Unlocking the Secrets of Selective Pollen Attraction in Flowers

A team of scientists from Nagoya University in Japan employed sophisticated microscopic technology to study the internal reproductive mechanism of the Arabidopsis plant. Their results, published in EMBO Reports, explain how a female flower preferentially attracts a single male counterpart. These findings offer information that could help boost seed production and agricultural breeding procedures.

Angiosperms, also known as flowering plants, are classified as having both male and female reproductive systems. The creation of a pollen tube begins during plant reproduction when a pollen grain carrying male gametes lands on the stigma of another flower. Sperm cells can reach an ovule's egg and central cells for fertilization, thanks to the tube, which extends through the style and into the ovary.

Using a two-photon microscope, the researchers developed an innovative microscopic approach to better understand this process. Yoko Mizuta, the lead author, stated that the three years of work were similar to a journey.

It involved delicate sample handling techniques and optimization of conditions, such as excitation wavelengths, for achieving deep imaging of flowers.”

Yoko Mizuta, Study Principal Author and Assistant Professor Institute of Transformative Bio-Molecules, Nagoya University

Using this approach, researchers observed for the first time the extension of several pollen tubes within a living pistil and their distinct attraction to female tissue.

This enabled them to discover a signal released by the maternal tissue that attracts pollen tubes, causing them to elongate along the stamen tissue and arrive at the site of fertilization. This is the signal that allows for precise control of one-to-one pollen tube guidance.

One-to-one pollen tube guiding is a vital step in plant reproduction that includes precisely navigating pollen tubes to individual ovules. This mechanism promotes the effective fertilization of angiosperms by promoting the particular connection of ovules and pollen tubes.

In addition to the signal that increases attraction among individuals, Mizuta and her colleagues discovered a repulsion signal. This signal was emitted after attracting a pollen tube, preventing the attraction of more pollen tubes.

In addition to the 45-minute blocking mechanism that keeps numerous sperm from fertilizing the same ovule, a repulsion signal sends rejected suitors to other unpaired ovules.

Mizuta added, “I find the repulsion system fascinating, the cells that generate the attraction system are mostly synergid cells, whereas the cells that generate the repulsion system include multiple types such as somatic and gametophytic cells at multistep levels. I find it very interesting that all couplings involve this mechanism of attracting and repelling.”

Further analysis revealed the complexities of the one-to-one pollen tube guiding process, showing a sophisticated regulatory system that involves several cells in both male and female plants. This precise management guarantees successful fertilization and efficient seed production, even in adverse circumstances.

Mizuta underlined the role of this process in increasing seed production.

By precisely orchestrating the behavior of pollen tubes, plants have evolved a mechanism to ensure successful fertilization and efficient seed production on dry land with a limited number of suitors,” Mizuta noted.

In addition to offering insightful knowledge on plant reproduction, this study might help agricultural breeding by boosting seed yield and germination rates.

Source:
Journal reference:

‌Mizuta, Y., et al. (2024) Deep imaging reveals dynamics and signaling in one-to-one pollen tube guidance. EMBO Reports. doi.org/10.1038/s44319-024-00151-4

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