NPS-2143 mg The occurrence of three Ag

The occurrence of three Ag-NORs per metaphase and/or a maximum of three nucleoli per nucleus in most of the varieties may be explained by chromosomal rearrangements or unequal crossing-over events that induce the deletion of the fourth active rDNA loci. Also, the chromosome pair that showed less intense 45S rDNA loci after FISH may correspond to a reduced number of copies of rRNA genes hampering their accurate detection by both silver staining and FISH techniques. Other possible explanation for this result may be the close position of the two rDNA loci resulting in the fusion of two signals due to the small length of the chromosomes. However, the three visible 45S rDNA sites are located on the terminal region of the chromosome arm, which is in accordance to the reported for most NPS-2143 mg (Roa and Guerra, 2012), and also with the karyotype of grapevine proposed by Haas and Alleweldt (2000). As verified in Fig. 2e, two of the four 45S rDNA hybridisation signals were more intense. The same effect was detected in other grapevine varieties in previous studies (Pereira et al., 2005, Pereira et al., 2014). This difference in the signals intensity can be explained by a variation in the number of copies of rRNA genes among the rDNA loci (Rogers and Bendich, 1987). In this work, some interphase cells presented two nucleoli with same size whereas others showed one bigger than the other. In interphase cells with three nucleoli, one of them was bigger than the other two (see Fig. 1). Considering this, it is possible that the loci with a smaller number of copies of rRNA genes form smaller nucleoli and the loci with a higher number of copies organize larger nucleoli. Another possibility is that the rDNA loci with fainter signals may be more condensed explaining its reduced activity or inactivity, leading to a very reduced frequency of three and four nucleoli per interphase nucleus (Coutinho et al., 2016). FISH detects all rDNA loci and sil ver staining detects the ones that were active in the previous interphase (Shaw, 2013). Among the 7 studied varieties, two of them stand out: Bastardo because it is the only that showed a maximum of two nucleoli per interphase leaf cells, and Pinot Noir because it was the only that presented a maximum of four nucleoli per nucleus in the root-tip cells. The remaining 5 varieties presented one to three nucleoli in both tissues. However, in the leaf nucleoli counts, the average percentage values of one, two and three nucleoli varied and showed statistically significant differences (p < 0.001) among varieties. Thus, when we analysed the average number of nucleoli per cell among varieties, statistically significant differences (p < 0.001) for the interaction of these two factors were detected. Hence, the nucleolar activity in leaves seems to be different than that occurring in root-tips. Variability between different V. vinifera varieties is common and has been observed at several levels. Genetic diversity has been extensively studied, mainly with microsatellites, in varieties from around the world, allowing the differentiation and establishment of phylogenetic relationships among varieties (Aradhya et al., 2003; Almadanim et al., 2007; Martínez et al., 2006). In cytological studies, it has been reported variations in the chromosomes length, centromere and satellite position among varieties, even though the chromosome spreads were performed with the same technique (Raj and Seethaiah, 1969; Raj and Seethaiah, 1973; Patil and Jadhav, 1985). Differences among phenotypes are the basis of the traditional methods to select and to identify varieties, which may include morphological traits such as leaves shape, area and vein pattern (Chitwood et al., 2014; Galet, 1979). More recently, leaf anatomic characteristics like the epidermis thickness, stomata and hair distribution, and the mesophyll structure, were also used for the differentiation of V. vinifera varieties (Monteiro et al., 2013).