Influence of growth regulators on growth and secondary metabolites of some medicinal plants from Lamiaceae family.
Medicinal plants have an important value in the socio-cultural, spiritual and medicinal use in rural and tribal lives of the developing countries [13,47,48,49,50]. People around the world use between 50,000 to 80,000 flowering plants for medicinal purposes . Medicinal and aromatic plants, are known to be used by 70% to 80 % of global population for their medicinal therapeutic effects as estimated by WHO .
The Lamiaceae (Labiatae) is one of the most diverse and widespread plant families in terms of ethnomedicine and its medicinal value is based on the volatile oils concentration . The Lamiaceae plant family is one of the largest families among the dicotyledons, being composed of more than 240 genera, many species belonging to the family being highly aromatic, due to the presence of external glandular structures that produce volatile oil . This oil is important in pesticide, pharmaceutical, flavouring, perfumery, fragrance and cosmetic industries .
Essential oils are the most important raw materials of the fragrance and aroma industry. They are also used in the food and pharmaceutical industries due to their therapeutic, antimicrobial and antioxidant activities. Nevertheless, they have biological activities that make them able to be used as herbicides, pesticides and anticancer compounds [1,6,18].
The aroma and fragrance industry is a billion-dollar world market which grows annually. Essential oils comprise the majority of compounds used by these industries. These sets of metabolites are formed mainly by monoterpenes, which are products of the plant's secondary metabolism. Biosynthesized from mevalonate and methylerythitol phosphate, the essential oil production depends not only on genetic factors and the developmental stage of plants, but also on environmental factors which could result in biochemical and physiological alterations in plants modifying the quantity and quality of the essential oil. These modifications impair aromatic plant production aimed at essential oil by reducing their quality. It is desirable to develop techniques of agronomical management to improve essential oil products and their specific compounds. Among other factors influencing essential oil production are plant growth regulators or plant hormones. Endogenous levels as well exogenous application could affect essential oil production and chemical composition .
The environmental factors can influence biochemical pathways and physiological processes that alter plant metabolism such as essential oil biosynthesis .
If we accept that growth regulators influence plant growth and development, affecting physiological and biochemical processes, or even gene regulation, there are numerous ways in which applications of those compounds could alter the essential oil production .
Growth regulators can influence essential oil production through effects on plant growth (biomass of leaves or flowers), essential oil biosynthesis and the number of oil storage structures. On the other hand, the time of exogenous application and kind of growth regulators can affect essential oil content.
This review summarizes experimental researches about growth regulators and their effects on growth and essential oil of some medicinal plants from Lamiaceae family.
The influence of phenylurea cytokinins DROPP and 4PU-30 on essential oil composition (GC analysis) of cineole-type spearmint cultivar CS-8-7 was studied. Increase of the major components 1,8-cineole (with 13.8- 22.5%) and p-cymene (with 13-16.5%) and nearly double decrease of carvacrol and thymol was observed. Since these alterations affected insignificantly the essential oil quality, they recommended application of 4PU-30 at 25 mg [L.sup.-1] and DROPP at 100 mg [L.sup.-1] in case the productivity and composition of essential oil were well-balanced and the specific pharmacological activity could be guaranteed .
In mint (Mentha arvensis) the use of 200 ppm of Kinetine resulted in an increase of biomass and essential oil yield .
Zlatev et al. [44,45,46], Iliev et al.  and Iliev [14,15] have established an increase of productivity of herbage, essential oil and rhizomes in M. piperita L. without unfavourable changes in essential oil composition after treatment with purine-type and urea-type cytokinins. The authors recommended phenylureatype cytokinins for practical use because, compared to purine-type, they are more active, not expensive and non toxic.
Applications of different forms of brassinosteroid analogues (ketonic and lactonic spirostane) resulted in an increase of fresh weight of leaves and higher menthol production in M. arvensis L. .
