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Main Conclusion: Silicon application mitigates phosphate deficiency in barley through an interplay with auxin and nitric oxide, enhancing growth, photosynthesis, and redox balance, highlighting the potential of silicon as a fertilizer for overcoming nutritional stresses. Silicon (Si) is reported to attenuate nutritional stresses in plants, but studies on the effect of Si application to plants grown under phosphate (Pi) deficiency are still very scarce, especially in barley. Therefore, the present work was undertaken to investigate the potential role of Si in mitigating the adverse impacts of Pi deficiency in barley Hordeum vulgare L. (var. BH902). Further, the involvement of two key regulatory signaling molecules--auxin and nitric oxide (NO)--in Si-induced tolerance against Pi deficiency in barley was tested. Morphological attributes, photosynthetic parameters, oxidative stress markers (O 2 ·- , H 2 O 2 , and MDA), antioxidant system (enzymatic--APX, CAT, SOD, GR, DHAR, MDHAR as well as non-enzymatic--AsA and GSH), NO content, and proline metabolism were the key traits that were assessed under different treatments. The P deficiency distinctly declined growth of barley seedlings, which was due to enhancement in oxidative stress leading to inhibition of photosynthesis. These results were also in parallel with an enhancement in antioxidant activity, particularly SOD and CAT, and endogenous proline level and its biosynthetic enzyme (P5CS). The addition of Si exhibited beneficial effects on barley plants grown in Pi-deficient medium as reflected in increased growth, photosynthetic activity, and redox balance through the regulation of antioxidant machinery particularly ascorbate-glutathione cycle. We noticed that auxin and NO were also found to be independently participating in Si-mediated improvement of growth and other parameters in barley roots under Pi deficiency. Data of gene expression analysis for PHOSPHATE TRANSPORTER1 (HvPHT1) indicate that Si helps in increasing Pi uptake as per the need of Pi-deficient barley seedlings, and also auxin and NO both appear to help Si in accomplishing this task probably by inducing lateral root formation. These results are suggestive of possible application of Si as a fertilizer to correct the negative effects of nutritional stresses in plants. Further research at genetic level to understand Si-induced mechanisms for mitigating Pi deficiency can be helpful in the development of new varieties with improved tolerance against Pi deficiency, especially for cultivation in areas with Pi-deficient soils., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Although, silicon - the second most abundant element in the earth crust could not supersede carbon (C) in the competition of being the building block of life during evolution, yet its presence has been reported in some life forms. In case of the plants, silicon has been reported widely to promote the plant growth under normal as well as stressful situations. Nanoform of silicon is now being explored for its potential to improve plant productivity and its tolerance against various stresses. Silicon nanoparticles (SiNPs) in the form of nanofertilizers, nanoherbicides, nanopesticides, nanosensors and targeted delivery systems, find great utilization in the field of agriculture. However, the mechanisms underlying their uptake by plants need to be deciphered in detail. Silicon nanoformss are reported to enhance plant growth, majorly by improving photosynthesis rate, elevating nutrient uptake and mitigating reactive oxygen species (ROS)-induced oxidative stress. Various studies have reported their ability to provide tolerance against a range of stresses by upregulating plant defense responses. Moreover, they are proclaimed not to have any detrimental impacts on environment yet. This review includes the up-to-date information in context of the eminent role of silicon nanoforms in crop improvement and stress management, supplemented with suggestions for future research in this field., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Exogenous applications of silicon (Si) can initiate cellular defence pathways to enhance plant resistance to abiotic and biotic stresses. Plant Si accumulation is regulated by several transporters of silicic acid (e.g. Lsi1, Lsi2, and Lsi6), but the precise mechanisms involved in overall Si transport and its beneficial effects remains unclear. In stressed plants, the accumulation of Si leads to a defence mechanism involving the formation of amorphous or hydrated silicic acid caused by their polymerization and interaction with other organic substances. Silicon also regulates plant ionic homeostasis, which involves the nutrient acquisition, availability, and replenishment in the soil through biogeochemical cycles. Furthermore, Si is implicated in modulating ethylene-dependent and jasmonate pathways, as well as other phytohormones, particularly under stress conditions. Crosstalk between Si and phytohormones could lead to improvements in Si-mediated crop growth, especially when plants are exposed to stress. The integration