Female versus male: Rumex thyrsiflorus Fingerh. under in vitro conditions. Does sex influence in vitro morphogenesis?

Abstract

Rumex thyrsiflorus Fingerh. is a dioecious plant with polymorphic sex chromosomes (XX in females, XY1Y2 in males). This species is an interesting plant for study on the structure and function of sex chromosomes, the sex ratio, and is also a valuable source of bioactive constituents. A procedure for the micropropagation of R. thyrsiflorus from hypocotyl explants, which can be useful for analyses of sex-specific morphogenetic reactions under in vitro conditions, was developed. The molecular analysis, based on genetic sex markers, allowed the sex of explants to be determined in order to create male or female in vitro cultures. Regeneration primarily occurred via indirect adventitious shoot formation as well as via somatic embryogenesis, which was confirmed by histological and scanning electron microscope (SEM) analyses. The highest frequency of explants that revealed a morphogenetic response with the highest number of regenerated adventitious shoot buds (average 11.5 shoots per explant) was obtained on a Murashige and Skoog (MS) medium supplemented with 2.27 µM thidiazuron (TDZ). Molecular analysis revealed a female-biased sex ratio under these conditions. The relationship between the sex of the explants and their morphogenetic potential was studied. The efficiency of morphogenesis varied between the two sexes and depended on the ratio of auxin and cytokinin in the medium. The germination pattern of male and female seeds under in vitro conditions was also analysed. No differences in germination time between male and female seeds and in terms of male and female seedling length were observed, which indicated that there was no competition between the sexes during seed germination when grown under uniform growth conditions.