Guadalupe Palomino

Nuclear genome size analysis of Agave tequilana Weber

Abstract Flow cytometric analysis of DNA content was performed using nuclei isolated from internal basal parts of young leaves in 8 varieties of Agave tequilana. The distributions of nuclear DNA content showed that more than 85% of leaf nuclei were in G0/G1 phase of the cell cycle. Nuclei with DNA content higher than 4C were not detected, indicating the absence of endopolyploidy. A. tequilana varieties lineño, azul listado, azul, moraleño, xiguin, and pata de mula were found to be diploid (2n =2x=60). These diploid varieties displayed a 2.5% variation in 2C DNA content, which ranged from 8.304 pg for var. lineño to 8.517 pg for var. pata de mula. No statistically significant differences were detected among all diploid varieties considered. This observation demonstrates that Agave belongs to plant taxa with a stable genome size. The mean 1Cx value (DNA amount of monoploid chromosome set .) calculated for diploid cultivars was equal to 4.202 pg DNA. Triploid var. bermejo (2n=3x=90) had 2C=12.513 pg DNA, i. e. approximately three times the 1Cx value. 2C DNA amounts of tetraploid (4x) and pentaploid (5x) var. chato were equal to 16.01 pg and 20.11 pg DNA, respectively. These values are also multiples of the 1Cx value, indicating a relationship between ploidy level and 2C DNA content. Nevertheless, the 1Cx values calculated for tetraploids and pentaploids were lower than the 1Cx value determined for diploids. This observation indicates a loss of certain DNA sequences after polyploidization. The results obtained form a basis for the application of flow cytometry in taxonomy, breeding and biotechnology of Agave tequilana.

Differencias cromosomicas entre algunas especies de los generos Sophora L. y Styphnolobium Schott

In this study chromosome numbers (2n) and karyotypes of Sophora secundiflora, S. velutina var. zimbabweensis, S. tomentosa, Styphnolobium japonicum, S. parviflorum, S. protantherum, S. burseroides, and S. conzattii were determined. The first three species presented 2n = 18, with a basic chromosome number of x = 9. These species had small variations in their karyotypes and one chromosome pair with secondary constriction. The other five species presented 2n = 28, x = 14 and their karyotypes were very similar, three pairs showing secondary constrictions. These results agree with Sousa and Rudds proposal to include species with 2n = 28 in the genus Styphnolobium

Karyotypic studies in Opuntia cochinera, O. hyptiacantha, and O. strepthacantha (Cactaceae)

Abstract Plants of Opuntia cochinera, O. hyptiacantha, and O. streptacantha species, collected in the Valley of Mexico, were consistently octoploids with a chromosome number 2n=8x=88, confirming a base chromosome number x=11 for the genus Opuntia. Karyotypes of the three species were homogeneous with 88 metacentric chromosomes. Interspecific variation of the genome was shown in chromosome size, genome length and chromosomes with satellites. The smallest chromosomes were found in O. hyptiacantha (1.07-2.50 μm), the intermediate size in O. cochinera (1.19-2.71 μm) and the largest in O. streptacantha (1.55-3.57 μm). Genome length was as follow: O. hyptiacantha had the smallest value (152.49 μm), O. cochinera an intermediate value (166.79 μm), and O. streptacantha the longest (210.99 μm). Opuntia cochinera presented 16 chromosomes with a satellite, this fact suggested an auto-octoploid origin. There were 6 chromosomes with a satellite in O. hyptiacantha and 20 in O. streptacantha, it indicated that both species had an allooctoploid origin; so it is possible to call these Opuntia species with genomes of partial homology.

Nuclear genome size and cytotype analysis in Agave cupreata Trel. & Berger (Agavaceae)

This study is a cytogenetic characterization by karyotyping and a determination of the DNA content by flow cytometry of wild populations of Agave cupreata from the Guerrero State, Mexico. Three of the studied populations were diploids (2n = 2x =60) and one population had tetraploid (2n = 4x = 120), pentaploid (2n = 5x = 150) and hexaploid (2n = 6x = 180) plants. Diploid populations had three different structural cytotypes. One population showed polyploid cytotypes. A. cupreata showed a bimodal karyotype of 10 large + 50 small chromosomes in diploids; 20 large + 100 small chromosomes in tetraploids and 25 large + 125 small chromosomes in pentaploids. In diploids, they had secondary constriction in one pair of the large chromosomes and, in the fourth or fifth large homologous chromosome groups, in polyploid plants. The arm ratio, the proportion of different types of large and small chromosomes, the mean of genome length and the asymmetry index of karyotypes clearly varied among diploid and polyploid cytotypes. The pattern of variation among Agave cupreata populations is probably due to rearrangements in the large and small chromosomes of the complement. The diploid populations displayed a 0.63% variation in 2C DNA content. The mean 2C DNA content was 7.88 pg; 1Cx value = 3.94 pg in diploids of Agave cupreata. Tetraploids had 2C = 16.54 pg DNA, i.e. approximately four times the 1Cx value; 2C DNA amounts of pentaploid and hexaploid were equal to 20.42 and 23.92 pg DNA, respectively. These values are also multiples of 1Cx value, indicating a relationship between the ploidy level and the 2C DNA content. The results shown are basic and useful information to develop biotechnology and breeding approaches for Agave cupreata.

