Assessment of the effect of silicon on antioxidant enzymes in cotton plants by multivariate analysis

Silicon modulate the non-enzymatic antioxidant defence system and oxidative stress in a similar way as boron in boron-deficient cotton flowers

Silicon (Si) application, especially via foliar application, may be promising to attenuate oxidative damage, as Si can improve the non-enzymatic antioxidant system of cotton flowers. However, studies that address the relationship between boron (B) and Si in cotton flowers are still scarce. Therefore, this paper aimed to evaluate the effect of silicon alone and added to the borate solution applied via foliar spray on the oxidative stress; proline, carotenoid, and phenol contents; and biomass production of cotton flowers grown under moderate B deficiency. The experiment was arranged in a completely randomized design with ten replicates and the following five treatments: control (cotton plants under boron deficiency); water application (without B and Si); boron application; silicon application; and B + Si. The application of B, Si, and B + Si reduced the malondialdehyde content in cotton petals by 45%, 48%, and 59%, respectively, and in cotton anthers by57%, 64%, and 67%, respectively. The dry matter of cotton petals in the respective treatments increased by 20%, 16%, 35%, and 44%, while the dry matter of cotton anthers increased by 40%, 24%, 48%, and 53%, respectively, compared to the treatment with water only. There was a strong relationship between B content and dry matter; Si content and the contents of phenols and proline; and carotenoid content and the contents of MDA and H₂O₂. B deficiency can induce oxidative stress specifically in the petals and anthers of cotton, with carotenoids being the main defense mechanism in flowers, while Si is capable of strongly activating defense mechanisms from phenol and proline. In conclusion, the development of organs related to reproduction is impaired by B deficiency. In addition, the foliar application of Si and B attenuates the effects of oxidative stress on the sepals and anthers of cotton, mainly favoring the development of cotton anthers.

Addition of silicon to boron foliar spray in cotton plants modulates the antioxidative system attenuating boron deficiency and toxicity

BACKGROUND

Boron (B) nutritional disorders, either deficiency or toxicity, may lead to an increase in reactive oxygen species production, causing damage to cells. Oxidative damage in leaves can be attenuated by supplying silicon (Si). The aim of this study was to assess the effect of increasing foliar B accumulation on cotton plants to determine whether adding Si to the spray solution promotes gains to correct deficiency and toxicity of this micronutrient by decreasing oxidative stress via synthetizing proline and glycine-betaine, thereby raising dry matter production.

RESULTS

B deficiency or toxicity increased H₂O₂ and MDA leaf concentration in cotton plants. H₂O₂ and MDA leaf concentration declined, with quadratic adjustment, as a function of increased leaf B accumulation. Proline and glycine-betaine leaf concentration increased under B-deficiency and B-toxicity. In addition, production of these nonenzymatic antioxidant compounds was greater in plants under toxicity, in relation to deficient plants. Adding Si to the B spray solution reduced H₂O₂ and MDA concentration in the plants under nutrient deficiency or toxicity. Si reduced H₂O₂, primarily in B-deficient plants. Si also increased proline and glycine-betaine concentration, mainly in plants under B toxicity. Dry matter production of B-deficient cotton plants increased up to an application of 1.2 g L^- 1 of B. The critical B level in the spray solution for deficiency and toxicity was observed at a concentration of 0.5 and 1.9 g L^- 1 of B, respectively, in the presence of Si, and 0.4 and 1.9 g L^- 1 of B without it. In addition, the presence of Si in the B solution raised dry matter production in all B concentrations evaluated in this study.

CONCLUSION

Our findings demonstrated that adding Si to a B solution is important in the foliar spraying of cotton plants because it increases proline and glycine-betaine production and reduces H₂O₂ and MDA concentration, in addition to mitigating the oxidative stress in cotton plants under B deficiency or toxicity.

