Proline priming: An efficient strategy to mitigate salinity impact at early developmental stages of the oilseed halophyte Cakile maritima

Seed germination is a vital process, yet extremely sensitive to salinity. This is particularly true for coastal halophytes like the annual oilseed species Cakile maritima, which faces the simultaneous impact of wind, salt-spray and seawater inundations in its natural biotopes. At the early developmental stages, this may jeopardize seed germination, plant establishment capacity and hence its development and persistence. Osmopriming is a pre-sowing approach aiming to improve seedling emergence and establishment in adverse environments. Here, we investigate the effect of proline (at 0, 1, 5, and 20 mM) pre-treatment on salt tolerance of C. maritima at the juvenile stage under salinity (0, 100, and 200 mM NaCl). Proline seed priming enhanced the germination rate (28% to 92%) and promoted seedling establishment of C. maritima by stimulating α-amylase activity even at the highest salinity (+55 %). Besides, after transfer of non-germinated seeds on distilled water, salt impact was fully reversible. At the seedling stage, chlorophyll fluorescence parameters showed that this osmoticum increased the maximal quantum yield of PSII photochemistry (Fv/Fm) and the quantum yield of photochemical energy conversion [Y(II)]. In contrast, the quantum yield of nonregulated nonphotochemical energy dissipation [Y(NO)] and the quantum yield of regulated nonphotochemical energy dissipation [Y(NPQ)], which might be correlated to the mitigation of the salt deleterious effects on PSII. Proline and carbohydrate concentrations also increased following priming. Overall, our data provide strong arguments for using proline at low doses (1 and 5 mM) as a successful priming agent to alleviate salinity-induced adverse effect on plants

Physiological and leaf metabolome changes in the xerohalophyte species Atriplex halimus induced by salinity

International audienceAtriplex halimus is a xerohalophyte plant, which could be used as cash crops. This plant was integrated in Tunisian government programs the aim of which is to rehabilitate saline areas and desert. To investigate its strategies involved in salt tolerance, A. halimus was grown hydroponically under controlled conditions with increasing salinity. Plants were harvested and analyzed after 60 days of treatment. The biomass of A. halimus increased by moderate salinity and decreased significantly at high salinity compared to control plants at 400 mM. Despite of the large amounts of Na+ observed in the leaves of Atriplex plants, leaf water contents and leaf succulence kept on increasing in treated plants and decreased over 150 mM NaCl. This confirmed the compartmentation and the efficient contribution of Na+ in the osmotic adjustment. Analysis of the metabolic profiles showed an accumulation of carbohydrates and amino acids. The leaf tissues preferentially stored proline, a alanine and sucrose. Increasing NaCl levels were also accompanied by a significant accumulation of malate in leaves. Involvement of these solutes in osmotic adjustment was considered low. Nevertheless, they seemed to have an important role in controlling photosynthesis which capacity was enhanced by low salinity and decreased with increasing salinity (evaluated by actual photochemical efficiency of photosystem II and chlorophyll contents). The unchanged maximum photochemical efficiency of photosystem II accompanied by the increase of the non-photochemical quenching, the enhancement of the total antioxidant activity and the decrease of the malondialdehyde contents in leaves showed efficient protection of membranes and photosystem II from photo oxidative damage. This protection seemed to be attributed to proline and sucrose largely accumulated in leaves treated with salt. (C) 2016 Elsevier Masson SAS. All rights reserved

Investigation of Na+ and K+ transport in halophytes: Functional analysis of the HmHKT2;1 transporter from Hordeum maritimum and expression under saline conditions

International audienceControl of K+ and Na+ transport plays a central role in plant adaptation to salinity. In the halophyte Hordeum maritimum, we have characterized a transporter gene, named HmHKT2;1, whose homologue HvHKT2;1 in cultivated barley, Hordeum vulgare, was known to give rise to increased salt tolerance when overexpressed. The encoded protein is strictly identical in two H. maritimum ecotypes, from two biotopes (Tunisian sebkhas) affected by different levels of salinity. These two ecotypes were found to display distinctive responses to salt stress in terms of biomass production, Na+ contents, K+ contents and K+ absorption efficiency. Electrophysiological analysis of HmHKT2;1 in Xenopus oocytes revealed distinctive properties when compared to HvHKT2;1 and other transporters from the same group, especially a much higher affinity for both Na+ and K+, and a Na+-K+ symporter behavior in a very broad range of Na+ and K+ concentrations, due to reduced K+ blockage of the transport pathway. Domain swapping experiments identified the region including the 5th transmembrane segment and the adjacent extracellular loop as playing a major role in the determination of the affinity for Na+ and the level of K+ blockage in these HKT2;1 transporters. Analysis (qRT-PCR) of HmHKT2;1 expression in the two ecotypes submitted to saline conditions revealed that the levels of HmHKT2;1 transcripts was maintained constant in the most salt tolerant ecotype while they decreased in the less tolerant one. Both the unique functional properties of HmHKT2;1 and the regulation of the expression of the encoding gene could contribute to H. maritimum adaptation to salinity