Plant growth promoting potential of urea doped calcium phosphate nanoparticles in finger millet (Eleusine coracana (L.) Gaertn.) under drought stress

Abstract

Drought is a leading threat that impinges on plant growth and productivity. Nanotechnology is considered an adequate tool for resolving various environmental issues by offering avant-garde and pragmatic solutions. Using nutrients in the nano-scale including CaP-U NPs is a novel fertilization strategy for crops. The present study was conducted to develop and utilize environment-friendly urea nanoparticles (NPs) based nano-fertilizers as a crop nutrient. The high solubility of urea molecules was controlled by integrating them with a matrix of calcium phosphate nanoparticles (CaP NPs). CaP NPs contain high phosphorous and outstanding biocompatibility. Scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD) were used to characterize the fabricated NPs. FE-SEM determined no areas of phase separation in urea and calcium phosphate, indicating the successful formation of an encapsulated nanocomposite between the two nano matrices. TEM examination confirmed a fiber-like structure of CaP-U NPs with 15 to 50 nm diameter and 100 to 200 nm length. The synthesized CaP-U NPs and bulk urea (0.0, 0.1% and 0.5%) were applied by foliar sprays at an interval of 15 days on pre-sowed VL-379 variety of finger millet (Eleusine coracana (L.) Gaertn.), under irrigated and drought conditions. The application of the CaP-U NPs significantly enhanced different plant growth attributes such as shoot length (29.4 & 41%), root length (46.4 & 51%), shoot fresh (33.6 & 55.8%) and dry weight (63 & 59.1%), and root fresh (57 & 61%) and dry weight (78 & 80.7%), improved pigment system (chlorophyll) and activated plant defense enzymes such as proline (35.4%), superoxide dismutase (47.7%), guaiacol peroxidase (30.2%), ascorbate peroxidase (70%) under both irrigated and drought conditions. Superimposition of five treatment combinations on drought suggested that CaP-U NPs at 0.5 followed by 0.1% provided the highest growth indices and defense-related enzymes, which were significantly different. Overall, our findings suggested that synthesized CaP-U NPs treatment of finger millet seeds improved plant growth and enzymatic regulation, particularly more in drought conditions providing insight into the strategy for not only finger millet but probably for other commercial cereals crops which suffer from fluctuating environmental conditions.

Significance of Phosphate Nano-Fertilizers Foliar Application: A Brief Real-Field Study of Quantitative, Physiological Parameters, and Agro-Ecological Diversity in Sunflower

“…Similarly, Mishra et al [61] found increases in various growth-promoting parameters including shoot and root length, shoot and dry weight, shoot and root fresh weight, and leaf area when applying CaP-urea with particle size > 100 nm through spray deposition at a low concentration of NFs on a finger millet under drought and irrigated conditions. Also, a statistically significant difference was observed with a grain yield of wheat of more than 20% when zinc-and magnesium-doped hydroxyapatite NPs modified with urea were utilized [12], which fully agrees with our results.…”

“…One of the pathways for the NPs to enter the plant is through the leaf stomata [61]. In the case of sunflower, the average stomata diameter corresponds to 28-30 µm [28].…”

“…Once they have interacted with the leaf surface, cell-to-cell transport within the plant could be worked on through plasmodesmata. Plasmodesmata have channels with a size range of 50-60 nm that are capable of communicating within cells and transporters [61], where both of our applied P-NFs had a size lower than 50 nm (Tables 2 and 3).…”

“…Based on our sunflower one-season physiology (Table 5), similar to the evaluation of quantitative parameters, it is evident that the most effective treatments were again the P-NFs. In these cases, it could be assumed that the effect of P was further enhanced by an increased nitrogen content in the plant, particularly in the leaves, which has a close relationship with stomatal regulation and movement [61] as well as stomatal conductance. This was directly confirmed with the Ig physiological index (Table 5) and indirectly through the variability of sunflower leaf stomatal parameters (Table 4).…”

“…Furthermore, it is expected that leaves with a higher nitrogen content also indicates higher chloroplast content [61] or potentially a more intense impact on photosynthesis [68].…”