Effect of Drought Stress and Application of Zinc Oxide on Hormonal Changes and Growth Status of Wheat Bread

Introduction Drought stress and Zn deficiency are important factors affecting the quantity and quality of wheat. Zn deficiency reduces photosynthesis and disorders protein synthesis that the consequence of such process is the gathering of amino acids and amides, and disordering of carbohydrates metabolism. Besides, in such a condition, the length of plants and the size of leaves reduce due to changes in Auxin metabolism, especially Indole Acetic Acid (IAA). Drought stress reduces leaf size, cell division, plant growth, amount of photosynthesis, protein synthesis and chlorophyll content. Balance of plant hormones is affected by both of these factors. Among the compounds with zinc element, Zinc oxide is known from the US Food and Drug Administration as one of the safest and most integral components of Zinc. Nanoparticles have attracted much attention for their distinct characteristics that are unavailable in conventional macroscopic materials. Obviously, increasing of zinc availability and reducing of drought effects can play an effective role in improving the present situation.Materials and Methods The present study was carried out using split plot experiment based on a randomized complete block design with three replications. Two factors of drought stress (irrigation at 90% of field capacity as non-stress condition, irrigation in 75% of field capacity as medium stress and irrigation in 50% of field capacity as severe stress) and application of zinc element (without treatment, spraying of 5 and 10 ppm of Nano Zinc Oxide and Zinc Oxide) were examined as factors of this study. In this study, parameters of Indole acetic acid, Abscisic acid, Gibberellic acid, Tryptophan, Amount of Zinc, Chlorophyll index, Protein, Total dry matter, Phytic acid, Proline, and Yield were measured.Results and Discussion Results of variance analysis of field data revealed that zinc element application in stress conditions could improve a number of parameters of this study. The interactions between drought and zinc on indole acetic acid, abscisic acid, gibberellin, zinc element values, chlorophyll index, protein, phytic acid at one percent probability level and total dry matter content at five percent probability level were significant. Application of nano-zinc oxide in 75% and 50% of field capacity, as well as non-application of Zinc in these conditions caused optimal changes in plant hormones, chlorophyll, protein, economic performance and proline. Application of zinc oxide increased 13.4 and 17.43 percent in the amount of indole acetic acid and gibberellin, while the use of zinc oxide reduced the acidity of 51.9 percent of abscisic acid under 90% field capacity. Zn content increased in seed from 1.13 to 1.83 mg kg and reduction of phytic acid from 19.2 to 16.6 percent under severe drought stress. Application of 10 ppm nano-zinc oxide showed a decrease in the negative effects of drought stress and improved quality of wheat.Conclusions As a general conclusion, it can be acknowledged that drought stress with effect on plant hormones, decreased the growth of shoot which causes reduced plant dry matter and plant yields. The use of zinc could increase the proline production and prevented chlorophyll degradation that causes reduced the effects of water stress and improved plant growth conditions. As a final result, these changes in Zinc application conditions could improve dry matter yield and economic yield.