of Si with reactive oxygen species (ROS) metabolism appears to be a part of the signaling cascade that regulates plant phytohormone homeostasis, as well as morphological, biochemical, and molecular responses. This review aims to provide an update on Si interplays with ROS, phytohormones, and other signaling molecules that regulate plant development under stress conditions., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Reckless use of herbicides like butachlor (Buta) in the fields represents a serious threat to crop plants, and hence to their productivity. Silicon (Si) is well known for its implication in the alleviation of the effects of abiotic stresses; however, its role in mitigating Buta toxicity is not yet known. Therefore, this study was carried out to explore the role of Si (10 µM) in regulating Buta (4 µM) toxicity in rice seedlings. Buta reduced growth and photosynthesis, altered nitric oxide (NO) level and leaf and root anatomy, inhibited enzyme activities of the ascorbate-glutathione cycle (while transcripts of associated enzymes, increased except OsMDHAR), as well as its metabolites (ascorbate and glutathione) and uptake of nutrients (Mg, P, K, S, Ca, Fe, etc. except Na), while addition of Si reversed Buta-induced alterations. Buta stimulated the expression of Si channel and efflux transporter genes- Lsi1 and Lsi2 while the addition of Si further greatly induced their expression under Buta toxicity. Buta increased free proline accumulation by inducing the activity of Δ 1 -pyrroline-5-carboxylate synthetase (P5CS) and decreasing proline dehydrogenase (PDH) activity, while Si reversed these effects caused by Buta. Our results suggest that Si-governed mitigation of Buta toxicity is linked with favorable modifications in energy flux parameters of photosynthesis and leaf and root anatomy, up-regulation of Si channel and transporter genes, ascorbate-glutathione cycle and nutrient uptake, and lowering in oxidative stress. We additionally demonstrate that NO might have a crucial role in these responses.

An emerging stress of nanomaterials in soil and water is of great concern as it limits crop productivity and affects humans as well. Therefore, it is required to manage this problem. Silicon and plant growth promoting rhizobacteria has gained the engaging role in agriculture as (bio-)fertilizers. However, their role against silver nanoparticles (AgNPs) is still not known. Hence, present study was envisaged to investigate role of Si, PGPR and phytohormone indole acetic acid (IAA) in regulating AgNP stress in Brassica juncea seedlings. The study highlighted the impact of various treatments with respect to overproduction of reactive oxygen species, signaling molecule nitric oxide, oxidative markers like antioxidant enzymes and nonenzymatic components of ascorbate-glutathione pathway. Interestingly, silicon when present with AgNPs enhanced toxicity by reducing growth and mechanistic properties of B. juncea. Moreover, the results highlight the role of PGPR and IAA towards reduction in toxicity by promoting the plant growth under stressed conditions. Treatments AgNP + Si + PGPR/IAA were observed to significantly reduce the stress and enhance plant growth against treatment AgNPs alone. This reversal in toxicity by PGPR and IAA along with Si suggests the idea to formulate and utilize their combination as biofertilizers for eradicating the stress in near future., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The role of silicon (Si) in alleviating biotic as well as abiotic stresses is well known. However, the potential of silicon nanoparticle (SiNP) in regulating abiotic stress and associated mechanisms have not yet been explored. Therefore, in the present study hydroponic experiments were conducted to investigate whether Si or SiNp are more effective in the regulation of UV-B stress. UV-B (ambient and enhanced) radiation caused adverse effect on growth of wheat (Triticum aestivum) seedlings, which was accompanied by declined photosynthetic performance and altered vital leaf structures. Levels of superoxide radical and H 2 O 2 were enhanced by UV-B as also evident from their histochemical stainings, which was accompanied by increased lipid peroxidation (LPO) and electrolyte leakage. Activities of superoxide dismutase and ascorbate peroxidase were inhibited by UV-B while catalase and guaiacol peroxidase, and all non-enzymatic antioxidants were stimulated by UV-B. Although, nitric oxide (NO) content was increased at all tested combinations, but its maximum content was observed under SiNps together with UV-B enhanced treatment. Pre-additions of SiNp as well as Si protected wheat seedlings against UV-B by regulating oxidative stress through enhanced antioxidants. Data indicate that SiNp might have protected wheat seedlings through NO-mediated triggering of antioxidant defense system, which subsequently counterbalance reactive oxygen species-induced damage to photosynthesis. Further, SiNp appear to be more effective in reducing UV-B stress than Si, which is related to its greater availability to wheat seedlings., (Copyright © 2016 Elsevier Masson SAS. All rights reserved.)