In field experiments with Japanese mint using different growth retardants, chlormequat chloride (2-chloroethyltrimethylammonium chloride) increased the oil content significantly and inhibited growth to some extent only, whilst ethephon (2-chloroethyl phosphonic acid) at 0.06% concentration significantly decreased growth but had no significant effect on oil content. Among the two oil components studied, menthone content only was significantly increased by 0.06% ethephon whereas the other growth retardants were ineffective. Correlation studies indicated a strong negative relationship of leaf/stem ratio with plant height and herb yield while a strong positive relationship was obtained between the latter two characters. The oil content of the plant was negatively correlated with herb yield and plant height but it was related positively with leaf/stem ratio .
In a study, application of 50 mg [L.sup.-1] cytokinin (BAP) on M. piperita L., at 15 and 30 days after the beginning of the experiment, resulted in an increase of plant dry matter. The time of application did not affect oil yield, but changed its chemical composition .
The effects of growth regulator applications (kinetin, IAA and Paclobutrazol) on field grown Salvia sclarea L. were studied during 2005 to 2006 at the Institute of Himalayan Bioresource Technology, Palampur, India. Growth was monitored by measuring plant height, canopy spread, leaf number, primary branches, and yield characteristics (inflorescence length and flower and oil yield). Quality was evaluated. Maximum height and leaf numbers were observed after application of kinetin 10 [micro]L [L.sup.-1] and IAA 50 [micro]L [L.sup.-1], respectively. Maximum flower and oil yield were observed after application with 40 [micro]L [L.sup.-1] paclobutrazol (PBZ) application. Application of 80 [micro]L [L.sup.-1] paclobutrazol increased the linalool-linalyl acetate content of the plant about 12% higher than the untreated control .
An experiment was conducted to evaluate the effect of gibberellic acid (GA) on sage (S. officinalis) plants. Application of 100 mg [L.sup.-1] GA resulted in higher essential oil content compared to control . The essential oil yield and chemical composition of S. officinalis L. have been analyzed. Leaf samples for essential oil analysis were harvested at different developmental stages after treatment with foliar fertilizer Agroleaf and foliar fertilizer + thidiazuron. In total, 10 constituents were identified and quantified. The main compounds in the essential oil that increased during the vegetative to the fruiting-set stage are a-thujon and camphor, whereas borneol, viridoflorol, and manool decreased. The effect of thidiazuron applied together with foliar fertilizer was established mainly at the flowering stage, increased essential oil yield by 16% over the control, and positively affected the percentage of [beta]-caryiophylene, a-humulene, viridoflorol, and manool. Application of foliar fertilizer resulted in a greater increase of essential oil yield at the flowering stage in the combined foliar and thidiazuron application over the control. Both treatments decreased camphor at flowering and fruiting stages .
In S. officinalis and Mentha piperita plants, enzymes that participate in the synthesis of compounds present in essential oil were extracted after treatment with 10 ppm of diphenylurea. It was observed that the activities of analyzed enzymes (bornyl pyrophosphate cyclase from S. officinalis and limonene cyclase from M. piperita) were higher in plants treated with hormone. Thus, the authors demonstrated that cytokinin foliar application stimulated essential oil accumulation, at least due to the direct effect on metabolism of monoterpenoids .
The study was conducted to determine the response of essential oils content and constituents, phenolic components and polyphenol oxidase (PPO) activity of thyme plants (Thymus vulgaris L.) to different bioregulators (gibberellic acid, GA3, indole3-butyric acid, IBA, benzyladenine, BA) and vitamins (ascorbic acid, thiamine and nicotinamide). Three cuttings were periodically sampled of the treated and untreated plants. Essential oil percent and its constituents, total phenolic compounds and their components as well as polyphenol oxidase activity were significantly affected by the foliar application of bioregulators and vitamins used. The results revealed the effectiveness of certain bioregulators or vitamins at each cutting for increasing essential oil content (in particular thymol and carvacrol) as well as phenolic compounds (in particular rosmarinic acid). The greatest oil percent was obtained at treatment 30 mg [L.sup.-1] of BA or nicotinamide in the herb sampled at cutting I and the increase in oil percent was 36 and 27%, respectively, over the control. At cuttings II and III, the essential oil percents were significantly decreased at most treatments, more so with 30 and 60 mg [L.sup.-1] GA3 .
