Biochemical Systematics and Ecology 36 (2008) 691–698

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Biochemical Systematics and Ecology

journal homepage: www.elsevier .com/locate/biochemsyseco

Potential allelopatic effects of stilbenoids and flavonoids from leaves ofCarex distachya Desf.

Antonio Fiorentino*, Brigida D’Abrosca, Severina Pacifico, Angelina Izzo, Marianna Letizia,Assunta Esposito, Pietro MonacoDipartimento di Scienze della Vita, Laboratory of Phytochemistry, Seconda Universita degli Studi di Napoli, Via Vivaldi 43, 81100 Caserta, Italy

a r t i c l e i n f o

Article history:Received 11 April 2008Accepted 26 July 2008

Keywords:Carex distachyaCyperaceaeCarexanesAllelopathyMediterranean macchiaStilbenoidsFlavonoids

* Corresponding author. Tel.: þ39 0823 274 576;E-mail address: antonio.fiorentino@unina2.it (A.

0305-1978/$ – see front matter � 2008 Elsevier Ltddoi:10.1016/j.bse.2008.07.002

a b s t r a c t

The potential allelopathic effects of 14 stilbenoids and five flavonoids, isolated from leavesof Carex distachya Desf., were evaluated on the seed germination and seedling growth ofthree coexisting Mediterranean species (Dactylis hispanica, Petrorhagia velutina, andPhleum subulatum). The structures of the metabolites have been elucidated on the basis oftheir spectroscopic features (1D and 2D NMR experiments and EI–MS and ESI–MS data).The bioassays showed species-specific effects of the metabolites from C. distachya,specially on the plant growth (root and shoot elongation) which resulted significantlystimulated or inhibited at 10�4 M concentration. The effects on root elongation is generallygreater than the shoot growth at all the tested concentrations (10�4–10�8 M). Cluster ofbiological data showed interesting relationships between the chemical structures of thecompounds and their biological effects.

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1. Introduction

On account of their static condition, plants interact with other organisms living in the same ecosystem through peculiarchemical signals. In fact, they biosynthesize a great variety of chemical substances known as secondary metabolites that,released in the environment, can positively or negatively affect the life of other coexisting plants or animals (Bouwmeesteret al., 2003).

It is known that Mediterranean macchia ecosystems are characterized by a high level of spatial variability and structuralcomplexity, depending mainly on its environmental conditions and disturbance history (Naveh, 1989). As a consequence it isclear to hypothesize that Mediterranean plant species have evolved and activated allelopathic mechanisms as life strategiestraits to growth and survive in this environment.

In order to investigate potential allelopathic interferences among plant species of the Mediterranean area (Esposito et al.,2008), we isolated and characterized new secondary metabolites, named carexanes, from Carex distachya Desf., an herbaceousplant growing in the Mediterranean macchia (D’Abrosca et al., 2005; Fiorentino et al., 2006a,b, 2008).

The genus Carex includes sedges that dominate wetlands, pastures, prairies, tundra, and the herb layer of temperateforests. World wide, there may be as many as 2000 species. Plant of the Carex genus are characterized by the production ofstilbene derivatives (Kawabata et al., 1995). In fact, resveratrol oligomers with antimicrobial and antibacterial activities havebeen identified in Carex fedia Nees var. miyabei (Franchet) T. Koyama (Suzuki et al., 1987). Kurihara et al. (1991) reported a newtetrastilbene, kobophenol A, from subterranean parts of Carex kobomugi, together with the known miyabenol C and

fax: þ39 0823 274 571.Fiorentino).

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A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698692

3-viniferin (Kurihara et al., 1990), while Kawabata et al. (1991), reported the structure of kobophenol B from Carex pumila. Leeet al. (1998) isolated the stilbene dimer, a-viniferin, inhibitor prostaglandin H2 synthase, from roots of Carex humilis. Menget al. (2001) reported the isolation and characterization of three oligostilbenes from the seeds of Carex pendula withecdysteroid antagonist activity.

In the present study, the chemical characterization of stilbenoid and flavonoid metabolites from C. distachya leaf extractwas reported, as well as the evaluation of their potential allelopathic effects on germination and seedling growth of Dactylishispanica, Petrorhagia velutina, and Phleum subulatum, three coexistent herbaceous species characteristic of the Mediterra-nean macchia.

