Response Characteristics Of Grape Root Border Cells To 4-HBA Stress

4-Hydroxybenzoic acid?4-HBA?is one of the most important autotoxins secreted by the grape root tips,and it has a low promotion and high inhibition effect on grape growth.RBCs are a layer of active cells around the root cap.Numerous studies have shown that RBCs have the function of protecting roots from adversity.In this experiment,‘Beta'?V.riparia×V.labrusca cv.?,one of the most common rootstock in Northern China,was used as materials to study the development characteristics of RBCs,and their response to 4-HBA stress was studied by comparative analysis of the number,activity,mucilage layer thickness,and secretion characteristics of the RBCs under 4-HBA stress.The major results are as follows:1.The development of grape RBCs is closely related to the growth of roots.The number and the thickness of the mucilage layer of RBCs increase first and then reduce with the root growth.When the root length is 25-30mm,the number of RBCs is the largest,about 200,and the thickness of the mucilage layer is the largest,about 9.3?m.The activity of RBCs was not significantly changed and remained at above 75%overall.2.4-HBA affects the development of RBCs and root growth.Low concentrations of4-HBA(50?g·mL^-1)promoted the release of RBCs,and high concentrations of 4-HBA(200?g·mL^-1)reduced the number and activity of RBCs.Pectin methylesterase?PME?promotes the release of RBCs,and the number of released RBCs is positively correlated with the PME activity of root cap.3.4-HBA induces secretion of slime from RBCs,thickens the mucilage layer of RBCs,and then protects the root tip to reduce the influence of stress factors.And 4-HBA treatment can induce more salicylic acid?SA?secretion of root tips and RBCs.At the same time,4-HBA affects the expression of key enzyme genes in plant phenylpropane metabolic pathway.The gene expression levels are inconsistent in root tips and RBCs.Low concentrations of 4-HBA(50?g·mL^-1)induced expression of PAL15,4CL and CCR genes in root tips,induced expression of PAL2,4CL and CCR in RBCs,inhibits PAL1,PAL2,and CAD expression in the root tips,inhibits the expression of PAL15 and CAD in RBCs.High concentrations of4-HBA(200?g·mL^-1)induced expression of PAL15,CAD and CCR gene in RBCs.4.A large amount of SA secreted by RBCs can moderately alleviate 4-HBA stress.Under high-concentration 4-HBA stress,the root growth of grape seedlings was significantly inhibited,the root tip was yellow and the viability of antioxidant enzymes was significantly reduced,and SA pretreatment can stimulate and induce the activity of SOD,POD,CAT,GR,APX and other antioxidant enzymes in the cells,making it maintained a relatively high level of activity under 4-HBA stress,which resulted in the removal of accumulated reactive oxygen species,which reduced the cellular MDA content and alleviated the damage to grape seedlings caused by high concentrations of 4-HBA stress.