Abstract
In plants, pollen has two sperm cells to perform double fertilization. Together with the two sperm nuclei and a vegetative nucleus, pollen consists of three nuclei at the time of fertilization. In contrast, two types of mature pollen grains exist, either containing one or two generative nuclei. Such difference in the nucleoploidity of mature pollen grains may affect pollen viability. We isolated an Arabidopsis mutant that has altered nucleoploidity. This mutant, nikaku, segregated normal tri-nuclear pollen grains and abnormal di-nuclear pollen grains to 1:1. Our genetic analysis showed that the di-nuclear phenotype was transmitted only maternally, and the transmission rate was always 1:1. These results suggest that pollen mitosis II is impaired in the mutation. Analysis of DNA contents in di-nuclear pollens revealed that the mutation blocked DNA replication, suggesting that nikaku may affect pollen mitosis II at an early step.
