Author's Personal Copy Montanoa Tomentosa Glandular Trichomes
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Author's personal copy Fitoterapia 80 (2009) 12–17 Contents lists available at ScienceDirect Fitoterapia journal homepage: www.elsevier.com/locate/fitote Montanoa tomentosa glandular trichomes containing kaurenoic acids chemical profile and distribution Ramón E. Robles-Zepeda a, Edmundo Lozoya-Gloria b, Mercedes G. López c, María L. Villarreal d, Enrique Ramírez-Chávez c, Jorge Molina-Torres c,⁎ a Departamento de Ciencias Químico Biológicas, Universidad de Sonora, Hermosillo, Sonora, Mexico b Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Irapuato, Irapuato, Guanajuato, Mexico c Departamento de Biotecnología y Bioquímica, Centro de Investigación y de Estudios Avanzados del IPN, Unidad Irapuato, Irapuato, Guanajuato, Mexico d Departamento de Productos Naturales, Centro de Investigación en Biotecnología, UAEM, Cuernavaca, Morelos, Mexico article info abstract Article history: Montanoa tomentosa has been used in traditional medicine in Mexico to treat diverse female Received 20 August 2008 health disorders; it is particularly useful in inducing childbirth. Microscopic analysis of leaf Accepted in revised form 3 September 2008 surfaces of M. tomentosa revealed the presence of glandular trichomes. The chemical profile Available online 14 September 2008 and distribution of glandular trichomes from different developmental stages of M. tomentosa leaves were investigated. Two diterpenic acids, kaurenoic and grandiflorenic were detected in Keywords: glandular trichomes through the glandular microsampling technique and GC/MS analysis. In Montanoa tomentosa the glandular trichomes of the leaves also up to twenty-six volatile terpenes were identified, Asteraceae β Zoapatle where -eudesmol and valencene were the most abundant terpenes. Glandular trichomes © 2008 Elsevier B.V. All rights reserved. Volatile terpenes Kaurenoic acid Grandiflorenic acid 1. Introduction of their exudates throughout leaf development may have important consequences for plant adaptation to abiotic and The aerial surface of most plants contains trichomes, which biotic factors [6]. can be divided into glandular (GT) and non-glandular (NGT). Montanoa tomentosa Cerv. (Asteraceae), a perennial shrub GTs are secretory structures varying in size, form, location, known as zoapatle or cihuapatli, has been used in traditional and function in plants of different species. Peltate and capitate medicine in Mexico to treat diverse female health disorders glandular trichomes are common in plants [1] and are [7,8], as for example inducing childbirth [9] and some authors constituted of four to eight cells in a single disc [2]. Glandular attribute theses pharmacological properties of M. tomentosa trichomes have a spherical morphology after reaching the to two diterpenic acids: grandiflorenic (GA) [kaura-9 (11), 16- mature stage. Their characteristic morphology develops as a dien-18-oic acid] and kaurenoic (KA) [kaur-16-en-18-oic acid] result of the accumulation of secretory products [3]. They [10]. These diterpenic acids are present in other plants and contain chemical compounds with diverse functions, includ- have been fully chemically characterized previously [11,12] ing defense [4]. Secondary metabolites in trichomes are (Fig. 1). ecologically bioactive compounds of interest as pesticides, Stereomicroscopic observation of the surface of leaves of pharmaceuticals, flavors, and fragrances [5]. Changes in M. tomentosa confirmed the presence of abundant glandular number of trichomes and in composition and concentrations trichomes. In the present work, we studied the distribu- tion and chemical profiles of glandular trichomes of leaves of M. tomentosa at different development stages. Emphasis is ⁎ Corresponding author. Tel.: +52 462 6239 645; fax: +52 462 6245 996. put in the presence of kaurenoic acids, putative bioactive com- E-mail address: [email protected] (J. Molina-Torres). ponents responsible for the ethnomedicinal use of this species. 0367-326X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.fitote.2008.09.002 Author's personal copy R.E. Robles-Zepeda et al. / Fitoterapia 80 (2009) 12–17 13 2. Experimental from about 700 glands, was dissolved in 500 μl of hexane: ethyl acetate (85:15). The solvent was evaporated to dryness 2.1. Plant under nitrogen and the residue re-suspended in 100 μlof ethanol. Samples were kept at 4 °C for further analysis. M. tomentosa leaves were collected from field-grown mature one-year-old plants cultivated at CINVESTAV-IPN, 2.4. Glandular trichomes terpenes content Unidad Irapuato (N 20° 43′ 8.9″, W 101° 19′ 42.6″ altitude 1740 m), Guanajuato, Mexico. Samples were collected form A more general procedure was used to evaluate the September to December after the rainy season. Dr. Jerzy terpenes content of the GTs. First, a surface extraction was Rzedowski from the Instituto de Ecología, Centro Regional del carried out with dichloromethane as previously described Bajío in Pátzcuaro, Michoacán, México