Silicon\u27s Role in Abiotic and Biotic Plant Stresses

Silicon (Si) plays a pivotal role in the nutritional status of a wide variety of monocot and dicot plant species and helps them, whether directly or indirectly, counteract abiotic and or biotic stresses. In general, plants with a high root or shoot Si concentration are less prone to pest attack and exhibit enhanced tolerance to abiotic stresses such as drought, low temperature, or metal toxicity. However, the most remarkable effect of Si is the reduction in the intensities of a number of seedborne, soilborne, and foliar diseases in many economically important crops that are caused by biotrophic, hemibiotrophic, and necrotrophic plant pathogens. The reduction in disease symptom expression is due to the effect of Si on some components of host resistance, including incubation period, lesion size, and lesion number. The mechanical barrier formed by the polymerization of Si beneath the cuticle and in the cell walls was the first proposed hypothesis to explain how this element reduced the severity of plant diseases. However, new insights have revealed that many plant species supplied with Si have the phenylpropanoid and terpenoid pathways potentiated and have a faster and stronger transcription of defense genes and higher activities of defense enzymes. Photosynthesis and the antioxidant system are also improved for Si-supplied plants. Although the current understanding of how this overlooked element improves plant reaction against pathogen infections, pest attacks, and abiotic stresses has advanced, the exact mechanism(s) by which it modulates plant physiology through the potentiation of host defense mechanisms still needs further investigation at the genomic, metabolomic, and proteomic levels

Anthropogenic perturbations of the silicon cycle at the global scale: Key role of the land-ocean transition

International audienceSilicon (Si), in the form of dissolved silicate (DSi), is a key nutrient in marine and continental ecosystems. DSi is taken up by organisms to produce structural elements (e.g., shells and phytoliths) composed of amorphous biogenic silica (bSiO(2)). A global mass balance model of the biologically active part of the modern Si cycle is derived on the basis of a systematic review of existing data regarding terrestrial and oceanic production fluxes, reservoir sizes, and residence times for DSi and bSiO(2). The model demonstrates the high sensitivity of biogeochemical Si cycling in the coastal zone to anthropogenic pressures, such as river damming and global temperature rise. As a result, further significant changes in the production and recycling of bSiO(2) in the coastal zone are to be expected over the course of this century

Effect of silicon rate and host resistance on blast, scald, and yield of upland price

Blast-resistant, partially resistant, and susceptible cultivars of rice were planted in soil amended with Si at 0, 500, or 1,000 kg/ha at two locations in eastern Colombia to assess differential responses to leaf blast, neck blast, and leaf scald, and to examine the quantity and quality of grains harvested. Leaf and neck blast on partially resistant and susceptible cultivars were reduced by Si as the rate of Si was increased. Depending on the location, the level of severity of leaf and neck blast on partially resistant cultivars, when fertilized with Si at 500 or 1,000 kg/ha, was lowered to that of resistant cultivars without Si. At both locations, yields were increased by as much as 42%, depending on the cultivar, by Si applied at 1,000 kg/ha. In general, high rates of Si reduced the number of broken grains harvested. Grain discoloration, regardless of cultivar or location, was reduced by as much as 70% at the high rate of Si. The application of Si to complement host resistance to blast and scald appears to be an effective strategy for disease management in rice and provides the added benefit of improving the quantity and quality of rice yields

A 5-day method for determination of soluble silicon concentrations in nonliquid fertilizer materials using a sodium carbonate-ammonium nitrate extractant followed by visible spectroscopy with heteropoly blue analysis: Single-laboratory validation

A 5-day method for determining the soluble silicon (Si) concentrations in nonliquid fertilizer products was developed using a sodium carbonate (Na 2CO3)-ammonium nitrate (NH4NO3) extractant followed by visible spectroscopy with heteropoly blue analysis at 660 nm. The 5-Day Na2CO3-NH4NO3 Soluble Si Extraction Method can be applied to quantify the plant-available Si in solid fertilizer products at levels ranging from 0.2 to 8.4% Si with an LOD of 0.06%, and LOQ of 0.20%. This Si extraction method for fertilizers correlates well with plant uptake of Si (r2 = 0.96 for a range of solid fertilizers) and is applicable to solid Si fertilizer products including blended products and beneficial substances. Fertilizer materials can be processed as received using commercially available laboratory chemicals and materials at ambient laboratory temperatures. The singlelaboratory validation of the 5-Day Na2CO 3-NH4NO3 Soluble Si Extraction Method has been approved by The Association of American Plant Food Control Officials for testing nonliquid Si fertilizer products. © 2013 Publishing Technology

Silicon enhances the accumulation of diterpenoid phytoalexins in rice: A potential mechanism for blast resistance

Although several reports underscore the importance of silicon (Si) in controlling Magnaporthe grisea on rice, no study has associated this beneficial effect with specific mechanisms of host defense responses against this fungal attack. In this study, however, we provide evidence that higher levels of momilactone phytoalexins were found in leaf extracts from plants inoculated with M. grisea and amended with silicon (Si+) than in leaf extracts from inoculated plants not amended with silicon (Si-) or noninoculated Si+ and Si- plants. On this basis, the more efficient stimulation of the terpenoid pathway in Si+ plants and, consequently, the increase in the levels of momilactones appears to be a factor contributing to enhanced rice resistance to blast. This may explain the lower level of blast severity observed on leaves of Si+ plants at 96 h after inoculation with M. grisea. The results of this study strongly suggest that Si plays an active role in the resistance of rice to blast rather than the formation of a physical barrier to penetration by M. grisea

