ROS Mediating Root Hydraulic Conductivity Transiently Response To ABA In Maize Roots

The plant hormone abscisic acid is an important factor response to water stress,which plays an important role in regulating the water balance of plant and inducing the stress tolerance.The function that ABA promote the Lpr of root by regulating AQP expression and activity is not only a transient effect,but also a long-time effect.The long-time effect is caused by aquaporin content.The transient effect is that cell water conductivity up to peak at 1h and return to the control level at 2h treatment by ABA,which mechanisms have not known yet.ROS,particularly H2O2 has became a new signaling molecule recent years which regulate aquaporin activity and then adjust the Lpr.Lpr could reduced by about 90%in 15 min treatment by H2O2,So we hypothesized that ROS may mediate the root hydraulic conductivity response to ABA transiently.In order to verify this hypothesis,we take maize(Zheng 958)for materials,and determinate their Lpr,active oxygen content,antioxidant enzyme activities and gene expression of NADPH oxidase and aquaporin gene expression after treatment by ABA concentration(0μM,2μM,5μM,10μM ABA treatment 1h)and time-course(5μM ABA treatment 0min,30min,1h,3h).Our study revealed the perception,transmission and response mechanisms of plant root system water transport to abiotic stress signal,that have a important theoretical significance for plant to keep balance in stress.The results of this study are as follows:1.Use pressure chamber technology to study the effect to Lpr in isolated maize root cause by different concentration of ABA treatment at the same time and the same concentration ABA treatment at different time,found that the Lpr response to both ABA concentration and time-course,Lpr increased significantly at 30 min,and peaked at 1h treatment by 5μM ABA.2.ABA treatment could reduce the levels of ROS in maize root instantly,which depended on ABA concentration.The variation of ROS content was contrary coincide with Lpr variation,suggested that the reduced content of ROS may result in transient stimulating effect of ABA on the Lpr.3.ABA treated on maize root 1h,four antioxidant enzymes activity increased significantly with the increased concentration of ABA,which is coincide with the reduced content of ROS corresponding to increased ABA concentration,suggested that ABA treatment significantly changed the activity of maize root enzymatic defense system.4.In maize roots,at least within one hour,NADPH oxidase-mediated and ABA-induced ROS synthesis is small.The synthesis of ROS is not changed in a short period,but the enzymatic clear system activity and gene expression are change significantly,resulting in the content of ROS reduced transiently.5.PIPs expression in maize root is very sensitive to low concentrations,low concentration can cause significant stimulating effect,further increases with the ABA concentration,PIPs expression remained constantly or even to decline.Increased greater than 100%in different subgroups are ZmPIP2;1.ZmPIP2;4、ZmPIP2;6 and ZmPIP1;1.Other subgroups increased by between 30%and 85%.Total trend is ZmPIP2 increase greater than the increase of ZmPIP1 class.Except some sub-class of ZmPIP expression have a phenomenon of slight decrease,others had no increase treated by ABA in 30min.Obviously,the level of ZmPIP gene expression can not explained the trend of Lpr with the ABA treatment time,which may be mainly caused by the change of protein activity in a short period.6.The protein expression of ZmPIP1;2 and ZmPIP2;1 didn’t increased after ABA treatment 30 min.There fore,the Lpr transient increased after ABA treatment was not caused by the increassion of ZmPIP expression.It might due to PIP activity stimulated by ABA in short period of time.The ABA may through induce the antioxidant defense system(antioxidant enzyme activity and gene expression)to reduce the content of the ROS mediated transient increase in Lpr.