alleviation of abiotic and biotic stress is now widely recognised and researched. Amongst the biotic stresses, Si is known to increase resistance to herbivores through biomechanical and chemical mechanisms, although the latter are indirect and remain poorly characterised. Chemical defences are principally regulated by several antiherbivore phytohormones. The jasmonic acid (JA) signalling pathway is particularly important and has been linked to Si supplementation, albeit with some contradictory findings. In this Perspectives article, we summarise existing knowledge of how Si affects JA in the context of herbivory and present a conceptual model for the interactions between Si and JA signalling in wounded plants. Further, we use novel information from the model grass Brachypodium distachyon to underpin aspects of this model. We show that Si reduces JA concentrations in plants subjected to chemical induction (methyl jasmonate) and herbivory (Helicoverpa armigera) by 34% and 32%, respectively. Moreover, +Si plants had 13% more leaf macrohairs than −Si plants. From this study and previous work, our model proposes that Si acts as a physical stimulus in the plant, which causes a small, transient increase in JA. When +Si plants are subsequently attacked by herbivores, they potentially show a faster induction of JA due to this priming. +Si plants that have already invested in biomechanical defences (e.g. macrohairs), however, have less utility for JA-induced defences and show lower levels of JA induction overall.

Silicon alleviates copper (Cu) toxicity in cucumber by increased Cu-binding capacity

Although silicon (Si) is known to increase plant resistance to metal toxicity stress, the mechanisms responsible for alleviation of copper (Cu) toxicity are still insufficiently clear. We investigated the role of Si on Cu-binding processes involved in buffering excessive Cu in cucumber (Cucumis sativus L.) tissues. Cucumber plants were subjected to moderate Cu toxicity stress (10 μM Cu) without (−Si) or with (+Si) supply of 1.5 mM Si. We analyzed total and cell wall concentrations of Cu and Cu-binding compounds (organic acids and Cu-proteins) along with parameters of oxidative stress (e.g. lipid peroxidation and lignification). Supply of Si decreased total Cu concentration in both root and leaf tissues, but increased the root cell wall Cu fraction. Also, Si increased superoxide dismutase (SOD) activity in 10 μM Cu-treated plants. Concomitantly, protein levels of Cu/Zn SOD isoforms (CSD1 and CSD2) in root tissues also increased in +Si plants. The leaf Cu-binding compounds, such as aconitate and plastocyanin (including the expression of CsPC gene) were higher in the +Si plants. Consequently, Si supply effectively lowered lipid peroxidation in both roots and leaves of Cu-stressed plants. Supply of Si enhanced both the accumulation of Cu-binding molecules (Zn/Cu SOD in roots; aconitate and plastocyanin in leaves), and the Cu-binding capacity of the root cell wall.

Climate warming and plant biomechanical defences: Silicon addition contributes to herbivore suppression in a pasture grass

Abstract Plants, notably the Poaceae, often accumulate large amounts of silicon (Si) from the soil. Si has multiple functional roles, particularly for alleviating abiotic and biotic stresses (e.g., defence against herbivores). Recent evidence suggests that environmental change, including temperature changes, can diminish Si accumulation which could affect functions such as herbivore defence. Using a field warming experiment, we grew a pasture grass (Phalaris aquatica) that was either supplemented or untreated with Si (+Si and −Si, respectively) under ambient and elevated (+2.8°C above ambient) air temperatures. We quantified soil water, plant growth rates, Si accumulation, leaf biomechanical properties and in situ relative growth rates of a herbivorous global insect pest (Helicoverpa armigera). Si supplementation promoted shoot and root biomass by c. 48% and 61%, respectively under ambient temperatures, but these gains were not apparent under warmed conditions. Warmer temperatures reduced Si uptake by −Si plants by c. 17%, potentially due to the lower levels of soil water content in warmed plots. Si supplementation, however, increased Si accumulation in leaves by c. 24% in warmed plots restoring Si levels to those seen under ambient temperatures. Si supplementation enhanced biomechanical properties in the leaves, but this was only statistically significant under ambient temperatures; leaves of +Si plants required 42% more force to fracture and were 30% tougher at the midrib than leaves of −Si plants. The relative growth rates of H. armigera declined by 56% when feeding on +Si plants under ambient temperatures, and while Si supplementation caused a trend towards declining herbivore growth rates under warmer conditions, this was not statistically significant. We conclude that climate warming may mitigate the beneficial effects of Si on Phalaris aquatica in the short term, potentially by reducing Si uptake. While Si uptake can be restored with Si supplementation, Si‐enhanced biomechanical defences against a global pest may not be fully restored under warmer temperatures. A plain language summary is available for this article.