performed species [13]. Briefly, each leaf section used for determination of GTS authentication. A voucher specimen (IEB-57689) was depos- density was subsequently submerged in 20 ml dichloro- ited in this Institute. methane for 20 s. Then, the solvent was evaporated under a nitrogen stream and the residue re-suspended in 1 ml of the 2.2. Leaf glandular trichomes distribution same solvent and kept at 4 °C for further analysis. Leaves were collected in four size ranges: 7 to 7.5 cm, 9 to 2.4.1. Grandiflorenic and kaurenoic acids evaluation 9.5 cm, 14 to 14.5 cm, and 15 to 15.5 cm. These were classified The identification and quantification of these acids was as new, young, mature and old leaves, respectively. Within accomplished as follows: 100 μl of each surface extract was these size ranges, the smaller leaves were found in a higher dissolved in hexane:ethyl acetate (85:15), and the diterpenic position in the plant, whereas the older leaves were found at acids present derivatized adding100 μl of a mixture of BSTFA lower level. In order to evaluate the glandular trichomes (GT) [bis-(trimethyl) sililtrifluoroacetamide from Sigma Co.] and distribution density, each leaf was divided in three zones TMCS (trimethylchlorosilane from Alltech) in a 100:5 v/v characterized as basal, middle and apical. relation and heating for 30 min at 60 °C. The derivatized The evaluation of GTs density in the different leaf zones compounds were analyzed using a gas chromatograph was performed with the aid of a stereomicroscope (Nikon coupled to a mass selective detector (GC-MSD Hewlett- SMZ-2B, Schott KL500 lamp). The average number of GTs was Packard 6890 Series II) equipped with a capillary column calculated. Three replicas were evaluated for each leaf size. HP-1 (30 m long, 0.25 mm internal diameter and 0.25 μm film thickness). Helium was used as the carrier gas, at a 2.3. Glandular trichomes microsampling constant flow rate of 1 ml/min. The injector temperature was maintained at 200 °C. The oven temperature profile was the Three replicas of GTs direct extraction (microsampling) following: 3 min at 150 °C, followed by a temperature were performed with micro capillaries (prepared from 10 μl increment rate of 4 °C/min up to 300 °C, then kept at 300 °C capillary tubes by heat stretching) under the stereomicro- for 20 min. The mass selective detector consisted of a scope at a 100x magnification. The glandular fluid collected quadrupole analyzer with the ionization source set at 70 eV. Scan parameters were: mass range from 30.0 to 550 uam with 5.36 scans per second, and the temperatures of source and quadrupole were 230 °C and 150 °C respectively. The mass spectra identification and calibration curves for these com- pounds were made by comparison with authenticated standards obtained as a gift from Dr. Raúl Enríquez (Instituto de Química, UNAM, México). 2.4.2. Terpenic compounds profile The GTs dichloromethane extract of basal, middle, and apical zones, from leaves of different sizes were analyzed by GC-MSD. One microliter of each extract was injected onto a GC (Hewlett-Packard 5890 series II) coupled to a mass selective quadrupole detector (Hewlett-Packard/MSD 5972 series) for the characterization of components present in the samples. Compound separation was carried out using a capillary column HP-FFAP (25 m long, 0.32 mm internal diameter and 0.52 μm film thickness from Hewlett-Packard). The carrier gas was helium at a constant flow rate of 1 ml/min. The in- jector temperature was maintained at 180 °C. The oven temperature program was: 3 min at 40 °C, followed by a temperature increment rate of 3 °C/min up to 120 °C and then at a rate of 5 °C/min up to 200 °C. This temperature was maintained for 13 min. Peaks were identified by comparison Fig. 1. Structure of diterpenic acids in this study: A) Kaurenoic acid; with the NIST 98 mass spectral database. Results are presented B) Grandiflorenic acid. as a percent of the total area produced by the compounds Author's personal copy 14 R.E. Robles-Zepeda et al. / Fitoterapia 80 (2009) 12–17 identified in each leaf zone. The values presented are the aver- age of three replicas. 3. Results and discussion 3.1. Leaf glandular trichomes distribution The abaxial surface presented numerous GTs and Non- Glandular trichomes (NGT). On the adaxial surface only NGTs were observed. Based on observations using a stereomicro- scope, the GTs were distributed on the leaf lamina, on sec- ondary, tertiary, and quaternary veins with the exception of the main vein, where only NGTs were observed. The GTs have a green-yellowish color and a spherical shape. NGTs in both surfaces were multicellular and erect varying in length. As the GTs were restricted to the abaxial side of the leaf, the results presented here on the density of GTs are exclusively related to the abaxial surface of the leaves. GTs density did not vary significantly between different zones of the new, mature, and old leaves, but in young leaves, a higher GTs density was observed throughout this surface, as shown in the graph presented in Fig.