2. Material and methods

2.1. Plant material

Plants of Carex distachya Desf. (Cyperaceae) were collected, in June 2004, in the ‘‘Castel Volturno’’ Nature Reserve (Caserta,Italy), a flat coastal area in the north of Naples (Southern Italy). The area is located on stabilized dunes of alluvial deposits andloose siliceous-calcareous sand, with a maximum elevation of 9 m above the sea level. The climate is typically Mediterraneanwith precipitations mostly occurring in autumn and winter with a drought period in summer. The soil is characterized byhomogeneous sand with 97.1% sand, 1.25% loam, 1.6% clay, poor in organic matter and nutrients (Rutigliano et al., 2004). Seedsof test species Phleum subulatum, Dactylis hispanica and Petrorhagia velutina were randomly collected in the field in June 2004,and stored in the laboratory at room temperature and darkness. Voucher specimens (C. distachya CE0278, P. subulatumCE0078, D. hispanica CE0089, P. velutina CE0115) have been deposited at the Herbarium of the Dipartimento di Scienze dellaVita of Second University of Naples.

2.2. Phytochemical study

2.2.1. General experiment proceduresThe preparative HPLC apparatus consisted of a pump LC-10AD (Shimadzu, Japan), a refractive index detector (Shimadzu

RID-10A) and a Shimadzu Chromatopac C-R6A recorder. Preparative HPLC was performed using a 250 � 10 mm i.d., 10 mm,Luna RP-8 (Phenomenex, Torrance, Canada, CA) column. Analytical TLC was performed on Merck Kieselgel (Darmstadt,Germany) 60 F254 or RP-8 F254 plates with 0.2 mm layer thickness. Spots were visualized by UV light or by spraying withH2SO4–AcOH–H2O (1:20:4). The plates were then heated for 5 min at 110 �C. Preparative TLC was performed on MerckKieselgel 60 F254 plates, with 0.5 or 1 mm film thickness. Flash column chromatography (FCC) was performed on MerckKieselgel 60 (230–400 mesh) at medium pressure. Column chromatography (CC) was performed on Merck Kieselgel 60 (70–240 mesh), Reversed Phase silica gel 100 C8 (230–400 mesh) (Fluka, Buchs, Switzerland), Fluka Amberlite XAD-4, or SephadexLH-20 (Pharmacia, Piscataway, USA) media. NMR spectra were recorded at 300 MHz for 1H and 75 MHz for 13C on a VarianMercury 300 spectrometer Fourier transform NMR, in CD3OD, DMSO and CDCl3 solutions at 25 �C. Proton-detected hetero-nuclear correlations were measured using HSQC (optimized for 1JHC ¼ 140 Hz) and HMBC (optimized for nJHC ¼ 8 Hz). UVspectra were performed on UV-1700 Shimadzu spectrophotometer in MeOH solution. Optical rotations were measured ona Perkin-Elmer 343 polarimeter. Electronic ionization mass spectra (EI–MS) were obtained with a HP 6890 instrumentequipped with a MS 5973 N detector. Electrospray mass spectra (ESI–MS) were acquired using a QuattroLC (Micromass,Manchester, UK) triple quadrupole instrument operating in the negative and positive ion mode.

2.2.2. Isolation of compoundsFresh leaves of C. distachya (5.77 kg) were extracted by maceration with EtOAc for 5 days at 4 �C in the darkness.The crude extract (30.0 g) was chromatographed by CC on SiO2, using hexane–EtOAc solutions as eluent, to give eight

fractions A–H.Fraction A, eluted with hexane–EtOAc (9:1), was purified on Sephadex LH-20 eluting with hexane–CHCl3–MeOH (3:1:1) to

have a fraction which was purified by preparative TLC with hexane–EtOAc (4:1) to furnish pure compounds 9 (3.5 mg) and 11(6.0 mg) and a mixture which was purified by RP-8 HPLC (MeCN–MeOH–H2O, 1:2:2) to give pure 10 (2.2 mg) and 12 (2.0 mg).

Fraction B, eluted with hexane–EtOAc (5:1), was re-chromatographed on Sephadex LH-20 with hexane–CHCl3–MeOH(3:1:1) to give a fraction which, purified by preparative TLC with hexane–EtOAc (4:1) furnished pure 4 (8.0 mg).

