CYTOGENETIC EVALUATION OF MICROSPOROCYTES OF SETCREASEA PURPUREA(BOOM) FLOWER

Abstract

Setcreasea purpurea Boom (Wandering Jews) belongs to the family Commelinaceae of the order Commelinales. The family, made up of 38 genera and about 600 species, occurs mostly in the tropical and warm regions of the world. Many are popular as garden or house ornamentals. It is a flower-bearing plant yet it is mostly propagated vegetatively due to the formation of sterile pollen grains thereby making pollination impossible. Cytogenetic study was carried out to observe the chromosome behaviour in the microsporocytes during meiosis with the aim of understanding the reasons behind the sterility of the pollen grains. Immature flower buds of Setcreasea purpurea were dissected in a Petri dish containing tap water. The microsporocytes were squashed using lactic acetic-orcein stain. Most microsporocytes observed from slides contained 12 bivalents. However, a few contained 10 bivalents and one quadrivalent or 8 bivalents and 2 quadrivalents. This shows that 2n = 24 in the microsporocytes. Other irregularities observed included laggards, abnormal disjunction, chromosome bridges and chromosome fragments all at anaphase-1 and micronuclei at telophase-1. Occurrence of laggards, chromosome bridge formation and micronuclei were low ranging from 1 to 3 in the population of S. purpurea studied. The consequence of these irregular chromosomes is their loss and non-inclusion in the daughter nuclei at telophase-I. The loss of these segments would result in loss of genes on them resulting in the unviable microspores at the end of meiosis. These microspores are the pollen grains in which a large number of them (about 90%) have been found to be sterile thereby making the plant to reproduce asexually by stem-tip cuttings