The efficient exclusion of excess Na from the cytoplasm and vacuolar Na(+) accumulation are the main mechanisms for the adaptation of plants to salt stress. This is typically carried out by transmembrane transport proteins that exclude Na(+) from the cytosol in exchange for H(+), a secondary transport process which is energy-dependent and driven by the proton-motive force generated by plasma-membrane and tonoplast proton pumps. Tonoplast enriched-vesicles from control and 150 mM NaCl-tolerant calli lines were used as a model system to study the activity of V-H(+)-PPase and V-H(+)-ATPase and the involvement of Na(+) compartmentalization into the vacuole as a mechanism of salt tolerance in Solanum tuberosum. Both ATP- and pyrophosphate (PP(i))-dependent H(+)-transport were higher in tonoplast vesicles from the salt-tolerant line than in vesicles from control cells. Western blotting of tonoplast proteins confirmed that changes in V-H(+)-PPase activity are correlated with increased protein amount. Conversely, immunodetection of the A-subunit of V-H(+)-ATPase revealed that a mechanism of post-translational regulation is probably involved. Na(+)-dependent dissipation of a pre-established pH gradient was used to measure Na(+)/H(+) exchange in tonoplast vesicles. The initial rates of proton efflux followed Michaelis-Menten kinetics and the V(max) of proton dissipation was 2-fold higher in NaCl-tolerant calli when compared to the control. H(+)-coupled exchange was specific for Na(+) and Li(+) and not for K(+). The increase of both the pH gradient across the tonoplast and the Na(+)/H(+) antiport activity in response to salt strongly suggests that Na(+) sequestration into the vacuole contributes to salt tolerance in potato.

Cell lines able to grow on media containing 50, 100, 150 or 200 mM NaCl were established from potato callus cultures by direct recurrent selection or gradual selection. In callus subjected to direct selection only small clusters of cells survived on medium with 150 or 200 mM NaCl, whereas on 100 mM small cell portions appear necrotic. When cell lines were obtained by successive subcultures on media with increased concentrations of NaCl, salt-tolerant calli were more compact and developed a greenish colour free from necrotic areas. The response of calli lines grown on media with NaCl was compared to control line. The NaCl-tolerant calli showed a decrease in relative growth rate and water content, with higher reductions in the 150 mM tolerant callus. Lipid peroxidation was increased in 50 mM and 100 mM NaCl-tolerant calli, while in 150 mM tolerant callus remained similar to 100 mM values. There was a significant increase in ascorbic acid content in 100 mM and 150 mM NaCl-tolerant calli as compared to the 50 mM, that was twofold the value found in the control. Also, the contents of soluble and insoluble proteins increased in salt-tolerant lines. SDS-PAGE of soluble proteins showed the synthesis of specific polypeptides in the presence of NaCl in culture medium and the synthesis of a new polypeptide.

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Cracking of sweet cherry (Prunus avium L.) fruits is caused by rain events close to harvest. This problem has occurred in most cherry growing regions with significant economic losses. Several orchard management practices have been applied to reduce the severity of this disorder, like the foliar application of minerals or growth regulators. In the present study, we hypothesized that preharvest spray treatments improve the physiological performance of sweet cherry trees and could also mitigate environmental stressful conditions. Effects of repeated foliar spraying of calcium (Ca), gibberellic acid (GA3), abscisic acid (ABA), salicylic acid (SA), glycine betaine (GB), and the biostimulant Ascophyllum nodosum (AN) on the physiological and biochemical performance of ‘Skeena’ sweet cherry trees during two consecutive years (without Ca in 2015 and in 2016 with addition of Ca) were studied. Results showed that in general spray treatments improved the physiological performance and water status of the trees. AN and ABA sprays were demonstrated to be the best compounds for increasing yield and reducing cherry cracking as well as improving photosynthetic performance and leaf metabolites content. In conclusion, AN and ABA might be promising tools in the fruit production system.