Water scarcity, one of the most damaging stresses, is responsible for the productivity losses in several crops and MAPs, especially in arid and semiarid regions (Albergaria et al., 2020). This abiotic stress, which is expected to increase in duration, frequency, and intensity as a result of climate change, affects the physiological and biochemical processes of several plants (Moustakas et al., 2022). Under water limitation, roots send a chemical signal through the xylem to the leaves, stimulating a partial stomatal closure to reduce water loss (transpiration) and prevent dehydration. As a result, there is a direct decrease in the CO₂ uptake (which is detrimental to photosynthesis) and, since NADPH is not used in the Calvin cycle, NADP⁺ is not available. These changes lead to increased levels of free radicals and ROS (Albergaria et al., 2020; Karalija et al., 2022; Moustakas et al., 2022), which negatively affect a wide range of plant processes, such as growth and development, loss of turgor leading to cell dehydration, photosynthesis, and many other metabolic parameters (Jan et al., 2018; Khare et al., 2020; Moustakas et al., 2022). Although some researchers suggest a positive effect of elevated CO₂ (resulting from fossil fuels burned by humans for energy and exacerbating the greenhouse effect) on crop yield by increasing photosynthesis, this does not appear to be sufficient to counteract the negative effects of severe drought on photosynthesis and yield (Moustakas et al., 2022). Drought tolerance traits are correlated with the accumulation of several compounds. Plants accumulate various organic solutes known as osmoregulators, osmoprotectants, or osmolytes (e.g., proline, soluble sugars, glycine betaine) to help cells maintain turgor pressure in their cytosol. Furthermore, another strategy to cope with drought stress is the enzymatic [e.g., catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), ascorbate peroxidase (APX)] and non-enzymatic antioxidant defense systems (e.g., glutathione, ascorbate, α-tocopherol, carotenoids, PC) capable of reducing ROS (Khare et al., 2020; Karalija et al., 2022; Moustakas et al., 2022).

Table 1 summarizes the effect of drought on EO and PC production in several Lamiaceae species. Salvia spp. are among the most important MAPs, and several studies have been conducted to evaluate their ability to respond to drought stress. Ramezani et al. (2020) investigated the effect of water deficit on the EO composition, namely, the five main metabolites (1,8-cineole, camphor, borneol, α- and β-thujone), in three genotypes of Salvia spp. [S. officinalis, S. reuterana (Yasuj), and S. reuterana (Urmia)] and showed that genetic differences could influence the quality and quantity of these compounds. In Salvia dolomitica Codd, drought stimulated the biosynthesis of sesquiterpene hydrocarbons, an important class of terpenoids for the pharmaceutical, food, and cosmetics industries. However, a negative effect was observed for monoterpene hydrocarbons (Caser et al., 2019). Camphor, the main oxygenated monoterpene in Salvia sinaloensis Fern (Caser et al., 2018) and Salvia fruticosa Mill (Chrysargyris et al., 2016) increased after water stress conditions. Similarly, in S. officinalis, the amount of monoterpenes increased tremendously in response to water stress, doubling after only 2 days (Radwan et al., 2017). In S. officinalis, all the EO subclasses were increased after drought exposure (Bettaieb et al., 2009).

Thymus is another genus that has been well studied in terms of drought tolerance, particularly Thymus vulgaris L., a MAP native to the western Mediterranean region of Europe. In soil-grown plants of T. vulgaris, water shortage led to a decrease in γ-terpinene content and a significant increase in thymol (Khalil et al., 2018). According to the study by Arpanahi et al. (2020), when Thymus daenensis Celak and T. vulgaris were subjected to low, mild, and severe water stress, EO content decreased in both species, although this decrease was more pronounced in T. daenensis. In other studies, the EO yield and composition in plants of this species differed among plant organs, as well as with developmental periods and growth conditions (Alavi-Samani et al., 2015; Llorens-Molina and Vacas, 2017; Mohammadi et al., 2018). With regard to in vitro culture, the major compounds of EOs from T. vulgaris callus were differentially affected by drought, with γ-terpinene increasing its content and thymol and carvacrol decreasing (Razavizadeh et al., 2019). The percentage of some chemical compounds in the EOs extracted from T. daenensis plants under reduced irrigation was higher than from unstressed plants. Nevertheless, the content of its main component (thymol) was significantly reduced under stressed conditions (Pirbalouti et al., 2014).

To investigate the effect of water shortage on the EO content of five Melissa officinalis L. genotypes, plants were irrigated with 40% of the soil water capacity for 3 months, and three of the five cultivars (‘Lorelei,’ ‘Gold Leaf,’ and ‘Quedlinburger Niederliegende’) showed no significant differences between stressed plants and the control. Nevertheless, under drought conditions, the cultivar ‘Soroksar’ increased EO production by 58%, while ‘Lemona’ accumulated only 35% (Szabó et al., 2017). To induce EO biosynthesis, holy basil (Ocimum tenuiflorum L. or O. sanctum L.) at juvenile and preflowering stages was exposed to drought stress for 5 days. In both stages, the content of three major compounds (eugenol, methyl eugenol, and β-caryophyllene) was significantly enhanced compared to the control (Nguyen et al., 2022).

