Utilization and transport of mannitol in Olea europaea and implications on salt stress tolerance

Abstract

Mannitol is one of the primary photosynthetic products and major phloem-translocated carbohydrate in Olea europaea L., an important and widespread crop in the Mediterranean basin. In O. europaea cell suspensions, we have previously identified and characterized a H+-dependent polyol transport system whose activity was correlated with OeMaT1 (Olea europaea Mannitol Transporter) expression. Addition of 100-500 mM NaCl to cultured cells enhanced the capacity of the polyol:H+ symport system and the amount of OeMaT1 transcripts, whereas it strongly repressed mannitol dehydrogenase activity. Cell viability as assessed by fluorescein diacetate and propidium iodide showed that mannitol-grown cells remained viable 24 h after a 250 and 500 mM NaCl pulse but sucrose-grown cells showed extensive loss of cell viability. OeMaT transcripts increased throughout maturation, suggesting that a OeMaT is involved in the accumulation of mannitol occurring during ripening of olive. These results suggest that, besides its role as carbon and energy source, mannitol contributes towards salt stress tolerance in O. europaea.