# The regulation of vacuole morphology in stigma papilla cells is involved in water transfer to pollen in Arabidopsis thaliana

## TL;DR

This study shows how vacuole changes in Arabidopsis stigma cells help transfer water to pollen, which is essential for successful fertilization.

## Contribution

The study introduces a live-cell imaging system to observe vacuole dynamics and links vacuole morphology to pollen hydration.

## Key findings

- Vacuoles in papilla cells change morphology before pollination through fusion and constriction.
- Inhibiting vacuole morphological changes reduces pollen hydration rates.
- ROP2 mutant papilla cells show less vacuole variation and faster pollen hydration.

## Abstract

The stigma papilla cells of Arabidopsis thaliana control water transport to pollen by regulating the morphology of vacuoles in papilla cells after pollination.

Pollen hydration is the first crucial response after pollination for successful fertilization. In the Brassicaceae family, papilla cells on the stigma supply water to pollen. In pollinated papilla cells, cellular responses essential for pollen hydration are induced. However, it remains unclear how papilla cells release water from inside the cells to the pollen. Here, we set up a live-cell imaging system for observing vacuole dynamics in Arabidopsis thaliana papilla cells and investigated the role of vacuole morphology in these cells in the regulation of water transfer to pollen. Before pollination, vacuoles in the papilla cells changed their morphology through fusion and constriction; however, after pollination, they formed larger vacuoles and exhibited reduced movement. Additionally, when the morphological variation of vacuoles in the papilla cells was inhibited by wortmannin treatment, the pollen hydration rate decreased in a concentration-dependent manner. In contrast, the vacuoles tended to be less constricted even before pollination and showed less variation than wild-type after pollination in Rho-like GTPase from plants 2 (ROP2) mutant papilla cells, where the pollen hydration rate is faster. We propose that the regulation of vacuole morphology in papilla cells is involved in water transfer to pollen during pollination.

The online version contains supplementary material available at 10.1007/s00497-025-00525-1.