Six species of the Lamiaceae family commonly cultivated in the Mediterranean region, namely, M. piperita (peppermint), Salvia lavandulifolia Vahl. (Spanish sage), Salvia sclarea L. (clary sage or clear eye), Thymus mastichina L. (Spanish marjoram), Thymus capitatus (L.) Hoff. et Link., and Lavandula latifolia Med., were subjected to water stress, and the EO content was evaluated. The results indicated that the only species affected by drought were S. sclarea and L. latifolia, with a corresponding decrease in their EO contents (García-Caparrós et al., 2019). Drought affects the chemical profile of EOs from R. officinalis. Gas chromatography/mass spectrometry (GC/MS) analysis showed that 10 volatile compounds were identified in the EOs of well-irrigated plants, while 13 volatile compounds were detected in non-irrigated plants. Linalool, limonene, 1,3-cyclopentadiene, 1,2,5,5-tetramethyl, and cyclohexane compounds were characteristic of the plants exposed to drought (Sarmoum et al., 2019). Two different subspecies of Origanum vulgare L., namely, ‘gracile’ and ‘virens,’ were exposed to mild and moderate drought, and it was observed that this stress significantly improved the EO content of gracile subsp. but did not affect the EO content of virens subsp (Morshedloo et al., 2017). The content of oxygenated monoterpenes, especially the major compound 1,8-cineole, was increased in drought-stressed Lavandula angustifolia Mill (Chrysargyris et al., 2016), S. officinalis (Kulak, 2020), and O. basilicum (Kulak, 2020). The yield and content of EOs extracted from plants such as O. basilicum (Pirbalouti et al., 2017; Kulak, 2020), Dracocephalum moldavica L (Kamalizadeh et al., 2019), Sideritis perfoliata L. subsp. perfoliate (Chrysargyris et al., 2019a), and S. officinalis (Kulak, 2020) were also higher under stressed than unstressed conditions.

As with EOs, several studies have shown that water stress affects PC production in Lamiaceae plants. The content of the main active constituents of Salvia miltiorrhiza Bunge (salvianolic acid B) (Liu et al., 2011) and S. officinalis (rosmarinic acid) grown in soil (Bettaieb et al., 2011) increased under moderate and severe water deficit. On the other hand, S. dolomitica (Caser et al., 2019) and S. sinaloensis (Caser et al., 2018) were subjected to moderate and severe drought stress, and total phenolic and flavonoid contents significantly decreased in both species compared to the control. Plantlets and callus cultures of Salvia leriifolia Benth. were exposed to polyethylene glycol (PEG) to induce osmotic stress in the culture media, and the levels of rosmarinic acid, caffeic acid, and salvianolic acid B increased significantly in all cultures grown under drought conditions (Hosseini et al., 2020). Scutellaria baicalensis Georgi is a traditional MAP known for its high flavonoid content, of which baicalin is the most important. Cheng et al. (2018) showed a significant improvement in baicalin production after subjecting S. baicalensis to moderate water stress, but this production decreased under severe stress. Drought stress also favored the production of secondary metabolites in Asiatic Moldavian dragonhead (D. moldavica), especially the phenolics rosmarinic, chlorogenic, and ρ-coumaric acids under moderate stress and caffeic acid and apigenin under higher stress conditions (Kamalizadeh et al., 2019). Thymus vulgaris plants irrigated with reduced amounts of water achieved an increase in polyphenol and flavonoid contents (Khalil et al., 2018). Thymus vulgaris in vitro cultures exposed to PEG-induced osmotic stress obtained the highest amount of total phenolics at 6% PEG (Razavizadeh et al., 2019), while in Thymus lotocephalus López and Morales, the total phenolic concentration decreased under 2%, 5%, and 7% PEG (Mansinhos et al., 2022a). Sweet basil (O. basilicum) showed an increase in total phenolic (Pirbalouti et al., 2017; Al-Huqail et al., 2020) and flavonoid contents in response to water deficit and an extremely significant decrease in carotenoid content (Al-Huqail et al., 2020). More recently, drought has been shown to improve the contents of the most abundant compounds in M. longifolia L., namely, rosmarinic, ferulic, caffeic, 2,3-dihydroxybenzoic, and 3,4-dihydroxybenzoic acids, as well as rutin. Furthermore, drought has been demonstrated to trigger the production of ρ-coumaric acid which was not detected in some accessions under control conditions (Moshrefi-Araghi et al., 2023). Other Lamiaceae species such as M. officinalis (Szabó et al., 2017), Perovskia atriplicifolia Benth., Perovskia abrotanoides Karel (Afshari et al., 2022), and L. angustifolia (Szekely-Varga et al., 2020a) improved their phenolic content when subjected to water stress.