Fraternali et al.  showed the effect of growth regulators on formation of storage structure in T. mastichina. Higher yield of essential oil was achieved in the medium with benzyladenine (BA) at a concentration of 0.1 mg [L.sup.-1]. plants treated with BA had a larger density of glandular hairs in their leaves. Najafian et al.  investigated the role of salicylic acid (SA) in inducing plant tolerance to salinity. The application of 150, 300 and 450 ppm SA to thyme (T. vulgaris L.) plants via foliar spraying provided protection against 50, 100 and 150 mM NaCl stress. SA treated plants had greater shoot and root dry weights compared to untreated plants when exposed to salt stress. SA application at 150 ppm significantly increased roots dry weight. Application of SA increased photosynthetic rates, mesophyll efficiency and water use efficiency in salt stressed plants. SA application increased electrolyte leakage compared to untreated plants. Beneficial effects of SA in saline conditions include sustaining the photosynthetic/transpiration activity and consequently growth, and may have contributed to the reduction or total avoidance of necrosis. SA, when used in appropriate concentrations, alleviates salinity stress without compromising the plants ability for growth under a favorable environment.
In vitro shoots of thyme (T. vulgaris L.) were established, and the effects of the auxin indole-3acetic (IAA) acid and the cytokinins benzyladenine (BA), zeatin (ZEA), and kinetin (KIN) at 1.0, 5.0, and 10.0 [micro]M on rooting, biomass production, and volatile compounds production by these plants were investigated. The volatiles were extracted by solid phase microextraction (SPME) and analyzed by gas chromatography. The highest biomass shoot growth was obtained with BA at 5.0 [micro]M, while IAA at all concentrations tested achieved 100% rooting frequency. The three major compounds were [gamma]-terpinene (22.8-38.8%), p-cymene (13.8-27.9%), and thymol (6.5-29.0%). Quantitative changes of these compounds were observed in response to the effect of varying growth regulators concentrations in the culture medium. Growing T. vulgaris L. plants in media supplemented with IAA at 1.0 [micro]M increased volatile compounds such as thymol by 315%. Nevertheless, the same major compounds were produced in all treatments and no qualitative changes were observed in the volatile profile of thyme plants .
In vitro Cultures of Lavandula angustifolia and Lavandula latifolia were established by germinating seeds of each species on Murashique and Skoog (MS) medium supplemented with 0.5 mg [L.sup.-1] Naphthaline Acetic Acid (NAA) incubated for three weeks in the dark at 28[degrees]C. The best shoot multiplication rates (2.0) and highest proliferation of L. angustifolia were obtained when internodal segments were subcultured on MS medium supplemented with 1.5 mg [L.sup.-1] Kinetin and 0.05 mg [L.sup.-1] NAA. Shoots were rooted on MS medium supplemented with 0.4 mg [L.sup.-1] of NAA or Indole Butyric Acid (IBA). Plants were successfully transferred to soil after two weeks of acclimatization in the greenhouse. Shoot multiplication rates and proliferation of L. latifolia were best when MS medium was supplemented with 0.5 mg [L.sup.-1] Benzyl Amino Purine (BAP), 0.05 mg [L.sup.-1] NAA or with 1.0, 1.5 or 2.0 mg [L.sup.-1] Kinetin and 0.05 mg [L.sub.-1] NAA. Shoots were rooted on MS supplemented with 0.3 mg [L.sup.-1] NAA .
