Zinc oxide nanoparticles improve lettuce (Lactuca sativa L.) plant tolerance to cadmium by stimulating antioxidant defense, enhancing lignin content and reducing the metal accumulation and translocation

Abstract

Cadmium (Cd) contamination is a serious global concern that warrants constant attention. Therefore, a hydroponic study was conducted to evaluate the effect of different concentrations (0, 1, 2.5, 5, 10, 15 mg/l) of zinc oxide nanoparticles (ZnONPs) on the Cd content in lettuce (Lactuca sativa L.) under Cd stress conditions. The results showed that Cd stress triggered a decrease in plant biomass, an increase in relative electrolyte conductivity (REC), a decrease in root activity, accumulation of reactive oxygen species (ROS) accumulation, and nutrient imbalance. The application of ZnONPs reduced the toxicity symptoms of lettuce seedlings under Cd stress, with the most pronounced effect being observed 2.5 mg/l. ZnONPs promoted the growth of lettuce under Cd stress, mainly in terms of increase in biomass, chlorophyll content, antioxidant enzyme activity, and proline content, as well as reduction in Cd content, malondialdehyde, and reactive oxygen species (ROS) in plant tissues. ZnONPs also enhanced the uptake of ions associated with photosynthesis, such as iron, manganese, magnesium, and zinc. In addition, ZnONPs increase the amount of lignin in the roots, which blocks or reduces the entry of Cd into plant tissues.

Effects of NaCl and CaCl2 as Eustress Factors on Growth, Yield, and Mineral Composition of Hydroponically Grown Valerianella locusta

“…The HNa treatment had significantly lower boron content compared to LCa. It is useful to note that even though zinc levels were lower than 200 mg Kg −1 of DW, which is a threshold that when exceeded can lead to phytoxicity [ 64 ], all treatments had accumulated zinc greater than 100 mg Kg −1 of DW. It is often referenced that the maximum threshold for zinc in vegetables is 99.4 mg of Zn per kg of dry weight [ 65 , 66 , 67 , 68 ].…”

More or Less: Recent Advances in Lignin Accumulation and Regulation in Horticultural Crops

“…Cu intensively increased PAL activity and lignin accumulation in a dose-dependent manner in copper-treated Matricaria chamomilla, revealing the establishment of a barrier against metal intrusion [56]. The lignin content in lettuce roots treated with cadmium increased by 18% compared with control group [57], whereas increased Zn exposure in growth media evidently reduced the lignin content in the leaves of watermelon seedlings [58].…”

Nano-enabled agrochemicals: mitigating heavy metal toxicity and enhancing crop adaptability for sustainable crop production

“…As NPs reduce Cd absorption and transport, several studies have shown that their addition can increase plant tolerance to the metal. For instance, ZnO-NPs have been demonstrated to lower Cd levels in maize [ 82 ], wheat [ 19 , 83 ], rice [ 9 ], and lettuce [ 84 ]. Application of SiNPs by foliar spray led to decreases in Cd levels in grains, roots, and shoots, with the reductions ranging from 20 to 80%, 20–65%, and 16–60%, respectively.…”

“…This functions as a means of protection against oxidative damage caused by Cd. Prominent instances are ZnO-NPs [ 9 , 82 , 84 , 121 , 122 ], Fe-NPs [ 117 , 119 , 123 , 124 ], TiO 2 -NPs [ 15 , 122 ], SiO 2 -NPs [ 88 , 117 , 125 ], CaO-NPs [ 11 ], Se-NPs [ 86 , 126 , 127 ], Ag-NPs [ 128 ], and CuO-NPs [ 90 , 91 ]. Cowpea plants’ roots and leaves exhibited increased CAT and APX activities and decreased MDA following the application of TiO 2 -NPs [ 118 ].…”