Soil salinity is known as the accumulation of excess ions, such as chloride (Cl⁻), sodium (Na⁺), sulfate (SO₄ ²⁻), magnesium (Mg²⁺), and calcium (Ca²⁺) in the soil (Butcher et al., 2016). This problem has a major impact on soil properties, altering texture and reducing aeration, porosity, and water conductance (Mahajan et al., 2020). According to Butcher et al. (2016), there are two main causes of salinization—primary (natural) and secondary (anthropogenic) salinization. Primary (or dryland), which usually occurs in arid and semiarid regions (with low rainfall and high evapotranspiration), is caused by the capillary rise of saline groundwater and/or by the natural accumulation of salts from a saline parent material. Secondary (or irrigation) salinity has an anthropogenic cause and results from the use of poor-quality irrigation water. The main consequence is a significant inhibition of plant growth, development, and function, as salinity interferes with the uptake of water and nutrients, such as carbon and nitrogen (Cordovilla et al., 2014). This inhibition occurs through two main mechanisms: osmotic/drought stress and specific ionic effects. The first one is related to the change in the osmotic potential of the soil solution surrounding the root, which inhibits the root water uptake. As a result, similar to drought, plants use osmolytes to increase their water uptake. Specific ion effects are physiological effects of individual salt components that accumulate in organic tissues and cause toxicity. A common indicator of most excessive ion levels is membrane damage (Butcher et al., 2016). Another adaptive strategy of plants against stress is the accumulation of secondary metabolites. Several reports have shown that these compounds are significantly affected by salinity and tend to be more abundant in plants exposed to salt stress (Assaf et al., 2022).

Changes in the production of EOs and PCs in Lamiaceae species in response to salinity have been reported by several authors ( Table 2 ). Origanum is an important genus of the Lamiaceae family. The response of O. vulgare plants to soil moisture regimes using fresh and saline water irrigation was evaluated, and it was found that the EO yield decreased significantly with increasing salinity. The amount of carvacrol, the dominant compound in this species (46.44%–77.96%), decreased with salt stress, in contrast to ρ-cymene and γ-terpinene, the second and the third most abundant compounds, respectively (Said-Al Ahl and Wahby, 2010). Origanum majorana (syn. Majorana hortensis Moench), known as marjoram or sweet marjoram, is a perennial herbaceous plant native to Cyprus and the eastern Mediterranean. The salinity effect is highly significant for the EO content of this species but depends on the severity of the treatment. EO yield increased significantly up to 55.5% at moderate salinity and decreased at high salinity (Jelali et al., 2011). In another study, 50–100 mM of NaCl decreased the EO yield and the content of several individual compounds of marjoram, including the most abundant (trans-sabinene hydrate), but increased the percentages of the other predominant compounds, namely, terpinene-4-ol and cis-sabinene hydrate (Baâtour et al., 2009). Two years later, the same authors showed that the influence of this stress on the EO composition of marjoram depends on several factors, such as the plant variety (i.e., Tunisian vs. Canadian) (Baâtour et al., 2011). In 19 accessions of O. basilicum, EO content was higher under salt stress than under control conditions. All accessions showed a high content of methyl chavicol, an active ingredient of various natural pesticides, pharmaceuticals, and fragrances, and the production of anethole and related structural analogs (Akbari et al., 2018). An increase in EO yield and compound content due to salinity has also been reported in O. basilicum plants (Bernstein et al., 2010; Hassanpouraghdam et al., 2011; Tarchoune et al., 2013; Elhindi et al., 2016; Farsaraei et al., 2020). In contrast, different authors showed a negative effect of salt stress on the EO amount of O. basilicum major compounds (Bahcesular et al., 2020; Masoudniaragh et al., 2021). More recently, Es-sbihi et al. (2021) investigated how salt stress affected the chemical profile of S. officinalis and found important changes in the composition of EO. NaCl decreased the EO yield from 1.2% to 0.4%, and while α-thujone, camphor, and 1,8-cineole were the major compounds of EOs under control treatment, these three components decreased in stressed plants, and thujanone emerged as a new major compound. Other reports also showed a strong effect of salt stress on the EO composition of Salvia spp. but with different results, especially depending on the salt concentration (Taarit et al., 2009; Valifard et al., 2014; Kulak et al., 2020). In S. sclarea, the application of 25 mM NaCl significantly increased the oil yield which decreased with increasing salt concentration (Taarit et al., 2011). Years later, the same authors found that the transcript of the cineole synthase 1 gene (SmCin1) accumulated in the leaves (11-fold) during the first hours of salinity treatment compared to the control.

