Estudos citogenéticos e citométricos em mamoeiro (Carica papaya L.)

• Autor(a) principal: Araújo, Fernanda Santos
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4664
• topic: Carica papaya; Cromossomos; Citogenética; Carica papaya; Chromosomes; Cytogenetics; CNPQ::CIENCIAS BIOLOGICAS::GENETICA::GENETICA VEGETAL

Carica papaya is one of the most economically important species of the Caricaceae family, with many industrial applications. Despite its importance, there is little information covering the cytogenetic and cytometric characterization of this species. Hence, this study is justified by the need to increase the knowledge related to papaya karyotype, nuclear DNA content and base composition. The specific objectives of this study were to: characterize papaya chromosomes, using image analysis resources; apply the acridine orange staining to mitotic chromosomes of C. papaya to identify nucleolar organizers regions (NORs); estimate the nuclear DNA content and determine the base composition of male, female and hermaphrodite plants of C. papaya, by the use of flow cytometry and verify if the cytometric data can differentiate the three sex types with regard to their DNA content and base pair frequencies. Root tips from hermaphrodite plants were pre-treated with amiprophosmethyl (APM) 3 µM for 15h, at 4ºC and fixed. Slides were prepared by cellular dissociation and air drying, and submitted to Giemsa and acridine orange staining. The association of cellular dissociation and air drying techniques to Giemsa conventional staining resulted in metaphasic and prometaphasic cells with individual and well spread chromosomes, without overlaps, with well defined primary and secondary constrictions. These characteristics enabled the homologues pairing and morphological classification of the chromosomes, with karyograms assembly of a hermaphrodite plant, which had 18 chromosomes, being 7 pairs metacentrics (1, 2, 3, 4, 5, 7 and 8) and 2 submetacentrics (6 and 9). The acridine orange staining allowed the identification of yellowish green bands in two chromosomes (1 and 2). The strong bands corresponded to NOR flanking regions, as sustained by the localization of chromosome 1 associated to the nucleolus. Considering the obtained results by the cytogenetic techniques, there were no morphological differences that could evidence a possible heteromorphic pair of chromosomes in the hermaphrodite plant of C. papaya. For the application of flow cytometry, leaves from the three sexual forms of papaya were submitted to the chopping procedure in an isolation buffer, followed by a staining buffer. The obtained suspension was passed through a filter and analyzed in a flow cytometer, to determine the total nuclear DNA content and base composition. The cytometric analyses evidenced histograms with peaks of G0/G1 nuclei with coefficients of variation (CVs) lower than 5%. The analysis of male, female and hermaphrodite plants nuclei, stained with propidium iodide (PI), allowed the calculation of the mean 2C DNA values, which were 0.67, 0.65 and 0.65 pg, respectively, and statistically equal, by the F test, for the three sex forms. The analysis of nuclei stained with 4 ,6-diamidino-2-phenylindole (DAPI) and chromomicin A3 (CMA3) enabled the calculation of AT/GC base pair frequencies of the three sex types, also statically equal, by the F test. Therefore, there was no significant difference between the three sex forms of papaya in relation to their total nuclear DNA content and base pair composition. In relation to the obtained mean values of nuclear DNA content and considering the morphological similarity of papaya chromosomes, each one of the 18 chromosomes would have, on average, 0.036 to 0.037 pg of DNA. Hence, in order to identify a probable pair of heteromorphic chromosomes, a tiny portion of the chromosome would have to be distinguished, corresponding to an amount of DNA under the limits of resolution of the cytogenetic and cytometric techniques employed in this study.