The responses of wheat seedling treated with silicon (Si; 10 μM) and lead (Pb; 100 μM) for 7 days have been investigated by analyzing growth, Pb uptake, chlorophyll fluorescence, oxidative stress, antioxidants and nutrients regulation. Results indicated that, Pb significantly (P<0.05) declined growth of seedlings which was accompanied by uptake of Pb. Under Pb stress, fluorescence parameters: Fv/Fm ratio and qP were significantly (P<0.05) decreased while NPQ was increased. Si addition alleviated Pb-induced decrease in growth and alterations in photosynthesis, and also significantly (P<0.05) lowered Pb uptake. Under Pb treatment, oxidative stress markers: hydrogen peroxide and lipid peroxidation were enhanced while DPPH(•) scavenging capacity and total phenolic compounds (TPCs) were decreased significantly, however, Si addition improved the status of antioxidants. The non-protein thiols (NP-SH) showed enhanced level under Pb stress. Pb stress considerably disturbed status of the nutrients as decrease in Ca, P, Mg, Zn and Ni contents while an increase in K, S, B, Cu, Fe, Mn and Na contents were noticed. Si addition maintained status of all the nutrients remarkably. The quickest method of element analysis: LIBS spectra revealed significantly lower uptake of Pb in seedlings grown under Si and Pb combination and same was correlated with the data of AAS. Overall results pointed out that excess Pb uptake disturbed status of nutrients, photosynthetic performance, antioxidant capacity, hence severe oxidative damage to lipids occurred. Further, Si supplementation successfully regulated these parameters by inhibiting Pb uptake hence maintained growth of wheat seedlings. Similar pattern of data recorded by the LIBS, AAS and ICAP-AES confirmed that LIBS may be one of the promising and authentic tools to monitor the mineral and metal distribution in the plants without hampering or disturbing the environment due to its eco-friendly and non-invasive nature., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The present study was aimed to investigate the effect of silicon nanoparticles (SiNp) against Cr (VI) phytotoxicity in pea seedlings. Results show that Cr(VI, 100 μM) significantly (P < 0.05) declined growth of pea which was accompanied by the enhanced level of Cr. Additionally, photosynthetic pigments and chlorophyll fluorescence parameters like F(v)/F(m), F(v)/F0 and qP were decreased while NPQ significantly (P < 0.05) increased under Cr(VI) treatment. Superoxide radical, hydrogen peroxide and malondialdehyde (MDA-lipid peroxidation) contents were enhanced by Cr(VI). Activities of antioxidant enzymes like superoxide dismutase and ascorbate peroxidase were increased by Cr (VI) while activities of catalase, glutathione reductase and dehydroascorbate reductase were inhibited significantly (P < 0.05). Micro and macronutrients also show decreasing trends (except S) under Cr(VI) treatment. However, addition of SiNp together with Cr(VI) protects pea seedlings against Cr(VI) phytotoxicity hence improved growth was noticed. In conclusion, the results of this study show that Cr(VI) causes negative impact on pea seedlings, however; SiNp protects pea seedlings against Cr(VI) phytotoxicity by reducing Cr accumulation and oxidative stress, and up-regulating antioxidant defense system and nutrient elements., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Silicon (Si)-mediated alleviation of Cr(VI) toxicity was examined in wheat seedlings using an in vivo approach that involves chlorophyll fluorescence, laser induced breakdown spectroscopy (LIBS) and anatomical changes. Exposure to Cr(VI) significantly reduced the growth and photosynthetic activities (chlorophyll fluorescence) in wheat which was accompanied by remarkable accumulation of this element in tissues. However, addition of Si to the growth medium alleviated the effects of Cr(VI). The LIBS spectra were used as a fingerprint of the elemental compositions in wheat seedlings, which showed a reduction in Cr accumulation following Si addition. Nutrient element levels (Ca, Mg, K and Na) declined in wheat following the addition of Cr (VI), as recorded by LIBS and inductively coupled plasma atomic emission spectroscopy (ICAP-AES). However, addition of Si along with Cr(VI) increased the contents of nutrient elements in wheat. LIBS, ICAP-AES and AAS showed a similar distribution pattern of elements measured in wheat. Anatomical observations of leaf and root revealed that Cr(VI) affected internal structures while Si played a role in protection from toxic effects. The results showed the suitability of chlorophyll fluorescence as a parameter and appropriateness of LIBS technique and anatomical procedures to elucidate Si-mediated alleviation of Cr(VI) toxicity. Furthermore, our results suggest that the measured parameters and techniques can be used non-invasively for monitoring the growth of crops under different environmental conditions., (Copyright © 2014 Elsevier Inc. All rights reserved.)