Mentha sp. is another important Lamiaceae genera with a wide range of culinary and aromatic uses, mainly due to their richness in EOs. Aziz et al. (2008) compared the effect of salt stress on the EO chemical composition of pennyroyal (Mentha pulegium L.), peppermint (Mentha piperita), and apple mint (Mentha suaveolens Ehrh.) and observed that the EO yields of the three species decreased compared to the untreated controls. The same occurred in M. piperita in another study, where the increase in salinity led to a decrease in EO content (Çoban and Göktürk Baydar, 2016). In hydroponically grown Mentha spicata L. plants, the highest amount of NaCl tested by the authors (100 mM) was the only one that improved the EO yield (Chrysargyris et al., 2019b). In hydroponically grown M. spicata plants, 150 mM of NaCl did not affect the total EO content, but there was an increase in total monoterpene hydrocarbons and a decrease in total oxygenated monoterpenes (Chrysargyris et al., 2019c).

The use of rosemary (R. officinalis) in the Mediterranean region is an attractive solution to avoid desertification and rapid soil erosion due to its great high resistance to environmental conditions (Sarmoum et al., 2019). Bidgoli et al. (2019) found a significant relationship between the percentage of rosemary EO and the increasing salinity stress. More specifically, in another study with R. officinalis, salinity altered the major EO compounds, strongly increasing the content of camphor, borneol, linalool, and verbenone, but decreasing β-pinene, α-pinene, and 1,8-cineole (El-Esawi et al., 2017). On the other hand, a 50% decrease in 1,8-cineole content was observed with increasing NaCl concentration (Tounekti et al., 2008). In the case of Thymus maroccanus Ball., which behaved as a moderately salt-tolerant species, the EO content did not change with increasing salt concentration (Belaqziz et al., 2009). An important finding was reported by Cordovilla et al. (2014), who showed that plant–plant interactions play a crucial role in stress tolerance. These authors studied the effects of salinity and the interaction between T. vulgaris and L. angustifolia and found that both plants grown alone were more tolerant to salt stress than when grown together. When exposed to the highest stress intensity (100 mM NaCl), all lavender plants survived, whereas thyme plants died. EO production increased with salinity in T. vulgaris, whereas in lavender, it depended on the presence of thyme. Salinity has an obvious effect on Lavandula stoechas L. (Vojodi Mehrabani et al., 2017; Valizadeh-Kamran et al., 2019), strongly influencing the EO composition. According to some authors, this could be due to the disruption of cytokine transport from roots to shoots and consequently changes in the ratio of cytokines and abscisic acid (Vojodi Mehrabani et al., 2017). A decrease in EO yield from M. officinalis under salt stress was observed although the number of new compounds increased. For example, neryl acetate and geranyl acetate were detected at 100–200 mM of NaCl, suggesting that this species activates the metabolic pathways to produce monoterpenes under salinity (Bonacina et al., 2017).

In addition to EO, salt stress altered the production of PCs by increasing its concentration in the tissues although it limited the biomass production of the plants (Baâtour et al., 2012). The highest levels of PCs were recorded in several Lamiaceae species grown in a medium containing NaCl (Baâtour et al., 2012; Valifard et al., 2014; Vojodi Mehrabani et al., 2017; Valizadeh-Kamran et al., 2019). A recent study investigated the influence of salinity on the production of PCs by two subspecies of O. vulgare, namely ssp. gracile and vulgare. The results indicated an improvement in the contents of quercetin and gallic, caffeic, and chlorogenic acids in ssp. gracile and quercetin and caffeic and cinnamic acids in ssp. vulgare following salt stress (Azimzadeh et al., 2023). Baâtour et al. (2012) investigated the effect of salinity on phenolics production by O. majorana at three developmental stages (early vegetative stage, late or preflowering vegetative stage, and flowering stage). The authors observed that salt stress led to an increase in total and individual phenolic contents (e.g., gallic acid, caffeic acid, and amentoflavone) particularly at the late or preflowering vegetative stage. In the flowering stage, salinity caused a significant stimulation of other phenolic acids (caffeic, syringic, chlorogenic, cinnamic, dihydroxyphenolic, and trans-2-hydrocinnamic acids). Furthermore, the degree of salinity stress (moderate or high) significantly influenced the phenolic content of O. majorana (Jelali et al., 2011). The results of different studies showed that the positive or negative effects of salinity on basil (O. basilicum) depend on the degree of tolerance of the different genotypes. For example, when comparing green Iranian and Genovese basil, salinity stress improved the phenolic acid content only in the former (Bekhradi et al., 2015). In the case of O. basilicum ‘Sweet Broadleaf’ and ‘Siam Queen’ cultivars, salt stress increased the leaf content of the two main phenolics (quercetin-rutinoside and rosmarinic acid) only in the ‘Sweet Broadleaf’ cultivar (Scagel et al., 2019). A salt-induced improvement in PC biosynthesis has also been described in Salvia mirzayanii (Valifard et al., 2014), M. piperita (Çoban and Göktürk Baydar, 2016; Khalvandi et al., 2019), M. pulegium (Oueslati et al., 2010), L. stoechas (Valizadeh-Kamran et al., 2019), Dracocephalum kotschyi Boiss (Vafadar et al., 2020), and Perilla frutescens L. Britt (Rouphael et al., 2019). In the case of L. angustifolia, flavonoids have been shown to play an important role in salinity tolerance (Szekely-Varga et al., 2020a). On the other hand, in other Lamiaceae species, such as Salvia coccinea (Grzeszczuk et al., 2018) and Salvia macrosiphon Boiss (Valifard et al., 2017), salinity-exposed plants showed a reduced accumulation of phenolics. Cinnamic acid was the major constituent in T. daenensis and T. vulgaris, and the concentration of 60 mM NaCl increased its content by more than 30% in both species compared to the control (Bistgani et al., 2019). With regard to rosmarinic acid, the most abundant compound in several Lamiaceae species, the results found in the literature vary, with significant decreases (Baâtour et al., 2012; Bahcesular et al., 2020) or increases (Bistgani et al., 2019; Rouphael et al., 2019; Scagel et al., 2019; Vafadar et al., 2020) in its content observed under salinity stress.

