AOBPreview originally published online on October 14, 2009
Annals of Botany 2009 104(7):1389-1395; doi:10.1093/aob/mcp256
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Vesicle formation in the membrane of onion cells (Allium cepa) during rapid osmotic dehydration
1 Department of Plant Agriculture, University of Guelph, Bovey Building, Guelph, Ontario, N1G 2W1, Canada
2 Laboratoire de Génie des Procédés Microbiologiques et Alimentaires, Université de Bourgogne/AgroSup Dijon, 1 Esplanade Erasme, 21000 Dijon, France
* For correspondence. E-mail gervais{at}u-bourgogne.fr
Received: 3 April 2009 Returned for revision: 19 May 2009 Accepted: 1 June 2009 Published electronically: 14 October 2009
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.
Key words: Allium cepa, vesicle formation, kinetics, osmotic, osmocytosis, exocytosis, plasmolysis, Lucifer Yellow CH
These authors contributed equally to this work.