Ferchichi Selma, Hessini Kamel, Dell Aversana Emilia, D Amelia Luisa, Woodrow Pasqualina, Ciarmiello Loredana F, Fuggi Amodio, Carillo Petronia
Laboratory of Extremophile Plants, Center of Biotechnology of Borj Cedria, University of Elmanar, B.P. 901, Hammam-Lif 2050, Tunisia.
Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania 'Luigi Vanvitelli', Via Vivaldi 43, 81100 Caserta, Italy.
Funct Plant Biol. 2018 Oct;45(11):1096-1109. doi: 10.1071/FP18046.
Hordeum maritimum With. (= H. marinum Huds. subsp. marinum, 2n=14) is a wild cereal present in the saline depressions of the Soliman and Kelbia Sebkhas, which contributes significantly to annual biomass production in Tunisia. This species is able to tolerate high NaCl concentrations at the seedling stage without showing symptoms of toxicity; however, the tolerance strategy mechanisms of this plant have not yet been unravelled. Our metabolite analysis, performed on leaves of H. maritimum during extended stress in comparison with Hordeum vulgare L. cv. Lamsi, has revealed an adaptive response of the wild species based on a different temporal accumulation pattern of ions and compatible metabolites. Further, wild and cultivated genotypes with contrasting salt-tolerant behaviour display different pattern of metabolites when salt stress is prolonged over 2 weeks. In particular, when exposed to up to 3 weeks of 200mM NaCl salt stress, H. maritimum is able to maintain lower leaf concentrations of sodium and chloride, and higher concentrations of potassium compared with H. vulgare. This likely restricts sodium entry into plants at the root level, and uses the toxic ions, glycine betaine and low levels of proline for osmotic adjustment. Under prolonged stress, the accumulation of proline increases, reaching the highest levels in concomitance with the decrease of potassium to sodium ratio, the increase of hydrogen peroxide and decrease of chlorophylls. The modulation of proline accumulation over time can be interpreted as an adaptive response to long-term salinity. Moreover, once synthetised glycine betaine is transported but not metabolised, it can contribute together with proline to osmotically balance H. maritimum leaves and protect them from oxidative stress. The 2-3 week delay of H. maritimum in showing the symptoms of stress and damages compared with H. vulgare could be important in the survival of plants when soil salinity is not a permanent condition, but just a transient state of stress.
海滨大麦（With.，= 盐生大麦Huds.亚种盐生大麦，2n = 14）是一种野生谷物，生长在索利曼和凯尔比亚盐沼的盐碱洼地中，对突尼斯的年生物量生产有重要贡献。该物种在幼苗期能够耐受高浓度的氯化钠，且不表现出毒性症状；然而，这种植物的耐受策略机制尚未被阐明。我们对海滨大麦叶片在长期胁迫下进行了代谢物分析，并与普通大麦品种Lamsi进行了比较，结果显示该野生物种基于离子和相容性代谢物不同的时间积累模式产生了适应性反应。此外，当盐胁迫延长超过2周时，具有不同耐盐行为的野生型和栽培型基因型表现出不同的代谢物模式。特别是，当暴露于高达200mM氯化钠的盐胁迫3周时，与普通大麦相比，海滨大麦能够维持较低的叶片钠和氯浓度，以及较高的钾浓度。这可能限制了钠在根部进入植物，并利用有毒离子、甘氨酸甜菜碱和低水平的脯氨酸进行渗透调节。在长期胁迫下，脯氨酸的积累增加，在钾钠比降低、过氧化氢增加和叶绿素减少的同时达到最高水平。脯氨酸积累随时间的调节可被解释为对长期盐度的适应性反应。此外，一旦合成，甘氨酸甜菜碱就会被运输但不被代谢，它可以与脯氨酸一起有助于海滨大麦叶片的渗透平衡，并保护它们免受氧化应激。与普通大麦相比，海滨大麦在表现出胁迫和损伤症状方面延迟2 - 3周，这在土壤盐度不是永久条件而是短暂胁迫状态时对植物的存活可能很重要。