Temperature is also one of the most important abiotic factors limiting plant growth and productivity (Israel et al., 2022). Heat and cold stresses affect various physiological, biochemical, and molecular plant characteristics (Mahajan et al., 2020). High temperature can induce leaf senescence and damage to cell membranes, chlorophylls, and proteins (Mansinhos et al., 2022b). Cold stress is also known to be one of the most damaging abiotic stresses, resulting in morphological changes, such as reduced biomass, reduced leaf surface area, leaf curling, and abscission. Biochemically, low temperature stimulates the biosynthesis of ROS, leading to the oxidation of proteins and lipids (Lianopoulou and Bosabalidis, 2014). The transcriptome and metabolism of plants are also significantly affected by cold, probably due to the direct inhibition of metabolic enzymes at low temperatures (Rastogi et al., 2019). Temperature strongly affects the production of secondary metabolites. However, reports on the effect of temperature on the EO content or phenolic profile of aromatic plants remain limited. The studies available in the literature on the effect of temperature stress on the production of EOs and PCs in Lamiaceae species are presented in Table 3 .

Some studies have shown that EO composition is affected by low temperatures. For example, O. tenuiflorum, an Ocimum species that grows well in tropical, subtropical, and warm temperate regions, was exposed to cold stress (4°C) for 5 days. After this period, the eugenol content increased from 17.7 to 45.2 mg/g_FW at the juvenile stage (30 days old). A significant improvement in methyleugenol and β-caryophyllene content was also observed at the juvenile and preflowering stages (Nguyen et al., 2022). On the other hand, other authors reported that eugenol and methyl eugenol concentrations in O. tenuiflorum EO decreased under cold conditions (Rastogi et al., 2019). O. basilicum plants were exposed to different temperatures of 4°C, 10°C, and 22°C (control) for 12 h, 24 h, and 48 h, and significant differences between treatments were found for almost all EO compounds. Linalool was the main compound, but there were no differences between the cold treatments and the control. On the contrary, the highest amount of the sesquiterpene germacrene D (the second most abundant compound) was found at 10°C for 12 h. In the case of geraniol and γ-cadinene, their maximum levels were observed at 4°C for 24 h (Senji and Mandoulakani, 2018). Lianopoulou and Bosabalidis (2014) compared the EO composition of Origanum dictamnus L. in winter and summer and observed that in summer, these plants produced more than twice the EO yield at higher temperatures than at lower temperatures. According to the authors, this higher EO yield in summer is correlated with the greater number of peltate glandular hairs found on summer leaves. This means that peltate hairs (and especially their head cells) are the only cells of all leaf tissues that possess the required enzymatic apparatus required for EO biosynthesis. Regarding the EO profile, there was also a variation in the main compounds, with the most abundant compound being ρ-cymene (59.2%) in winter and carvacrol (42.4%) in summer. Interestingly, the same authors repeated the same study on another Lamiaceae species, Teucrium polium L., and observed the opposite results, a significantly higher EO yield of winter leaves compared to summer leaves. Nevertheless, the authors again correlated the higher EO yield with the higher number of peltate glandular hairs in winter leaves (Lianopoulou et al., 2014). The maximum content and yield of Thymus transcaucasicus Ronn. EO were observed at 25°C compared to 15°C and 20°C (Manukyan, 2019).

