Journal Article

Vesicle formation in the membrane of onion cells (<i>Allium cepa</i>) during rapid osmotic dehydration

Akym Assani, Sylvie Moundanga, Laurent Beney and Patrick Gervais

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 104, issue 7, pages 1389-1395
Published in print December 2009 | ISSN: 0305-7364
Published online October 2009 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcp256
Vesicle formation in the membrane of onion cells (Allium cepa) during rapid osmotic dehydration

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Optimization of osmotic dehydration in different plant cells has been investigated through the variation of parameters such as the nature of the sugar used, the concentration of osmotic solutions and the processing time. In micro-organisms such as the yeast, Saccharomyces cerevisiae, the exposure of a cell to a slow increase in osmotic pressure preserves cell viability after rehydration, while sudden dehydration involves a lower rate of cell viability, which could be due to membrane vesiculation. The aim of this work is to study cytoplasmic vesicle formation in onion epidermal cells (Allium cepa) as a function of the kinetics of osmotic pressure variation in the external medium.

Methods

Onion epidermal cells were submitted either to an osmotic shock or to a progressive osmotic shift from an osmotic pressure of 2 to 24 MPa to induce plasmolysis. After 30 min in the treatment solution, deplasmolysis was carried out. Cells were observed by microscopy during the whole cycle of dehydration–rehydration.

Key Results

The application of an osmotic shock to onion cells, from an initial osmotic pressure of 2 MPa to a final one of 24 MPa for <1 s, led to the formation of numerous exocytotic and osmocytic vesicles visualized through light and confocal microscopy. In contrast, after application of a progressive osmotic shift, from an initial osmotic pressure of 2 MPa to a final one of 24 MPa for 30 min, no vesicles were observed. Additionally, the absence of Hechtian strand connections led to the bursting of vesicles in the case of the osmotic shock.

Conclusions

It is concluded that the kinetics of osmotic dehydration strongly influence vesicle formation in onion cells, and that Hechtian strand connections between protoplasts and exocytotic vesicles are a prerequisite for successful deplasmolysis. These results suggest that a decrease in the area-to-volume ratio of a cell could cause cell death following an osmotic shock.

Keywords: Allium cepa; vesicle formation; kinetics; osmotic; osmocytosis; exocytosis; plasmolysis; Lucifer Yellow CH

Journal Article.  4662 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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