Phytotoxic activity of crude aqueous extracts and fractions of young leaves of Sapindus saponaria L. (Sapindaceae)

ARTICLES

Phytotoxic activity of crude aqueous extracts and fractions of young leaves of Sapindus saponaria L. (Sapindaceae)

Patrícia Umeda Grisi^I,*; Sônia Cristina Juliano Gualtieri^I; Marli Aparecida Ranal^II; Denise Garcia de Santana^III

^IUniversidade Federal de São Carlos, Departamento de Botânica, São Carlos, SP, Brazil

^IIUniversidade Federal de Uberlândia, Instituto de Biologia, Uberlândia, MG, Brazil

^IIIUniversidade Federal de Uberlândia, Instituto de Ciências Agrárias, Uberlândia, MG, Brazil

ABSTRACT

The aim of this study was to evaluate the phytotoxic potential of aqueous extract of young leaves of Sapindus saponaria L. (soapberry) on the diaspore germination and seedling growth Lactuca sativa L. (lettuce) and Allium cepa L. (onion), as well as to determine, by bioassay-guided fractioning, whether the fractionated extracts of those leaves are phytotoxic to Triticum aestivum L. (wheat) coleoptiles. The aqueous extract was prepared using 100 g of dried plant material dissolved in 1000 ml of distilled water, resulting in a concentration of 10.0%. Distilled water was added in order to obtain dilutions of 7.5%, 5.0%, and 2.5%. The extraction was carried out with young leaves (in powder form) and organic solvents of various polarities. We fractioned the ethyl acetate extract using column chromatography. The phytotoxic potential of the aqueous extract of young leaves S. saponaria varied according to the receiving species and the concentration-dependent inhibitory effect. The ethyl acetate extract, specifically fraction 6 (57-70), had the greatest inhibitory effect on the elongation of wheat coleoptiles, indicating that the compounds responsible for the phytotoxic effect reside within this fraction.

Key words:Allium cepa L., Lactuca sativa L., phytotoxicity, soapberry, Triticum aestivum L

Introduction

Sapindus saponaria L. (Sapindaceae), popularly known as the soapberry, is a native, pioneer, evergreen or semi-deciduous, heliophytic tree species, small in size, used in landscaping and in recovery plans for areas of degradation. It is typically found in humid areas, including the northern, northeastern and central-west regions of Brazil (Albiero et al. 2001). The wood is moderately heavy, hard and compact. Soapberry wood also has low natural durability and is used in civil construction. The soapberry fruit contains high levels of saponins and is used in fabric laundering, as well as for treating ulcers, skin sores and inflammation (Pelegrini et al. 2008).

Studies using high-performance liquid chromatography with ultraviolet detection and mass spectrometry have shown that the major glycosides present in soapberry fruit are saponins derived from the triterpenes hederagenin and oleanolic acid, as well acyclic sesquiterpene oligoglycosides. Using these methods of analysis, 30 saponins and 63 acyclic sesquiterpene oligoglycosides have been detected (Murgu & Rodrigues-Filho 2006; Pelegrini et al. 2008). Saponins display diverse behaviors, such as molluscicidal, and piscicidal, anti-inflammatory, analgesic, expectorant, antioxidant, antiviral, antibacterial and antifungal activity (Sparg et al. 2004).

Some secondary metabolites of plants play a fundamental role in the defense interactions with predators, pathogens and competitors (Croteau et al. 2000), which characterizes allelopathic interactions mediated by phenols, terpenes, alkaloids, polyacetylenes, fatty acids and peptides, among others. These substances can be produced in any plant organ, although in very low concentrations and with characteristics intrinsic to the plant, such as, for example, species and age (Rizvi & Rizvi 1992; Gatti et al. 2004). Most of these secondary metabolites exhibit biological activity and have been used in the pharmaceutical and agrochemical industries (Hamburger & Hostettmann 1991; Vyvyan 2002; Pelegrini et al. 2008).

