Research On Mechanism Of Leaf Color Mutant Radiated By Carbon Ions In Wandering Jew (Tradescantia Fiumiensis)

The thermo-sensitive leaf color mutant of Wandering jew(Tradescantia fiumiensis)was obtained by irradiated heavy ions at HIRFL.The young leaves of this mutant are pink under low-temperature conditions,and the turn back to green under high-temperature conditions,but the leaf lower epidermis of the mutant keep purple under two temperature conditions.The leaf color mutant is an ideal material for study on the photosynthetic system structure,chlorophyll metabolism,chloroplast development,photosynthesis and a series of physiological metabolic processes.It is also an important material in genetic and breeding.To elucidate the material bases and physicochemical factors associated with leaf color mutation of Wandering jew irradiated using carbon ions.The leaf color mutant and its wild type were used as material to investigate the properties of leaf color under different temperature conditions,including chloroplast structures,anthocyanin/flavone contents and photosynthetic characters.Moreover,by using transcriptomics,the molecular mechanism of the leaf color mutant changed by different temperature were investigated in this project.Unigene and public information platform of Wandering jew were constructed,the key different expression genes and metabolic pathway of leaf color were identified as well.The main results of our research are described as follows:(1)The young shoots of geranium were exposed to carbon ions and one thermo-sensitive leaf color mutant was obtained at dosage under 20 Gy irradiation.Under different temperature conditons,the color of leaf,stem and petal and other biological traits of mutant displayed significant differences between mt and WT.However,compared to WT,the chromosomal polyploidy were not changed in mutant leaves.(2)Compared to wild type,a large amount of purple anthocyanins were distributed in the lower epidermis of the mt-7 ? leaves,and a small amount of anthocyanins were also observed in the vascular tissue and sponge tissue of mt-7 ? leaves under microscopic examination.Only a small amount of anthocyanins were distributed in the lower epidermis of the mt-25? leaves? The anthocyanins were disappeared and in stead of a large amount of chlorophyll in the sponge tissue and vascular tissue of mt-25? leaves.The epidermal cells of the mutant leaves were not showed significant difference under different temperature conditions,however,the stomatas in the lower epidermis showed significant difference between WT and mt leaves under scanning electron microscope examination.Chloroplasts of mutants exhibited abnormal morphology and distribution at 25?,and under 7?temperature conditions,the chloroplasts converted into leucoplast in leaves on mutants under transmissionelectron microscope.(3)Temperature change affected the rate of color transition,chlorophyll and anthocyanin concentrations in leaves on mutants.Compared to WT,the total chlorophyll contents and carotenoid contents were significant reduced 45% and 94%,respectively.However,the anthocyanin concentration 21 fold incease in mt-7 ? leaves.However,under 25 ?temperature conditions,the coloration patterns were similar between WT and mt-25 ?leaves.Different blade types of parameters with chlorophyll fluorescence from excitation instrument analyse indicated that,under 7 ? temperature conditions,the light reaction center parameter ABS/RC,TRO/RC and ETO/RC were significant higher than WT,however,the FV/FM,PIABS,?EO and ?O were significant lower than WT.Under 25 ? temperature conditions,the FV/FM and PIABS were lower than WT,but there is no significant difference about light reaction center parameter result in mt-25? leaves.(4)HPLC analysis of anthocyanins in mutant and wild type leaves revealed that the contents of cyanidin,petunidin and delphinidin were significantly lower than those of under low-temperature conditions(7?),except pelargonidin was not detected in mutant leaves under room-temperature conditions(25 ?).The HPLC profile also indicatedthe highest levels of flavonols in mutant leaves at 7? significantly.(5)Molecular analysis indicated that all the anthocyanin biosynthetic genes and regulatory genes were constitutively up-regulated in mutant leaves at 7 ?.The other anthocyanin biosynthesis and regulatory genes showed similar expression levels between mutant and wild type,except PAL,CHS,ANS were up-regulated at 25?.(6)RNA sequencing was executed to estabolish the transcriptome databases of Wandering jew.A total of 91565 unigenes were obtained,and 44733 of which were identified as putative homologs of annotated sequences in public databases.15368 unigenes?12401unigenes and 6456 unigenes were identified in library of WT vs mt-25?,WT vs mt-7? and mt-25 ? vs mt-7 ?,respectively.The KEGG pathway results showed that,a mount of unigenes involved in anthocyanin biosynthesis,chlorophyll biosynthesis,photosynthesis and photosynthesis-antenna proteins.The expression level of 7 unigenes involved in anthocyanin biosynthesis and 10 unigenes involved in chlorophyll biosynthesis were detected using quantitative real-time PCR in this study.Among those genes,under low-temperatures conditions,7 unigenes involved in anthocyanin biosynthesis which showed higher expression levels in the mt-7 ? leaves than WT.Meanwhile,10 unigenes involved in chlorophyll biosynthesis were down-regulated in the mt-7 ? compared to WT plants.However,the partial unigenes involved in chlorophyll biosynthesis and anthocyanin were up-regulated in the mt-25? compared to WT plants,such as POR and ANS.And,some unigenes involved inanthocyanin biosynthesis which expression level were down regulated in mt-25?,especially PAL.