Efeito do silicato de cálcio e da autoclavagem na supressividade e na conducividade de dois solos à Rhizoctonia solani

The effect of calcium silicate slag and soil sterilization on the natural suppressiveness of a Typic Acrustox (clay Dark Red Latosol – LEa) and the natural conduciveness of an Oxic Haplustoll (TRe) to Rhizoctonia solani were studied under greenhouse conditions. The experimental design was a three-replicate completely randomized one, with 2 x 3 x 2 factorial combination of the following treatments: two soil kinds (LEa and TRe, collected at 0-20 cm layer); three treatments with and without soil sterilization, calcium silicate slag and nontreated control; and uninfested and infested with R. solani. Each soil material was infested previously with 800 mg of the inoculum per kg soil. Application of silicate was done mixing 0,63 g of this product with 1 kg each soil material and incubated for 30 days. The application of silicate increased the exchangeable Ca2+ and bases amount in both soils. The decrease in the aluminum saturation level from 70 to 19% and the increase in base saturation from 9 to 21% altered significantly the natural suppressiveness of LEa to R. solani. Application of silicate to the TRe had no effect on its conduciveness, for its natural eutrophic character, which is benefic to R. solani development. Sterilization by autoclavation did not influence disease development on bean by R. solani. This suggests that possibly other abiotic factors were responsible for either suppressiveness or conduciveness of these soils.Objetivou-se verificar o efeito da aplicação de silicato de cálcio e da esterilização na supressividade natural de um Latossolo Vermelho-Escuro (LEa) álico textura muito argilosa e na conducividade natural de uma Terra Roxa Estruturada eutrófica (TRe) ao fungo Rhizoctonia solani, em condições de casa de vegetação. Utilizou-se o delineamento inteiramente casualizado em esquema fatorial 2 x 3 x 2. Os fatores foram: duas classes de solo (LEa e TRe - 0-20 cm); três tratamentos (esterilização ou não por autoclavagem, aplicação de silicato e testemunha) e infestação ou não com R. solani, com três repetições e 16 plântulas de feijoeiro por parcela. A aplicação de silicato foi feita incorporando 0,63 g do produto em 1 kg de cada material de solo, seguido de incubação por 30 dias. Para promover a infestação artificial, foram colocados 800 mg de inóculo em 1 kg de cada material de solo. O silicato de cálcio aumentou os teores de Ca trocável e a soma de bases nos dois solos. Um decréscimo na saturação por Al de 70 para 19% e um aumento na saturação por bases de 9 para 21% alteraram significativamente a supressividade natural do LEa à R. solani. Com relação à TRe, a aplicação de silicato não teve nenhum efeito na sua conducividade, dado ao seu natural caráter eutrófico, o qual já é favorável ao desenvolvimento deste fungo. A esterilização não influiu no desenvolvimento de R. solani, o que sugere que os fatores abióticos foram os responsáveis pela supressividade ou conducividade desses solos

Silicon and manganese on rice resistance to blast

Blast, caused by the fungus Pyricularia oryzae, is the most important fungal disease of rice. The effect of silicon (Si) and manganese (Mn), and their interaction, on rice resistance to blast was investigated. Rice plants (cultivar "Metica 1") were grown in hydroponic solution with 0 or 2 mmol L-1 of Si and with 0.5, 2.5, and 10 mmol L-1 of Mn. Sixty-day-old plants were inoculated with a conidial suspension of P. oryzae and the incubation period (IP), the number of lesions (NL) per cm² of leaf area, the lesion size (LS), and blast severity were evaluated. Blast severity was scored at 48, 72, 96, and 144 hours after inoculation and data were used to obtain the area under blast progress curve (AUBPC). Silicon concentration was significantly higher in leaf tissues of plants supplied with this element than on its absence, regardless of Mn rates. There was no significant difference in Si concentration among the Mn rates for both - Si and +Si treatments. The Mn concentration was significantly higher in the tissues of plants from the - Si treatment as compared to plants of the +Si treatment, but only at the rate of 10 mmol L-1 of Mn. There was a significant increase in Mn concentration as the rates of this micronutrient increased from 0.5 to 10 mmol L-1 regardless of the Si treatments. The IP significantly increased in the +Si treatment. The Mn rates had no effect on the IP regardless of the Si treatments. The NL was significantly lower in the presence of Si regardless of the Mn rates. The Mn rates had no effect on NL regardless of the Si treatments. The addition of Si to the nutrient solution significantly reduced both LS and AUBPC regardless of Mn rates. However, in the absence of Si, the values for LS and AUBPC were significantly lower at the Mn rate of 10 µmol L-1 as compared to the rate of 0.5 µmol L-1. Overall, the results from this study showed the potential of Si to decrease blast development on rice regardless of the foliar concentration of Mn