Allelochemicals affect various metabolic processes in organisms, including changes in membrane permeability, ion absorption (Gniazdowska & Bogatek 2005) and inhibition of electron transport in respiration and photosynthesis (Abrahim et al. 2000), as well as changes in enzyme activities (Singh et al. 2009) and inhibition of cell division (Teerarak et al. 2010). Because of these changes, allelopathy is recognized as an important ecophysiological process in ecosystems, influencing primary and secondary plant succession, structure, composition and dynamics of native or cultivated plant communities (Rizvi & Rizvi 1992).

For advances in technological terms and to increase the potential applicability of the results of allelopathy, it is necessary to identify the fractions or allelochemicals responsible for phytotoxic activity, as well as to identify which compounds have potential for use as growth regulators and herbicides (Dayan & Duke 2006). Therefore, certain methods, such as bioguided fractionation, are being used to study new phytotoxic compounds. Bioguided fractionation consists of performing bioassays at each step of fractionation, in order to determine which fractions display the highest level of biological activity (Macías et al. 2006).

The phytochemical composition of the fruit of S. saponaria is known to have important pharmaceutical properties (Guarim Neto et al. 2000; Pelegrini et al. 2008). However, few studies have made reference to the phytochemical analysis of the leaves of the species (Grisi et al. 2012). Consequently, the objective of this study was to assess the phytotoxic potential of the aqueous extract of the young leaves of S. saponaria on diaspore germination and seedling growth of lettuce (Lactuca sativa L.) and onion (Allium cepa L.), as well as to analyze, through bioguided fractionation, the phytotoxic effects of its fractions on the elongation of Triticum aestivum L. (wheat) coleoptiles.

Materials and methods

In November of 2008, young leaves of S. saponaria were collected from 10 trees in the city of São Carlos, Brazil (22º02'S; 47º52'W). The region is characterized by the Aw climate type (Köppen, 1948), with dry winters (April to September) and wet summers (October to March). The morphological criterion used to identify the young leaves was the light green coloration and and texture of the membranous type.

After collection, the leaves were dried at 40ºC for 72 h and ground in an industrial mill to obtain dried plant material. The aqueous extract was prepared at a ratio of 100 g of dried plant material to 1000 ml of distilled water, in a final concentration of 10.0%. The extract remained at rest for 30 min at 4ºC and was then filtered using an electric vacuum pump coupled to a Buchner funnel lined with filter paper (Gatti et al. 2004). The resulting extract was collected in a beaker and distilled water was added, making dilutions of 7.5%, 5.0% and 2.5%.

Osmotic potential and pH of the extract

The pH of the aqueous extract was measured with a pH meter (PM608; Analion, Ribeirão Preto, Brazil) and molar concentration was measured with an automatic osmometer (5004 MICRO-OSMETTE; Precision Systems, Natick, MA, USA). The osmotic potentials of the most concentrated extracts of young leaves were calculated.

Germination bioassay

The four concentrations obtained from the aqueous extract of young leaves were applied to the cypselas (sensu Marzinek et al. 2008) of lettuce (L. sativa cv. Grand Rapids) and seeds of onions (A. cepa cv. Baia Periforme). Four replicates of 30 diaspores were seeded in Petri dishes over two sheets of filter paper moistened with 5 ml of the aqueous extract or distilled water (control treatment). Each dish was covered with a transparent plastic film to prevent evaporation. The experiment was conducted in a germination chamber at 25ºC under constant white fluorescent light and average irradiance of 12.26 ± 6.49 µmol m^-2 s^-1, as recommended by Iganci et al. (2006) and Povh et al. (2007). The experimental design was completely randomized. Readings were taken every 12 h during the first seven days, and every 24 h until germination had stabilized, using the embryo protusion as criterion for germination. We evaluated the initial, final and mean germination time, germinability, mean germination rate, rate (Maguire's index), coefficient of variation of the germination time, uncertainty and synchronization (Ranal & Santana 2006).

