Study On The Response Of Isoprene Emission To Norflurazon And NaHSO₃ And Its Regulatory Mechanism

The synthesis and release of isoprene(2-methyl-1,3-butadiene,isoprene)play an important role in plant abiotic stress,but the synthesis of isoprene is limited by many factors.Under stress conditions,the synthesis,release and regulation mechanism of isoprene are still unclear.In this study,Nanlin 3804(Populus deltoids)was treated with norflurazon(inhibits carotenoid synthesis,600?M)and NaHSO₃(inhibits plant photorespiration,4.5 m M)to illustrate the synthesis and regulation of isoprene by isoprene emission rate.The results showed:1.Effect of norflurazon on isoprene emission(1)In the 28? clean water control,compared with the basic state,the GOX,Y(I),O₂^-and H₂O₂were significantly reduced at 50 min.Among them,H₂O₂ was also significantly decreased at 100 min.While CAT activity was significantly increased at 100 min.(2)Treated with 38? clean water alone,compared with the basic state,the leaf transmission rate,photorespiration rate and GOX activity increased significantly.At this time,Y(I),Y(II),q L and CAT activity increased significantly,indicating that the actual photochemical yield increased,leading to DMADP pool size and isoprene emission rate increased significantly.(3)With 28? norflurazon treatment alone,photosynthetic parameters and photorespiration rate of leaves did not change significantly.Compared with 50 min,GOX activity was significantly enhanced at100 min,and NPQ increased after treatment for 100 min.These results all indicate that the carotenoid synthesis pathway is inhibited after norflurazon treatment,and the energy accumulated in the cells.(4)When leaves were treated at a high temperature of 38? for 50 min,adding norflurazon and continuing 38? treatment,after adding norflurazon,the photorespiration rate and isoprene emission rate decreased,and the DMADP pool size increased.CAT activity decreased significantly,while the content of H₂O₂ and O₂^-increased.These results indicate that addition of norflurazon caused a certain degree of oxidative damage to the leaves under stress.(5)When leaves were treated with 28? norflurazon for 50 min,continuing norflurazon treatment and adding 38? high temperature treatment,after adding the 38? high temperature,the net assimilation rate decreased,the transmission rate,photorespiration rate,isoprene emission rate and DMADP pool size increased significantly.It shows that more carbon assimilation products are used in the synthesis and release of isoprene.2.Response of isoprene emission after NaHSO₃ and norflurazon treatments(1)In the 28? clean water control,compared with the basic state,GOX activity decreased significantly at 50 min.Stomatal conductance and transmission rate was decreased significantly at 100min.H₂O₂ content decreased significantly at both 50 min and 100 min.O₂^-content increased significantly at 50 min.Isoprene emission rate,NPQ and CAT activity increased significantly at 100 min.(2)When leaves were treated with 28? NaHSO3 for 50 min,adding norflurazon and continuing NaHSO3 treatment,after NaHSO₃ treatment for 50 min,the photorespiration rate and GOX activity decreased,net assimilation rate,stomatal conductance,transmission rate,isoprene emission rate and DMADP pool size decreased significantly.The intercellular CO₂concentration,NPQ,CAT activity and O₂^-content increased significantly.After adding norflurazon,net assimilation rate,stomatal conductance,intercellular CO₂ concentration,transmission rate,photorespiration rate,isoprene emission rate and DMADP pool size decreased.GOX activity,rate constant of Isps reaction,NPQ and O₂^-content increased.These results indicate that the accumulation of the energy of NaHSO₃ treatment causes damage to cell,and the energy is further accumulated after the addition of norflurazon.(3)When leaves were treated with 28? norflurazon for 50 min,adding NaHSO₃ and continuing norflurazon treatment,after adding NaHSO₃,the net assimilation rate,stomatal conductance and transmission rate decreased significantly,and the intercellular CO₂ concentration increased significantly,indicating decrease of net assimilation rate is caused by non-stomatal factors.Compared with the basic state,after adding NaHSO₃,the photorespiration rate decreased significantly.DMADP pool size and rate constant of Isps reaction decreased but there was no significant difference,indicating that the significant decrease of isoprene emission rate is the result of the combined action of substrate and enzyme.In summary,the relationship between isoprene emission and photosynthesis is not a simple linear relationship.In the presence of mild stress,DMADP pool size and isoprene emission rate increases significantly,photochemical products are more used for the synthesis of isoprene to maintain plant homeostasis and enhance plant resistance.In the presence of severe stress,photosynthetic organs are damaged and the net assimilation rate decreased,resulting in a decrease in DMADP pool size and a rapid decrease in isoprene emission rate.