Nuclear genome size and karyotype analysis in Mammillaria species (Cactaceae)

Abstract Seven species of Mammillaria were studied, all diploid: 2n=2x=22, x=11. Genome size was determined by flow cytometry, varied from 2C DNA =3.20 pg, 1570 Mbp (1 Cx) in M. crucigera, to 2C DNA = 3.04 pg, 1490 Mbp in M. flavicentra. The variation of these species in the nuclear content of DNA was 5% and was not significant (P = 0.3469). This indicates that they are small, very stable genomes, in which changes in DNA content are not very evident. The variation among species, however, was clearly evident in the relative length (L%) and arm ratio (r), the proportion of metacentrics and submetacentrics, and the position of satellites. The karyotype for M. albilanata, M. dixanthocentron and M. flavicentra was 11m, and in M. huitzilopochtli, 10m + 1 sm. Only one pair of chromosomes was observed with satellite in the four species. M. dixanthocentron and M. flavicentra, species considered synonymous, exhibited the satellite on different chromosomes. The interspecific variation observed among the species of Mammillaria is possibly due to spontaneous structural changes in their chromosomes. These mechanisms of restructuring in the genome of these species have not involved significant changes in nuclear DNA content. The Mammillaria species exhibited an endopolyploidy pattern with 2–16 C DNA content in the stem parenchyma, which may give them alternative strategies for adaptation in arid environments.

Nuclear genome size and cytotype analysis in Agave parviflora Torr. subsp. flexiflora Gentry (Asparagales, Asparagaceae)

This study presents the cytogenetic characterization by karyotyping and a determination of the DNA content by flow cytometry of wild adult plants, plants grown from seeds of wild plants and bulbils of Agave parviflora subsp. flexiflora from Bacadehuachi to Nacori Town, Sonora, Mexico. The analyzed plants were diploids (2n = 2x = 60) and had three different structural cytotypes. The cytotype observed in wild adult plants was 44m + 4sm + 10st + 2t, the cytotype found in plants grown from seeds was 48m + 8st + 4t and the cytotype displayed by bulbils was 44m + 2sm + 14st. Agave parviflora subsp. flexiflora showed a bimodal karyotype of 10 large + 50 small chromosomes. All diploid plants had a secondary constriction in one pair of the large chromosomes. The arm ratio, the proportion of different types of large and small chromosomes, the mean of genome length and the asymmetry index of karyotypes clearly varied among all three diploid cytotypes. The pattern of variation among all the types of plants is probably due to rearrangements in the large and small chromosomes of the complement. Differences in the amount of nuclear 2C DNA = 8.20 pg in diploid wild adult plants and 8.21 pg in bulbils were significantly different when compared to 2C DNA = 8.07 pg of diploid plants grown from seeds. The different types of plants displayed 1.7% variation in the 2C DNA content and the mean 2C DNA content was 8.16 pg; 1Cx value = 4.08 pg. The results here reported consist of basic and useful information to set conservation strategies and breeding approaches for Agave parviflora subsp. flexiflora.

Chromosome analysis of Mammillaria supertexta, M. crucigera and M. haageana and their comparison with M. san-angelensis (Cactaceae)

Abstract This is the first report of chromosome number in Mammillaria supertexta, M. crucigera and M. haageana, which was the same in the three species: 2n=22, x=11. This number coincides with the number reported for the genus Mammilaria and for the Cactaceae family. However, interspecific variation was observed in the karyotypes: M. supertexta exhibited longer chromosomes (1.79–3.21 μm) and those of M. haageana were shorter (1.51–2.69 μm); in M. crucigera the chromosomes were 1.63–2.74 μm. The chromosomes of M. san-angelensis (0.80–1.70 μm) are the shortest (Palomino et al. 1999). Likewise, variation in the length of the haploid genome (LG) was observed: 26.84 μm for M. supertexta; of 23.81 μm for M. crucigera; and 23.06 μm for M. haageana. The LG of M. san-angelensis was shorter than that of the above species (13.83 μm). The karyotypic formula for M. supertexta and M. crucigera was 10m+1sm, and in M. haageana it was 9m+2sm. A pair of chromosomes with satellites was observed in M. supertexta and M. haageana, and in M. crucigera two pairs of chromosomes were observed with satellites. Unlike these species, M. san-angelensis exhibited no sm chromosome; all were metacentric, and like M. crucigera, there were two pairs of chromosomes with satellites. The index of asymmetry calculated for M. supertexta was 43.44%, for M. crucigera it was 42.55%, and for M. haageana it was 42.71%, indicating that the karyotypes were symmetric. The karyotype of M. haageana (9m+2sm) was different from that determined for M. san-angelensis (11m), thus showing divergence in its genomes. Hunt (1987) considers them to be synonymous, and complementary studies on morphology, hybridization, and cytogenetics are needed to determine the taxonomic category of these plants. M. haageana exhibited a total of 11 bivalents, a chiasmata frequency (Fq) = 13.86 and a recombination index (RI) = 24.86. These results are different from those of M. san-angelensis whose Fq = 16.74 and RI = 27.74. The higher RI in M. san-angelensis indicates that this species has more possibilities of forming new genetic combinations in its progeny and more opportunities of adapting to environmental changes than M. haageana with a lower RI. The interspecific variation observed among the four species of Mammillaria is possibly due to spontaneous structural changes in their chromosomes.

