| P.deltoides x P.eurarmericana cv.('Nanlin895')is a specie with high reproduction capacity and important timber in coastal areas.The hybrid variety INRA 717-1B4(Populus tremula L.x P.alba L.'717' poplar)is a kind of important tree species with strong stress resistance,potential application value to vegetation restoration,prevention of soil erosion and saline-alkali soil remediation.In order to more thoroughly analyze the changes of the antioxidant system and the content of oxidative products in apoplast of two poplars under different salt concentrations and MeJA added with salt stress,two poplars in vitro culture were used as materials,and in this study,the expression of related antioxidant enzyme genes and physiological and biochemical responses in apoplast under salt stress and MeJA treatment were studied.That will lay the foundation for the selection of poplar salt-resistant varieties and further exploration of the salt-tolerance mechanism of poplars.The specific conclusions are as follows:1.The responses of the apoplastic AsA-GSH Cycle in '895' and '717'poplar leaves to different salt concentrationsAfter two poplars were treated with 0 mmol/L,25mmol/L and 75mmol/L NaCl for 5 days and 10 days,the lower concentration of salt(25mmol/L)increased root length and stem length of the two poplars,while growth was inhibited at 75mmol/L NaCl.When the apoplast of '895'poplar was treated with 25mmol/L NaCl salt,the MDA content decreased.75mmol/L NaCl caused a significant increase in malondialdehyde(MDA)content in the apoplast of two poplars compared to the control.Under 75mmol/L NaCl treatment,the contents of hydrogen peroxide(H2O2)in two poplars increased significantly compared with the control,and the prolongation of the treatment time also aggravated the accumulation of H2O2.Under the 25mmol/L NaCl treatment,the activity of peroxidase(POD)in the apoplast of '895' poplar was significantly increased,and the activity of dehydroascorbate reductase(DHAR)was weakened compared to the control.The activity of Ascorbate peroxidase(APX)increased when treated with 25mmol/L NaCl for 10 days compared to the control.Under the 75mmol/L NaCl treatment,the activity of glutathione reductase(GR)in the '895' poplar and '717' poplar apoplasts increased significantly.When '717' poplar apoplast was treated with NaCl for 10 days,the activities of POD?APX and GR all increased as the increasing of salt concentration.The contents of the antioxidants ascorbic acid(AsA)and reduced glutathione(GSH)in two poplar apoplasts were significantly increased under treatment with 75mmol/L NaCl,and increased with increasing treatment concentration and treatment time,and the contents of AsA and GSH were increased.AsA and GSH contents were maintained at a high level.Therefore,the two poplars activated the excess reactive oxygen species(ROS)clearance mechanism when treated with 25mmol/L NaCl,and the 75mmol/L NaCl treatment broke the ROS balance.From the data of root and stem length?antioxidant system and oxidation products,it could be comprehensively seen that '717' poplar was more resistant to higher concentration of salt(<75 mmol/L)than '895'poplar.2.The responses of the apoplastic AsA-GSH Cycle in '895' and '717'poplar leaves todifferent concentration of MeJA under salt stressUnder 75mmol/L salt stress treatment,the growth of two poplars was inhibited and the production of oxidation products was accelerated.The activity of antioxidant enzymes was significantly enhanced compared to the control.The antioxidant content was also significantly higher than that of the control.After adding MeJA to the salt treatment,stem length and root length of two poplars increased significantly compared to the control.The addition of 50?mol/L MeJA and 250?mol/L MeJA with salt treatment reduced the content of H2O2 and MDA in the apoplast,while 500?mol/L MeJA made H2O2 and MDA levels increased in the apoplast of two poplars,indicated that 500?mol/L MeJA was too high for two poplars.When the apoplasts of two poplars were treated for 5 days,the activities of APX and GR were significantly higher than those of saline treatment at a higher concentration(500?mol/L)of MeJA,however,with the treatment time was prolonged,500?mol/L MeJA resulted in the activity of POD and GR in the apoplast reduced compared to the 250?mol/L MeJA treatment.When the poplars was treated for 10 days,the content of AsA and GSH in apoplast increased after salt treatment with 250?mol/L MeJA,which was higher than that of salt-treated control.Therefore,the addition of MeJA played a role in reducing the oxidative damage caused by salt stress on the apoplast of two poplars.Two kinds of poplars' apoplast were treated with salt stress for 5 days,500?mol/L MeJA attenuated the oxidative damage better,but when treated for 10 days,the lower concentration(250?mol/L)MeJA was better than other concentrations in helping the two poplar apoplasts to adapt to salt stress and maintain a certain degree of adaptability to salt stress.3.The expression of gene of AsA-GSH Cycle in '895' and '717'poplar leaves to MeJA under salt stressTreated with 75 mmol/L NaCl for 24h,the expression of DHAR?APX and GR gene of the two poplars were increased compared to the control.In particular,the expression of DHAR gene was significantly increased in the two poplars compared to the control for resisting oxidative damage associated with salt stress and maintaining the balance of ROS in the plants.Compared with '717' poplar,the expression levels of DHAR.APX and GR gene in '895' poplar were higher than those in saline control,indicating that '895' poplar was more sensitive to salt stress.After 250?mol/L MeJA was added,the expression levels of the three enzymes in the AsA-GSH cycle of the two poplars increased significantly compared with the saline treatment control,indicating that part of the gene expression of antioxidant enzyme in AsA-GSH cycle system in the two poplars were increased after adding 250?mol/L MeJA for 24 h.In conclusion,the lower salt treatment(25 mmol/L)promoted the growth of two poplars,stimulating the antioxidant system,while at higher concentrations growth was inhibited and ROS balance was broken.'717' poplar was more resistant to higher concentrations of salt(<75 mmol/L)than '895' poplar.The effect of 500?mol/L MeJA on reducing the oxidative damage of apoplast was better when the two kinds of poplar apoplasts were under salt stress for a short period of time,but when treated for a long time,250?mol/L MeJA could better help the two poplars apoplast adapt to salt stress and maintain a certain degree of adaptability to salt stress.When 250?mol/L MeJA added for 24h,the expression levels of DHAR,APX and GR gene of two poplars were increased.'895' poplar was more sensitive to salt stress than '717' poplar. |
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