Fraction C, eluted with hexane–EtOAc (4:1) was re-chromatographed on Sephadex LH-20 eluting with hexane–CHCl3–MeOH (3:1:1) to obtain pure 5 (40.0 mg) and two further fractions; the first was purified by RP-8 HPLC, eluting with MeOH–MeCN–H2O (2:2:1) to give pure metabolites 1 (6.0 mg), 2 (7.0 mg) and 3 (4.0 mg). the second fraction was purified bypreparative TLC using CHCl3–Me2CO (9:1) to give pure 8 (3.0 mg).

Fraction D, eluted with hexane–EtOAc (7:3), was re-chromatographed on Sephadex LH-20 using hexane–CHCl3–MeOH(3:1:1). The eluate was purified by RP-8 HPLC with MeCN–MeOH–H2O (2:2:1) to obtain pure 14 (17.6 mg).

Fraction E, eluted with hexane–EtOAc (3:2), was chromatographed on Sephadex LH-20 eluting with hexane–CHCl3–MeOH(3:1:1) to give a fraction which, purified by RP-8 HPLC with MeCN–MeOH–H2O (2:2:1), furnished pure metabolites 6 (2.0 mg),7 (1.0 mg) and 13 (16.0 mg).

A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698 693

Fraction F, eluted with hexane–EtOAc (2:3), was chromatographed on Sephadex LH-20, eluting with hexane–CHCl3–MeOH(3:1:1) to give a fraction which was purified by flash chromatography on SiO2 with CHCl3–Me2CO (17:3) to give pure 18(6.3 mg).

Fraction G, eluted with EtOAc, was chromatographed on Sephadex LH-20 eluting with hexane–CHCl3–MeOH (2:1:1) togive two fractions; the first was re-chromatographed by CC on RP-8 silica with MeCN–H2O (1:4), led to the isolation of pure 15(50.0 mg); the second fraction was purified by RP-8 HPLC eluting with MeCN–MeOH–H2O (4:7:9) to have pure 16 (7.9 mg).

Fraction H, eluted with MeOH, was chromatographed by CC was chromatographed by CC on RP-18 silica eluting withMeOH–MeCN–H2O (1:1:3). The eluate was chromatographed on Sephadex LH-20 eluting with MeOH–H2O (4:1) to givea fraction which purified by RP-8 HPLC with MeCN–MeOH–H2O–01%TFA (1:4:14) to give pure metabolites 17 (7.9 mg), 18(2.0 mg), and 19 (3.0 mg).

2.2.3. Identification of compounds

2.2.3.1. Pallidol (14). [a]D25 0� (MeOH; c, 0.95,); ESIMSþ m/z 477 [M þ Na]þ, 455 [M þ H]þ; ESIMS� m/z 453 [M � H]�; 1H and

13C NMR data according to those reported in literature (Khan et al., 1986).

2.2.3.2. Tricin (15). ESIMSþ m/z 353 [M þ Na]þ, 331 [M þ H]þ; ESIMS� m/z 329 [M � H]�; 1H and 13C NMR data according tothose reported in literature (Kong et al., 2004).

2.2.3.3. Tricin 40-O-(erythro-b-guaiacylglyceryl)ether (16). [a]D25 � 4.3� (MeOH; c, 0.38); ESIMSþ m/z 549 [M þ Na]þ, 527

[M þ H]þ; ESIMS� m/z 525 [M � H]�; 1H and 13C NMR data according to those reported in literature (Bouaziz et al., 2002).

2.2.3.4. Apigenin-6-C-b-D-xylopyranosyl-8-C-b-D-glucopyranoside (17). [a]D25 þ 74.5� (MeOH; c, 1.11,); ESIMSþ m/z 587

[M þ Na]þ; ESIMS� m/z 563 [M � H]�; 1H and 13C NMR data according to those reported in literature (Park et al., 2007).

2.2.3.5. Apigenin-6-C-b-D-glucopyranosyl-8-C-b-D-xylopyranoside (18). [a]D25 þ 13.0� (MeOH; c, 0.10); ESIMSþ: m/z 587

[M þ Na]þ; ESIMS� m/z 563 [M � H]�; 1H NMR and 13C NMR: see Table 1.