Transcriptome Analysis Reveals New Insights into the Bacterial Wilt Resistance Mechanism Mediated by Silicon in Tomato.

Bacterial wilt is a devastating disease of tomato caused by soilborne pathogenic bacterium Ralstonia solanacearum. Previous studies found that silicon (Si) can increase tomato resistance against R. solanacearum, but the exact molecular mechanism remains unclear. RNA sequencing (RNA-Seq) technology was used to investigate the dynamic changes of root transcriptome profiles between Si-treated (+Si) and untreated (−Si) tomato plants at 1, 3, and 7 days post-inoculation with R. solanacearum. The contents of salicylic acid (SA), ethylene (ET), and jasmonic acid (JA) and the activity of defense-related enzymes in roots of tomato in different treatments were also determined. The burst of ET production in roots was delayed, and SA and JA contents were altered in Si treatment. The transcriptional response to R. solanacearum infection of the +Si plants was quicker than that of the untreated plants. The expression levels of differentially-expressed genes involved in pathogen-associated molecular pattern-triggered immunity (PTI), oxidation resistance, and water-deficit stress tolerance were upregulated in the Si-treated plants. Multiple hormone-related genes were differentially expressed in the Si-treated plants. Si-mediated resistance involves mechanisms other than SA- and JA/ET-mediated stress responses. We propose that Si-mediated tomato resistance to R. solanacearum is associated with activated PTI-related responses and enhanced disease resistance and tolerance via several signaling pathways. Such pathways are mediated by multiple hormones (e.g., SA, JA, ET, and auxin), leading to diminished adverse effects (e.g., senescence, water-deficit, salinity and oxidative stress) normally caused by R. solanacearum infection. This finding will provide an important basis to further characterize the role of Si in enhancing plant resistance against biotic stress.

Changes in leaf gas exchange and chlorophyll a fluorescence on soybean plants supplied with silicon and infected by Cercospora sojina

AbstractFrogeye spot, caused by Cercospora sojina, is one of the major diseases causing yield losses in soybean. Considering the potential of silicon (Si) to attenuate the physiological impairments imposed by pathogens infection, this study investigated its effect on leaf gas exchange and chlorophyll (Chl) a fluorescence parameters as well as on the concentrations of photosynthetic pigments and carbohydrate pools on soybean plants from cultivars Bossier and Conquista (susceptible and resistant to frogeye spot, respectively) grown in hydroponic culture containing 0 or 2 mM Si (−Si and +Si plants, respectively) that were noninoculated or inoculated with C. sojina. Plants from cultivar Bossier were more susceptible to frogeye spot compared to cultivar Conquista regardless of Si supply. Frogeye spot severity increased by Si supply regardless of the cultivar. There were no changes in the physiological parameters for noninoculated +Si plants. Even though the susceptibility of plants from cultivar Bossier to frogeye spot increased by Si supply, they showed lower values for the leaf gas exchange parameters, photochemical efficiency and concentration of photosynthetic pigments. The impairments imposed by C. sojina infection on the physiology of plants from cultivar Conquista were governed chiefly by reductions in stomatal conductance regardless of Si supply. The increase in hexose concentration for inoculated plants of the two cultivars was associated with their resistance to frogeye spot. Considering that the increased susceptibility of +Si plants from cultivar Conquista did not result in physiological impairments, it is plausible to rule out that the lower photosynthetic efficiency of plants from cultivar Bossier occurred due to a sharp reduction in the photosynthetically active leaf tissue.

