Research Article |
Corresponding author: Natália Padilha de Oliveira ( natybiologia2006@gmail.com ) Academic editor: Ekaterina Badaeva
© 2024 Natália Padilha de Oliveira, Gabriel de Siqueira Gesteira, Maria do Socorro Padilha de Oliveira, Lisete Chamma Davide.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Oliveira NPde, Gesteira GdeS, Padilha de Oliveira MdoS, Davide LC (2024) Interphase nuclei, karyotypes and nuclear DNA amounts in five species of Oenocarpus (Arecaceae). Comparative Cytogenetics 18: 59-72. https://doi.org/10.3897/compcytogen.18.117597
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The genus Oenocarpus Martius, 1823 (Arecaceae) includes five species commonly used in Amazonia, especially for their fruits. Little is known about the cytogenetic characteristics and DNA amounts of these species, except for O. bataua (Martius, 1823). This study characterized and compared the types of interphase nuclei, the chromosome sets, and estimated the nuclear DNA amounts of Oenocarpus bacaba (Martius, 1823), O. bataua, O. distichus (Martius, 1823), O. mapora (H. Karsten, 1857) and O. minor (Martius, 1823). Standard cytogenetic analyses and estimates of the nuclear DNA amount by flow cytometry were carried out. These are the first reports of chromosome numbers and DNA amounts, except for O. bataua, as is the description of the chromatin distribution in interphase nuclei and karyotype for all species. All species presented 2n = 36, confirming the previous report for O. bataua. Differences between karyotype formulas and the positioning of secondary constrictions were observed. There were no significant differences for the nuclear DNA amounts among species. The constancy in chromosome number and variations in karyotype formulas suggest the occurrence of chromosome rearrangement as an important mechanism in Oenocarpus speciation.
C-value, cytogenetic analyses, flow cytometry, karyogram, karyotype asymmetry, palms
The family Arecaceae includes approximately 2,400 species in 190 genera, and is considered to be one of the most abundant among the monocotyledons (
Cytogenetics offers information for the characterization of germplasm banks, as well as for the management of these resources in genetic breeding programs (
Studies involving species of this subfamily can contribute to understanding karyotype evolution in the Arecaceae.
The analysis of nuclear DNA amounts by flow cytometry in plant species allows estimation of genome sizes, for comparison with chromosome numbers, ploidy levels and detection of numerical alterations (
In this context, this study characterized and compared interphase nuclei morphology and chromosome sets, and estimated the amount of nuclear DNA for O. bacaba (Martius, 1823), O. bataua, O. distichus (Martius, 1823), O. mapora (H. Karsten, 1857) and O. minor (Martius, 1823). These are the five most useful species, and samples are maintained for study and improvement by Embrapa Eastern Amazon, Amazon, Belém, Pará.
Seeds obtained from three accessions of O. bacaba, O. bataua, O. distichus, O. mapora, and O. minor, kept at the Active Germplasm Bank of Embrapa Eastern Amazon, in Belém, Pará, Brazil, were used in both analyses. Analysis was authorized by the federal institutions CGEN (process no. 02000.002611/2012-60) and IBAMA (process no. 02001.001558/2006-21). Vouchers are deposited in the IAN Herbarium, Belém, and details of each accession are presented in Table
Number of individuals and origin of Oenocarpus sp. genotypes used on analyses.
Species | Number of indivuduals | Origin |
---|---|---|
O. bacaba | 1 | Magazão-AP |
1 | Macapá-AP | |
1 | Porto Grande-AP | |
O. bataua | 1 | Irituia-PA |
2 | Anajás-PA | |
O. mapora | 3 | Abaetetuba-PA |
O. distichus | 3 | Oriximiná-PA |
O. minor | 3 | Terra Santa-PA |
Root tips were pre-treated with colchicine 0.1% for 5 h at 4 °C, fixed in Carnoy’s solution (3:1 alcohol/acetic acid) and stored at -20 °C. Slide preparation used the squashing technique (
The slides were examined in a bright-field microscope (Leica DMLS), equipped with a digital camera (Nikon Digital Sight DS-Fi1) to digitalize the best nuclei and metaphases. In order to evaluate chromatin organization at interphase, 500 nuclei were analyzed for each species. Ten metaphases were selected to determine the chromosome number for each species, of which five were used for karyotype construction, after obtaining the measurements of the short (s) and long (l) arms of the chromosomes, using the IMAGE TOOL 3.00 program from The University of Texas Health Science Center in San Antonio (http://ddsdx.uthscsa.edu/dig/download.html). The total length of the chromosome (Cti = l + s), arm ratio (AR = l/s), total length of the haploid set (TLHS = ΣCti/2), and relative length of each chromosome (RL = Cti/TLHS × 100), and were estimated. Chromosome morphology was described based on arm ratios, following
For karyotype asymmetry, the intrachromosomal asymmetry (A1), which quantify the relative differences in the centromere position among chromosomes of a complement, and the interchromosomal asymmetry (A2), which quantify the heterogeneity in chromosome size, were calculated following
Nuclear DNA amounts were estimated by flow cytometry, using leaf tissue, following
Only semi-reticulate interphase nuclei were found (Fig.
