Cytogenetic Characterization of <i>Passiflora megacoriacea</i> K.Port.-Utl. Employing Image Cytometry

Abstract

The Passiflora coriacea complex encompasses the species P. megacoriacea K.Port.-Utl., P. coriacea Juss and P. sexocellata Schltdl, and the morphological similarities among the species have posed challenges for taxonomic and phylogenetic studies in the past. Image cytometry (ICM) has been used to improve the karyotype characterization in some plant species and has allowed the identification of small variations in the DNA content between homomorphic chromosomes. The aim of the present study was to determine the chromosome number, characterize the karyotype and measure the chromosomal DNA content in P. megacoriacea using classical cytogenetic and ICM approaches. We observed a chromosome number of 2n=12, with the chromosomes 1-3 and 5 classified as submetacentric and chromosomes 4 and 6 as metacentric in all metaphase plates. The nuclear DNA content (1C= 0.51 pg) was measured by flow cytometry and then distributed proportionally to mean integrated optical density values calculated by ICM from Feulgen stained chromosomes. So, the mean 1C chromosomal DNA content varied of 0.129 pg for chromosome 1 to 0.054 pg for chromosome 6. We can thus establish that the ensemble analysis of qualitative and quantitative parameters allowed us the first karyotype characterization of P. megacoriacea, providing data to a better taxonomic delimitation among the species of the P. coriacea Juss complex.

Scaling Laws for Mitotic Chromosomes

“…This result appears in the classic cytogenetics text by Darlington (1937) , and it has been confirmed by modern methods using human cell cultures ( Sumner, 1991 ; Booth et al, 2016 ). Second, the lengths of the chromosomes in a dividing cell are approximately proportional to their DNA content ( Mayall et al, 1984 ; Praca-Fontes et al, 2014 ; Lacerda et al, 2019 ). Both these observations have only been quantified in a small number of species, and should be regarded as preliminary, although they are known to hold true in human cells.…”