The Study On The Auxin's Distribution During The Development Of Carpel Of Capsella Bursa-pastoris

Capsella bursa-pastoris (shepherd's-purse) is a small annual ruderal and a member of the Brassicaceae or mustard family. Both Capsella bursa-pastoris and Arabidopsis thaliana are weeds of Cruciferae. They share a high genetic and Biologyogical homologous. But their carpel and pod morphology appears a distinct difference that in Arabidopsis is a cylinder-shaped silique while in Capsella bursa-pastoris the heart-shaped silicle. As we all known that the auxin plays a significant role in plants organ identity and morphogenesis. We estimate that may the auxin spatio-temporal distribution in carple development of Capsella bursa-pastoris causes the differential cell division orientation and cell division frequence. It contributes to the identical silicle pattern of Capsella bursa-pastoris carpel.For an in vivo analysis of the auxin pattern in carpel of Capsella bursa-pastoris that the auxin responsible DR5 elements promoter are synthesized and recombinated with the GFP reporter gene and cloned into pBI121 Ti plasmid. The plant expression vector named pBI121-DR5::GFP comprising a specific auxin promoter DR5 and green fluorescent protein gene GFP was transformed into Capsella bursa-pastoris with Agrobacterium tumefaciens infiltration of inflorescence. We harvest the seeds and several transgenic seedings obtained via kanamycin resistance screening and PCR detecting with special primers. The transgenic seedlings are planted untill flowering and are subjected to observation. The GFP fluorescence distribution in floral organ showes strong signals in stigma. It indicates that higher concentration auxin distribution in stigma. It is very important to build up apical-basal auxin gradient during carpel development. This phenomenon is parallel with the auxin pattern in carpel in Arabidopsis thaliana. Identically, we observed stronger fluorescence signals in two lateral upper region of the early stage of carpel that is quite different from Arabidopsis. It showes that the auxin in Capsella bursa-pastoris maintains a further lateral gradient distribution with the two upper margin auxin maximum as well as the apical-basal gradient in carpel. Therefore a conclusion can be drawn that apical-basal asymmetric distribution along with upper lateral polar transport of auxin that bring about the pattern formation of carpel in Capsella bursa.Accumulate research demonstrate that the growth responses of plant to light and gravity are mediated by asymmetric distribution of the phytohormone auxin. The most reason is the polarity localization of the auxin efflux carrier PIN3. We carried out a homologous clone of the PIN3 cDNA of Capsella bursa-pastoris and its coding region is 1952 bp,which can be translated into 649 amino acids. Bioinformatics analysis shows that CbPIN3 gene and AtPIN3 gene share high homology and their protein isoelectric, molecular weight and mature protein size with very little differences.These indicate that this two proteins are same in function. However, there are differences in key sites,suggesting that functional variance also existence in this two proteins. Researches on expression regulation of CbPIN3 gene and distribution of CbPIN3 protein need to be conducted in the near future. It was only when we revealed auxin's lateral polarity distribution molecular mechanism during the development of Carpel of Capsella bursa-pastoris that can we make clear short pod morphogenesis from molecular level.