Abstract: Dose soil salinization,an important factor affecting agricultural sustainable development in the arid and semi-arid regions of western China,can not only inhibite the crop seed germination,growth and development, but also affect the crop yield and income. Alkali stress differs from salts stress to the impact on the plant growth. However,few researches have been done on alkali stress. Oat(Avena nuda L.) is a widely grown crop for use as foodstuff and feedstuff in the arid and semiarid regions of northwest China. In order to explore the effect of different concentrations of alkalic salt on the seeds germination of a new variety of oat(Dingyou No. 6) and the physiological mechanism in response to different alkali treatments on oat seedlings cultured in Hoagland solution,after surface-sterilized with 3% Javel water for 10 min,the plump and excellent seeds were germinated for 5 days on two layers of filter paper and wetted respectively by the NaHCO₃ solution(0,50,100,150,200 and 250 mmol·L^-1) at 25℃. When the oat seeds which had been surface-sterilized with 3% Javel water for 10 min and were sowed in the plastic pots with perlite had three leaves,severally treated the seedlings by Hoagland nutrient solution with different concentration of NaHCO₃ at 0,50,100,150 and 200 mmol·L^-1 in the greenhouse. After 7 days of NaHCO₃ treatment,the O₂^-production rate,H₂O₂ and malondialdehyde contents,plasma membrane permeability,antioxidant system activity and osmotica content were determined in oat seedling leaves;after 14 days of NaHCO₃ treatment,the biomass and water content were detected in the seedlings. All assays were replicated at least four times to minimize experimental errors. The results show that:with the increasing of NaHCO₃ concentration, the seed germination rate,germination index and vigor index respectively decreased by 26.6%~91.0%, 40.0%-95.5% and 66.8%-98.6%,and the seedlings dry weight was lessened by 5.0%-69.4%,but plant water content changed little,which indicated seeds germination and seedling growth were significantly suppressed in oat under alkalic salt treatment;the O₂^- production rate,hydrogen peroxide,MDA contents and plasma membrane permeability in seeding leaves respectively increased by 74.0%-74.0%,2.6%-107.9%,22.2%-102.9% and 46.9%-287.4% compared with the control group;catalase activity and free amino acid contents increased gradually by 40.4% and 129.5% under 200 mmol·L^-1 NaHCO₃ treatment,respectively;comparing with the control group,peroxidase activity decreased first and then increased,and increased overall by 2.58 fold at 200 mmol·L^-1 NaHCO₃ concentration,the organic acid content significantly increased by 22.9% than that of control group at equal NaHCO₃ concentrations;ascorbic acid and glutathione contents decreased consistently as the concentration of NaHCO₃ increased,and the activities of superoxide dismutase and ascorbate peroxidase,total soluble protein, boiling stable protein,boiling unstable protein,soluble sugar and proline contents exhibited a humped-curve trend in leaves,which were all lower than the control group under 200 mmol·L^-1 NaHCO₃ treatment. It can be concluded that alkalic salt has significant inhibitory effect on seed germination and seedling growth of oat,the imbalances of reactive oxygen species metabolism in the seedling leaves and more energy consumption for osmotic adjustment by accumulating organic solutes might be two important reasons for the growth of oat seedlings to be inhibited under alkali treatment.

Key words: Avena nuda L., alkalic salt, seed germination, reactive oxygen metabolism, osmotica