To evaluate the osmotic effect of the extract obtained, we performed a germination bioassay with lettuce and onion diaspores in solutions of polyethylene glycol 6000 (PEG 6000) at -0.2 and -0.3 MPa, as well as the control (0 MPa), following recommendations by Villela et al. (1991). The experiment was performed using the same methodology described for the germination bioassay.

The term "diaspore" has been used throughout the text to refer to both types of dispersion units studied. When the lettuce and onion were referred to individually, the specific name of their diaspores were used; in this case, cypsela and seed, respectively.

Growth bioassay

The dispersion units of lettuce and onion were germinated in distilled water, and only seedlings with up to 3 mm of primary roots were transferred into clear plastic boxes (21.0 × 14.3 × 6.0 cm) containing, as a substrate, filter paper moistened with 15 ml of distilled water (control) or aqueous extracts of young leaves at the same concentrations adopted for the germination test. The boxes were kept in a growth chamber at 25ºC, with a photoperiod of 12 hours and mean irradiance of 13.38 ± 7.96 µmol m^-2 s^-1. Four replicates of 20 seedlings were used in a completely randomized experimental design. After seven days, the seedling shoots and primary root lengths were measured in a random sample of 10 seedlings per replicate, using a caliper. The seedlings were classified as normal or abnormal, according to the specifications established by Brasil (2009), and dead seedlings were quantified.

Chemical extraction

We used 600 g of powder S. saponaria young leaves and 6000 ml of organic solvents. In a glass container with a cover, we performed extraction with the following solvents, in ascending order by polarity: hexane, dichloromethane, ethyl acetate, acetone and methanol. For each solvent, the container was kept in an ultrasonic bath for 30 min. The mixture was then filtered through a Buchner funnel lined with filter paper and coupled to a vacuum pump. The extract was evaporated in a rotary evaporator under reduced pressure at 40ºC. This extraction was repeated three times for each solvent (Macías et al. 2010). Thus, the extracts obtained after filtering and drying were hexane, dichloromethane, ethyl acetate, acetone and methanol.

Wheat coleoptiles bioassay

Wheat caryopses (T. aestivum cv. BRS Camboatá) were sown in plastic boxes lined with two sheets of filter paper (moistened with 10 ml of distilled water) and covered with aluminum foil. The boxes were maintained in the dark at 25ºC for 72 h. Shoots were placed in a Van der Weij guillotine and the apical meristem (2 mm) was cut and discarded. The next 4 mm of the coleoptile sections were removed and used for bioassay. All manipulations were performed under green safelight (Macías et al. 2010).

The solutions were prepared with 10 mg of each extract, pre-dissolved in 5 µL ml^-1 of dimethyl sulfoxide and diluted in a phosphate-citrate buffer (250 ml distilled water, 5 g sucrose, 0.2625 g citric acid and 0.725 g dibasic potassium phosphate, pH 5.6), at concentrations of 800, 400 and 200 ppm. In test tubes were added 2 mL of the solutions containing five wheat coleoptiles (Macias et al. 2010). We used a negative control, containing buffer solution and dimethyl sulfoxide, and a positive control, containing nicosulfuron herbicide (40 g L^-1).

The tubes were randomly distributed among the different treatments and were maintained at 25ºC in the dark under a constant rotation of 0.25 rpm, with three repetitions per treatment (Macias et al. 2010). After 24 h, the coleoptiles were removed from the tubes and measured using the image digitization program (Image-Pro plus; Media Cybernetics, Silver Spring, MD, USA).

Chromatographic fractionation

The ethyl acetate extract obtained from direct solvent extraction, selected based on the wheat coleoptile bioassay, was submitted to fractionation on a chromatography column containing common silica as the stationary phase, under atmospheric pressure. For the mobile phase (Fig. 1), we used hexane 100 (250 ml); hexane/acetone at 95:5 (1400 ml), 90:10 (1100 ml), 80:20 (1500 ml), 70:30 (1000 ml), 60:40 (1000 ml), 40:60 (1000 ml), and 20:80 (900 ml); acetone 100 (500 ml); and methanol 100 (500 ml).

