Citogenética, quantidade de DNA e indução de poliploidia em Pfaffia glomerata Spreng

Abstract

The genus Pfaffia (Amaranthaceae) comprises 33 species distributed in the neotropics. Thanks to some chemicals found in the genus that resemble those found in the genus Panax (Korean ginseng), the species P. glomerata is known as "Brazilian ginseng". P. glomerata is commonly used as tonic, phrodisiac, rejuvenator, anti-fatigue, anti-stress and against gastric disorders. Its medicinal properties are attributed to the compounds mainly found in their tuber roots, being the β-ecdysone the most explored by the pharmaceutical and cosmetic industries. Despite its economical and medicinal importance, few studies have been done to investigate the genetic aspects of the species. In this work, cytometric and chromosomal analyzes were made with diploid and induced polyploid of P. glomerata. The polyploidization occurred by in vitro chromosome doubling, using antimitotic agents (colchicine and oryzalin) at different concentrations and exposure times. Flow cytometry analysis showed 2.41 pg (2n = 34) and 4.79 pg (2n = 68) of DNA amounts. Both P. glomerata diploid and tetraploid were analyzed by conventional staining techniques and chromosomal differential staining by CMA3/DA/DAPI banding and rDNA FISH. In spite of the small sizes of chromosomes, it was possible to identify their primary constrictions and a pair of satellites chromosomes in the diploid and two pairs in the polyploid. Karyograms and idiograms were assembled. Karyotypic formulas were 16M + 1SM considering the 2n = 34 genome and 32M + 2SM considering 2n = 68. The interphase nuclei seem to reticulated. The fluorochrome CMA3/DA/DAPI banding revealed all chromosomes with centromeric DAPI+ bands indicating a heterochromatic region around the centromeres. A CMA+ band, with different extension between the homologous was observed on the short arm of one chromosome pair. The FISH technique with rDNA 45S and 5S sequences revealed two signals to each probe for the diploid genome and four signals in the polyploid genome. Homologous chromosomes are heteromorphic when considering the rDNA regions here investigated. The content of β ecdysone present in the methanol extract of the roots of P. glomerata with four months of cultivation was 0.32% for the diploid and 0.48% for the tetraploid suggesting an increase of 50% on the tetraploid comparing with the diploid. Pollen structure was determined by Erdtman acetolysis, and no differences were observed between diploid accessions. This is the first report of DNA amount in the genus Pfaffia and data obtained with FISH using 45S and 5S rDNA probes have not been published elsewhere. The β-ecdysone quantification suggests that chromosome duplication is an alternative to increase the economical value of the species.