| dc.description.abstract | Polyploidy in angiosperms is an influential factor to trigger apomixis, the reproduction of
asexual seeds. Apomixis is usually facultative, which means that both sexual and
apomictic seeds can be formed by the same plant. Environmental abiotic stress, e.g.
light stress, can change the frequency of apomixis. Previous work suggested effects of
stress treatments on meiosis and megasporogenesis. We hypothesized that polyploidy
would alter the stress response and hence reproductive phenotypes of different
cytotypes. The main aims of this research were to explore with prolonged
photoperiods, whether polyploidy alters proportions of sexual ovule and sexual seed
formation under light stress conditions. We used three facultative apomictic,
pseudogamous cytotypes of the Ranunculus auricomus complex (diploid, tetraploid,
and hexaploid). Stress treatments were applied by extended light periods (16.5 h) and
control (10 h) in climate growth chambers. Proportions of apomeiotic vs. meiotic
development in the ovule were evaluated with clearing methods, and mode of seed
formation was examined by single seed flow cytometric seed screening (ssFCSS). We
further studied pollen stainability to understand effects of pollen quality on seed formation.
Results revealed that under extended photoperiod, all cytotypes produced significantly
more sexual ovules than in the control, with strongest effects on diploids. The stress
treatment affected neither the frequency of seed set nor the proportion of sexual seeds nor
pollen quality. Successful seed formation appears to be dependent on balanced maternal:
paternal genome contributions. Diploid cytotypes had mostly sexual seed formation, while
polyploid cytotypes formed predominantly apomictic seeds. Pollen quality was in
hexaploids better than in diploids and tetraploids | en_US |
