عنوان مقاله [English]
Background and objectives: Investigations showed that the pollution of heavy metals, especially lead, in fields has caused tension and decreased yield. This issue has caused concern about the risk of consuming contaminated food for human health. The role of plant regulators in heavy metal stress conditions has been of interest in recent years. Lead and zinc (in high concentration) are toxic metals for plants, which are easily absorbed by the plant's root system. As a result, they cause damage to plant growth and development and prevent enzyme activity. Maize is economically important for harvesting seeds and fodder. However, in areas contaminated with metal stress, due to the absorption of metals by the plant, the yield of the cultivated plant in these areas decreases, for this purpose, an experiment aimed at the effect of concentration and different methods of salicylic acid hormone on growth, photosynthesis and anatomical characteristics. and physiological in corn under the stress of zinc and lead metals and also the possibility of reducing the risk of toxicity of these elements is investigated.
Materials and methods: In order to investigate the mitigating effects of two methods of applying salicylic acid hormone on corn plants under heavy metal stress, the experiment was carried out as follows. The concentration of metals included: different concentrations of lead (0 and 250 mM) and zinc (0 and 2500 mM) and the treatments were with two methods of foliar spraying and priming in zero concentrations (distilled water), 750 and 1500 μmol salicylic acid and a group of seeds without stress and no treatment were considered as controls. By implementing a factorial design on morphological traits (height, plant temperature, temperature difference between the environment and leaves, and leafing ratio) and physiological traits (membrane stability index, chlorophyll fluorescence, proline, soluble sugars, carotenoid, protein and some enzymes) as well as the absorption of lead and zinc metals in the root tissue and the aerial part of the plant under hydroponic cultivation conditions. The obtained results were subjected to statistical analysis using SPSS statistical software. The mean comparison of experimental data was also done with Duncan's test. Excel 2003 software was used to draw the figures.
Results: Morphological traits such as: plant temperature, difference between Environment and leaf temperature and physiological traits such as: proline, soluble sugars, carotenoid, protein and some enzymes increased and some other traits such as: height, and leafing ratio, index Membrane stability, chlorophyll fluorescence decreased compared to the control. These traits showed better results in seed priming treatment without stress. However, the use of foliar spray under lead-zinc and lead stress improved the stress effects by reducing the absorption of heavy elements by the root system.
Conclusions: SA activates the defense system of plants by synthesizing a number of proteins and increasing proline osmolytes and soluble sugars and enzymatic and non-enzymatic antioxidants such as carotenoids. As a result of reducing the oxidative stress and protecting the chloroplast membrane and the photosynthetic apparatus, the photosynthetic production is improved, resultly, the height and the proportion of the leaves increased. SA also prevents the absorption of heavy metals by the root system of the plant and its transfer to the aerial part of the plant, which reduces the signs of stress in the aerial part of the plant. By applying salicylic acid, some properties were improved by reducing the effects of stress. The use of foliar spraying improved the physiological and morphological traits during plant growth and worked better than the seed priming method. resultly, in farms with two metals lead and zinc, it is possible to tolerate the stress of these two metals by foliar spraying treatment.