Abstract
Accessions of Plectranthus barbatus (Lamiaceae), a medicinal plant, were investigated using a cytogenetic approach and flow cytometry (FCM). Here, we describe for the first time details of the karyotype including chromosome morphology, physical mapping of GC rich bands (CMA3 banding), as well as the mapping of 45S and 5S rDNA sites. All accessions studied showed karyotypes with 2n = 30 small metacentric and submetacentric chromosomes. The CMA3 banding and fluorescent in situ hybridization techniques revealed coincidence between CMA3 bands and 45S rDNA sites (6 terminal marks) while for the 5S rDNA were observed 4 subterminal marks no coincident with CMA3 marks. For nuclear genome size measurement, the FCM procedure provided histograms with G0/G1 peaks exhibiting CV between 2.0–4.9 and the mean values obtained for the species was 2C = 2.78 pg, with AT% = 61.08 and GC% = 38.92. The cytogenetic data obtained here present new and important information which enables the characterization of Plectranthus barbatus.
Highlights
The genus Plectranthus L' Herit. (Lamiaceae) contains nearly 300 species distributed in tropical Africa, Asia, Australia and Brazil (Lukhoba et al 2006, Alasbahi and Melzigh 2010)
Chromosome lengths ranged from 2.51–1.86 μm (Table 1) and the Karyotype formulae (KF) was KF = 14m+1sm
The 45S rDNA signal were observed in three chromosome pairs on the terminal portion (Fig. 1 B1–B3), while 5S rDNA signals were observed in subterminal portion of two chromosome pairs, in the short arm of chromosomes 9 and 12, respectively (Fig. 1 A1–A3)
Summary
The genus Plectranthus L' Herit. (Lamiaceae) contains nearly 300 species distributed in tropical Africa, Asia, Australia and Brazil (Lukhoba et al 2006, Alasbahi and Melzigh 2010). Many species show important medicinal properties and a large variation in morphology, chemistry as well as in the chromosome number, ranging from 2n = 14 to 2n = 84 (Morton 1962, De Wet 1958, Lukhoba et al 2006, Alasbahi and Melzig 2010). One of the most important species traditionally used in folk medicine, Plectranthus barbatus Andr., shows a large morphological variation and is commonly cited by innumerous synonyms such as P. forskohlii Briq, P. forskalaei Willd., P. kilimandschari (Gürke) H. H. Willemse, Coleus forskohlii Briq., C. kilimandschari Gürke ex Engl., C. coerulescens Gürke, C. comosus A. Rich., and C. barbatus (Andr.) Benth (Lukhoba et al 2006, Alasbahi and Melzig 2010)
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