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Salt stress, among other abiotic stresses, has a high impact on crop yield. Salt tolerance is a multifactorial trait that involves the ability of cells to retain K ions, regulate reactive O species (ROS) production, and synthesise new molecules to cope with osmotic stress. In the present work, two different cultivars of Cucumis sativus L. (cv. Parys, sensitive; cv. Polan, tolerant) were selected based on their germination capabilities under 100 mM NaCl. The capacity of these two cultivars to tolerate salt stress was analysed using several different physiological and genetic approaches. K+ fluxes from roots, as an immediate response to salinity, showed the higher ability of cv. Polan to maintain K+ compared with cv. Parys, according to the expression level of inward rectifying potassium channel 1 (AKT1). ROS production was also investigated in both cultivars and a higher basal ROS level was observed in cv. Polan than in cv. Parys. Concurrently, an increased basal level of respiratory burst oxidase homologue F (RBOHF) gene was also found, as well as a strong induction of the ethylene responsive factor 109 (ERF109) transcription factor after salt treatment in cv. Polan. Our data suggest that roots’ ability to retain K+, a higher level of RBOHF and a strong induction of ERF109 should all be considered important components for salt tolerance in C. sativus.

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A B S T R A C TPlants survive stressful conditions by employing three main strategies: escape, tolerance, and survival. Experiments were conducted to pinpoint the response strategy adopted by Tetradenia riparia to cadmium (Cd) stress by monitoring several physiological parameters and plants' ability to recover once the stress receded. Cadmium (30 and 150 mM) strongly affected shoot and root growth in a dose dependent manner, with almost complete inhibition of shoot growth, stomatal opening and CO 2 assimilation in plants exposed to 150 mM CdSO 4 . Independently of the CdSO 4 concentrations, plants excluded Cd from the aboveground tissues, with concentrations in shoots remaining around 0.1 mmol g À1 dry mass.Furthermore, Cd stress was associated with a decline in methylation of Lys4 of histone H3, likely associated with the transition from an active to a quiescent state. Surprisingly, Cd also induced the initiation of root primordia in T. riparia stems, which, once placed in a Cd-free media, quickly (24 h) developed into adventitious roots, which were likely the driving factor of the rapid resumption of leaf elongation and photosynthetic activity, which increased almost 20-fold over the 3 weeks of recovery. Therefore T. riparia ability to survive Cd stress was mediated by quiescence, which associated with an excluder strategy and stem root primordia formation, enabled rapid resumption of growth under Cd-free conditions.

Salinity is one of the most severe factors that limits the yield of filed, because most of crops employed in agriculture is salt sensitive. This losses in yield is mainly due to drought and high salinity of field and this situation will be worst with global climatic changes. In particular the toxicity of Na is due to its ability to inhibit enzyme function directly by binding to inhibitory sites or indirectly by displacing K from activation sites. Plants have evolved a wide range of mechanisms to adapt and mitigate this kind of abiotic stress. Here we reviewed sensing and signaling mechanisms of salt stress and the tolerance strategies in plants.

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