Beneficial Effects of Silicon Application in Alleviating Salinity Stress in Halophytic Puccinellia Distans Plants

Little is known on the impact of silicon (Si) nutrition in halophytes. Accordingly, response of Si accumulating halophyte Puccinellia distans to Si nutrition was investigated. The experiment was carried out as factorial in a completely randomized design. Plants were hydroponically raised for six weeks under two salinity (0 and 200 mmol L− 1 NaCl) and Si (0 and 1.5 mmol L− 1 Na2SiO3) levels. Si improved plant dry weight and water relations under salinity. Salinity decreased the plant relative water content (RWC) but Si increased this parameter. Transpiration rate and stomatal density however, declined by salinity and Si even intensified these salt effect. Si affected salt tolerance mechanisms in P. distans. Thus, +Si plants had greater soluble sugars and amino acids and lower Na+ but increased cellulose and lignin and Na+ secretion from leaves. These possibly indicate more efficient osmotic adjustment and better operation of either salt exclusion and / or excretion mechanisms. In congruence, Si greatly enhanced the activity of H+-ATPase in both roots and shoots. +Si plants had reduced stress symptoms evidenced by lower proline and reduced electrolyte leakage indicating better membrane functioning. Altogether, Si application led to better performance of P. distans plants under saline conditions.

Silicon Promotes Growth of Brassica napus L. and Delays Leaf Senescence Induced by Nitrogen Starvation.

Silicon (Si) is the second most abundant element in soil and has several beneficial effects, especially in plants subjected to stress conditions. However, the effect of Si in preventing nitrogen (N) starvation in plants is poorly documented. The aim of this work was to study the effect of a short Si supply duration (7 days) on growth, N uptake, photosynthetic activity, and leaf senescence progression in rapeseed subjected (or not) to N starvation. Our results showed that after 1 week of Si supply, Si improves biomass and increases N uptake and root expression of a nitrate transporter gene. After 12 days of N starvation, compared to -Si plants, mature leaf from +Si plants showed a high chlorophyll content, a maintain of net photosynthetic activity, a decrease of oxidative stress markers [hydrogen peroxide (H2O2) and malondialdehyde (MDA)] and a significant delay in senescence. When N-deprived plants were resupplied with N, a greening again associated with an increase of photosynthetic activity was observed in mature leaves of plants pretreated with Si. Moreover, during the duration of N resupply, an increase of N uptake and nitrate transporter gene expression were observed in plants pretreated with Si. In conclusion, this study has shown a beneficial role of Si to alleviate damage associated with N starvation and more especially its role in delaying of leaf senescence.

Silicon induced Fe deficiency affects Fe, Mn, Cu and Zn distribution in rice (Oryza sativa L.) growth in calcareous conditions

A protective effect by silicon in the amelioration of iron chlorosis has recently been proved for Strategy 1 species, at acidic pH. However in calcareous conditions, the Si effect on Fe acquisition and distribution is still unknown. In this work, the effect of Si on Fe, Mn, Cu and Zn distribution was studied in rice (Strategy 2 species) under Fe sufficiency and deficiency. Plants (+Si or-Si) were grown initially with Fe, and then Fe was removed from the nutrient solution. The plants were then analysed using a combined approach including LA-ICP-MS images for each element of interest, the analysis of the Fe and Si concentration at different cell layers of root and leaf cross sections by SEM-EDX, and determining the apoplastic Fe, total micronutrient concentration and oxidative stress indexes. A different Si effect was observed depending on plant Fe status. Under Fe sufficiency, Si supply increased Fe root plaque formation, decreasing Fe concentration inside the root and increasing the oxidative stress in the plants. Therefore, Fe acquisition strategies were activated, and Fe translocation rate to the aerial parts was increased, even under an optimal Fe supply. Under Fe deficiency, +Si plants absorbed Fe from the plaque more rapidly than –Si plants, due to the previous activation of Fe deficiency strategies during the growing period (+Fe + Si). Higher Fe plaque formation due to Si supply during the growing period reduced Fe uptake and could activate Fe deficiency strategies in rice, making it more efficient against Fe chlorosis alterations. Silicon influenced Mn and Cu distribution in root.