Lavender (L. dentata) showed a higher amount of leaves when cultured in vitro with 0.1 mg [L.sub.-1] BA. The number of glands on the surface of leaves treated with BA was smaller, however they are not disrupted. In addition, the leaves showed an intense green color and remained young for a longer time. The observed effect was associated with leaf senescence delay and secretory gland differentiation, which keep them in the pre-secretory stage. Auxin (IBA) was also used. Plants treated with IBA presented a small number of glands, but were disrupted (post secretory stage), indicating that auxin accelerated their differentiation .
Immature plants of Lavandula angustifolia x L. latifolia (cv. Twickle Purple) were sprayed with Atrinal and P293 when the growing shoots bore four to six expanded leaves. Atrinal increased the number of inflorescences per plant by stimulating otherwise dormant axillary buds on the shoots of the current season. The number of nonflowering shoots arising on older wood was also increased. The number of florets and the fresh weight per inflorescence were reduced, but the number of florets per plant was increased overall. Oil content per plant was doubled without altering oil composition or floret structure. Flower stalks were shortened below and between the floral nodes. Atrinal sprays achieved a machine-harvestable canopy in 3-year-old plants. Untreated plants required a full year longer to develop similar canopies. P293 and manual disbudding were not as effective as Atrinal. It is suggested that such spray treatments have a useful potential in reducing the time required for the development of the mature canopy form, and so obtaining earlier financial returns on establishment costs .
Delavari et al.  investigated the role of salicylic acid pretreatment (0.01, 0.1mM) in inducing salt tolerance in sweet basil. Germination percentage, length of shoot, fresh and dry weight, photosynthetic pigments and [K.sup.+] concentration were decreased in response to high salinity,in this species, high salinity increased the level of [Na.sup.+], lipid peroxidation, coefficient allometry, MDG and proline. Salicylic acid pretreatment (especially 0.01mM) alleviated the adverse effects on salinity stress on all parameters measured.
Application of Methyl-jasmonate (0.5 mM) increased significantly the quantity of monoterpenes in basil (Ocimum basilicum). The content of terpenes in plants treated with methyl-jasmonate was higher than that found in control plants. The increase in eugenol and L-linalool compared to control plants was 56% and 43%, respectively. They concluded an increase in phenylpropanoid pathway products derived from phenylalanine ammonia-lyase (PAL), as well as an increase in the number of transcripts of the enzymes present in subsequent steps of the pathway, which explains the eugenol increase .
In an experiment, GA3 (0, 50, 100, 150 and 200 ppm) were sprayed to the basil foliage 24 hours after transplanting. Another factor was nitrogen (0.2, 0.4 and 0.6 g N [L.sup.-1]). The optimum growth of basil was achieved on 0.4 g N [L.sup.-1] and 100 ppm [GA.sub.3] .
Tavares et al.  indicated that increase of BAP (Banzyl adenine pourin) concentration up to 1 mg [L.sup.-1] gave greatest efficiency in shoot number of Melissa officinalis.
Sato et al.  reported that 8.8 [micro]mol BAP in 11.42 [micro]mol caused increase proliferation rate in shoot tip explants in M. officinalis.
On the media containing 3 mg [L.sup.-1] BAP, (82 to 90%) of explants showed shoot proliferation with 3.2 to 4.1 shoots per explant average [20,21].
An experiment with lemon balm grown in medium supplemented with auxin and cytokinin (IAA 11.42 [micro]mol [L.sup.-1], BA 8.87 [micro]mol [L.sup.-1] and IAA+BA), indicated an increase of 1.4 fold on nerol and 4.1 fold on geraniol .
An experiment in Iran showed the interaction between drought stress and salicylic and ascorbic acids on some biochemical characteristics of Satureja hortensis. The study showed that in the presence of both salicylic and ascorbic acids, the harsh influences of water deficit reduced and some growth parameters increased. It seemed that two external acids were able to enhance the tolerant ability of the plant to aridity stress .
