Impact of Coated Zinc Oxide Nanoparticles on Photosystem II of Tomato Plants

Abstract

Zinc oxide nanoparticles (ZnO NPs) have emerged as a prominent tool in agriculture. Since photosynthetic function is a significant measurement of phytotoxicity and an assessment tool prior to large-scale agricultural applications, the impact of engineered irregular-shaped ZnO NPs coated with oleylamine (ZnO@OAm NPs) were tested. The ZnO@OAm NPs (crystalline size 19 nm) were solvothermally prepared in the sole presence of oleylamine (OAm) and evaluated on tomato (Lycopersicon esculentum Mill.) photosystem II (PSII) photochemistry. Foliar-sprayed 15 mg L−1 ZnO@OAm NPs on tomato leaflets increased chlorophyll content that initiated a higher amount of light energy capture, which resulted in about a 20% increased electron transport rate (ETR) and a quantum yield of PSII photochemistry (ΦPSII) at the growth light (GL, 600 μmol photons m−2 s−1). However, the ZnO@OAm NPs caused a malfunction in the oxygen-evolving complex (OEC) of PSII, which resulted in photoinhibition and increased ROS accumulation. The ROS accumulation was due to the decreased photoprotective mechanism of non-photochemical quenching (NPQ) and to the donor-side photoinhibition. Despite ROS accumulation, ZnO@OAm NPs decreased the excess excitation energy of the PSII, indicating improved PSII efficiency. Therefore, synthesized ZnO@OAm NPs can potentially be used as photosynthetic biostimulants for enhancing crop yields after being tested on other plant species.

Mechanistic Approach on Melatonin-Induced Hormesis of Photosystem II Function in the Medicinal Plant Mentha spicata

“…When the OEC fails to efficiently reduce the chlorophyll molecule at the PSII RC, it results in damaging oxidations in PSII [59]. Consequently, donor-side photoinhibition is often associated with the production of ROS [55,[62][63][64]. The minor increase in ROS generation that we observed (Figure 7c), as a result of donor-side photoinhibition (Figure 2b), can be attributed to a malfunction of the OEC (Figure 2a).…”

“…The increased ETR of mint plants at the GL, following the spray with 100 µM MT, (Figure 5a), could be due to a decreased NPQ (Figure 3d) [79,80]. The observed donor-side photoinhibition, reflected by the reduced Fv/Fm (Figure 2b), decreased NPQ (Figure 3d), enhancing the ETR (Figure 5a) [63,81]. The increased effective quantum yield of PSII photochemistry (Φ PSII ), 72 h after the spray with 100 µM MT at the GL intensity (Figure 3a), resulted in increased values of ETR (Figure 5a).…”

“…Relative chlorophyll content was measured in Mentha spicata leaves 72 h after the foliar spray with distilled water (control), 10 µM MT, and 100 µM MT, using a portable Chlorophyll Content Meter (Model Cl-01, Hansatech Instruments Ltd., Norfolk, UK). Values were expressed in relative units [63,124].…”

Modification of Tomato Photosystem II Photochemistry with Engineered Zinc Oxide Nanorods

“…The application of ZnO NPs can enhance crop yield, providing an effective solution for nutrient supplementation in farming systems, and these NPs were characterized as a novel alternative for sustainable agricultural development [11,12]. It has been proposed that ZnO NPs can be used as photosynthetic biostimulants for enhancing crop yields [13], as they possess insecticidal [14], antifungal [15], and antibacterial properties [16]. The impact of ZnO NPs on metabolic attributes and the photosynthetic function of rice seedlings in hydroponic culture was found to be concentration-dependent when improving the qualitative and quantitative characteristics of the plants [17].…”

“…It also allows the pre-symptomatic monitoring of plant stress symptoms [36][37][38]. Chlorophylla fluorescence analysis is a capable tool for evaluating NP effects on plant function and to monitor plant−NP relations [2,13,39].…”