Responses of active oxygen metabolism and osmotica accumulation of Avena nude L.seedlings to NaCl stress

A sand culture experiment was conducted to study the effects of NaCl stress on the seedling's growth,active oxygen metabolism,and osmotica contents of Avena nude L.(cultivar Dingyou No.6).Six levels(0,50,100,150,200,and 250 mmol·L-1) of NaCl were installed.NaCl stress inhibited the seedling growth significantly,and the inhibition was aggravated with increasing concentration of NaCl.The maximum concentration of NaCl that the seedlings could be in resistance to was about 150 mmol·L-1.With the increasing concentration of NaCl,the leaf O2-· production rate and H2O2 and malondialdehyde contents increased dramatically,the activities of superoxide dismutase,guaiacol peroxidase,and ascorbate peroxidase decreased after an initial increase,and the catalase activity increased gradually after a rapid decrease.The NaCl stress decreased the leaf glutathione content markedly,but the ascorbic acid content was less affected.Under NaCl stress,the leaf proline content had a significant increase.With the increasing concentration of NaCl,the leaf Na+ content increased markedly,the K+ content and K+/Na+ ratio were in adverse,the plasma membrane H+-ATPase activity and the contents of total soluble protein,heat-stable protein,and heat-unstable protein decreased after an initial increase,the free amino acid content decreased first and increased then,and the soluble sugar content presented a trend of decrease-increase-decrease.All the results indicated that the imbalance of leaf active oxygen metabolism,the disturbance of leaf Na+ and K+ homeostasis,and the more consumed energy for osmotic adjustment by accumulated organic solutes under NaCl stress could be the main causes for the growth inhibition of the seedlings.