Effects Of Exogenous Gaba On The Seed Germination And Seedling Growth Of Nitraria Sibirica Pall.under Salt Stress

Nitraria plants are strong halophyte and xerophyte in China.Among the plants in Nitraria of Nitrariaceae,Nitraria sibirica Pall.exhibited strong tolerance to salt and drought.In this experiment,the seeds of N.sibirica were used as experimental materials to study the their germination with the application of different concentrations(2.5-10 mmol/L)of exogenous γ-aminobutyric acid(GABA)under 25-125 mmol/L Na Cl stress.The effects of exogenous GABA at different concentrations(0-10 mmol/L)on the growth of annual N.sibirica seedlings under 0-400 mmol/L Na Cl stress were studied.The results are as follows:(1)The increasing in the Na Cl concentration was associated with a significant decrease in the germination rate,germination potential and vigor index of N.sibirica seeds.High concentration Na Cl seriously inhibited the growth and germination of seeds.The ad dition of exogenous GABA could alleviate the salt stress of N.sibirica seeds.The effect of 5 and 10 mmol/L GABA solution was better.It could promote the germination of N.sibirica seeds,make them quickly germinate to the peak and reduce the salt damage index.(2)With the increasing of Na Cl concentration,the radicle length,coleoptile length and transport rate of storage material all decreased to some extent,but they were not inhibied as obviously as germination rate.Under high concentrations(75 and 125 mmol/L)of Na Cl stress,the related indices of N.sibirica were significantly affected by GABA concentration.High concentration GABA could significantly promote the coleoptile length of N.sibirica seeds,while exogenous GABA could only promote the radicle length under high concentration Na Cl stress.Under Na Cl stress,10 mmol/L GABA solution could increase the transport rate of storage materials,promote the growth of seeds,and alleviate the poor development of seeds under Na Cl stress.(3)With the increasing of Na Cl concentration,the ratio of root to shoot increased first and then decreased.After the application of exogenous GABA,the ratio of root to shoot decreased with the increases of GABA concentration.The effect of exogenous GABA on stem de velopment was stronger than that on root.The plant height decreased with the increases of Na Cl concentration.When the Na Cl concentration reached the maximum,i.e.400 mmol/L,the plant height decreased to the lowest value.In salt stress groups under GABA treatment,the plant height of N.sibirica seedlings generally increased compared with the control group,but the effect was more obvious at GABA concentration of 5 mmol/L.GABA can promote the growth of N.sibirica seedlings and alleviate salt stress.(4)The increasing of Na Cl concentration was associated with a gradual decrease in the relative water content of N.sibirica seedlings.When the Na Cl concentration reached the maximum,the relative water content of N.sibirica leaves decreased to the lowest value.When exogenous GABA was applied,the effect of 5 mmol/L GABA was the best,while that of 10 mmol/L GABA was the worst.With the increase of Na Cl concentration,the succulence degrees of N.sibirica leaves increased.The succulence degrees of N.sibirica leaves were generally lower than that of the control group without GABA under the same concentration of Na Cl stress after the application of exogenous GABA.(5)With the increasing of Na Cl concentration,the chlorophyll content in the leaves of N.sibirica decreased first and then increased,however,it was lower than that in the blank control group.When exogenous GABA was applied and the concentration of Na Cl was 0 or 400 mmol/L,with the increase of GABA concentration,the chlorophyll content decre ased significantly.Under low salt stress,the chlorophyll content of leaves progressively increased with increasing the concentration of exogenous GABA.(6)With the increasing of Na Cl concentration,the electrolyte leakage rate of N.sibirica leaves increased significantly,and the permeability of plasma membrane increased significantly.After the application of exogenous GABA,the electrolyte leakage rate of N.sibirica leaves decreased remarkedly,which was lower when the concentration of GABA was 10 mm ol/L.With the increase of Na Cl concentration,the malondialdehyde(MDA)content in the leaves of N.sibirica decreased first and then increased,and goes for a maximum at the Na Cl concentration of 400 mmol/L.After the application of exogenous GABA,the c ontent of MDA in the leaves of N.sibirica increased,but decreased in the salt stress group,especially in the high salt stress group.(7)With the increasing of Na Cl concentration,the content of soluble sugar increased.After the application of exogenous GABA,the content of soluble sugar in the leaves of N.sibirica decreased as compared with the blank control group.When the concentration of Na Cl was 200 mmol/L and the concentration of exogenous GABA was 5 mmol/L,the content of soluble sugar decreased to the lowest level.As the concentration of Na Cl increases,the content of soluble protein decreased,and reached the maximum at Na Cl concentration of 200 mmol/L.After adding exogenous GABA,the content of soluble protein first increased and then decrea sed with the increases of GABA concentration,and reached the maximum at GABA concentration of 5 mmol/L.When exogenous GABA concentration was higher than 5 mmol/L,the content of soluble protein decreased.With the increases of Na Cl concentration,the pro line content in N.sibirica leaves increased first and then decreased,but generally increased.After adding exogenous GABA,the proline contents of blank control group and high concentration salt stress group increased first and then decreased with the increases of GABA concentration.However,the proline content of 200 mmol/L group decreased first and then increased with increasing the GABA concentration.(8)As the concentration of Na Cl increases,the activity of glutamate decarboxylase(GAD)in the leaves of N.sibirica increased first and then decreased.The GAD activity reached the maximum at the concentration of 200 mmol/L Na Cl.After adding 5 mmol/ L GABA,the GAD activity decreased,while after adding 10 mmol/L GABA,the activity increased at 0 and 400 mmol/L salt concentration.The activity of GAD decreased to the lowest level when Na Cl concentration was 400 mmol/L and GABA was 5 mmol/L.(9)With the increasing of Na Cl concentration,the content of endogenous GABA in N.sibirica leaves increased first and then decreased.It goes for a maximum at the Na Cl concentration of 200 mmol/L.Under high salt stress,the content of endogenous GABA first decreased and then increased with the increase of exogenous GABA concentration.However,the endogenous GABA content decreased with the increase of exogenous GABA content.