Polyploidy and apomixis in accessions of Senna rugosa (G.Don) H.S.Irwin & Barneby

Abstract

Senna rugosa (G.Don) H.S.Irwin & Barneby (Leguminosae) is a species from the Brazilian Cerrado commonly used for medicinal purposes. Chromosome variability (n = 14 and 28) described for this species indicates the occurrence of chromosome races and recent polyploidization in its evolution history. The aim of this study was to verify the relationship between ploidy level and occurrence of polyembryony in 5 accessions of S. rugosa. Cytogenetic analysis revealed the type of interphasic nuclei, chromosome number and morphology, and nuclear DNA content. Frequency of polyembryony was estimated by germination test. Pollen grain viability was estimated by different techniques. There was variability among the accessions of S. rugosa for interphasic nucleus type (semireticulate and nonreticulate), genome size (2.57 to 2.80 pg/2C), and polyembryony frequency (from 2 to 4 embryos). Pollen grain viability was 2.5% to 20%, depending on the technique used. Numeric chromosome variability was found among meristematic cells from each individual (2n = 28 to 2n = 112), with prevalence of 2n = 56. In mitotic metaphases with 2n = 56, all chromosomes were metacentric and of similar size. The data described, combined with previous descriptions of irregularities in chromosome pairing, suggest that S. rugosa is an autopolyploid facultative apomictic species, with interpopulation variability for level of apomixis expression.

Intra- and interspecific karyotypic variations of the genus Senna Mill. (Fabaceae, Caesalpinioideae)

“…Chromosome records of the genus Senna also demonstrated variations in ploidy levels, especially for S. rugosa (2n = 42, 56 and 112; Resende et al 2014), S. aversiflora (2n = 56; Matos et al 2011;present work) and S. gardneri (2n = 52 and 104, Matos et al 2011). Those variations could be a result of autopolyploidy, because hybridizations within the genus Senna are rarely viable, even among species having different morphotypes (see, for example, Holman & Playford 2000).…”

“…Chromosome counts are available for approximately 20 % of the species of Senna, with a predominance of 2n = 28, although there are also records of 2n = 22, 24 and 26 (Goldblatt 1981;Souza & Benko-Iseppon 2004;Biondo et al 2005a;Matos et al 2011;Resende et al 2013;Rice et al 2015); records of polyploidy, such as 2n = 42, 56 and 112 in Senna rugosa (Resende et al 2014), 2n = 56 in S. aversifl ora, and 2n = 52 and 104 in S. gardneri (Matos et al 2011) have also been cited. The consistent record of 2n = 28 for most species demonstrates that the basic number may be x = 14, while the other numbers (x = 11, 12 and 13) apparently reflect disploidy events (Goldblatt 1981).…”

Chromosomal Mapping of Tandem Repeats Revealed Massive Chromosomal Rearrangements and Insights Into Senna tora Dysploidy

“…In Senna, x = 7 is considered as the base chromosome number after the discovery of Senna rugosa cytotypes with a haploid chromosome number of n = 7 (Resende et al, 2014 ), suggesting that species with the predominant 2 n = 28 could technically be diploidized tetraploids. Comparing the chromosomal distribution of S. tora tandem repeats between S. occidentalis and S. tora , we hypothesize that the extant S. tora genome, like many angiosperms, has experienced at least two rounds of WGD in the immediate past.…”

Pollen structure and function in caesalpinioid legumes

“…In contrast with Papilionoideae and Mimosoideae, caesalpinioid species are predominantly diploid (Khatoon and Ali, 2006; Bennett and Leitch, 2012). A few exceptions occur in the tribe Cassieae, such as Senna rugosa (Biondo et al, 2005; Resende et al, 2014) and two tetraploid subspecies of Chamaechrista (Biondo et al, 2006), but pollen structure is imperfectly known in these species, and no correlation with large pollen size has been reported. The genus Cassia shows a range of 2C DNA amounts (from 1.30 to 2.54 pg) in different species at the same ploidy level (Ohri et al, 1986), but the corresponding pollen data are unknown.…”