# Development and Holocrine Secretion of Resin Ducts in Kielmeyera appariciana (Calophyllaceae)

## TL;DR

This study explores how resin ducts in Kielmeyera appariciana develop and release secretions through a unique holocrine process involving cell death.

## Contribution

The study identifies the first documented case of holocrine secretion in plant resin ducts, involving programmed cell death and cytoskeleton rearrangement.

## Key findings

- Resin is synthesized in plastids and endoplasmic reticulum and stored in vesicles and vacuoles.
- Secretion release involves programmed cell death triggered by reactive oxygen species and cytoskeleton rearrangement.
- Cellulase activity precedes cell wall rupture to release the secretion into the duct lumen.

## Abstract

The modes of formation and release of secretion are complex processes that occur in secretory ducts and their description has great divergence in some species. The use of modern techniques to detect hydrolytic enzymes, cytoskeleton arrangement and indicators of programmed cell death may help clarify the processes involved during the ontogeny of that gland. The goal of our study was to analyze subcellular changes during schizogenous formation and secretion production and release into the lumen in resin ducts of Kielmeyera appariciana. Our results demonstrate the participation of pectinase through the loosening of the central cells of the rosette, which subsequently split from each other through polarized growth mediated by a rearrangement of the microtubules. The resin is mainly synthesized in plastids and endoplasmic reticulum and is observed inside vesicles and small vacuoles. The secretion release is holocrine and occurs through programmed cell death related to the release of reactive oxygen species, causing cytoplasm darkening, chromatin condensation, vacuole rupture and plastid and mitochondria degeneration. Cellulase activity was identified prior to the rupture of the cell wall, causing the release of secretion into the lumen of the duct. The participation of the cytoskeleton was observed for the first time during schizogeny of ducts as well as programmed cell death as part of the process of the release of holocrine secretion. This type of secretion release may be a key innovation in Kielmeyera since it has not been observed in ducts of any other plant thus far.