Mechanisms underlying the adjustment of cell volume of Olea europaea in response to salt stress

Abstract

Olea europaea cell cultures we have previously identified and characterized a polyol:H+ symport system whose activity was correlated with OeMaT1 (Olea europaea Mannitol Transporter) expression. Salt (100-500 mM NaCl) enhances the capacity of the transport system and the amount of OeMaT1 transcripts, whereas it strongly represses mannitol dehydrogenase activity, enzyme responsible for the first step of the polyol intracellular oxidation. Results suggest that this primary photosynthetic product in O. europaea, is an important osmoprotectant, besides its role role as carbon and energy source. Consistently, mannitol-grown cells remain viable 24 h after a 250 and 500 mM NaCl pulse but sucrose-grown cells show extensive loss of cell viability, as assessed by fluorescein diacetate and propidium iodide. Salt treatments are always associated with a drastic reduction in cell volume over a 12 h period, but the addition of the endocytic inhibitor wortmannin prevents cell retraction and promotes cell dead. Results suggest the involvement of plasma membrane internalization, as an additional osmotic adjustment mechanism against salt stress in O. europaea. Currently, we are using confocal imaging to monitor endocytic vesicles formation using the fluorescent cell membrane marker FM1-43.