This procedure yielded 129 fractions, which were grouped in accordance with data obtained through thin layer chromatography, resulting in a total of 10 fractions (Fig. 1). Each chromatoplate was observed under ultraviolet light at wavelengths of 254 and 365 nm, and revealed with Oleum (a solution containing 10 ml of sulfuric acid, 200 ml of acetic acid and 40 ml of distilled water), and then heated to 150ºC. The resulting fractions were subjected to bioassay with wheat coleoptiles, as previously described.

Statistical analysis

The data were subjected to normality (Shapiro-Wilk) and homogeneity (Levene) tests. When those two assumptions were met, an analysis of variance (ANOVA) was applied, followed by Tukey's test, at a significance level of 0.05. In case of a lack of normality or homogeneity or both, the non-parametric Kruskal-Wallis and Dunn tests were applied for pairwise comparisons at a significance level of 0.05.

Polynomial or exponential regression models were adjusted when the ANOVA F was significant. The goodness of the models was evaluated by its coefficient of determination (R²). For the variables that showed no significant differences between treatments, the means were represented in the figures with their standard deviations.

Results and discussion

The aqueous extract of S. saponaria young leaves showed phytotoxic effect on the germination of lettuce and onion diaspores. The extract had a strong inhibitory effect on the lettuce: at concentrations of 7.5% and 10.0%, no cypsela germinated (Fig. 2 and Tab. 1). The estimated maximum final germination time of onion seeds was 169 h in extract at a concentration of 4.11%, and there was a linear reduction in germinability of 8% for each addition of 0.01 mg ml^-1 of extract. The coefficient of variation of the germination time (12.13%), as was uncertainty (0.73 bits) and the rate of onion seeds (0.02666 seeds h^-1) were lower at a concentration of 10.0%, indicating late germination and greater homogeneity of germinated seeds (Fig. 2). Other variables showed no significant differences between the concentrations (Fig. 2 and Tab. 1). Lettuce cypselas are widely used in allelopathy tests and are known for their sensitivity to plant extracts, which have the potential not only to reduce germinability but also to slow mean germination rate and other germination process variables (Wandscheer & Pastorini 2008; Scrivanti 2010, Souza et al. 2010).

In growth bioassays, the absence of normal seedlings of lettuce treated with extract of S. saponaria young leaf, can be seen at concentrations of > 2.5% (Fig. 3), while for the onion from the 5% concentration (Fig. 4). In addition, we observed a linear increase of 6.05% of dead lettuce seedlings for each 0.01 mg ml^-1 of extract added, and the proportion of dead onion seedlings reached its maximum estimated (91.32%) at a concentration of 12.55% (Fig. 3 and 4). The lowest shoot length for lettuce and onion seedlings were recorded at estimated concentrations of 7.30% and 7.59%, respectively (Fig. 3), whereas the lowest root length was recorded at concentrations of 6.95% and 7.09%, respectively (Fig. 4).

The main features found among abnormal lettuce and onions seedlings treated with S. saponaria young leaf extracts were the rotting, necrosis, complete atrophy or total absence of roots and shoots. These anomalies have been recorded in studies of lettuce seedlings treated with extracts of Aristolochia esperanzae Kuntze (Gatti et al. 2004) and Esenbeckia leiocarpa Engl. (Souza et al. 2010). The root system was more sensitive to allelochemicals than shoot seedling Root sensitivity to allelochemicals is well documented in the literature, as it is one of the characteristics that best indicates the phytotoxicity of plant extracts (Inoue et al. 2010; Souza et al. 2010; Grisi et al. 2012). This can be attributed to the fact that root growth is characterized by high metabolic rates and the roots are therefore highly susceptible to environmental stress, such as allelochemicals in the substrate (Cruz-Ortega et al. 1 998).

