Cytology and pollen morphology of Bougainvillea glabra ‘Elizabeth Angus’, a cultivar with low pollen fertility

Abstract

In this study, we analysed the pollen morphology, male gametophyte development, and callose deposition dynamics of Bougainvillea glabra ‘Elizabeth Angus’ to explore the period and mode of pollen abortion and the relationship between pollen morphology and fertility. Fertile pollen grains of ‘Elizabeth Angus’ and B. spectabilis ‘Pink Panther’ were larger than sterile pollen grains. Compared with the control ‘Pink Panther’, proportion of ‘Elizabeth Angus’ pollen grains with columellae was lower. Many abnormal phenomena were observed in pollen mother cells (PMCs) during meiosis, including laggard chromosomes, uneven chromosome separation, chromosome separation asynchrony, pentads, and micronuclei. At the early uninucleate stage, microspore development was abnormal, with deformed and shrunken pollen grains. Callose deposition was normal at meiosis and the tetrad stages of PMCs, but abnormal at the early mononuclear stage, with blocked microspore development. The complex abnormal chromosomal behaviour and delayed callose degradation in the early mononuclear stage during meiosis may account for the low pollen fertility of ‘Elizabeth Angus’. The size of the pollen grains and the morphology of the outer wall were associated with fertility; the larger pollen grains showed superior fertility, and the fertility of the pollen grains was associated with a certain number of columellae in the pollen wall. This study provides a theoretical basis for the genetic breeding of Bougainvillea.