Study On Tissue Culture And Rooting Mechanism Of Lagerstroemia Indica ’Ziqi’

Lagerstroemia Indica ’Ziqi’ is a Lythraceae of the genus Lagerstroemia(Lythraceae).It is the seed of ’Ebony Flame’ induced by 60Co-γ ray radiation,a new variety of Lagerstroemia indica,bred from seedlings.Its leaves gray-purple,purple-red flower color,set viewing flowers,viewing leaves in one,with a high ornamental value,a broad market prospects.At present,there is no report about tissue culture of Lagerstroemia indica ’Ziqi’,which restricts its large-scale application.The stem segments with axillary buds of Lagerstroemia indica ’Ziqi’ were used as experimental materials,the selection and disinfection of explants,subculture and rooting culture of plantlets,the content of endogenous hormones in tissue culture and the expression of LiPLT gene during rooting were studied,the aim of this study was to establish the technique system of tissue culture and rapid propagation of Lagerstroemia indica ’Ziqi’,to explore the regulation mechanism of endogenous hormones during tissue culture,and to explore the role of LiPLT gene in rooting process.The main results are as follows:(1)In the selection of explants,the lower stem segments were more suitable for explants.In the selection of sterilizing time of stem segments,the survival rate was the highest 81.1%when treated with 0.1%HgCl2 for 10 min.The selection of explants should be the lower stem segments,and the disinfection time should be 10 min.(2)In the process of plantlet proliferation,different basic medium,different cytokinin and auxin species and concentration ratio had significant effects on plantlet proliferation.The results showed that the optimal medium for subculture was DKW+6-BA 1.0 mg·L-1+NAA 0.2 mg·L-1+sucrose 30.0 g·L-1+Agar 15g·L-1,with the highest multiplication coefficient of 5.68.(3)During the rooting induction of plantlets in vitro,different basic medium,auxin concentration,activated carbon concentration and dark culture time had significant effects on rooting of plantlets in vitro.The optimal rooting medium was 1/2 DKW+IBA 0.6 mg·L-1+Sucrose 15.0 g·L-1+Agar 5.0 g·L-1,the rooting rate was 94.0%.(4)The induction of cluster buds in tissue culture seedlings is mainly regulated by endogenous GA3 and IAA,The content of GA3 and IAA was higher and the content of ABA and ZR was lower in the process of multiplication.The addition of plant growth regulators with proper concentration had an effect on the content of endogenous hormones,which was beneficial to the proliferation and growth of cluster buds.GA3/ZR,GA3/ABA and IAA/ZR fluctuated greatly in the process of proliferation,which indicated that they regulated the growth of plantlets in vitro.IAA was the main factor to induce rooting of plantlets in tissue culture.Adding exogenous IBA could significantly increase the content of endogenous IAA;the high IAA/ZR ratio promoted the differentiation and growth of root primordium and the elongation of adventitious roots,IAA/ZR value fluctuated most during rooting,which indicated that IAA/ZR was the main factor regulating the rooting of tissue culture plantlets of Lagerstroemia indica ’Ziqi’.(5)LiPLT gene was cloned from tissue culture plantlets of Lagerstroemia indica’Ziqi’,the CDS sequence of LiPLT gene was 693 bp in length and encoded 230 amino acids.The expression level was the highest in root and the lowest in leaf.In the process of rooting,LiPLT gene increased firstly and then decreased,which was similar to the change of endogenous IAA content,the addition of auxin to the culture medium affected the expression of LiPLT gene,and promoted the expression of LiPLT gene in the plantlets.