There are some studies in the literature related to heat stress. Plant extracts of R. officinalis are routinely used for food preservation and cooking, cosmetics, or in herbal medicine for anti-inflammatory and antimicrobial purposes, as well as for the treatment of diabetes and cardiovascular disorders (Degner et al., 2009). Two accessions of this species were exposed to 12°C/6°C day/night, and both accessions showed an increase in carnosic and caffeic acid levels, while rosmarinic acid, carnosol, naringin, hispidulin, and cirsimaritin showed different responses (Luis et al., 2007). Elevated temperature (2.5°C–3.0°C above ambient) had a significant effect on the EO composition of S. sclarea, especially for the abundant linalyl acetate, almost doubling its concentration (Kumar et al., 2020). Similarly, the pattern of the monoterpene linalool, the most abundant component of the EO of L. angustifolia, was affected by temperature (Hassiotis et al., 2014). Linalool is widely used as an additive in 60%–80% of perfumed hygiene and cleaning products such as detergents, lotions, soaps, and shampoos and as an insecticide against fruit flies, cockroaches, and fleas (Senji and Mandoulakani, 2018). Some reports were found in the literature regarding the influence of temperature on PC biosynthesis. Recently, the effect of different temperature treatments (15°C, 20°C, 25°C, and 30°C) on the phenolic profile of in vitro cultures and micropropagated plants of two Mediterranean aromatic plants, T. lotocephalus and Lavandula viridis L’Hér, was evaluated. For both species, the production of phenolic acids (especially rosmarinic acid) increased with increasing temperature in micropropagated plants, whereas the opposite was observed in in vitro cultures (Mansinhos et al., 2022b). Another study also investigated the effect of constant air temperature (15°C, 20°C, and 25°C) on phenolic production of T. transcaucasicus plants grown in pots, and the temperature of 25°C was the most favorable for the best recovery of rosmarinic acid (Manukyan, 2019). Temperature stress led to a significant increase in total phenolics and flavonoids in basil (O. basilicum) leaves subjected to the highest temperature treatment (55°C) (Al-Huqail et al., 2020). In spearmint (M. spicata), heat significantly reduced the levels of total phenolic acids and especially rosmarinic acid (Fletcher et al., 2005). A high accumulation of rosmarinic acid was also obtained in M. officinalis under heat stress (38°C for 5 h) (Pistelli et al., 2019).

The three main factors of light that strongly affect plant growth and other physiologic, biochemical, and metabolic processes are quality, quantity, and duration (Israel et al., 2022; Gonçalves et al., 2023). Despite the importance of light in several plant processes, it can also act as a stress factor. Secondary metabolites play an essential role in coping with light stress. The impact of light stress on the biosynthesis of EO and PC in Lamiaceae species is presented in Table 4 . The spectral quality of light is a common parameter that is typically accessed through the use of light-emitting diodes (LEDs). For example, O. basilicum, one of the most extensively studied species within the Lamiaceae family, was cultivated under four distinct monochromatic light sources, each of which was irradiated with a specific wavelength: blue (470 nm), blue-green (500 nm), green (525 nm), and red (660 nm). After 70 days, the authors observed that the greatest concentration of EO was observed in the leaves grown under blue light and that 1,8-cineole was the most abundant compound, irrespective of light quality (Amaki et al., 2011). Similarly, P. abrotanoides and P. atriplicifolia were subjected to four distinct artificial light treatments (red, blue, red-blue, and white) generated by LEDs. The results indicated that the highest wavelengths caused a reduction and an increase in monoterpene and sesquiterpene contents, respectively (Ghaffari et al., 2019). The production of EOs from other Lamiaceae species, including M. piperita, M. spicata, and M. longifolia, was enhanced by the application of LED treatments (Sabzalian et al., 2014).

The impact of UV radiation on plants is a topic that has been extensively researched. Although the Earth’s surface only receives 20% of UV-B radiation, this energy provides sufficient energy to cause several biological injuries to plants, including damage to DNA. For this reason, UV-B is the most extensively studied type of UV radiation (Mansinhos et al., 2024). The plant photoreceptors of plants respond to UV-B radiation, regulating plant growth and metabolism. This increases the plant’s capability to protect itself from the harmful consequences of UV radiation (Hosseinabadi et al., 2024). Chang et al. (2008) investigated the impact of solar irradiance and UV-B radiation (Chang et al., 2009) on O. basilicum, demonstrating a positive effect of both treatments on linalool, a key taste compound in basil. Similarly, O. sanctum was subjected to UV-B radiation. While the content of the EO major compound (eugenol) was not affected by the treatment, the EO yield increased by 42% (Kumari and Agrawal, 2011). The analysis of volatile oils in fresh leaf samples of basil demonstrated that UV-B irradiation also stimulated the synthesis of 1,8-cineole and linalool. In contrast, no effect was observed on the volatile composition of the EO. The (partial) absence of light can also serve as a stimulus for the production of bioactive compounds. Aeollanthus suaveolens, popularly known as Catinga-de-mulata, is employed by the Amazonian population for the treatment of pain. The chemical profile of this medicinal plant was studied in response to two light intensities, namely, 50% and 100% of sunlight. It was observed that the concentration of the most abundant compound (E)-β-farnesene was increased by half shade treatment (Barbosa et al., 2021). Additionally, intermediate shading (50% of sunlight) demonstrated a beneficial impact on the yield of R. officinalis EO, resulting in an increase of 29% compared to full solar irradiance (Raffo et al., 2020). Conversely, the impact of prolonged darkness on the composition of EO from this species was examined, and no discernible differences in monoterpenes and sesquiterpenes were observed between the light- and dark-grown leaves (Böszörményi et al., 2020). In a recent study, Hosseinabadi et al. (2024) examined the impact of varying harvesting times on the yield of EO from M. officinalis. Their findings indicated a positive correlation between the increase in UV-B levels during the summer months and the EO yield. The influence of photosynthetically active radiation (PAR) and UV-B radiation on the EO of sage (S. officinalis), lemon balm (M. officinalis), and lemon catmint (Nepeta cataria L.) was investigated by Manukyan (2013). The highest yield and content of EO were observed in N. cataria, with both parameters significantly enhanced by both radiations. In the case of S. officinalis, no significant differences were observed. In contrast, the radiation displayed a negative effect on the EO content of M. officinalis.

