Kinetic analysis on the motility of liverwort sperms using a microscopic Computer-Assisted Sperm Analyzing system

Some of the plant species including embryophytes (especially, bryophytes and ferns) utilize the sperms but not pollens for their sexual reproduction. Because sperm motility is one of the most important features for the fertility in human and animals, percentage of motility and the kinetic parameters for swimming and the guidance to eggs (taxis) are well focused in the field of reproductive biology to evaluate and improve the male infertility. However, the nature of plant sperms is rarely known even more than a century has passed since the first microscopic observations of sperms in embryophytes as in the cases in Ginkgo biloba and Cycas revoluta, commonly known as sperm-generating plant species, have been made in the end of 19th century. In the present study, we performed high throughput analysis on the sperm motility in the most common liverwort, Marchantia polymorpha L. using a Computer-Assisted Sperm Analyzing (CASA) system. Time-dependent changes in kinetic parameters of Marchantia sperm motility from high to low motility states suggested that amplitude of lateral head displacement, rather than its frequency play key roles in the speed and distance of swimming at high motility state. From the average lifetime of high motility state and the speed of migration, the distance traveled by Marchantia sperms, due to their own motility, are estimated to be less than 3 cm, suggesting that motility of Marchantia sperms might mainly play a key role in the final fertilization step, but not in the long-distance travelling from the patchily distributed colonies of male strains to those of female strains, often being apart by few meters in the field.