2.2.3.6. Luteolin-6-b-D-glucopyranosyl-8-C-b-D-xylopyranoside (19). [a]D25 þ 34.8� (MeOH; c, 0.20); ESIMSþ m/z 603 [M þ Na]þ;

ESIMS� m/z 579 [M � H]�; 1H NMR and 13C NMR: see Table 1.

Table 11H and 13C-NMR assignment of C-glycoside flavones 18 and 19 in DMSOd6

Position 18 19

d 1H (J) d 13C d 1H (J) d 13C

2 – 161.9 – 164.93 6.62 s 102.6 6.59 s 100.24 – 179.0 – 182.95 – 159.1 – 158.46 – 107.6 – 108.77 – 159.5 – 158.98 – 106.8 – 104.49 – 154.1 – 155.710 – 104.9 – 103.210 – 120.8 – 120.120 7.98 d (7.5) 127.8 7.37 d (1.8) 113.330 6.88 d (7.5) 120.4 – 149.540 – 156.7 – 150.450 6.88 d (7.5) 120.4 6.84 d (8.0) 116.560 7.98 d (7.5) 127.8 7.38 dd (8.0, 1.8) 122.2Glc1 4.77 d (9.5) 73.5 4.78 d (9.5) 73.9Glc2 3.89 ov 71.6 3.91 ov 69.0Glc3 3.66 ov 77.2 3.65 ov 77.4Glc4 3.88 m 70.9 3.87 ov 70.8Glc5 3.64 ov 82.5 82.8Glc6 4.01 dd (11.5, 2.1) 62.3 3.99 dd (12.3, 1.8) 62.2

3.86 dd (11.5, 4.7) 3.84 dd (12.3, 5.1)Xyl1 4.73 d (9.5) 73.7 4.70 d (9.5) 74.5Xyl2 3.89 ov 70.4 3.91 ov 70.4Xyl3 3.71 ov 79.1 3.71 ov 79.6Xyl4 3.59 ov 70.7 3.55 ov 70.3Xyl5 3.77 ov 69.1 3.76 ov 69.1

3.67 ov 3.69 ov

s ¼ singlet; d ¼ doublet; dd ¼ doublet of doublet; ov ¼ overlapped. The J value in Hz are reported in the brackets.

A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698694

2.3. Phytotoxicity test

A preliminary phase has been carried out to select seeds for uniformity. To this end a considerable number of seeds wereobserved under a binocular microscope to discard all undersized or damaged ones. A preliminary test to evaluate thegerminability of the three selected species was carried out on these seeds in a growth chamber KBW Binder 240 at 27 �C in thedark. The observed percentage of germinability for Phleum subulatum, Dactylis hispanica and Petrorhagia velutina was of 98.7%,88.7% and 98.3% respectively. The bioassay experimental design included the use of three blocks of 100 seeds for each speciesand each treatment was conducted in ten replicates. Ten seeds of each species were poured onto a sheet of Whatman N� 1filter paper in a Petri dish (50 mm of diameter). For each metabolite bioassay, three different concentrations have been tested:10�4 M pure metabolite solution (defined as High), 10�6 M and 10�8 M solutions (defined as Medium and Low, respectively).The test solution of pure metabolites (10�4 M) was prepared using (2-[N-morpholino]ethanesulfonic acid (MES; 10 mM,pH 6), while the others (10�6–10�8 M) were obtained by dilution.

For each pure metabolite bioassay, parallel controls were carried out. After adding 10 seeds and 1.0 mL test solution, thePetri dishes were sealed with Parafilm� to ensure closed-system models. The dishes were placed in a growth chamber KBWBinder 240 at 27 �C in the dark. Four days later (no more germination occurred after this time), germination percentage wasanalyzed. Successively, seedlings were frozen at �20 �C to avoid subsequent growth until the root and shoot elongationmeasurement. Germination rate, root length and shoot length were recorded by using a Fitomed� system (Castellano et al.,2001), that allowed automatic data acquisition and statistical analysis by its associated software. Data are reported aspercentage differences with respect to control. Therefore, zero represents the control, positive values show stimulation whilenegative values represent inhibition of the studied parameters.

