Silicon nanoparticles enhanced the growth and reduced the cadmium accumulation in grains of wheat (Triticum aestivum L.)

Pot experiments were carried out to study the effects of rice straw (RS) and rice straw ash (RSA) on the growth of early rice and α-diversity of bacterial community in soils around rare earth mining areas of Xunwu and Xinfeng counties in South Jiangxi of China The results showed that the exploitation of rare earth resources leads to soil pollution around rare earth mining areas and affects the growth of rice, and the content of rare earth elements (REEs) in rice was positively correlated with that in soils and negative correlated with dry weight of rice; The addition of RS to soils around REE mining area can inhibit growth of early rice, and the dry weight of rice grains, shoots, roots is lower when compared with the controls, while the content of REEs is higher The α-diversity of soil bacterial decreases, which promotes the growth of Pseudorhodoferax, Phenylobacterium and other bacteria of the same kind, and inhibits the growth of beneficial bacteria The addition of RSA to soils had no significant effect on α-diversity of soil bacterial but promoted the growth of Azospira and other beneficial bacteria, inhibited the growth of Bryobacter and other bacteria of the same kind, significantly improved the dry weight of grains, shoots and roots of early rice, and reduced the content of REEs in these parts of rice It can be concluded that RS is unsuitable to be added to the planting soil of early rice in REE mining area, while RSA is suitable

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Effects of rice straw and rice straw ash on rice growth and α-diversity of bacterial community in rare-earth mining soils.

The role of silicon (Si) in alleviating biotic and abiotic stresses in crops is well evidenced by empirical studies; however, the mechanisms by which it works are still poorly known. The aim of this study is to determine whether or not phytolith composition and distribution in wheat are affected by drought and, if so, why. Durum wheat was grown using hydroponics in the presence of polyethylene glycol (PEG)-6000 to perform a water-stress simulation. We developed an original method for in situ analysis of phytoliths in leaves via X-ray imaging. PEG was efficient in inhibiting water uptake by roots and creating stress, and prevented a small fraction of Si from being accumulated in the shoots. The application of Si with PEG maintained shoot and root fresh weights (FW) and relative water content at higher values than for plants without Si, especially at PEG 12%. Our data show that, under water stress in the presence of Si, accumulation of phytoliths over the veins provides better support to the leaf, thus allowing for a better development of the whole plant than in the absence of Si. The development of silicified trichomes in durum wheat depends primarily on the availability of Si in soil and is not an adaptation to water stress.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.14554

Effect of phytoliths for mitigating water stress in durum wheat

Cd is a non-essential metal and is hazardous for plant growth. Although Zn is regarded as an essential element, its elevated levels are highly toxic for plants. Silicon (Si) fertilization and Arbuscular mycorrhiza (AM) have been recognized in alleviating phytotoxicity of heavy metals. Benefits of Si are limited in legumes because they are low Si accumulators. Recently, reports have indicated increased Si uptake in a few plants through mycorrhization. The present work investigated the roles of Si and/or Rhizophagus irregularis on growth, nutrient acquisition, proline biosynthesis and productivity of two pigeonpea genotypes (metal tolerant—PUSA 2002, metal sensitive—PUSA 991) under Cd (25, 50 mg kg−1), Zn (600, 1000 mg kg−1) stress. Plants were subjected to potassium silicate (300 mg kg−1) alone and in combination with R. irregularis. Cd and Zn stress hampered growth, chlorophylls, nutrients uptake and productivity with more negative effects in PUSA 991 than PUSA 2002. AM improved root biomass and nutrient status (P, N, Mg, Fe), whereas Si was more effective in increasing shoot biomass, K and Ca under both heavy metals. Moreover, AM boosted proline biosynthesis by enhancing glutamate dehydrogenase and pyrroline-5-carboxylate synthetase activities along with a decline in proline dehydrogenase activity under heavy metal stress. Application of AM to Si-amended soils was highly beneficial in modulating proline biosynthesis and further improving growth, nutrient, water status and yield with complete amelioration at Zn600, 1000 as well as Cd25 in PUSA 2002 due to its better ability for mycorrhizal symbiosis. Highly positive impacts of combined applications (+Si+AM) could be correlated to mycorrhiza-mediated enhanced Si uptake and resultant metal tolerance.

