Cytogenetic Study of the Genus Thymus (Lamiacea) in Iran

Document Type : Research Article

Authors

• M. Moradi ¹
• H. Nastari Nasrabadi ²
• K. Ghasemi Bezdi ³

¹ Faculty of Agriculture and Animal Science, University of Torbat-e Jam, Torbat-e Jam, Iran

² University of Torbat-e Jam

³ Department of Agricultural and Horticultural Research, Agricultural and Natural Resources Research and Education Center of Khorasan Razavi, Agricultural Research, Education and Extension Organization (AREEO), Mashhad, University of Torbat-e Jam, Iran

10.22067/jhs.2022.72022.1082

Abstract

Introduction
 The Genus Thymus is one of the most important genera of the Lamiaceae family. According to Jalas (1971), Thymus is divided into eight sections: Micantes, Mastichina, Piperella, Teucrioides, Pseudothymbra, Thymus, Hyphodromi, and Serpyllum. About 18 species exist in some areas of Iran and most of them belong to Serpyllum Section and kotschiani Subsection. Chromosomal information is an important key for taxonomy, phylogeny, evolution, genetics and breeding in thyme. Therefore, this work was carried out to study the cytogenetic characteristics of genus Thymus belonging to the Subsection Kotschyani for breeding purposes and taxonomy.
Materials and Methods
Seeds were collected from 5 wild populations and germinated on wet filter paper at 20 ^oC. One cm long roots were pretreated with 8-hydroxyquinolin and then washed in distilled water and fixed in carnoy solution for 24 hours. Hydrochloric acid (1N) was applied for 7 min to hydrolyze the roots. Staining was done by orcein for 24 h at room temperature. Stained roots squashed in one drop of 45% acetic acid and examined by a ZEISS Axiophot compound microscope. Cells in metaphase stage were photographed with a D450; Canon Inc. Japan digital camera. Ten well prepared metaphasic cells were selected and some chromosomal characteristics such as total chromosomal length (TL), long arm length (L), short arm length (S), the arm ratio (AR) [LA/SA], and centromeric index (CI), were measured using Micro Measure ver. 3.3 software. The following karyological parameters were determined: total chromosome form (TF%), intrachromosomal asymmetry index (A₁) and interchromosomal asymmetry index (A₂). Karyotypic characteristics have been determined using the symmetry classes of Stebbins (SC). Karyotype formula was determined from chromosome morphology based on centromere position in accordance with the classification of Levan.
Results and Discussion
 This study reports the chromosome number and meiotic behavior of 31 populations belonging to 8 species of Thymus Subsect. kotschyani from Iran. In most species of this subsection, the base number of chromosome x = 15 and two diploid and tetraploid ploidy levels with chromosome number of 2n = 30 and 60 were observed. Only in T. migricus species, the base number of chromosome x = 14 was reported with two levels of diploid and tetraploid ploidy and chromosome numbers of 2n= 28 and 56. The chromosomes were mostly metacentric (m) or sub-metacentric (sm) in all species Among the various species with basic number of x= 15, the highest percentage of TF and the lowest amount of A₁ were observed in populations belonging to T. eriocalyx (T7) indicating that this species has the most symmetric karyotypes. The lowest percentage of TF and the highest amount of A₁ are in population of T. lancifolious (27) and T. fedtschenkoi (T28) species; this shows that the species has the most asymmetric karyotype among the species of this subsection. The highest amount of A₂ was observed in T. eriocalyx (T7) species, indicated the asymmetry between chromosomes and chromosomal length. The difference in the number of chromosomes, ploidy levels and karyotype asymmetry in the populations and different species may be related to different environmental conditions in their habitat, pollination system (cross pollination) or polyploidy (Aneuploidy) in this genus.
Conclusion
 The results showed that basic chromosome number in most species is 15 (x= 15). Two ploidy levels (diploid and tetraploid) were observed among different species. Chromosomes in most species, were metacentric and sub-metacentric. Based on intra- chromosomal symmetry (A₁ and TF) T. eriocalyx species (T7) has the most symmetric and most primitive karyotype and the species T. lancifolius (T27) and T. fedtschenkoi (T28) have the most complete and the most asymmetric karyotypes. Also based on inter- chromosomal symmetry, (A₂) T. eriocalyx (T) species has the most asymmetric karyotype.

Keywords

• Cytogenetic
• Karyotype
• Subsec. Kotschyani
• Taxonomy
• Thymus spp

20.1001.1.20084730.1401.36.4.10.3

Main Subjects

• Medicinal Plants

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References

1- Azizian, D., & Bakhshi-Khanik, Gh. (2002). Principles and Methods of plant classification, Tehran, Payamenoor, 141 pp.