Biochar and exogenous calcium assisted alleviation of Pb phytotoxicity in water spinach (Ipomoea aquatica Forsk) cultivated in Pb-spiked soil

The consumption of vegetables grown in Pb-polluted soils causes serious threats to human health around the globe. In this study, we evaluated the Pb toxicity alleviation in water spinach grown of pot experiments in Pb-spiked soil treated with biochar and exogenous calcium. The results showed that both biochar and exogenous calcium alleviated Pb stress in water spinach, which was mainly manifested on its improved soil health and increased growth and decreased Pb uptake. Incorporation of 3% biochar significantly reduced CaCl₂ extracted Pb by 53.6% and decreased Pb accumulation in roots (67.1%) and shoots (80.8%). Our also findings indicated that Pb detoxification mechanism of biochar and exogenous calcium was totally different, while they can induce a synergistic impact on water spinach Pb stress alleviation. The combination of biochar and exogenous calcium in Pb-contaminated soil remediation may complement each other and reduce Pb entry into the human body through vegetables.

Multivariate Analysis Reveals Different Responses of Antioxidant Defense in Wheat Plants Exposed to Arsenic (As) and Cadmium (Cd)

Background:

Multivariate analysis is a chemometric tool that has been little explored to determine physiological status under heavy metal stress. Nevertheless, PCA has an unexplored potential to determine the plant physiologic status and its modification under stress factors like heavy metals.

Objectives:

This work aims to assess the physiological and biochemical effects and responses of wheat plants under the different exposition of As and Cd using multivariate models.

Materials and Methods:

Wheat plants growing in a greenhouse were exposed to 0, 10 and 50 mg kg-1 soil of As and 0, 10 and 33 50 mg kg-1 soil of Cd until growth stage 5. After 56 days, wheat leaves and roots were collected to determine dry weight, lipid peroxidation and the activity of three enzymes: catalase, ascorbate peroxidase and guaiacol peroxidase. These measures were considered as the variables of three performed multivariate models to determine physiological status.

Results:

Through the interpretation of score plot and loading plot in combination, it was possible to determine that both As and Cd affect chlorophyll content and antioxidant response. However, a chlorophyll decrease and a lipid peroxidation increase were observed together with an inhibition of antioxidant response more accentuated in wheat plants exposed to As than those exposed to Cd.

Conclusions:

Multivariate analysis allows us to determine the differences between the physiological behavior of both stressors, which turn this chemometric tools useful for the characterization of a physiological response.

Silicon-induced thermotolerance in Solanum lycopersicum L. via activation of antioxidant system, heat shock proteins, and endogenous phytohormones

BACKGROUND

Abiotic stresses (e.g., heat or limited water and nutrient availability) limit crop production worldwide. With the progression of climate change, the severity and variation of these stresses are expected to increase. Exogenous silicon (Si) has shown beneficial effects on plant growth; however, its role in combating the negative effects of heat stress and their underlying molecular dynamics are not fully understood.

RESULTS

Exogenous Si significantly mitigated the adverse impact of heat stress by improving tomato plant biomass, photosynthetic pigments, and relative water content. Si induced stress tolerance by decreasing the concentrations of superoxide anions and malondialdehyde, as well as mitigating oxidative stress by increasing the gene expression for antioxidant enzymes (peroxidases, catalases, ascorbate peroxidases, superoxide dismutases, and glutathione reductases) under stress conditions. This was attributed to increased Si uptake in the shoots via the upregulation of low silicon (SlLsi1 and SlLsi2) gene expression under heat stress. Interestingly, Si stimulated the expression and transcript accumulation of heat shock proteins by upregulating heat transcription factors (Hsfs) such as SlHsfA1a-b, SlHsfA2-A3, and SlHsfA7 in tomato plants under heat stress. On the other hand, defense and stress signaling-related endogenous phytohormones (salicylic acid [SA]/abscisic acid [ABA]) exhibited a decrease in their concentration and biosynthesis following Si application. Additionally, the mRNA and gene expression levels for SA (SlR1b1, SlPR-P2, SlICS, and SlPAL) and ABA (SlNCEDI) were downregulated after exposure to stress conditions.

