The Research Of Root-shoot Interaction Mechanism On Cotton Leaf Scenescence

In order to elucidate the hormonal mechanism of cotton root-dominated type,the formation of different root-shoot interactions were observed.In this research,we will use early senescence CCRI41 and late senescence CCRI49 with common graft(single scion grafts onto one rootstock)and Y graft(two scions graft onto one rootstock),by high potassium(2.5 mmol/L)and low potassium cultivated in hydroponics experiment,low potassium stress(0.03 mmol/L)induced leaf senescence.Under low potassium condition,the leaf of scion with CCRI41 senescence much heavier than that of CCRI49.So it is root-dominated type.After grafted 4 weeks results showed that the concentration of ZR+Z or iPA+iP in roots and the youngest fully expanded leaf and their delivery rate in xylem sap regarding 1-grafting combinations with CCRI41 as rootstock were significantly lower than those with CCRI49 as rootstock in most of situations.However,the results of free ABA level were exactly opposite.With respect to the Y-grafting of CCRI41 and CCRI49,the results were similar to those of 1-grafting,whereas the role of root was not absolutely predominant any more.In order to study the different types of root-shoot interaction of anatomical mechanism,this study observed the formation process of grafted cotton.Usually cotton graft healing process is subdivided into 3 stages:(1)the formation and thickening of the isolation layer,the formation of initial adhesion(2 d after grafting),cambium cells dedifferentiation of callus(small);(2)callus produced,break isolation layer,isolation layer becomes thinner,new vascular dimensional basic formed(4 d after grafting);(3)callus began to differentiate into a new organization,the basic isolation layer is absorbed and connected between the stock and the scion,thus forming a new plant is different from that of rootstock and scion(6 d after grafting).During the development of cotton graft,CTK and IAA could regulate the formation of callus and promote the repair of vascular tissue,and ABA was negatively regulated and may promote the differentiation of callus.There was no anatomical difference between different types of root-shoot interaction during the graft union formation.In order to study the effects of root-shoot interaction mechanism regulatory sites-hypocotyl,this study observed the hypocotyl tissue anatomical structures.In the present study,we observed the anatomy of scion hypocotyls of both patterns under K deficiency(0.03 mmol L-1),and evaluated if it is associated with the flux of CTK and ABA in xylem.Results showed that after-grafted hypocotyls were inhibited in growth and differentiation of primary and early secondary xylem than non-grafted plants.I type grafting showed the scion lignification influenced by rootstock,and the development of the vessel related to the scion itself,and showed the trend after 2 weeks,and Y grafting did not show this trend.When grafted 4 weeks,in terms of I type grafts of shoot-dominated pattern,the anatomy of scion hypocotyl was clearly influenced by rootstocks,which is inconsistent with the fact that the delivery rate of CTK and ABA in scion xylem was mainly affected by shoot.For Y type grafts of shoot-dominated pattern,the scion with greater CTK flux accompanied by lower ABA flux showed growth superiority as compared with its counterpart.However,the two processes referring to flux of phytohormone in scion xylem and scion growth likely occur concomitantly but not causally.As the results of CTK andABA flux in scion xylem,the anatomy of scion hypocotyls of root-dominated pattern was obviously altered by rootstock in I grafts.Nonetheless,they might be also concomitant processes rather than cause and effect.Additionally,there were significant differences in anatomy between two different scions of Y grafts of root-dominated pattern,which is disagreement with the similar CTK and ABA flux in xylem of two scions.In conclusion,the scion hypocotyl anatomy of either shoot-or root-dominated pattern regarding cotton leaf premature senescence induced by K deficiency is independent of CTK and ABA flux in its xylem.In addition,the differences in scion hypocotyl anatomy between two cultivars in I graft type were inconsistent with their differences in Y graft type,which is possibly due to shoot-shoot interaction in Y graft.So we concluded that the after grafting anatomical development may be independent of the root-shoot interaction type.Potassium deficiency induced conditions,leaf easy senescence CCRI41 graft with late senescence SCRC22 and CCRI49,showed the different root-shoot interaction types,shoot-dominated type and root-dominated type.This two root-shoot interaction types with related to the flux of scion phytohormones(ZR+Z.iPA+iP ? ABA),regardless of with the development of grafting process development and hypocotyl anatomical structure of 1-4 weeks after grafting.