Assessing the Influence of Electric Cues and Conductivity on Pollen Tube Growth via Lab-On-A-Chip Technology

Abstract

Pollen tubes are believed to react to a combination of chemical, mechanical, and electrical cues during its journey through the pistil in order to achieve fertilization. Despite extensive work dedicated to the subject it is still not clear how these exogenous guidance signals work or how they are processed internally. Using Lab-on-a-chip (LOC) technology, we assessed the influence of electric fields on pollen tube growth at the microscale. Microelectrodes were integrated into the LOC in order to enable the application of electric fields in a controlled manner. Due simulation of the LOC electrical configuration and characterization of the pollen growth medium conductivity were carried out. DC and AC electric fields were applied to batches of Camellia japonica pollen grains under various conditions. Results show that pollen tube growth is increasingly degraded as the applied DC electric field increases. Furthermore, germination is completely inhibited for sufficiently strong fields. AC electric fields, however, had a restoring effect as growth is promoted as frequency increases beyond 100 mHz, which suggests a significant role of the medium conductivity in enabling cell growth. Interestingly, no sign of pollen tube orientation was found under any tested condition, weakening the much debated argument for electrotropism in pollen tubes. When exposed to a highly localized field, pollen tubes did not deviate. This work suggests that both strength and frequency of an applied electric field influence pollen tubes, and most likely living cells in general, in a much more subtle way rather than being a macro scale exogenous guiding signal.