For better understanding of silicon (Si)-mediated increase in metal tolerance in plants, the alterations in growth, mineral elements and anatomical features were investigated in rice seedlings exposed to Si (10 μM) and aluminium (Al; 50 μM). Al decreased seedling growth which was accompanied by an increase in Al accumulation. In contrast, addition of Si alleviated toxic effects of Al and led to the decrease in Al accumulation. Magnesium (Mg) and zinc (Zn) contents were decreased by Al; however, Si addition prevented decrease in Mg and Zn contents. Manganese (Mn) content was increased by Al while Si addition did not have a significant effect on Mn content under Al treatment. Al exposure decreased frequency of stomata and root hairs, length of root hairs and leaf epidermal cells, and distorted the structure and integrity of mesophyll cells and phloem; however, addition of Si reduced these abnormalities. Results showed that Si addition protected rice seedlings against Al toxicity by decreasing Al accumulation and by maintaining level of some mineral elements, and the key structures of leaf and root.

The individual impact of silicon (Si) and nitric oxide (NO, as sodium nitroprusside) on metal toxicity in various plant species has been well documented; however, their combined action in the regulation of metal stress has never been tested yet. Therefore, this study investigates the effects of the combined application of Si and NO in the mitigation of Cd toxicity in wheat seedlings. Seedlings grown on Cd has a significantly declined growth due to an increased accumulation of Cd and oxidative stress markers (due to downregulation of antioxidant defense system particularly ascorbate‐glutathione cycle) and a decreased accumulation of NO and Si. Additionally, the altered leaf and root structures resulted into a declined photosynthetic efficiency. However, the addition of Si and NO alone as well as combined significantly alleviated Cd toxicity in wheat seedlings by lowering the accumulation of Cd and oxidative stress markers and improving leaf and root structures, which are collectively responsible for a better photosynthetic rate under Cd toxicity, and hence an improved growth was noticed. Particularly, the application of Si and NO in combination lowered the oxidative stress markers via upregulating the antioxidant defense system (particularly AsA‐GSH cycle) suggesting the increased efficacy of Si + NO against the Cd toxicity in wheat seedlings as compared to their alone treatments. [ABSTRACT FROM AUTHOR]

Arsenic (As) negatively affects plant development. This study evaluates how the application of silicon (Si) can favor the formation of adventitious roots in rice under arsenate stress (AsV) as a mechanism to mitigate its negative effects. The simultaneous application of AsV and Si up-regulated the expression of genes involved in nitric oxide (NO) metabolism, cell cycle progression, auxin (IAA, indole-3-acetic acid) biosynthesis and transport, and Si uptake which accompanied adventitious root formation. Furthermore, Si triggered the expression and activity of enzymes involved in ascorbate recycling. Treatment with L-NAME (N G-nitro L-arginine methyl ester), an inhibitor of NO generation, significantly suppressed adventitious root formation, even in the presence of Si; however, supplying NO in the growth media rescued its effects. Our data suggest that both NO and IAA are essential for Si-mediated adventitious root formation under AsV stress. Interestingly, TIBA (2,3,5-triiodobenzoic acid), a polar auxin transport inhibitor, suppressed adventitious root formation even in the presence of Si and SNP (sodium nitroprusside, an NO donor), suggesting that Si is involved in a mechanism whereby a cellular signal is triggered and that first requires NO formation, followed by IAA biosynthesis. [ABSTRACT FROM AUTHOR]