Arbuscular Mycorrhiza Rhizophagus irregularis and Silicon Modulate Growth, Proline Biosynthesis and Yield in Cajanus cajan L. Millsp. (pigeonpea) Genotypes Under Cadmium and Zinc Stress

Accumulation of reactive oxygen species (ROS), and their destructive effects on cellular organelles are the hallmark features of plants exposed to abiotic stresses. Plants are well-equipped with defensive mechanisms like antioxidant systems to deal with ROS-induced oxidative stress. Silicon has been emerged as an important regulator of plant protective mechanisms under environmental stresses, which can be up-taken from soil through a system of various silicon-transporters. In plants, silicon is deposited underneath of cuticles and in the cell wall, and help plant cells reduce deleterious effects of stresses. Furthermore, silicon can provide resistance to ROS-toxicity, which often accounts for silicon-mediated improvement of plant tolerance to different abiotic constraints, including salinity, drought, and metal toxicity. Silicon enhances the ROS-detoxification ability of treated plants by modulating the antioxidant defense systems, and the expression of key genes associated with oxidative stress mitigation and hormone metabolism. Silicon also displays additive roles in ROS-elimination when supplied with other external stimuli. Here, we discuss recent findings on how silicon is able to modulate antioxidant defense of plants in response to oxidative stress triggered by different abiotic constraints. We also review interactions of silicon with other signaling molecules, including nitric oxide, ROS, polyamines, and phytohormones in the mediation of plant protection against abiotic stress-induced oxidative damage.

Silicon in mitigation of abiotic stress-induced oxidative damage in plants.

Silicon (Si) frequently accumulates in plants tissues, mainly in roots of dicotyledons, such as cowpea. By contrast, Cadmium (Cd) is a metal that is extremely toxic to plant metabolism. This research aims to investigate if the deposition of Si in root can reduce Cd contents and minimize its negative effects on leaves, measuring gas exchange, chlorophyll fluorescence, antioxidant metabolism, photosynthetic pigments and growth, which may explain the possible role of Si in the attenuation of Cd toxicity in cowpea. This study had a factorial design, with all factors completely randomized and two Cd concentrations (0 and 500 µM Cd, termed as – Cd and + Cd, respectively) and three Si concentrations (0, 1.25 and 2.50 mM Si). Si reduced Cd contents in the roots and in other plant organs, such as stems and leaves. The Si contents were highest in roots, followed by stems and leaves, which was explained by the passive absorption of Si. The application of Si promoted increase in both the macro- and micronutrient contents in all tissues, suggesting that Si mitigates the effect of Cd on nutrient uptake. Si attenuated Cd-mediated effects on light absorption of photosystem II (PSII), increasing the effective quantum yield of PSII photochemistry and the electron transport rate. Additionally, toxic effects induced by Cd on gas exchange were mitigated by the action of Si. Plants treated with Cd + Si showed increase in the activities of antioxidant enzymes and reductions in oxidant compounds; these modifications were promoted by Si via detoxification mechanisms. Increases in the photosynthetic pigments and growth of plants treated with Si and exposed to Cd stress were detected and were due to the reduced deterioration of cell membranes and maintenance of chloroplasts, which had positive repercussions on growth and development. This study validated the hypothesis that the accumulation of Si in roots induces benefits on metabolism and alleviates the toxic effects caused by Cd in leaves of cowpea.

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Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants

Silicon (Si) is a beneficial element to higher plants. Its effects frequently linked to physiological, morphological, nutritional, and molecular aspects in plants. This study aimed to measure the compounds linked to oxidative stress and cell damages, besides to evaluate the consequences of exogenous Si application on photosynthetic pigments in maize plants (hybrid 30F53YH Pioneer). The experiment employed an entirely randomized design with two silicon treatments (0 and 2 mM Si). The experiment was assembled with five replicates for a total of 10 experimental units, with one plant in each unit. Parameters measured were hydrogen peroxide, glutathione, electrolyte leakage and malondialdehyde, besides chlorophylls and carotenoids. The silicon application did not cause significant changes in hydrogen peroxide, glutathione, electrolyte leakage and malondialdehyde in leaf and root tissues of plant. On the other hand, the exogenous Si induced significant increases in CHL 'a', CHL 'b' and total CHL. This study proved that silicon promotes beneficial effects on photosynthetic pigments and stability of the cell membrane due to maintenance in oxidant compounds in young 'Zea mays' plants. Therefore, the application of 2 mM Si can be recommended to maximize the chlorophylls in maize crop, which needs further studies on economic reliability.

Carla Leticia Figueredo de Carvalho Souza

Papers

Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants

Beneficial repercussion of silicon (Si) application on photosynthetic pigments in maize plants.