Semi-reticulate interphase nuclei found for Oenocarpus spp. A O. bacaba B O. bataua C O. distichus D O. mapora E O. minor. Scale bar: 10 µm.
Mitotic metaphases of Oenocarpus spp. showing 2n = 36 A O. bacaba B O. bataua C O. distichus D O. mapora E O. minor. Scale bar: 10 µm.
The chromosome number was also constant among species: 2n = 36 (Fig.
Mean values of total length of haploid set and DNA amount of Oenocarpus sp.
Species | O. bacaba | O. bataua | O. distichus | O. mapora | O. minor |
---|---|---|---|---|---|
TLHS (µm) | 51.835a | 61.823a | 54.001a | 63.712a | 59.053a |
2C DNA amount (pg) | 6.794a | 6.457a | 6.554a | 6.483a | 6.960a |
Karyograms of Oenocarpus spp. based on the metaphases displayed previously A O. bacaba B O. bataua C O. distichus D O. mapora E O. minor. Scale bar: 10 µm.
In the karyotypes of the five species two chromosome pairs with secondary constrictions were observed, all located in the terminal portion of the long arm. In O. bacaba secondary constrictions occurred in chromosome pairs 8 and 13, and presented 0.60 and 0.53 µm, respectively (Fig.
Idiograms of Oenocarpus spp. including length (L), relative length (RL), and morphology (MO) of each chromosome pair A O. bacaba B O. bataua C O. distichus D O. mapora E O. minor. Scale bar: 5 µm.
The results of the karyotype asymmetry analysis were coincident for the methodologies proposed by
Karyotype asymmetry for the five Oenocarpus species according to
Species | Karyotype Asymmetry | ||
---|---|---|---|
Stebbins | Zarco (A1 e A2) | ||
O. bacaba | 3c | 0.5767 | 0.3693 |
O. bataua | 2b | 0.4046 | 0.3274 |
O. distichus | 3b | 0.5361 | 0.344 |
O. mapora | 3b | 0.5497 | 0.3412 |
O. minor | 3b | 0.5241 | 0.3373 |
Scatterplot for karyotype asymmetry of the five Oenocarpus species based on the intrachromosomal asymmetry index (A1) and the interchromosomal asymmetry index (A2), according to
As for the 2C amount of nuclear DNA, the average values found for the species varied between 6.46 pg, in the O. bataua, and 6.96 pg, in the O. minor (Table
Except for O. bataua, the chromosome counts obtained in this study, as well as the karyotypes, the morphology of interphase nuclei and nuclear DNA amounts of the species are new. The chromosome number found for the O. bataua confirms the prior report (
As for the type of interphase nuclei, in the Arecaceae there are reports on the occurrence of three types of nuclei, reticular, semi-reticular and areticular, and this characteristic has proven to be constant among congener species, and sometimes even in superior taxonomic levels such as tribes (
The number of chromosomes found for the Oenocarpus species was the same as that found for other species of the tribe Euterpeae (
The chromosome number for Arecaceae species varies from 2n = 26 to 2n = 36 (
Other chromosome numbers have been reported for species of the subfamily Arecoideae, to which the genus Oenocarpus belongs.
As for the secondary constrictions, in Arecaceae species it is common to find one or two pairs of chromosomes bearing nucleolus organizer regions (NORs), but five pairs occur in Pseudophoenix vinifera ((Mart.) Beccari, 1912) (
Based on the karyotypes of the species studied here and emphasizing the differences between the positioning of the centromere and the secondary constrictions, it can be inferred that alterations, especially structural rearrangements, such as translocations and pericentric inversions, as well as activities related to the transposable elements, accumulated during the evolution of this genus. According to
Regarding the nuclear DNA amounts, similar results have been found for other palm species from the same subfamily. Cocos nucifera, Elaeis guineensis and Attalea spp. (Kunth, 1816), all with 2n = 32 chromosomes, and Acrocomia aculeata (2n = 30) had their 2C DNA value estimated at 3.76 pg (
The nuclear DNA amount in palm species, unlike the number of chromosomes, presents large variation (
The five species of Oenocarpus follow the majority of the tendencies identified in the Arecaceae family, such as the constancy in chromosome number within the genus and little variation for nuclear DNA amounts. However, other studies are seeking to understand more clearly the mechanisms involved in the karyotype differentiation of these species, as well as consolidating phylogenetic inferences suggested for this genus.
We thank the staff of the Plant Breeding Laboratory of Embrapa Eastern Amazon for providing assistance during this study. We also thank Embrapa for funding the research project [Proc. 01.06.01.007.09.00 and 01.15.02.002.11.00 Germplasm Bank of Palm Species], and CNPq for granting the first author a scholarship [Process 181411/2007-5].
Natália Padilha de Oliveira https://orcid.org/0000-0001-8413-5495
Gabriel de Siqueira Gesteira https://orcid.org/0000-0002-4106-7346
Maria do Socorro Padilha de Oliveira https://orcid.org/0000-0002-4753-2018
Lisete Chamma Davide https://orcid.org/0000-0003-2719-5584
Size of each chromosome and total length of haploid set (TLHS) for Oenocarpus species
Data type: xlsx
Explanation note: Asterisk (*) indicates second constriction.