Nanoparticle-pollution has associated severe negative effects on crop productivity. Hence, methods are needed to alleviate nano-toxicity in crop plants. The present study aims to evaluate if the exogenous hydrogen sulfide (H 2 S) application in combination with silicon (Si) could palliate the harmful effects of copper oxide nanoparticles (CuO NPs). Fifteen day-old rice (Oryza sativa L.) seedlings were used as a model plant. The results indicate that simultaneous exogenous addition of 10 μM Si and 100 μM NaHS (as an H 2 S donor) provided tolerance and enhanced defence mechanism of the rice seedlings against 100 μM CuO NPs. Thus, it was observed in terms of their growth, photosynthetic pigments, antioxidant enzyme activities, the content of non-enzymatic components, chlorophyll fluorescence and up-regulation of antioxidant genes. Si and NaHS stimulated gene expression of silicon (Lsi1 and Lsi2) and auxin (PIN5 and PIN10) transporters. Taken together, data indicate that H 2 S underpins the beneficial Si effects in rice seedlings against the oxidative stress triggers by CuO NPs, and stimulation of enzymatic components of the ascorbate-glutathione cycle being the main factor for the beneficial effects triggered by the couple of Si and H 2 S. Therefore, it could be concluded that the simultaneous application of Si and H 2 S promote the resilience of the rice seedlings against the oxidative stress induced by CuO NPs. [Display omitted] • CuO NPs declined growth of rice seedlings. • Silicon alleviated CuO NPs stress. • Si and NaHS stimulated gene expression of silicon and auxin transporters. • H 2 S strengthens Si impact against the oxidative stress triggers by CuO NPs in rice seedlings. [ABSTRACT FROM AUTHOR]

The present study was aimed to investigate copper (Cu) toxicity alleviatory potential of silicon in Vigna radiata L. (mung bean) seedlings. Moreover, attention has also been paid to find out whether endogenous nitric oxide (NO) has any role in Si-governed alleviation of Cu stress. The length of root and shoot, fresh weight, and biochemical attributes were adversely affected by Cu exposure. However, application of Si rescued negative effects of Cu. Cu exposure decreased cell viability, and enhanced cell death and levels of oxidative stress markers (O 2 •‾, H 2 O 2 and MDA), but Si significantly mitigated these effects of Cu. Application of Cu substantially stimulated the activities of superoxide dismutase and guaiacol peroxidase while inhibited activity of catalase. However, Si addition reversed this effect of Cu. Ascorbate and glutathione contents in roots and shoots were declined by Cu but stimulated by Si. Moreover, we noticed that addition of Nω-nitro- L -arginine methyl ester hydrochloride (L-NAME) and sodium tungstate (Tung) further augmented Cu toxicity but addition of sodium nitroprusside rescued adverse effects of L-NAME and Tung. Altogether, data suggest that though Si was able in alleviating Cu toxicity in mung bean seedlings but it requires endogenous nitric oxide. • Cu declined growth of mung bean seedlings. • Silicon alleviated Cu stress. • Si stimulated antioxidant enzymes. • NO is involved in Si governed mitigation of Cu stress. [ABSTRACT FROM AUTHOR]

Uncontrolled application of herbicides in the agricultural field poses a severe risk to crops by affecting their yields. Therefore, methods are required to reduce the toxic effects of herbicides in plants. Studies indicate that silicon (Si) provides tolerance and enhances defence mechanism of the plant against abiotic stress. But its role in alleviating Metsulfuron methyl (Meth) herbicide induced toxicity in wheat seedlings is still not known. This study highlighted the potential of exogenous addition of Si in the alleviation of toxic effect of Meth herbicide in wheat seedlings. The exposure of wheat seedlings to Meth herbicide reduced the growth, photosynthetic pigments, antioxidant enzyme activity and nitric oxide (NO) content. Further, Meth herbicide also increased cell death and decreased cell viability in root tips. However, addition of Si reversed Meth-induced these alterations. Moreover, Si also activates antioxidant system which helps in scavenging of free radicals generated under Meth herbicide stress in wheat seedlings. Application of Si to Meth treated wheat seedlings