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采用CPD(PI和DAPI组合)染色对番茄减数分裂粗线期和有丝分裂中期染色体进行了显带分析,随后用两种不同的45SrDNA克隆在相同的分裂相进行了荧光原位杂交定位分析。CPD染色在8条粗线期染色体上显示出了10条红色的CPD带纹,在6对有丝分裂中期染色体上显示出了12条CPD带纹。有丝分裂中期染色体上的CPD带纹与粗线期染色体上显著的带纹具有对应性。用改良的CPD染色程序清晰而稳定地显示出这些特征性的CPD带纹为番茄的染色体,特别是有丝分裂中期染色体提供了新的识别标记。用番茄的一个45S rDNA克隆进行的荧光原位杂交,不仅在位于2号染色体短臂的随体上显示了强的杂交信号,而且在粗线期染色体的5个CPD带区或有丝分裂中期染色体的4对CPD带区显示了弱的杂交信号。然而,用来自小麦的45S rDNA克隆pTa71进行的原位杂交却只在随体上显示了杂交信号。鉴于所用的两个45S rDNA克隆在序列上的差异,推断在番茄基因组中只有随体含有45S rDNA单位的编码区,即番茄只有一对45S rDNA位点。
Banding of the mitochondrial pachytene and mitotic metaphase chromosomes of tomato was carried out by CPD (PI and DAPI combination) staining, followed by fluorescence in situ hybridization localization analysis using two different 45S rDNA clones in the same split phase. CPD staining showed 10 red CPD bands on 8 pachytene chromosomes and 12 CPD bands on 6 pairs of metaphase chromosomes. The CPD bands on metaphase chromosomes of mitosis are corresponding to the prominent bands on the pachytene chromosomes. Clear and consistent with the modified CPD staining procedure, these characteristic CPD bands have been shown to provide novel markers for tomato chromosomes, particularly mitotic metaphase. Fluorescence in situ hybridization with a 45S rDNA clone of tomato not only displayed a strong hybridization signal on the satellite on the short arm of chromosome 2 but also on the 5 CPD bands of the pachytene or the mitotic metaphase 4 shows weak hybridization signals to the CPD band. However, in situ hybridization with the 45S rDNA clone pTa71 from wheat revealed only the hybridization signal on the satellite. Given the sequence differences between the two 45S rDNA clones used, it is inferred that only the coding region for the 45S rDNA unit contained in the tomato genome, ie, the tomato has only a pair of 45S rDNA sites.