An evidence on diffused centromeres in Drosera chromosomes provided by scanning electron microscopy

Abstract

ABSTRACT. The freeze-cracking technique was applied to chop and divide cell randomly in root meristems of Drosera falconeri into two pieces and obtain ultrastructural information on chromosomes, nucleoli, mitotic spindles and their attached sites on chromosomes as well as the poles. Certain phenomenon on diffused-centromeric chromosomes were found to strongly support Kondo's hypothesis on "diffused-centromeres in Drosera chromosomes." The mitotic spindles were 60~90 nm diameter at many separate portions on a poleward side of prometaphase and metaphase chromosomes. During the course of investigations in a series of chromosome cytology in Drosera and its close relatives made by Kondo and his associates (Kondo 1966;1969, 1971, 1973, 1984, Kondo and Olivier 1979, Kondo and Lavarack 1984, Kondo and Segawa 1988, Kondo hypothesized that Drosera might have "Diffused centromeres" for the first time since their chromosomes showed commonly relatively wide nonstaining gap between the chromatids of chromosome and non-visible, localized centromeric-regions throughout mitotic prophase, prometaphase and metaphase. suggested that it might be a case of polycentric (or diffused centromeric) chromosomes due to lack of single, localized centromere. Observations of C-banding and silver staining on chromosomes of Drosera petiolaris confirmed that the chromosome in the genus could have C-banding pattern and numerous silver-staining position segments suggesting multi-centromeres (Kondo and Lavarack 1984). Among the dicot genera, only Drosera chromosomes were concluded to have diffused centromeres (Kondo and Lavarack 1984). Later, Sheikh and Kondo (1995), Hoshi and Kondo (1998a, b) and Nontachaiyapoom et al. (2000) supported Kondo's hypothesis on the "diffused-centromeres in Drosera chromosome". KEYWORDS:The present study by using scanning electron microscopy on the cracking flozen specimen of Drosera falconeri chromosomes used displayed new evidence with respect to diffused centromeres. MATERIALS AND METHODSPlant material Drosera falconeri Kondo et Tsang collected in a small population along the Fennis River in Northern Territory, Australia was chosen because it had big size chromosomes and not so great numbers of chromosomes as 2n=12. Respective chromosomes of the species from mitotic early prophase to late metaphase and even anaphase showed distinct characteristics of wide, non-staining gap between chromatids (Kondo 1984). Plants of the species were easily, vegetatively propagated and supplied enough research materials within a short time in vivo and in vitro.Cracking frozen specimens Root tips of D. falconeri were harvested and fixed in either 3:1 (v/v) methanolacetic acid or 3:1 (v/v) ethanol-acetic acid at 4°C for 24 h. Fixed root-tips of the species were washed in a series of ethanol from 90, 70, 50, 30, 20 and finally to 10%. They were excised under a stereo microscope to remove non-meristematic tissues. They were rinsed with phosphate buffer solution at pH 7.4 for 10 min each, three times and were, then, treated in 1% O S O 4...

Genomes of the Venus Flytrap and Close Relatives Unveil the Roots of Plant Carnivory

“…In congruence with the observed overall reduction in gene content, 1,912 groups were contracted in the Droseraceae. These included genes involved in kinetochore formation [17,18] (Figure S5), which have previously been shown to be associated with the occurrence of holocentric chromosomes [19][20][21]. Further losses affected the ubiquitin (UBQ) gene family often involved in stress responses (Figure S5) and genes related to root development (Figure S5).…”

Over two orders of magnitude difference in rate of single chromosome loss among sundew (DroseraL., Droseraceae) lineages

“…Holocentric chromosomes have a centromere along their entire length rather than localized in the typical, X-shaped, monocentric chromosome. Because chromosomes of all Drosera except D. regia (Shirakawa, Nagano, et al, 2011) and D. slackii (Bennett and Cheek, 1990) lack a visible centromere constriction (Nontachaiyapoom et al, 2000; Kondo and Nontachaiyapoom, 2008), and all eight species tested so far undergo successful mitotic segregation after breakage (Sheikh et al, 1995; Furuta and Kondo, 1999; Shirakawa, Hoshi, et al, 2011; Zedek et al, 2016; Kolodin et al, 2018), researchers have hypothesized holocentromeres to be present in almost all Drosera . However, the distribution of phospho-histone 2A threonine-120, a histone commonly associated with the centromeric and pericentric region (Dong and Han, 2012; Wanner et al, 2015), indicates monocentromeres in three species from D .…”

Evolution of genome size and genomic GC content in carnivorous holokinetics (Droseraceae)

“…Possibly, the major peculiarity of Droseraceae compared with other carnivorous lineages (including Lentibulariaceae) is its holokinetic chromosomes, which are typical for Drosera species (Rothfels and Heimburg, 1968;Sheikh et al, 1995;Kondo and Nontachaiyapoom, 2008;Shirakawa et al, 2011a, b; with a possible exception of D. regia (Shirakawa et al, 2011b). In contrast to monocentric chromosomes, whose kinetochore formation is restricted to the small areas of the centromeres, holokinetic chromosomes lack primary constrictions and their kinetochores are formed along their poleward surfaces (Bure s et al, 2013;Cuacos et al, 2015).…”