The utilization of spectrally tunable LEDs for elicitation has also demonstrated promising potential for augmenting PC production in several species, including M. officinalis (Chai et al., 2023), Plectranthus scutellarioides L (Dörr et al., 2019), Agastache rugosa (Fischer & C.A. Meyer) O. Kuntze (Zielińska et al., 2019), and Nepeta nuda L. (Petrova et al., 2022). In a recent study, Chai et al. (2023) evaluated the impact of three distinct light treatments on rosmarinic acid production. The treatments included a) three different spectrally tuned light treatments, b) white LED, and c) sunlight. The optimal result was achieved with the blue-enriched light treatment (red:blue:green:far-red, 40%:35%:15%:10%). Additionally, the leaves of P. scutellarioides grown with a ceramic metal halide lamp (CDM) and LED light exhibited the highest concentration of rosmarinic acid (Dörr et al., 2019).

In addition to the type of light, the intensity of light also influences the production of PC. In the case of N. nuda, the high light intensity of LEDs (blue:red:far-red, 15%:75%:10%) stimulated the production of PC-like compounds, including rosmarinic acid, isoquercetin, rutin, cirsimaritin, and naringenin. Conversely, a lower intensity significantly upregulated the production of chlorogenic acid (Petrova et al., 2022). With regard to ultraviolet radiation, there is substantial evidence indicating the considerable impact of UV-B radiation on the production of PC (Luis et al., 2007; Sakalauskaitė et al., 2012; Tang et al., 2014). O. basilicum was subjected to two different intensities of UV-B radiation (2 kJ m⁻² day^-1 and 4 kJ m⁻² day^-1) for 7 days. A comparison with the control revealed that the total PC levels were significantly higher in both UV treatments (Sakalauskaitė et al., 2012). The application of UV-B radiation resulted in an increase in the concentrations of rosmarinic and carnosic acids in rosemary plants, as well as naringin and carnosol (Luis et al., 2007). Similarly, the use of different UV-B light intensities was found to activate chrysin synthesis in S. baicalensis L., which was not detected in the control plants (Tang et al., 2014). The impact of UV-B radiation and PAR on PC production was also investigated in S. officinalis, M. officinalis, and N. cataria. The application of PAR treatment was found to be conducive to PC accumulation in M. officinalis, while intensive UV-B radiation was observed to stimulate the highest PC production in S. officinalis (Manukyan, 2013). Furthermore, PAR enhanced the biosynthesis of the phenolic acids rosmarinic, caffeic, and ferulic in Moluccella laevis L (Zielińska et al., 2020).

The accumulation of heavy metals (HMs) in the soil, air, and water is influenced by a number of factors, including metal industries, mining, and intensive agriculture. These activities can lead to the accumulation of essential HMs, such as copper (Cu), iron (Fe), zinc (Zn), and magnesium (Mg), which are required for plant growth and development. However, they can also result in the accumulation of non-essential HMs, such as lead (Pb), nickel (Ni), arsenic (As), mercury (Hg), chromium (Cr), and cadmium (Cd), in excess of acceptable limits (Mishra and Chandra, 2022; Gonçalves et al., 2023; Das et al., 2024). Soil contamination with HMs represents a significant environmental concern, with significant implications for human health. HMs can disrupt the normal functioning of the organs, leading to a range of illnesses, including abdominal pain, skin eruptions, ulcers, and cancer (Jezler et al., 2015). Furthermore, HMs are a significant threat to plant health, impeding photosynthesis, respiration, and nutrient uptake. The literature indicates that essential HMs are harmful to plants when present in high amounts, whereas non-essential metals are particularly injurious even when present in small concentrations (Mishra and Chandra, 2022; Das et al., 2024). In order to mitigate the effects of free radicals associated with HM stress, plants typically accumulate elevated levels of secondary metabolites that function as antioxidant agents (Gonçalves et al., 2023). Table 5 presents a summary of the effects of HM stress on the production of EOs and PCs of MAPs from the Lamiaceae family. A number of studies have been conducted in the literature which report the impact of HMs on the EOs of Ocimum spp. (Rai et al., 2004; Zheljazkov et al., 2006; Prasad et al., 2011; Siddiqui et al., 2013; Fattahi et al., 2019). The composition of the EOs of O. basilicum was found to be altered by the presence of Ni, Cr, Cd, and Pb, with the type and concentration of the HMs influencing the extent of the changes (Prasad et al., 2011). Fattahi et al. (2019) reported that Cd and Pb stimulated the EO yield and induced a positive influence on EO composition, with a notable impact on the production of its most abundant compound estragole. Similarly, Cd and Pb (individually and in combination) enhanced the limonene and 1,8-cineole contents in O. basilicum EOs, yet had no impact on the content of their major compounds menthol and menthone (Zheljazkov et al., 2006). O. tenuiflorum L. was subjected to a range of Cr concentrations (10, 20, 50, and 100 mM), which resulted in the production of eugenol, its major compound, particularly at 20 mM (Rai et al., 2004). Lower doses of As induced the accumulation of the major compounds (eugenol, methyl chavicol, and linalool) of O. tenuiflorum, O. basilicum, and O. gratissimum L. EOs. It is encouraging to note that no evidence of As was found in the EOs of any species, which makes these EOs suitable for industrial applications (Siddiqui et al., 2013).