2- Daftari, Z., & Safarnejad, A. (2012). Karyotypic study of four Thymus species (T. pubescens, T. fedtschenkoi, T. daenensis, T. lancifolius). Iranian Journal of Rangelands and Forests Plant Breeding and Genetic Research 19(2): 241-250.

3- Funamoto, T., Kondo, K., Smirnov, V.S., Tatarenko, V.I., Motohashi, T., & Damdinsuren, O. (2008). A comparison of chromosome characters in tree species of Thymus (Lamiaceae) collected in Russia and Mongolia Altai. Chromosome Botany 3: 1-6.

4- Hornok, L. (1991). Effect of envirmental factors on the production of some essential oil plants. Horticultural 23: 30-57.

5- Huziwara, Y. (1962). Karyotype analysis in some genera of compositae, futher studies on the chromosome of Aster. American Journal of Botany 49: 116-119.

6- Jalas, J. (1982). Thymus in: Rechinger, K.H Flora Iranica no. 150. Graz. pp 532-551

7- Jalas, J. (1971). Notes on Thymus L. (Labiatae) in Europe supraspecific classification and nomenclature. Botanical journal of the Linnean Society. 64, pp. 199-235.

8- Jamzad, Z. (2009). Thymus and Satureja species of Iran, publication of Research Institute of Forests and Rangelands, 171 pp.

9- Javadi, H., Hesamzadeh Hejazi, S.M., & Babayev, M. (2009). Karyotypic studies of three Thymus (Lamiaceae) species and population in Iran. Caryologia 62(4): 316-325. https://doi.org/10.1080/00087114.2004.10589697.

10- Kalvandi, R., Hesamzadeh Hejazi, S.M., Atri, M., Mirza, M., Zamzad, Z., & Safikhani, K. (2012). Karyotype analysis among 10 populations of Thymus eriocalyx (Ronniger) Jalas species in Iran, Annals of Biological Research 3(8): 3916-3925.

11- Levan, A., Fredga, K., & Sanberge, AA. (1964). Nomenclature for centromeric position on chromosomes. Hereditas 52: 201–220. http://doi.org/10.1111/j.1601-5223.1964.tb01953.x.

12- Lewis, H.L. (1980). Polyploidy in species. In: W.H. Lewis (ed.) Polyploidy, Basic Life Science 13: 103-144.

13- Leung, A.Y., & Foster, S. (1996). Encyclopedia of common natural ingredient: used in food, drugs and cosmetics. A Wiley Interscience Publication-John Wiley&Sons Inc. 649 pp.

14- Mahdavi, S., & Karimzade, G. (2010). Karyologycal and nuclear DNA content variation in som Iranian endemic Thymus species (Lamiaceae). Journal of Agricultural Science and Technology 12(4): 447-458.

15- Martonfi, P., & Martonfiova, L. (1996). Thymus chromosome numbers from Carpathians and Pannonia. Thaiszia Journal of Botany Kosice 6: 25-38.

16- Mehrpur, S., Mirzaie-Nodoushan, H., Majd, A., & Sefidkon, F. (2002). Karyotypic studies of two Thymus species. Cytologia 67: 343-346.

17- Mewes, S., Kruger, H., & Pank, F. (2008). Physiological, morphological, chemical and genomic diversities of different origins of thyme (Thymus vulgaris L.). Genetic Resource Crop Evolution 55: 1303-1311.

18- Morales, R. (2002). The history, botany and taxonomy of the genus Thymus.In: Stahl-Biskup, E. and Saez, F. Thyme, The genus Thymus. Taylor and Francies Group. 332pp.

19- Rechinger, K.H. (1982). Flora Iranica. Graz: Akademische Druck- und Verlagsanstalt.

20- Romero Zarco, C. (1986). A new method for estimating karyotype asymmetry. Taxonomy 35: 526–530.

21- Safari, H., Hesamzade, M., Jalilian, N., & Ziaeenasab, M. (2008). Investigation of karyotypic variation in three species of Sophora sp. Iranian Journal of Forest and Rangeland’s Plant Breeding and Genetic Researches 16: 27-37.

22- Stebbins, GL. (1971). Chromosomal evolution in higher plants. Edward, Arnold. London. 216 pp.

23- Yavari, A., Nazeri, V., Sefidkon, F., & Hassani, M.E. (2010). Karyotypic study on some populations of Thymus migricus Klokov & Desj-Shost. Horticulture, Environment, and Biotechnology 51(2):101-105.

24- Ziaei Nasab, M., Hesamzadeh Hejazi, S.M., Bihamta, M.R., Mirza, M., & Naderi-shahab, M.A. (2012). Assessment of karyotypical variation among 16 populations of Thymus daenensis Celak and Thymus kotschyanus Boiss. species in Iran. African Journal of Biotechnology 11: 1028-1036. https://doi.org/10.5897/AJB11.2441.