Production and optimization of rosmarinic acid, a phenolic acid and an economically important metabolite, was investigated in the callus cultures established from the mature seeds of S. hortensis L. (summer savory) plant. Gamborg's B5 basal medium, supplemented with indol butyric acid (IBA) (1.0 mg [L.sup.-1]), [N.sup.6]-benzyl aminopurine (6-BA) (1.0 mg [L.sup.-1]) and sucrose (2.5%, w/v), was employed for the establishment and maintenance of the callus cultures. The highest biomass yield was obtained from the medium supplemented with 1.0 mg [L.sup.-1] IBA and 5.0 mg [L.sup.-1] 6-BA. In the case of the rosmarinic acid accumulation, an opposite relationship was determined between the growth and rosmarinic acid production. While the highest biomass yield was obtained from the medium containing 1.0 mg [L.sup.-1] IBA and 5.0 mg [L.sup.-1] 6-BA, the highest rosmarinic acid accumulation was obtained from the medium supported with 1.0 mg [L.sup.-1] IBA and 1.0 mg [L.sup.-1] 6-BA. .
In vitro cultures of Persian oregano (Origanum vulgare L.) and Arabian oregano (O. syriacum L.) were initiated from seeds on Murashige and Skoog (MS) medium containing 2.0 mg [L.sup.-1] Gibberellic Acid (GA3) and 15 g [L.sup.-1] sucrose. Callus induction was experimented by culturing leaf discs at different levels (0.0, 0.1, 0.5, 1.0, 1.5 or 2.0mg [L.sup.-1]) of 2,4-dichlorophenoxyacetic acid (2,4-D). Best callus induction and fresh weight were obtained at lower levels (0.1 or 0.5 mg [L.sup.-1]) of 2,4-D. Callus maintenance was tested on different levels (0.5, 1.0, 1.5, 2.0, or 2.5 mg [L.sup.-1]) of N6-Benzyladenine (BA) or Thidiazuron (TDZ) (with or without 0.5 mg [L.sup.-1] 2,4D). The largest callus diameter (12.5 mm) of O. vulgare L. was obtained when TDZ was at 1.0 mg [L.sup.-1] without using 2,4-D. Adding 2,4- D at 0.5 mg [L.sup.-1] was inhibitory on callus growth and diameter during 30 days of incubation when used in combination with TDZ or BA. BA gave less callus growth and smaller diameter than TDZ for the two species. O. syriacum L. callus was best grown when TDZ was 1.5 mg [L.sup.-1] (with or without 0.5 mg [L.sup.-1] 2,4-D). Callus from the third generation was friable and able to release cells in cell suspension culture. Cells were successfully subcultured every 17 days on liquid MS media supplemented with 1.0 mg [L.sup.-1] TDZ for both Origanum spp. O. syriacum L. grown under greenhouse conditions, produced higher oil yield (1.76 %) than in vitro grown plants (1.17 %), whereas O. vulgare L. was a poor oil producing plant in this study. Callus and cells produced very low oil percentage compared to intact plants. Thymol was identified by gas chromatography analysis in O. Syriacum L. intact plants. Ex vitro plants gave 13.1 % thymol while in vitro cultures gave 5.9 %. No thymol was identified in O. vulgare L. intact plants or in oil produced from callus and cells in both species .
The study was undertaken to determine a possible role of polyamines (putrescine, spermidine, spermine) as antioxidants in salt tolerance of O. majorana. Salinity generally induced variable changes in growth and content of oil. Foliar application of any polyamines counterbalanced the effects of salinity. In general, the degree of stimulation differed according to the type and concentration of the used additive [4,].
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Shahram Sharafzadeh, Mahdi Zare
Department of Agriculture, Firoozabad Branch, Islamic Azad University, Firoozabad, Iran
Shahram Sharafzadeh; Department of Agriculture, Firoozabad Branch, Islamic Azad University, Firoozabad, Iran.
E-mail: email@example.com or firstname.lastname@example.org; Tel: +98-9177158317.