Mentha is another Lamiaceae genus extensively studied in terms of EO production in response to HM stress (Zheljazkov et al., 2006; Prasad et al., 2010; Affholder et al., 2013; Jezler et al., 2015; Sá et al., 2015; Kilic and Kilic, 2017; Lajayer et al., 2017; Azimychetabi et al., 2021). The application of Cu (5 mg kg⁻¹) and Zn (10 mg kg⁻¹) (Lajayer et al., 2017) resulted in an increase in the yield and content of EO in M. pulegium. The presence of Cd (10–40 ppm) was found to decrease the major compound, menthol, while simultaneously increasing the menthofuran and pulegone contents in M. piperita EO (Azimychetabi et al., 2021). In a recent study, Safarian et al. (2023) demonstrated that the relative abundance of the enzymes menthol reductase and pulegone reductase were upregulated in M. piperita, in contrast to menthofuran synthase, which was downregulated during Pb stress. Furthermore, the authors demonstrated the crucial role of menthol in mitigating the effects of this environmental stress. In Mentha arvensis L., the cellular alterations induced by HM application (Pb and Cd, 8–128 mg kg⁻¹) were insufficient to produce phytotoxicity in the plant or modify the EO yield (Jezler et al., 2015). A pot culture experiment was conducted to investigate the impact of two concentrations (30 and 60 mg kg⁻¹) of Cr and Pb on the yield and chemical composition of EOs from three plant species: marjoram (M. arvensis), bergamot mint (M. citrata Ehrh.), and peppermint (M. piperita). The EO content of the three species decreased with both concentrations of both metals but increased EO yield in M. piperita. The effect of increasing concentrations of Pb (900, 1,800, 3,600, 7,200, and 9,000 mg kg⁻¹) on the yield and chemical composition of EO of garden mint (Mentha crispa L.) was investigated. The EO yield was approximately 10-fold higher under extreme contamination conditions compared to that produced by the control. Moreover, although the majority of compounds were not detected under the Pb context, the content of its major component (carvone) increased from 39.3% (control) to 85.32%–95.04% after growth in Pb-contaminated soils (Sá et al., 2015). The presence of Cd in the soil negatively influenced the EO content in M. officinalis L. subsp. officinalis. The highest Cd concentration (30 mg kg⁻¹) resulted in a 97% decrease in EO content (Kilic and Kilic, 2017). Conversely, an increased biosynthesis of sesquiterpenes in EO was observed in rosemary plants growing in contaminated regions with Pb, As, Zn, and Cu (Affholder et al., 2013). The presence of heavy metals, including Cd, Zn, Cu, and Pb, in the environment resulted in a reduction in the concentrations of α-thujon, β-thujon, viridoflorol, and β-cariophyllene in the EOs of S. officinalis. Conversely, the levels of 1,8-cineole, camphor, bornylacetate, and borneol were significantly enhanced (Stancheva et al., 2009).

A limited number of studies were identified in the literature that examined the influence of HMs on the biosynthesis of PCs in Lamiaceae species. Basilicum polystachyon (L.) Moench, a MAP found in Asia, Africa, and India, was cultivated in vitro with mercury (II) chloride and lead (II) nitrate. In cultures exposed to Hg and Pb, the esterified forms of vanillic acid and caffeic acid were respectively the major PCs, which were not detected in the control (Das et al., 2024). In a further in vitro study, using cell suspension cultures, O. basilicum was exposed to different concentrations (5–200 µM) of cadmium chloride (CdCl₂) (Açıkgöz, 2020). The highest contents of rosmarinic and chicoric acids were achieved at 5 µM, while the highest accumulation of the flavonoids rutin and quercetin was observed at 10 µM. Finally, the effect of three HMs (Ni, Cu, Zn), at distinct concentrations, was studied in O. vulgare. It was observed that increasing levels of Zn and Cu caused a decrease in the PC concentration (Kulbat-Warycha et al., 2020).