also up-regulated silicon transporter gene Lsi1 (silicon influx transporter) and some of the antioxidant enzyme genes. All together, the data indicate that Si has capability of alleviating Meth herbicide stress in wheat seedlings but it appears that endogenous NO has a positive role in this endeavour of Si. • Metsulfuron methyl herbicide significantly reduced growth of wheat plants. • But, addition of silicon alleviated metsulfuron methyl induced stress in wheat. • Furthermore, supplementation of Si up -regulated the expression level of both stress associated genes and Si transporters gene (Lsi1) under metsulfuron methyl stress. • NO is involved in Si governed alleviation of metsulfuron methyl induced stress in wheat. [ABSTRACT FROM AUTHOR]

The rising heavy metal contamination of soils imposes toxic impacts on plants as well as other life forms. One such highly toxic and carcinogenic heavy metal is hexavalent chromium [Cr(VI)] that has been reported to prominently retard the plant growth. The present study investigated the potential of silicon (Si, 10 µM) to alleviate the toxicity of Cr(VI) (25 µM) on roots of wheat (Triticum aestivum L.) seedlings. Application of Si to Cr(VI)-stressed wheat seedlings improved their overall growth parameters. This study also reveals the involvement of two phytohormones, namely auxin and cytokinin and their crosstalk in Si-mediated mitigation of the toxic impacts of Cr(VI) in wheat seedlings. The application of cytokinin alone to wheat seedlings under Cr(VI) stress reduced the intensity of toxic effects of Cr(VI). In combination with Si, cytokinin application to Cr(VI)-stressed wheat seedlings significantly minimized the decrease induced by Cr(VI) in different parameters such as root-shoot length (10.8% and 13%, respectively), root-shoot fresh mass (11.3% and 10.1%, respectively), and total chlorophyll and carotenoids content (13.4% and 6.8%, respectively) with respect to the control. This treatment also maintained the regulation of proline metabolism (proline content, and P5CS and PDH activities), ascorbate-glutathione (AsA-GSH) cycle and nutrient homeostasis. The protective effect of Si and cytokinin against Cr(VI) stress was minimized upon supplementation of an inhibitor of polar auxin transport- 2,3,5-triiodobenzoic acid (TIBA) which suggested a potential involvement of auxin in Si and cytokinin-mediated mitigation of Cr(VI) toxicity. The exogenous addition of a natural auxin – indole-3-acetic acid (IAA) confirmed auxin is an active member of a signaling cascade along with cytokinin that aids in Si-mediated Cr(VI) toxicity alleviation as IAA application reversed the negative impacts of TIBA on wheat roots treated with Cr(VI), cytokinin and Si. The results of this research are also confirmed by the gene expression analysis conducted for nutrient transporters (Lsi1 , CCaMK , MHX , SULT1 and ZIP1) and enzymes involved in the AsA-GSH cycle (APX , GR , DHAR and MDHAR). The overall results of this research indicate towards possible induction of a crosstalk between cytokinin and IAA upon Si supplementation which in turn stimulates physiological, biochemical and molecular changes to exhibit protective effects against Cr(VI) stress. Further, the information obtained suggests probable employment of Si, cytokinin and IAA alone or combined in agriculture to maintain plant productivity under Cr(VI) stress and data regarding expression of key genes can be used to develop new crop varieties with enhanced resistance against Cr(VI) stress together with its reduced load in seedlings. [Display omitted] • Silicon regulates the cytokinin and IAA crosstalk and improve the growth. • Silicon reduces the CrVI accumulation through cytokinin and IAA crosstalk. • Auxin-cytokinin crosstalk modulates Si-mediated regulation of photosynthetic attributes of Cr(VI)-stressed wheat seedlings. • Auxin and cytokinin are crucial companions for Si-mediated nutrient homeostasis against Cr(VI)-stress. • Si balances the ascorbate-glutathione cycle through auxin-cytokinin crosstalk under Cr(VI) stress. [ABSTRACT FROM AUTHOR]