Interplay of an array of salt-responding mechanisms in Iranian borage: Evidence from physiological, biochemical, and histochemical examinations.

In order to address the lacuna of data on the response of physiological and biochemical attributes and chemical compounds of glandular trichomes of Iranian borage (Echium amoenum Fisch. & C.A.Mey.) to saline water (0, 25, 50, 75, and 100 mM NaCl) an experiment was conducted on 13 genotypes. Genotypic differences and salt-induced modifications in chlorophyll concentration and fluorescence, plant growth, relative water content, proline concentration, antioxidant defense, and chemical compounds of glandular trichomes upon exposure to salt stress were observed. Chlorophyll and carotenoids concentrations and catalase (EC 1.11.1.6) and ascorbate peroxidase (EC 1.11.1.11) activities were either enhanced or remained unchanged in the presence of moderate salt concentrations (i.e. 25 and 50 mM NaCl) in a majority of the genotypes. Though, 75 and 100 mM NaCl were modestly and severely detrimental, respectively, to the majority of the genotypes. The 75 and 100 mM NaCl led to substantial increases and decreases in the Na and K, respectively, resulting in notable increase in the Na/K. Increases in proline, total phenolic compounds, and alkaloids concentrations, essential oils, alkaloids, and phenolic compounds of the glandular trichomes were concomitant to decreases in the relative water content, leaf area, maximum quantum efficiency of photosystem II, shoot and root dry masses. This study revealed, for the first time, that Iranian borage tolerates 25 and 50 mM NaCl and antioxidative enzymes as well as secondary metabolites such as alkaloids and phenolic compounds accumulated mainly in the trichomes play key role in this regard.