Effect of seed priming and cadmium on seedling physiological traits and produced seed germination indices of sorghum (Sorghum bicolor L.) SOR834 genotype

Introduction In recent years, soil pollution with heavy metals such as cadmium had a progressive trend and causes serious problem in production of crops in polluted zones. Heavy metals released from stationary and mobile origins can be transported in water, air and soil and can be even absorbed by plants, animals and human bodies. Trace elements are currently of great environmental concern. Nowadays, one of the most important environmental problems is pollution of agricultural soils occurs by heavy metals due to human activities. Nowadays, soil pollution with heavy metals as a result of human activities is considered one of the most important environmental stresses in plants, which can lead to the production of reactive oxygen species such as hydrogen peroxide cause. Priming application of gibberellic acid, salicylic acid and potassium nitrate as a suitable option is considered to reduce the toxic effects of cadmium.This study was designed to investigate the effects of priming on physiological traits and sorghum seed germination under cadmium chloride and nitrate stress was conducted in the greenhouse of Yasouj University in 2015. Materials and Methods experiment was conducted as a factorial based on CRD design with three replications. Treatments first factor were including 800 mg/l gibberellic acid, 0.3 mM salicylic acid, 1% potassium nitrate and control (non-prime). The second factor was included cadmium chloride and nitrate each in four levels (0, 7.5, 15 and 30 mg per kg of soil). Then cadmium chloride and nitrate was added by spraying into soil. Then planting pots were filled with seven kilograms of soil, and after one month (because of the homogeneity of the heavy metal), 4 seeds primed for planting in pots were planted with different levels of cadmium chloride and nitrate. The chlorophyll index, chlorophyll fluorescence, leaf soluble protein and antioxidant enzyme activities were measured. Also, post-harvest seed quality traits including percentage and germination rate, uniformity and vigor and seed weight and seedling length and weight were measured. Results and Discussion The results showed that the interaction of cadmium and priming for soluble protein, Catalase enzyme, Superoxide dismutase enzyme and seedlling height was significant. The effect of cadmium showed that cadmium chloride 30 mg per kg of soil seed weight decreased to 24% compared to control. Generally all levels of cadmium compared to the control (no cadmium) had a depressing effect on seed weight. Priming planted seeds with 0.3 mM of salicylic acid leads to increase the germination rate and length vigor index of seeds of sorghum under cadmium stress. Also the most weight vigor index was observed in 15 mg per kg of soil cadmium chloride and nitrate and the lowest was belonged to 7.5 and 30 mg per kg of soil cadmium chloride treatments. In relation to the slow germination under stress cadmium cell membrane probably one of the important points is that it is severely damaged cell to leak out and vigor will be reduced. Priming with the reconstruction of damaged cells and reduce barriers to the growth of the fetus and increase the quality and quantity of protein synthesis, increases the development and tolerance to environmental stresses. Speed up seed germination can as a result of increasing enzymes such as Alpha-amylase, increased levels of bio-energy charged in the form of increasing the amount of ATP, increase the synthesis of DNA and RNA, increasing the number and improving mitochondrial function is at the same time. Conclusions In general, seed priming with 800 milligrams per liter of gibberellic acid, and 0.3 mM of salicylic acid, improved the biochemical and physiological indices of main plant such as increased soluble protein and chlorophyll content, cause to sorghum seedlings resistance to cadmium toxicity and improved the seedling growth and seed weight. As a result, seeds produced in these conditions, have more germination rate and vigor index than the control (non-use of priming).