Effects of Root Excision and Water Stress on Root Hydraulics and TaPIPs Expression in Wheat Seedlings

Abstract

Root excision can break water balance between water uptake by roots and transpriation in shoots and induce hydraulic responses of roots,which is helpful to explain how hydrostatic gradient regulates root hydraulic traits.To explore the regulation mechanisms of root hydraulics to the broken whole plant water balance by root excision and water stress,we investigated the changes of individual root(Lproot) and cortex cell(Lpcell) hydraulic conductivities of wheat(Triticum aestivum,cv.Changwu 134) after root excision and water stress with root and cell pressure probes.The transcription levels of TaPIP1;2 and TaPIP2;5 were also measured with quantitative real-time PCR.Root excision or water stress treatment significantly reduced the leaf transpiration rate and stomatal conductance of wheat seedlings,but the Lproot or Lpcell of the remained roots had no significant changes.The transpiration rate,stomatal conductance,leaf water potential,Lproot,and Lpcell of root-excised plants were significantly higher than those of plants under water stress.However,these parameters of plants with both root excision and water stress were significantly lower than those with a single treatment or the control.Irrespectively of root excision or water stress,Lpcell had a significantly positive correlation with Lproot(R2= 0.97,P 0.05),which suggested the accordance in root water uptake ability at cell level and individual root level.Root excision significantly up-regulated the relative mRNA contents of TaPIP1;2 and TaPIP2;5 in wheat roots,but water stress had an effect of down-regulation.The relative mRNA contents of TaPIP1;2 and TaPIP2;5 of root excised and water stressed seedlings were the lowest in the four treatments.These results may suggest that root excision could reduce the tolerance of wheat seedling to the following water stress;cortex cell hydraulic conductivity could be accordant with individual root hydraulic conductivity during wheat root hydraulics regulation;and TaPIP1;2 and TaPIP2;5 may be involved in regulating root hydraulics of wheat.