Background The use of organic nanoparticles to improve drought resistance and water demand characteristics in plants seems to be a promising eco-friendly strategy for water resource management in arid and semi-arid areas. This study aimed to investigate the effect of chitosan nanoparticles (CNPs) (0, 30, 60 and 90 ppm) on some physiological, biochemical, and anatomical responses of Salvia abrotanoides under multiple irrigation regimes (30% (severe), 50% (medium) and 100% (control) field capacity). Results The results showed that drought stress decreases almost all biochemical parameters. However, foliar application of CNPs mitigated the effects caused by drought stress. This elicitor decreased electrolyte conductivity (35%), but improved relative water content (12.65%), total chlorophyll (63%), carotenoids (68%), phenol (23.1%), flavonoid (36.4%), soluble sugar (58%), proline (49%), protein (45.2%) in S. abrotanoides plants compared to the control (CNPs = 0). Furthermore, the activity of antioxidant enzymes superoxide dismutase (86%), polyphenol oxidase (72.8%), and guaiacol peroxidase (75.7%) were enhanced after CNPs treatment to reduce the effects of water deficit. Also, the CNPs led to an increase in stomatal density (5.2 and 6.6%) while decreasing stomatal aperture size (50 and 25%) and semi-closed stomata (26 and 53%) in leaves. Conclusion The findings show that CNPs not only can considerably reduce water requirement of S. abrotanoides but also are able to enhance the drought tolerance ability of this plant particularly in drought-prone areas. Graphical abstract

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Phenolic acids, as the predominant secondary metabolites of Salvia species, are largely used in pharmaceutical industries. The main aim of the study was to establish hairy root cultures of Salvia virgata Jacq. Also, the effects of methyl jasmonate (22.4 and 11.2 ppm), Ag + ions (5 and 2.5 ppm), and yeast extract (100 and 50 ppm) were assessed on total phenol, total avonoid, rosmarinic acid, salvianolic acid A, and caffeic acid contents in the hairy roots after 1, 3 and 5 days of exposure. Results showed the used Agrobacterium rhizogenes strains (A4, ATCC15834, R1000, GM1534, and C58C1) differed in their ability to induce hairy roots on leaf explants. The transformed roots were molecularly con rmed using rolC gene and the highest transformation frequency (56 %) was obtained by ATCC 15834 strain. Among the established hairy root lines, the highest amount of rosmarinic acid (0.45 ± 0.01 mg/g DW) and dry root biomass (2.29 ± 0.04 g) was obtained in AT3, the line which was induced by ATCC 15834 strain. The maximum accumulation of total phenol (123.6 ± 0.93 mg GAE/g DW), total avonoid (5.09 ± 0.07 mg QUE/g DW), rosmarinic acid (18.45 ± 0.8 mg/g DW), salvianolic acid A (2.11 ± 0.04 mg/g DW) and caffeic acid (2.61 ± 0.02 mg/g DW) was observed in the hairy roots elicited with 22.4 ppm methyl jasmonate on day three after treatment. The results support that elicitation could be an effective procedure for the improvement of caffeic acid derivatives production in S. virgata hairy root cultures.Furthermore, it has shown that RA and Sal-B could improve memory and cognitive impairment related to Alzheimer's disease (Shen et al. 2017;Gok et al. 2018). Chemically, CA is the basic structural unit of phenolic acids in Salvia species. Rosmarinic acid is an ester of CA and 3, 4-dihydroxyphenyllactic acid, and Sal-B is identi ed as a dimmer of RA (Wang et al. 2019) (Fig. 1).Biosynthesis of phenolic acids occurs mainly via the phenylpropanoid and tyrosine-derived pathways (Di et al. 2013). Many of the encoding genes for the critical enzymes in the biosynthetic pathways of phenolic acids, including phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), hydroxycinnamate coenzyme A ligase (4CL), tyrosine aminotransferase (TAT), 4-hydroxyphenylpyruvate reductase (HPPR), rosmarinic acid synthase (RAS), and a cytochrome P450-dependent monooxygenase (CYP98A14), were identi ed in S. miltiorrhiza (Di et al. 2013;Zhang et al. 2014;Wang et al. 2015;Xing et al. 2018b).Due to the genetic stability, large biomass output, and high biosynthetic capacity, hairy root (HR) culture is considered as an alternative technique for secondary metabolite production, compared to native plant roots and cell/callus cultures (Hu and Du 2006;Ono and Tian 2011). Moreover, the application of HR cultures in many industrial and scienti c elds, including designing of bioreactors, recombinant protein production, phytoremediation, and metabolic and genetic engineering, has been reported (Ashihara et al. 2011;Doran 2013; Kuma 2018).It has demonstrated that the ...

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