Abstract
Silicon has not been cataloged as an essential element for higher plants. However, it has shown beneficial effects on many crops, especially under abiotic and biotic stresses. Silicon fertilization was evaluated for the first time on plants exposed to fluctuations in an Fe regime (Fe sufficiency followed by Fe deficiency and, in turn, by Fe resupply). Root and foliar Si applications were compared using cucumber plants that were hydroponically grown in a growth chamber under different Fe nutritional statuses and Si applied either to the roots or to the shoots. The SPAD index, Fe, and Mn concentration, ROS, total phenolic compounds, MDA concentration, phytohormone balance, and cell cycle were determined. The results obtained showed that the addition of Si to the roots induced an Fe shortage in plants grown under optimal or deficient Fe nutritional conditions, but this was not observed when Si was applied to the leaves. Plant recovery following Fe resupply was more effective in the Si-treated plants than in the untreated plants. A relationship between the ROS concentration, hormonal balance, and cell cycle under different Fe regimes and in the presence or absence of Si was also studied. The contribution of Si to this signaling pathway appears to be related more to the induction of Fe deficiency, than to any direct biochemical or metabolic processes. However, these roles could not be completely ruled out because several hormone differences could only be explained by the addition of Si.
Highlights
Plants take up silicon in the form of monosilicic acid, Si(OH)4
This work aimed to evaluate for the first time the effect of root and foliar Si application on cucumber plants grown at different Fe statuses: Fe sufficiency, Fe deficiency, and after re-fertilization with Fe to establish the utility of Si fertilizers for this crop
The role of salicylic acid (SA) in the tolerance of the abiotic stress has been studied, the results showed the levels of endogenous SA and reactive oxygen species (ROS) that increased in stressed plant cells, and the absence of SA can suppress the production of antioxidant enzymes (APX and CAT) which are responsible for ROS degradation (Hossain et al, 2015)
Summary
Its concentration ranges in soil solutions from 0.1 to 1.4 mM (Marschner, 1995). This element has not been cataloged as essential for higher plants, the addition of Si to soils has exhibited beneficial effects for the growth of many plants, under conditions of abiotic and biotic stresses (for a review, see Hernández-Apaolaza, 2014; Liang et al, 2015). The Si effect on the mitigation of different stresses has been studied in species such as cucumber (Cucumis sativus), rice (Oryza sativa L.), and soybean. Silicon Addition and Fe Regime (Glycine max), among others (Miyake and Takahashi, 1985; Gonzalo et al, 2013; Carrasco-Gil et al, 2018). Coskun et al (2019) proposed a model that concluded that the Si effects were indirectly caused by Si deposition in the apoplast and that there was no biochemical role for Si(OH) in terms of any interactions with intracellular constituents or enzymes
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