| Chrysanthemum is one of ten traditional famous flowers in China and four cut flowers in the world, which has a great ornamental value and commercial value. The pedicel is from the base of flower to the top of stem with a leaf, whose curvature is an important cut flower export grade indicators. In addition, the cut flower which was in the harvest to go through the set of goods, wholesale, transportation, retail and other sectors will inevitably be subjected to water stress. When the water stress reaches a certain level, the flower neck shows bending, which resulting in reduced quality, and severely reduced the vase life of cut chrysanthemum.Aphids are the major pests which harm to cut chrysanthemum, and its prevention has become a major problems in the cut flower industry. Cultivating a new germplasm with resistance to aphids is a key to the cut chrysanthemum, which could improve the yield, quality and promote the industrialization.The study analyzes the differences of'H5'which resistant to bent beck and aphid and 'QX101'which has no resistance. We comparied the pedicel structure, the change of the defense enzyme activity, lignin content and the expression of the key genes in the lignin biosynthesis pathway in two different varieties of cut chrysanthemum, and hoped to explain the mechanism of the resistance of bent neck and aphids. The main results are follows:(1) We designed the degenerate primers by comsulting the other plant COMT gene's conserved sequence, and cloned cDNA sequence of COMT gene of cut chrysanthemum using PT-PCR and RACE techniques. The gene was named CgCOMT and the accession number is AB500859. Sequence analysis showed that, CgCOMT gene has 1301bp length, 1065bp open reading frame (ORF), and 355 amino acids were encoded.(2) As pedicel rigidity is a key component of postharvest quality of the spray cut chrysanthemum, the morphology, anatomy and physiolology of the pedicel at various stage of flower bud development were compared in two contrasting charysanthemum cultivars. The pedicel of the cultivar with the better resistance ('H5') showed a higher proportion of vascular elements, high lignin content, CgCOMT gene expression and relative water contents throughout all floral stages. Pedicel rigidity was related to ratio of vascular structure, relative water content and lignin content, and this may be because the lignin provides the water transport capacity and mechanical strength. The CgCOMT gene expression was also prove that the lignin content is directly with the pedicel rigidity.(3) PAL activity, POD activity, lignin content, histochemical staining, the expression of the key gene in lignin biosynthesis pathway were compared in'H5'which is resistant variety and'QX101'which has no resistant. The results showed that PAL activity level, POD activity level, lignin content, the key gnen PAL,COMT,F5H,POD were significantly changed after aphids inoculation, and the resistant varieties ('H5') has a fast response and a increased amplitude. It supposed that the lignin accumulation closely related to aphid resistance. We also used MeJA to induce the two cultivars, and found that the key gene in lignin biosynthesis pathway has a rapid response, and the lignin accumulated significantly. It was further proof of increased lignin content was a way to increase the aphid resistance. |
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