The dual role of citrate in cooperation with iron oxide nanoparticles and bulk (α-Fe2O3), as a courier of iron or an iron detoxifier, in repeated foliar spray in evening primrose (Oenothera biennis L.) plants.

Abstract: The effects of repeated foliar spray of nano and bulk iron oxide (α-Fe2O3) were physiologically investigated at four levels (0, 0.1, 0.25, and 0.5 g l-1 ) with and without citrate interaction on iron deficiency and excess stress during plant growth in pot conditions. There were no significant differences between nano and Balk treatments in terms of growth changes, iron absorption, and the possibility of transferring to the roots. But there were significant differences in terms of the antioxidant capacity variations, citrate detoxification effects, and the amounts of toxicity at high levels. Iron oxide increased total iron, active iron, chlorophyll, biomass, and antioxidants; at high levels, growth is reduced especially in nano. At all levels citrate made differences, so that at level 0.1 g l-1 like a nutritional operator increased biomass, chlorophyll, and antioxidants. At 0.25 g l-1 , there was antioxidant activity burst and chlorophylls increased; however, it reduced growth to similar conditions without citrate. At 0.5 g l-1 , it decreased toxicity and iron availability but increased growth and antioxidants; these effects were more significant in nano. It seems that in nano treatments; enzymatic antioxidants, flavonoids, and phenolic compounds, and in the bulk; proline, carotenoids, and peroxidase enzymes were effective in the maximum decrease in oxidants. Confirming the importance of inducing an efficient antioxidant system in response to environmental stresses, here growth improvement of plants grown in iron-poor soils with iron oxide, and the healing effects of interacting with citrate in toxic conditions, at least in some cases, were related to the increase in antioxidant capacity and its vital role in the redox balance and stability of iron homeostasis. Keywords: iron oxide nanoparticle, bulk iron oxide, citrate, foliar spray, oxidative system, physiological parameters, Oenothera biennis L