The Mechanism Of Auxin Involving In Bulbil Formation Of Lilium Lancifolium

Lilium lancifolium Thunb.belongs to the genus Lilium of the family Liliaceae.It is widely distributed and has strong resistance.Besides highly ornamental valve,L.lancifolium is also edible and of great medicinal valve.As a natural triploid,it is highly sterile and does not produce seeds,but it can form bulbils in the axilla of leaves for reproduction and dissemination as an asexual reproductive organ.However,the regulation mechanism of the initiation of bulbil formation in L.lancifolium has not been revealed.Studies have shown that auxin plays an important role in the formation and development of plant axillary organs,but the role of auxin in the formation of bulbils has not been reported.Based on the establishment of in vitro stem segment culture system,the axillary stem segments with the part leaf were inoculated into the medium containing auxin or auxin inhibitors NPA,TIBA and PCIB.The effects of auxin on the formation of bulblet in vitro stem segments were analyzed by combining anatomical study,hormone analysis and gene expression analysis.The main results are as follows:1.The system of bulbil induction of L.lancifolium stem segments in vitro was establishedIn order to solve the uncertainty of the time and position of bulblets formation under natural condition,a vitro induction system for bulbil fornation of L.lancifolium was established: Dormancy breaking of bulbs by refrigeration,Elongation culture of shoot tips in tubes,Bulbil induction of stem segments,Observation of the dynamic changes in leaf axillary.A stable research platform was established for studying the mechanism of bulbil formation in lilium spp..2.Exogenous auxin at a certain concentration promoted the bulbil formation of L.lancifolium stem segments in vitroHistomorphological observation showed that 0.2 mg/L IAA could promote the formation of bulbils in vitro stem segments,while auxin transport inhibitors NPA,TIBA and auxin function inhibitor PCIB could inhibit this process in varying degrees.Among them,auxin transport inhibitor TIBA had stronger inhibition effect and could delay the bulbil formation for 14 days.3.The dynamic relationship of different hormones in leaf axillary during bulbil formation were determinedDuring the process of bulbil formation,the content of auxin in axillary changed greatly,and the content of cytokinin increased in general.The initiation of bulbil formation depended on the stimulation of relatively high concentration of auxin.In the early stage,both exogenous IAA and TIBA reduced the auxin content in axilla,but the concentration of auxin increased continuously after treated by TIBA in the later period,which inhibited the formation of bulbils.4.The expression patterns of different genes in leaf axillary during bulbil formation were determinedExogenous IAA could rapidly promote the expression of auxin-responsive genes ARF2,ARF9 and TIR1,as well as the cytokinin signal transduction gene ARR1.In contrast,TIBA aould inhibit the expression of ARF2,ARF9 and ARR1,but promote the expression of TIR1.During bulbil formation,the expression of CYCD3-1,related to cell division,increased.The use of TIBA could inhibit the expression of CYCD3-1.The results showed that exogenous auxin promoted bulbil formation by inducing the expression of auxin responsive genes ARF2,ARF9 and TIR1 and cytokinin signal transduction gene ARR1 to rise rapidly.TIBA,an auxin transport inhibitor,significantly inhibited the expression of ARF2,ARF9 and ARR1,thus delaying the innitation of bulbils.