Nuclear genome size, ploidy level and endopolyploidy pattern in six species of Opuntia (Cactaceae)

This study describes the haploid chromosome number (n), recombination index (RI), ploidy level and DNA content by DNA flow cytometry of six Opuntia (prickly pear) species from Mexico. Opuntia heliabravoana was diploid (2n =2x = 22, x = 11) with RI = 26; O. jonocostle, O. matudae and O. oligacantha were hexaploid (2n = 6x = 66) with RI = 74, 71, and 83, respectively; and O. hyptiacantha and O. tomentosa were octoploid (2n = 8x = 88) with RI = 99 and 103, respectively. The 2C DNA content was 3.81 pg in Opuntia heliabravoana. For hexaploid species 2C DNA content was: O. jonocostle = 5.84, O. matudae = 5.91 and O. oligacantha = 5.98 pg. The octoploid species O. hyptiacantha and O. tomentosa showed 2C DNA = 7.39 and 7.43 pg, respectively. The 1Cx = 1.91 pg for diploid O. heliabravoana was 52% higher than the hexaploid species (mean 1Cx = 0.99 pg) and 48% higher than the octoploid species (mean 1Cx = 0.93 pg). These results suggest a loss of some DNA sequences after polyploidization in these Opuntia species. All accessions showed endopolyploidy, defined by the presence of nuclear populations of 2, 4 and 8C in cells of the stem parenchyma. The presence of endopolyploidy and polyploidy in prickly pear provide these plants with adaptive advantages in arid and semiarid environments. These results provide useful guidelines to set conservation strategies and breeding approaches for Opuntia species.

Nuclear genome size and chromosome number in the Mexican genus Pittocaulon (Asteraceae)

Abstract Estimation of nuclear DNA content and chromosome number of four species of Pittocaulon (Asteraceae, Senecioneae), a small genus of Mexican succulent shrubs, was performed. The chromosome number 2n = 6x = 60 was found for the species examined. Chromosome numbers for P. bombycophole, P. filare and P. velatum are reported for the first time. Nuclear DNA content was estimated by flow cytometry, the 2C-values ranged from 14.573 pg in P. filare to 17.179 pg in P. praecox. This is the first study of nuclear DNA content carried out in the genus, which represents a significant contribution in the subtribe Tussilagininae. A high degree of congruence was found between nuclear DNA content and the phylogenetic relationships among species of the genus.

Nuclear genome size and karyotype analysis of Agave angustifolia Haw. “Cimarron” and “Lineño” (Asparagales, Asparagaceae)

Abstract This study is a cytogenetic characterization by karyotyping and determination of the DNA content by flow cytometry of Agave angustifolia Haw. “Cimarron” and “Lineño” that were collected in the southern region of the State of Jalisco, Mexico. These cultivars are particularly important in the production of spirits. A. angustifolia “Cimarron” and “Lineño” were found to be diploids with 2n=2x=60, also, both showed a bimodal karyotype consisting of 10 large + 50 small chromosomes. A. angustifolia “Cimarron” had a karyotype of 42 m+4sm+6st+8t, while the karyotype observed in “Lineño” was of 48 m+2sm+2st+8t. The arm ratio, the proportion of different types of large and small chromosomes, the mean of genome length and the asymmetry index of karyotypes clearly varied between both cultivars, and had a secondary constriction in one pair of the large chromosomes. A. angustifolia “Cimarron” showed a constriction on pair 2 of telocentric chromosomes and “Lineño” on pair 5. The variation between both cultivars is probably due to rearrangements in the large and small chromosomes of the complement. No statistically significant differences were detected in the amount of nuclear 2C DNA = 8.217 pg for “Cimarron” to 8.179 for “Lineño”. The different type of plants displayed 1.7% variation in the 2C DNA content and the mean 2C DNA content was 8.198 pg; 1Cx value = 4.099 pg. The results here reported consist of basic and useful information to set conservation strategies and breeding approaches for Agave angustifolia “Cimarron” and “Lineño”.