Corresponding author: A. Kharrat-Souissi (
Academic editor: Julio R. Daviña
The Buffelgrass (
In the south of Tunisia, the ecosystems are characterized by a high level of anthropogenic disturbance and have been characterized by several factors such as climatic variations and overgrazing (
Most flowering plants are polyploids, since polyploidization is a ubiquitous event in plant evolution (
The cytogenetic information provided by combination of chromosome banding and fluorescence
The objective of the current study was to elucidate the possible changes in number and location of rDNA sites through different ploidy levels of
The geographical origins of
Geographical origin, genome size, ploidy level, number of 5S and 18S rDNA loci in Tunisian populations of
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South of Tunisia city | MR01 |
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3.03 ±0.03SD | 36 | 4 | 4 | 4 | |
East of Teboulta | SA02 |
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4.56±0.01 | 54 | 6 | 6 | 6 | |
Meknassi Pist | ME04 |
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3.74±0.09 | 45 | 5 | 5 | 5 | |
Haddej Pist I | ME06 |
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4.34±0.06 | 54 | 6 | 6 | 6 | |
Haddej pist II | ME08 |
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3.63±0.03 | 45 | 5 | 5 | 5 | |
Gabès | ME09 |
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4.55±0.03 | 54 | 6 | 6 | 6 | |
El Hamma - Menzel Habib | ME10 |
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4.46±0.09 | 54 | 6 | 6 | 6 | |
Gabès- 45 Km – Medenin | JF12 |
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4.57±0.05 | 54 | 6 | 6 | 6 | |
Metameur-18Km- Toujane | JF14 |
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4.49±0.11 | 54 | 6 | 6 | 6 | |
IRA of Ben Guerdane-35 km-sidi Mahdi | ST24 |
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4.47±0.04 | 54 | 6 | 6 | 6 | |
National park of Sidi Toui (Est) | ST25 |
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4.48±0.04 | 54 | 6 | 6 | 6 | |
IRA of Ben Guerdane - 50 km - Sidi Mahdi | ST26 |
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4.30±0.08 | 54 | 6 | 6 | 6 | |
Remada-Dhibat (oued el Anguar) | DH28 |
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4.34±0.04 | 54 | 6 | 6 | 6 |
Geographical origin of 13 populations of
A slightly modified air drying technique (
GC-rich heterochromatin staining with chromomycin A3 (CMA3, Sigma Aldrich Co., Steinheim, Germany) was performed following
The FISH experiment was carried out with two different specific probes of ribosomal DNA (rDNA) simultaneously according to the protocol of
At least five metaphasic chromosome plates were used for karyometrical analysis and construction of idiogram. Chromosomes were classified according to their size and shape related to the centromere position. Terminology used for centromere position follows that of
The chromosomes of
The results of 5S and 18S ribosomal genes mapping in
Because many of the chromosomes are similar in size and morphology, chromosome identification for karyotype analysis is very difficult for
Morphometric data concerning the karyotype of tetraploid
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1 | 1.64 (0.15) SD | 1.79 (0.12) | 3.43 | 1.09 | 47.92 | m |
2 | 1.54 (0.18) | 1.72 (0.12) | 3.27 | 1.12 | 47.27 | m |
3 | 1.46 (0.20) | 1.77 (0.11) | 3.23 | 1.21 | 45.30 | m |
4 | 1.48 (0.19) | 1.65 (0.14) | 3.13 | 1.11 | 47.29 | m |
5 | 1.42 (0.17) | 1.64 (0.13) | 3.06 | 1.16 | 46.36 | m |
6 | 1.42 (0.17) | 1.62 (0.12) | 3.04 | 1.14 | 46.76 | m |
7 | 1.34 (0.17) | 1.60 (0.13) | 2.94 | 1.19 | 45.59 | m |
8 | 1.34 (0.18) | 1.50 (0.12) | 2.84 | 1.12 | 47.17 | m |
9 | 1.21 (0.17) | 1.54 (0.14) | 2.75 | 1.26 | 44.16 | m |
10 | 1.17 (0.16) | 1.46 (0.13) | 2.63 | 1.24 | 44.56 | m |
11 | 1.13 (0.18) | 1.38 (0.09) | 2.51 | 1.23 | 44.84 | m |
12 | 1.13 (0.11) | 1.31 (0.09) | 2.44 | 1.17 | 46.15 | m |
13 | 1.05 (0.12) | 1.27 (0.10) | 2.32 | 1.20 | 45.38 | m |
14 | 1.04 (0.11) | 1.26 (0.09) | 2.29 | 1.22 | 45.14 | m |
15 | 1.01 (0.13) | 1.15 (0.13) | 2.16 | 1.14 | 46.69 | m |
16 | 0.98 (0.13) | 1.09 (0.12) | 2.07 | 1.11 | 47.41 | m |
17 | 0.91 (0.15) | 1.05 (0.11) | 1.96 | 1.16 | 46.36 | m |
18 | 0.84 (0.10) | 0.98 (0.12) | 1.82 | 1.17 | 46.08 | m |
The GC-rich DNA regions detected in hexaploids are distributed in telomeric regions of chromosomes and corresponded to the 18S rDNA loci. This colocalization of GC rich heterochromatin and rDNA has already been reported for numerous plants and animal species (
It was obvious to notice that the number of 5S and 18S rDNA sites corresponded to the ploidy level. In tetraploid individuals it was four, in pentaploids five and in hexaploids six signals. Similar phenomenon occurred in polyploids of some other genera, such as
Tetraploid individuals of
A comparison of hybridization patterns between the two probes revealed identical results within each ploidy level of
In analyzed individuals of
The size and the intensity of both hybridization signals slightly varied among investigated individuals. This can be explained by different copy number of repeats among rDNA sites which has been also detected in several other plant species (
The distribution of investigated populations of
In the present study the number of signals of 5S and 18S rDNA loci in pentaploids was intermediate between tetraploids and hexaploids. This result seems to indicate that pentaploid individuals might have derived from hybridization events between tetraploids and hexaploids. Although the apomictic mode of reproduction known as apospory displayed by most
Our data of the FISH experiments show proportional increase of ribosomal loci number during polyploidization processes. However ploidy level increases with aridity (from tetraploid to hexaploid) and give a cytogenetic basis to the considerable differentiation noted between north (humid area) and south (arid area) Tunisian populations of
The authors are grateful to O. Robin for assistance in cytogenetic and to A. Vucicevic for linguistic help. They are also indebted to the Ministry of Education and Science of Tunisia, CNRS (Centre National de la Recherche Scientifique) and Comité Mixte de Coopération Universitaire France-Tunisie (CMCU, project n° 09G 0901) for their financial support.