Karyotype analysis in some accessions of Iranian borage (Echium amoenum)

Abstract

The Iranian borage (Echium amoenum) is a biennial or perennial herb belonging to the family Boraginaceae. It is distributed mostly in the north of Iran and on the slopes of Alborz mountains. As a medicinal herb, Iranian borage is used for treatment of depression and some nervous diseases. Though many studies have focused on morphological and phytochemical diversity of various accessions of this plant, the number of studies focusing on cytotaxonomy of different accessions of this species is rather small. Thus, the present study focused on cytogenetic analysis of several accessions of Iranian borage. The terminal meristem of root tips was placed in a 0.002 mole 8-hydroxyquinolone for 4 hours, and then fixated in a fixator solution (3:1 acetic acid/alcohol) for 24 hours. The root tips were finally softened in 1 mole hydrochloric acid for 8 minutes in room temperature, dyed with 2% acceto-orcein stain for 10 minutes, and squashed on microscopic slide. The cells were photographed at the metaphase stage of mitosis, when the chromosomes were well separated. Long arm, short arm, long to short arm ratio and chromosome indices of metaphase cells were calculated. Figures summarized the idiogram based on the short arm length of eight pairs of chromosomes. According to our results, a basic chromosome counts of x=8 (2n=2x=16) was determined for all tested accessions. All analyzed plant cytotypeswere diploid.The largest total chromosome length belonged to the accession from Jannat Roodbar region with 78.16 µm, while the shortest came from Esfahan with 51.10 µm. Analysis of metaphase karyotypes showed that centromeres were mainly located in the center (metacentric) or close to the center (submetacentric) of the chromosomes. The number of metacentric chromosomes was 10-12 out of 16 chromosomes. Accession of Roobdar had the largest centromeric index, i.e. 0.66, while accessions from Divrood, Qazvin and Mashhad had the lowest centromeric indices of 0.38-0.39. In addition, the long to short arm ratio varied between 1.51 and 1.66. Tested accessions showed lower diversity in terms of karyological characteristics and had symmetric karyotypes. However, given asymmetry indices in terms of chromosome types, overall chromosome shape, classification based on cluster and principal component analyses, and inclusion within three classes of Stebbins (A3, B2, B3), the studied accessions showed evolutionary differences with each other that could be a source of useful cytogenetic information for breeding purposes, and may be used to further understanding of evolution and accession genesis of Iranian borage species.