The Alleviation Effects Of Mechanical Wounding On Chilling Injury In Wheat Leaf And Underling Physiological Mechanisms

Chilling is one of the major environmental factors that affect the growth and development of wheat plant.Mechanical wounding is a common stress that occurs in crop productions.Therefore,it’s of great importance to study the effect and mechanism of mechanical wounding on leaves of wheat plant in response to chilling stress.In this study,wheat cultivar Yangmai 16 was selected under pot cultivation to do the experiments:(1)In order to detect the effect of mechanical wounding on different areas of wounded leaves,one side alone the main vain of the 9th expanded leaves were wounded and then the plants were treated with-3℃ for 6 h at 2 h and 12 h after wounding.(2)In order to test the effect of mechanical wounding on wounded and neighbor unwounded leaves in response to chilling stress,mechanical wounding was conducted in the 5th leaf at 6 leaf stage and the plants were treated with chilling stress at 12 h,24 h,48 h,120 h and 240 h after wounding for 48 h with the temperature of-2℃/-3 ℃(day/night respectively).The main results are as follows:1.The resistance of various unwounded areas of wounded leaf in response to chilling from strong to weak:basal>local>distal The resistance of chilling showed various in areas of wounded leaf.The base of wounded leaf showed the the maximum photochemical efficiency(Fv/Fm)values the best,and then is the central and the top of the wounded leaf compared with the control that just treated with chilling stress.In contrast,the superoxide radical(O2-.)production rate and malondialdehyde(MDA)content was highest in top of the wounded leaf,and then is the central and the base of wounded leaf,indicating that the top of wounded leaf was injured most.The activities of ascorbate peroxidase(APX),catalase(CAT)and glutathione reductase(GR)were highest in base of wounded leaf,and then the central and top of wounded leaf,the same trend was also found in signal molecules of hydrogen peroxide(H2O2),nitric oxide(NO)and abscisic acid(ABA),suggesting that these molecules were transfered mainly to the base of wounded leaves.2.Mechanical wounding decreased the tolerance of wounded leaves to chilling The wounded leaves after chilling treatments showed a decrease in net photosynthetic rate(Pn),stomatal conductance(gs),Fv/Fm and the photochemical efficiency(ΦPSII),while an increase in non-photochemical quenching coefficient(NPQ)became increased,which indicate that the photosynthetic capacity decreased after the mutipile stresses of wounding and chilling;Besides,the O2-.production rate and MDA content increased,suggesting a reactive oxgen species burst and the damage of the plasma membrane;Moreover,the activities of superoxide dismutase(SOD),APX and GR increased.These results indicated that mechanical wounding,together with chilling can impair the photosynthesis and increased the degree of reactive oxgen species injury of wounded leaves,but it didn’t scavenge all of the excess reactive oxgen species.3.Mechanical wounding enhanced the tolerance of the upper unwounded leaves to chillingThe upper unwounded leaves after chilling showed an increase in Pn,gs,Fv/Fm andΦPSII,while a decrease in NPQ became decreased,indicating that the photosynthetic capacity decreased after the mutipile stresses of wounding and chilling;Besides,the the O2-.production rate and MDA content decreased,suggesting a suppression of the reactive oxgen species and the alleviation of the plasma membrane;Moreover,the activities of SOD,APX,CAT and GR increased to scavenge the excess reactive oxgen species.The contents of signal molecues H2O2,NO and ABA increased impling an active signal transduction.These results indicated that mechanical wounding enhanced the chilling tolerance of the upper unwounded leaves.In conclusion,the resistance of chilling showed various in areas of wounded leaf.The resistance of chilling stress was higher in the base of wounded leaf than that of the central and distal of the leaves.mechanical wouding impaired the photocapacity of wounded leaf,activied the reactive oxgen species and ultimately weakened the resistance to chilling stress.Mechanical wounding enhanced chilling tolerance of the upper unwouned leaeaves,mainly increased the photosynthetic rate,decreased the O2-’ production rate,alleviated the membrane lipid peroxidation,enhanced the antioxidant system and increased the signal molecules,such as H2O2,NO and ABA.