The statistical significance of differences between groups was determined by a Student’s t-test, calculating mean values forevery parameter (germination average, shoot and root elongation) and their population variance within a Petri dish. The levelof significance was set at P < 0.05 (Castellano et al., 2001).

O

OR

R1

H

R2O

OR

R1

H

R2

HO

carexane A (1)carexane B (2)carexane C (3)carexane D (4)carexane J (10)

RHHHHMe

R2HOHOHHOH

carexane E (5)carexane F (6)carexane G (7)carexane K (11)

R2HOHOHH

OORO

COOH

carexane H (8)carexane L (12)

R1OOOO

OH

O

O

carexane I (9)R1HMe

R1OH, HOOOO

RHHHMe

O

O

OH

OH H

H

H H

HO

OH

HOOH

OHHO

distachyasin (13) pallidol (14)

H

H

Fig. 1. Chemical structures of stilbenoids 1–14.

O

O

OH

OHO

OH

O

O

O

O

OHO

OH

O

OH OH

O

OH

15

16

HO

OH

O

O

17

O

OH

HO

HO

O

HO

OH

OH

OH

OH

HO

OH

O

OH

O

RHOH

O

HO

OH

OH

O

HO

OH

HO

HO

R

1819

Fig. 2. Chemical structures of flavonoids 15–19.

A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698 695

Moreover a numerical clustering of data bioassay was made on the basis of percentage differences from control. Anaverage linkage agglomeration criterion and the Euclidean distance as dissimilarity coefficient was applied by the softwareAddinsoft XLSTAT-Pro 7.5.

3. Results and discussion

From the EtOAc extract of Carex distachya were isolated twelve new secondary metabolites, named carexanes A–I (Fig. 1)characterized by a new molecular skeleton deriving from stilbenoid precursors (D’Abrosca et al., 2005). The peculiarity ofthese compounds is an unusual tetracyclic structure bringing a hydroxyl at the C-3 carbon and a methoxyl group at the C-5carbon. The compounds differ among them by the oxidation state of the B ring and by trans or cis C–D ring juncture (Fior-entino et al., 2006a). Carexanes H and L (8 and 12) are seco-carexanes characterized by the loss of the B ring due to anoxidative cleavage of the C-7/C-8 bond. Finally carexane I has a tricyclic structure lacking of the C ring (Fiorentino et al.,2006b). Besides these compounds, a more oxidized metabolite, named distachyasin (13), which structure, characterized bya carbonyl group at the C-3 carbon and ad hydroxyl at C-2 carbon, was elucidated by HRESIMS, NMR and X-ray diffraction, wasalso isolated (Fiorentino et al., 2006c).

In order to complete the phytochemical study of the leaf extract to evaluate their potential allelopathic effect, we identifieda resveratrol dimer and five flavone derivatives. Compound 14, known as pallidol (Fig. 1), was already isolated from Cissuspallida (Khan et al., 1986) and reported as naturally occurring antitumor agent (Ohyama et al., 1999). Compound 15, tricin(Fig. 2), is reported as allelochemical from allelopathic rice seedlings (Kong et al., 2004), while compound 16 has beenidentified as its 40-O-(erythro-b-guaiacylglyceryl)ether (Bouaziz et al., 2002).

The study of the more polar components of the EtOAc leaf extract led to the identification of three C-glycosides flavones(Fig. 2) identified as apigenin-6-C-b-D-xylopyranosyl-8-C-b-D-glucopyranoside (17), already identified as constituent of Sasaborealis leaves (Park et al., 2007), apigenin-6-C-b-D-glucopyranosyl-8-C-b-D-xylopyranoside (18) and luteolin-6-C-b-D-glucopyranosyl-8-C-b-D-xylopyranoside (19) (Cummis et al., 2006). To the best of our knowledge, all the paper reportingcompounds 18 and 19, lacked of their spectroscopic data, and the NMR assignment of this compound was reported in Table 1.