Photosynthesis impairments and excitation energy dissipation on wheat plants supplied with silicon and infected with Pyricularia oryzae

Considering the effect of silicon (Si) in reducing the blast symptoms on wheat in a scenario where the losses in the photosynthetic capacity of the infected plants is lowered, this study investigated the ability of using the incident light, the chloroplastidic pigments (chlorophylls and carotenoids) alterations and the possible role of carotenoids on the process of light dissipation on wheat plants non-supplied (-Si) or supplied (+Si) with Si and inoculated or not with Pyricularia oryzae. For + Si plants, blast severity was reduced compared to -Si plants. Reductions in the concentration of photosynthetic pigments (total chlorophyll, violanxanthin + antheraxanthin + zeaxanthin, β-carotene and lutein) were greater for inoculated -Si plants than for inoculated + Si ones. The α-carotene concentration increased for inoculated -Si and +Si plants in comparison to non-inoculated plants limiting, therefore, lutein production. Higher functional damage to the photosystem II (PSII) was noticed for inoculated -Si plants with reductions in the values of maximum quantum quenching, photochemical yield of PSII and electron transport rate, but higher values for quenching non-photochemical. This finding also contributed to reductions in the values of light saturated rate photosynthesis and light saturation point for -Si plants which was attenuated for inoculated + Si plants. Increase in dark respiration values occurred for inoculated plants than for non-inoculated ones. The Si supply to wheat plants, besides reducing blast severity, contributed to their better photosynthetic performance. Moreover, inoculated + Si plants coped with drastic losses of light energy dissipation processes (fluorescence and heat) by increasing the concentration of carotenoids which helped to maintain the structural and functional viability of the photosynthetic machinery minimizing, therefore, lipid peroxidation and the production of reactive oxygen species.

Silicon Supplementation Alters the Composition of Herbivore Induced Plant Volatiles and Enhances Attraction of Parasitoids to Infested Rice Plants

Silicon (Si) is important in plant defenses that operate in a direct manner against herbivores, and work in rice (Oryza sativa) has established that this is mediated by the jasmonate signaling pathway. Plant defenses also operate indirectly, by the production of herbivore induced plant volatiles (HIPVs) that attract predators and parasitoids of herbivores. These indirect defenses too are mediated by the jasmonate pathway but no earlier work has demonstrated an effect of Si on HIPVs. In this study, we tested the effect of Si supplementation versus Si deprivation to rice plants on subsequent HIPV production following feeding by the important pest, rice leaffolder (Cnaphalocrocis medinalis). Gas chromatography–mass spectrometry analyses showed lower production of α-bergamotene, β-sesquiohellandrene, hexanal 2-ethyl, and cedrol from +Si herbivore-infested plants compared with -Si infested plants. These changes in plant chemistry were ecologically significant in altering the extent to which parasitoids were attracted to infested plants. Adult females of Trathala flavo-orbitalis and Microplitis mediator both exhibited greater attraction to the HIPV blend of +Si plants infested with their respective insect hosts compared to -Si infested plants. In equivalent studies using RNAi rice plants in which jasmonate perception was silenced there was no equivalent change to the HIPV blend associated with Si treatment; indicating that the effects of Si on HIPVs are modulated by the jasmonate pathway. Further, this work demonstrates that silicon alters the HIPV blend of herbivore-infested rice plants. The significance of this finding is that there are no earlier-published studies of this phenomenon in rice or any other plant species. Si treatment to crops offers scope for enhancing induced, indirect defenses and associated biological control of pests because parasitoids are more strongly attracted by the HIPVs produced by +Si plants.

