## 1 Introduction
### Salt Tolerance Mechanism of Halophytes: Role of Secondary Metabolites
#### 1.3.1. Modification in Morphology or Anatomy  
Salt stress induces anatomical modifications in roots, stems, and leaves of halophytes. Under high salinity, _C. cilliaris_ conserved water by increasing sclerification in the cortex and pH region and decreasing root thickness with a greater proportion of parenchyma cells, and rich density of vesicular hairs and trichomes on leaves might be essential for water conservation and salt excretion [28]. The pattern of adaptation is species specific and variable among different species, i.e., _Salicontia perennas_ (C\({}_{3}\) sp.) showed larger variation in leaf functional traits, both at the level of cell morphology and membrane system (chloroplast envelope and thylakoid); however, _Climacoptera crassa_ (C\({}_{4}\) sp.) showed an increase of the mesophyll cell surface, expansion of the interface area between mesophyll and bundle sheath cells, and an increased volume of the latter [29]. These modifications were compensated for the scarce CO\({}_{2}\) supply and increased salt concentration. _Chloris gayana_ is a C\({}_{4}\) monocot halophyte that tolerates salinity by accumulating the highest level of Na\({}^{+}\) and Cl\({}^{-}\) in xylem parenchyma and epidermal cells but maintaining the lowest level in photosynthetically active mesophyll and bundle sheath cells. Furthermore, it was lowered more than in respective vacuoles [30]. Several genotypes of _Trifolium fragjferum_ were grown at different salinity levels in controlled conditions. The accumulation of mineralome was both genotypic and organ specific. Maximum Na\({}^{+}\) and Cl\({}^{-}\) were accumulated \begin{table}
\begin{tabular}{c c c} \hline \hline
**Species** & **Secondary Metabolites** & **Economic Value** & **Reference** \\ \hline _Suada fraticosa_ & & Effective against _B. subtilis, P. aeruginosa,_ & [15] \\ _Cenchurus cilliaris_ & Stigmasta-5, 22-Dien-3-ol, & and _S. aureus_ & [16] \\ _Cenchurus cilliaris_ & 6,6-Dideutero-nonen-1-ol-3 & & Used in Pharmaceutical Industry & [16] \\ _Chenopodium quinaa_ & Phytoesteroids and polyphenols & Seed protein content twice that of rice, & [17] \\ _Lespedeza bicolor_ & Ptreocarpans, lespedezol, dihydrobespedezol_ & & Significant virucidal activity & [18] \\ _Sunada vermiculata_, & Camphor, benzoic acid ester, borneol, \(\alpha\) & antimicrobial and antioxidant activity & [19] \\ _Salsola cyclophila_ & Tarpineol, hexahydrofaresyl acetone & & \\ _Thumus gisunloats_, & thymol, alpha pinene & as natural pesticide in organic agriculture & [20] \\ _Saturaj cuneifolia_ & & bactericidal activity against _B. subtilis_ and & \\ _Tamura africana_, & Rutin, Gallic acid, Kaempferol 3-O-glucose & _S. aureus_, strong antifungal effect against & [21] \\ _Suada fraticosa_ & & _C. albicans_ & \\ _Tecticornia sp._ & Celossianin II, isocolosianin II, & indigenous edible halophyte in Australia & [22] \\ _Canyphire_ & carvacrol, 2,3-dimethoxybenzoic acid, & In vitro inhibition of diabetes-related \\ _Armitism L._ & naringenin, catechhin, and t-cinamic acid & enzymes, antioxidant potential & [23] \\ _Artemisia sampestris_ & quinic, chlorogenic and caffe acids, coumarin & Pharmaceutical, cosmetic, and/or & [24] \\ _subsp. marnitma_ & sulfates, and dicafoylquinic acids & food industries & \\ _Limonium algarrenese_ & & & \\ \multicolumn{2}{c}{} & extract metabolites present in leaves & Antioxidant, anti-inflammatory, & \\ \multicolumn{2}{c}{} & extract identified through & neuroprotective, and & [25] \\ \multicolumn{2}{c}{} & LC-ESI(r)-HRMS/MS & & \\ \multicolumn{2}{c}{} & quercetin and myricetin or myricetin & & \\ \multicolumn{2}{c}{} & 3-rhamoside & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont. in leaf petioles followed by leaf blades and stolons; the Zn concentration increased in all plant parts, and the Ca\({}^{+2}\) and Mg\({}^{+2}\) concentrations decreased [31]. In another study, it was reported that _T. fragiferum_ showed high competitive ability based on better physiological salinity tolerance [32]. _Solanum chilense_ is a halophyte sp.