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

Abstract

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.

Roles of osmoprotectants in improving salinity and drought tolerance in plants: a review

“…toxicity which can ultimately disrupts K ? uptake by root cells, and exerts severe toxic effects on enzymes at the genetic level and thus, causing impairment in normal plant metabolism (Conde et al 2011). Shahbaz et al (2013) have observed decrease in K ?…”

Transgenic peanut overexpressing mtlD gene confers enhanced salinity stress tolerance via mannitol accumulation and differential antioxidative responses

“…In olive, it is reported that salinity stress tolerance involves both production and transport of mannitol through mannitol transport system (OeMaT1) gene expression (Conde et al 2011). This clearly means that both synthesis and transport of mannitol are equally important in imparting salinity stress tolerance.…”

“…The negative effect of soil salinity stress on plants is a complex phenomenon with major consequences like hyperosmotic stress, ion cytotoxicity (mostly due to Na ? , Cl -and SO 4 -), nutritional imbalance and oxidative stress, which causes a series of changes at physiological, biochemical and molecular level (Conde et al 2011).…”

“…Synthesis of mannitol takes place in mature leaves, which is then translocated via phloem to heterotrophic sink tissues, where it is either stored or oxidized to mannose through mannitol-1-phosphate dehydrogenase (MTD) and used as a carbon and energy source (Conde et al 2011). It is one of the most commonly occurring polyols in nature, with the exception of Archaea, animals (Bonin et al 2015) and also not reported in peanut (Abebe et al 2003;Bhauso et al 2014b).…”

Conservación de plantas regeneradas in vitro y análisis de la variación somaclonal de Cinchona officinalis, Linneo

“…Esto ha sido observado en el cultivo de Olea europea con un significativo incremento del crecimiento y proliferación de brotes (García et al 2002;Conde et al 2011). Así también, el tipo de agente osmótico y fuente de carbono usado influirá sobre la recuperación posterior de los explantos ya que tendrá un efecto evidente en la tasa de crecimiento (Gollagunta et al 2005).…”