Foliar or Subirrigation Silicon Supply Mitigates High Temperature Stress in Strawberry by Maintaining Photosynthetic and Stress-Responsive Proteins

Silicon (Si) is the second most abundant element in the soil and is known to help in crop productivity. Si improves photosynthesis as well as remediates nutrient imbalances and abiotic stresses in plants. The impact and the importance of different sources, concentration, and supply of Si in improving the propagation of horticultural crops are limited. Thus, the present study focused on the supply, concentration, and source of Si on two important Korean strawberry cultivars ‘Sulhyang’ and ‘Maehyang’ under temperature stress. The high temperature (41 °C) resulted in oxidative stress in the form of H2O2 and O2 1− localizations in the -Si- and Si-treated plants as compared to 25 or 33 °C in both cultivars. However, Si, especially that from K2SiO3 source, had the ability to relieve the stress level. The immunoblots of two important photosynthetic proteins PsaA and PsbA showed decreased expression levels in the -Si plants under 41 °C temperature stress, whereas the expression levels were retained in the Si-supplied plants, particularly with K2SiO3 as the Si source. In both 25 and 33 °C, no changes in expressions of PsaA and PsbA were observed. Interestingly, the expression of three important stress-responsive proteins, superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT), were abundantly increased in the Si-treated plants under high-temperature stress (41 °C) and decreased in the –Si-treated plants except in those grown in 25 or 33 °C. The observed responses to silicon supply in high temperature stressed-plants indicate that Si, particularly in the form of K2SiO3, has a significant role in limiting the negative effects of high temperature stress by maintaining the photosynthetic proteins and stress-responsive proteins of the ascorbate glutathione defense mechanism. Moreover, these results also depict that Si application is a good way to maintain the health of plants at the propagation stage even under high temperatures of greenhouses.

The functional ecology of plant silicon: geoscience to genes

Podcast

Silicon‐Induced Changes in the Antioxidant System Reduce Soybean Resistance to Frogeye Leaf Spot

AbstractFrogeye leaf spot (FLS), caused by the fungus Cercospora sojina, is one of the most important soybean diseases and can cause great yield losses. Several studies have demonstrated that silicon (Si) enhances the plant antioxidant system, especially when they are subjected to stresses. Thus, this study was designed to evaluate the effect of Si on soybean resistance to FLS, on the antioxidant system, on the concentration of reactive oxygen species and on cellular damage during the infection process of C. sojina. Plants from cultivars Bossier and Conquista, susceptible and resistant to FLS, respectively, were supplied with either 0 (−Si) or 2 mm (+Si) and non‐inoculated or inoculated with C. sojina. FLS severity was greater for Bossier than for Conquista, regardless of the Si supply, and it was increased by Si for both cultivars. The activities of the most antioxidant enzymes were lower in the +Si plants than in the −Si plants when they were not inoculated. Inoculated plants usually showed an increased enzyme activities and higher concentrations of ascorbate and reduced glutathione than did the non‐inoculated plants, regardless of Si supply. At advanced stages of fungal infection, the +Si‐inoculated plants from Bossier had higher activity of most antioxidant enzymes and higher concentrations of superoxide and malondialdehyde compared to the non‐inoculated plants as a result of an increased oxidative stress. The results from this study provide the first evidence that Si reduces the basal activity of antioxidant enzymes in soybean leaves leading to an increase in host susceptibility to FLS.

The role of silicon in enhancing resistance to bacterial blight of hydroponic- and soil-cultured rice.

Here we report for the first time that bacterial blight of rice can be alleviated by silicon (Si) added. In both inoculated and uninoculated plants, shoot dry weight was significantly higher in the +Si plants than in the −Si plants. A soil-cultured trial showed that disease severity was 24.3% lower in the Si-amended plants than in the non-Si-amended plants. Plants that were switched from −Si to +Si nutrient solution and simultaneously inoculated with Xoo also exhibited the same high resistance to bacterial blight as the plants that were treated continuously with Si, with control efficiencies of 52.8 and 62.9%, respectively. Moreover, total concentrations of soluble phenolics and lignin in rice leaves were significantly higher in the +Si plants than in the −Si plants. Polyphenoloxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities in rice leaves were observed to be higher in the +Si plants than in the −Si plants. The expression levels of Os03g0109600, Prla, Rcht2 and Lox2osPil, were also higher in +Si plants than in −Si plants post-inoculation during the experimental time. Addition of Si resulted in increased Pal transcription, and inhibited CatA and Os03g0126000 expression in the earlier and later stages of bacterial inoculation, respectively.