In order to evaluate their potential allelopathic effects, all of the stilbenoids and flavonoids were tested on Dactylishispanica, Petrorhagia velutina and Phleum subulatum at 10�4 (High, H), 10�6 (Medium, M) and 10�8 (Low, L) concentrations.The results have been analyzed using a multivariate approach. The dendrogram resulting from hierarchical agglomerativeanalysis of the stilbenoids 1–14 is reported in Fig. 3A. The cluster showed three main branches I–III. The cluster I consisted inmetabolites 9 and 11. Both the compounds are characterized by two methoxyls in C-3 and C-5 on aromatic A ring. The

9 11 7 6 14 13 1 3

0

20

40

60

80

100

120

140

160

180

200

Dis

sim

ila

rity

I

IIbIIa IVa IVbIII

A

1615181719

0

20

40

60

80

100

120

140

160

Dissim

ilarity

V VI VII

B

8 5 24

Fig. 3. Dendrograms of metabolites from leaves of C. distachya. A. Stilbenoids; B. flavonoids.

A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698696

presence of a further hydroxyl moiety on the same ring in 11 probably didn’t play a role in the efficacy exercise resultingdeactivated from the contiguous functions. The second cluster, containing the most polar compounds 5–8, can be divided intwo subcluster IIa and IIb; the first included the alone seco-carexane 8, while compounds 5, 6, and 7, bringing two hydroxyland a methoxyl in the A ring. The third branch is constituted from pallidol (14) which showed no structural similarity with thecarexanes even if it has the same stilbenic derivation. The forth cluster consisted in two homogenous classes: the firstincluded the carexanes A–D (1–4) characterized by a hydroxyl and a methoxyl in the A ring, while the second contained onlydystachyasin (13) characterized by a totally modified A ring. These data suggested the fundamental role of the A ring for thebiological activity.

Also the multivariate analysis of the bioassay results of flavonoids (Fig. 3B) indicated a clear structure-activity rela-tionship showing three main branches IV–VI. Cluster IV included the alone C-glycoside of the luteolin (19), cluster V isformed by the two C-glycosides of the apigenin (17 and 18), finally, cluster VI grouped the tricin 15 and its guayacylglycerolconjugate 16.

The average trend of metabolites belonging to the same branch of the clusters (Fig. 3A,B) are showed in Fig. 4. Among thestilbenoids, pallidol (branch III) and distachyasin (branch IVa) resulted the most toxic metabolites on the germination(Fig. 4A), together with the C-glycosides 17–19. In particular compound 19 (branch V) resulted inhibiting the germination ofP. subulatum at the highest concentration, but became stimulating at 10�6 and 10�8 M solutions. The effects on plant growth

-50

-25

0

25

50

% fro

m co

ntro

l

D. hispanica P. velutina P. subulatum

GerminationA

-70

-35

0

35

70

% fro

m co

ntro

l

Root elongationB

-70

-35

0

35

70

I IIa IIb III IVa IVb V VI VII

% fro

m co

ntro

l

Shoot elongationC

Branches

Fig. 4. Effects (% from control) of stilbenoids and flavonoids from C. distachya on germination, root and shoot elongation of D. hispanica, P. velutina andP. subulatum. Data are reported as average trend of metabolites belonging to the same branch of the clusters reported in Fig. 3. A: Germination; B: root elongation;C: shoot elongation.

A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698 697

revealed different behaviors. Among carexanes, compounds 9 and 11 (branch I) significantly stimulated the root growth at thehighest concentration. Also the compounds included in the branch II were potent stimulants, especially on D. hispanica, whilepallidol and distachyasin (branch III and IVa, respectively) were the most toxic on P. subulatum. The effects of flavones on theroot elongation were less important than those observed on seed germination. All of the stilbenoids resulted inhibiting orlightly stimulating on the seedling growth with the only exception of P. velutina that was stimulated over 50% by the seco-

A. Fiorentino et al. / Biochemical Systematics and Ecology 36 (2008) 691–698698

carexane 8. The apigenine glycosides (branch VI) as well as the tricin metabolites (branch VII) had a similar toxic effect on allthe three test species on the seedling growth.

From the present study, it is clear that stilbenoid and flavonoid metabolites from leaves of C. distachya potentially affect thegrowth of coexisting herbaceous plants. In particular, these compounds can show inhibiting or stimulating effects, dependingon the target species. In this context it is reasonable to suppose that C. distachya metabolites can play a fundamental role aschemical signals. Further studies are in progress to evaluate the role of these compounds in the soil of the same plantcommunity.

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