CONCLUSION

Si treatment resulted in greater tolerance to abiotic stress conditions, exhibiting higher plant growth dynamics and molecular physiology by regulating the antioxidant defense system, SA/ABA signaling, and Hsfs during heat stress.

Silicon-mediated role of 24-epibrassinolide in wheat under high-temperature stress

High temperature poses a severe extortion to productivity of many crops like wheat. Therefore, well documented roles of brassinosteroid (BR) and silicon (Si) in terms of abiotic stress tolerance, the current study was designed to evaluate the response of wheat (Triticum aestivum L. Var. PBW-343) to 24-epibrassinolide (EBL) mediated by silicon grown under high temperature stress. At 10- and 12-day stage after sowing, the seedlings were administered Si (0.8 mM) through the sand, and the plants at 20, 22, or 24 days after sowing (DAS) were given EBL (0.01μM) through foliage. Plants were treated to high-temperature stress (35/28 or 40/35 °C), for 24 h with 12-h photoperiod in plant growth chamber at 25- and 26-day stage of growth. High temperatures cause significant reduction in growth performance and photosynthesis-related attributes at 35 days after sowing. However, antioxidant enzymes and proline content also augmented substantially with increasing temperature. BR and Si enhanced antioxidant activity and proline content, which was earlier increased by the high temperature. It is established that interaction of EBL and Si considerably improved the growth features, photosynthetic efficacy, and several biochemical traits under high-temperature stress through elevated antioxidant system and osmoprotectant.

Changes in Amino Acid Profile in Roots of Glyphosate Resistant and Susceptible Soybean (Glycine max) Induced by Foliar Glyphosate Application

Amino acid profiles are useful to analyze the responses to glyphosate in susceptible and resistant soybean lines. Comparisons of profiles for 10 amino acids (Asp, Asn, Glu, Gln, Ser, His, Gly, Thr, Tyr, Leu) by HPLC in soybean roots were performed in two near isogenic pairs (four varieties). Foliar application of glyphosate was made to soybean plants after 5 weeks of seeding. Roots of four varieties were collected at 0 and 72 h after glyphosate application (AGA) for amino acid analysis by HPLC. Univariate analysis showed a significant increase of several amino acids in susceptible as well as resistant soybean lines; however, amino acids from the major pathways of carbon (C) and nitrogen (N) metabolism, such as Asp, Asn, Glu and Gln, and Ser, increased significantly in susceptible varieties at 72 h AGA. Multivariate analysis using principal component analysis (2D PCA and 3D PCA) allowed different groups to be identified and discriminated based on the soybean genetic origin, showing the amino acid responses on susceptible and resistant varieties. Based on the results, it is possible to infer that the increase of Asn, Asp, Glu, Gln, and Ser in susceptible varieties would be related to the deregulation of C and N metabolism, as well as changes in the growth mechanisms regulated by Ser.

Screening and Expression of a Silicon Transporter Gene (Lsi1) in Wild-Type Indica Rice Cultivars

Silicon (Si) is one of the most prevalent elements in the soil. It is beneficial for plant growth and development, and it contributes to plant defense against different stresses. The Lsi1 gene encodes a Si transporter that was identified in a mutant Japonica rice variety. This gene was not identified in fourteen Malaysian rice varieties during screening. Then, a mutant version of Lsi1 was substituted for the native version in the three most common Malaysian rice varieties, MR219, MR220, and MR276, to evaluate the function of the transgene. Real-time PCR was used to explore the differential expression of Lsi1 in the three transgenic rice varieties. Silicon concentrations in the roots and leaves of transgenic plants were significantly higher than in wild-type plants. Transgenic varieties showed significant increases in the activities of the enzymes SOD, POD, APX, and CAT; photosynthesis; and chlorophyll content; however, the highest chlorophyll A and B levels were observed in transgenic MR276. Transgenic varieties have shown a stronger root and leaf structure, as well as hairier roots, compared to the wild-type plants. This suggests that Lsi1 plays a key role in rice, increasing the absorption and accumulation of Si, then alters antioxidant activities, and improves morphological properties.