Mannitol Transport and Mannitol Dehydrogenase Activities are Coordinated in Olea europaea Under Salt and Osmotic Stresses

The intracellular accumulation of organic compatible solutes functioning as osmoprotectants, such as polyols, is an important response mechanism of several plants to drought and salinity. In Olea europaea a mannitol transport system (OeMaT1) was previously characterized as a key player in plant resp...

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Published in:Plant and cell physiology 2011-10, Vol.52 (10), p.1766-1775
Main Authors: Conde, Artur, Silva, Paulo, Agasse, Alice, Conde, Carlos, Gerós, Hernâni
Format: Article
Language:English
Subjects:
Biological Transport - drug effects
Cloning, Molecular
Droughts
Mannitol - metabolism
Mannitol - pharmacology
Mannitol Dehydrogenases - genetics
Mannitol Dehydrogenases - metabolism
Molecular Sequence Data
Olea - drug effects
Olea - enzymology
Olea - genetics
Olea - physiology
Osmosis - drug effects
Phylogeny
Polyethylene Glycols - pharmacology
Potassium Chloride - pharmacology
Protective Agents - pharmacology
Sodium Chloride - pharmacology
Stress, Physiological - drug effects
Sucrose - pharmacology
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Summary:The intracellular accumulation of organic compatible solutes functioning as osmoprotectants, such as polyols, is an important response mechanism of several plants to drought and salinity. In Olea europaea a mannitol transport system (OeMaT1) was previously characterized as a key player in plant response to salinity. In the present study, heterotrophic sink models, such as olive cell suspensions and fruit tissues, and source leaves were used for analytical, biochemical and molecular studies. The kinetic parameters of mannitol dehydrogenase (MTD) determined in cells growing in mannitol, at 25°C and pH 9.0, were as follows: K m, 54.5 mM mannitol; and V max, 0.47 μmol h−1 mg−1 protein. The corresponding cDNA was cloned and named OeMTD1. OeMTD1 expression was correlated with MTD activity, OeMaT1 expression and carrier-mediated mannitol transport in mannitol- and sucrose-grown cells. Furthermore, sucrose-grown cells displayed only residual OeMTD activity, even though high levels of OeMTD1 transcription were observed. There is evidence that OeMTD is regulated at both transcriptional and post-transcriptional levels. MTD activity and OeMTD1 expression were repressed after Na+, K+ and polyethylene glycol (PEG) treatments, in both mannitol- and sucrose-grown cells. In contrast, salt and drought significantly increased mannitol transport activity and OeMaT1 expression. Taken together, these studies support that olive trees cope with salinity and drought by coordinating mannitol transport with intracellular metabolism.
ISSN:0032-0781
1471-9053
DOI:10.1093/pcp/pcr121