We found that S. saponaria young leaf extracts had a pH of 6.21, with an osmotic potential of -0.32 MPa. Although extreme acidity or alkalinity have been shown to have a negative effect on germination and seedling development (Souza Filho et al. 1996), we observed no such effect related to the pH of the extract.

In PEG-6000 solutions with osmotic potentials of 0, -0.2 and -0.3 MPa, respectively, 89%, 86% and 82% of lettuce cypselas germinated, compared with 90%, 89% and 86% of onion seeds. Considering that solutions with osmotic potential of -0.3 MPa did not significantly influence the germinability of these diaspores, we can infer that the reduction in the germination occurred mainly due to the presence of substances with phytotoxic activity in these extracts. Our decision to perform chemical extraction and fractionation of the powder of S. saponaria young leaves was based on these results, which indicated that the aqueous extract of the leaves is phytotoxic to lettuce and onions, inhibiting diaspore germination and seedling growth.

The various extracts, obtained through the direct extraction of the powder of S. saponaria young leaves with organic solvents, had varying yields (Fig. 1). Extracts with the highest polarity, such as that obtained with methanol (12.647 g), showed the highest yields. This might be due to the presence of free sugars, glycosylated products and hydrosoluble proteins (Stacciarini-Seraphin 2001) in the young leaves of the species.

As can be seen in Fig. 5, the extracts that showed significant inhibitory effect, compared to the negative control, were those obtained with ethyl acetate or acetone, and a similar effect was observed for the positive control (herbicide). The maximum inhibition recorded was 72% (at 800 ppm) for the ethyl acetate extract and 54% (at 400 ppm) for the acetone extract. Therefore, we selected the ethyl acetate extract for use in the column chromatography fractionation. In addition, the inhibitory effect of the ethyl acetate extract on the elongation of wheat coleoptiles was similar to that of the herbicide, which presented 72% inhibition at a dilution of 800 ppm. For most of the extracts tested, we observed no dose-dependent relationship, which can be explained by their low solubility in aqueous media.

As can be seen in Weston et al. (1989) and An et al. (2000), ethyl acetate has often been used to extract phytotoxins from plant residues. The ethyl acetate fraction obtained from the ethanol extract of Senna occidentalis (L.) Link had effects on the germination and growth of lettuce, tomato and onion that are similar to those obtained with commercial herbicides (Cândido et al. 2010). In addition, Souza Filho et al. (2006) showed that the ethyl acetate fraction from the leaves of Myrcia guianensis (Aubl.) DC. has an inhibitory effect on the germination of Mimosa pudica L..

From the ethyl acetate extract, we obtained 11 fractions (Fig. 1), which were subjected to bioassay with wheat coleoptiles. There was significant inhibition in relation to the negative control in the fractions 4 (at 800 ppm), 6 (at 200, 400 and 800 ppm), 7 (at 200, 400 and 800 ppm), 8 (at 200 ppm), 9 (at 200, 400 and 800 ppm) and 10 (at 200, 400 and 800 ppm). In terms of the mean length of wheat coleoptiles, fraction 6 showed the highest inhibitory activity (5.83 mm), similar to that of the herbicide (5.50 mm), indicating that the fraction contains organic compounds that are phytotoxic (Fig. 6).

In fractions 8, 9 and 10, the shortest wheat coleoptile lengths (5.20 mm, 5.99 mm and 6.01 mm, respectively) were recorded at the 200 ppm dilution (Tab. 3), indicating that phytotoxic activity is greater at lower dilutions. Phytotoxic potential can vary as a function of the concentration of the solutions tested. Some authors claim that the action of allelochemical substances is not very specific and that the same substance can perform several functions, depending on its concentration and form of translocation (Maraschin-Silva & Aquila 2005).

Young leaves, for lack of physical protection, such as thorns and trichomes, often depend on the production of secondary metabolites to defend themselves against environmental aggression, such as that of herbivores. Because many species defend themselves metabolically in their juvenile stages of development (Bryant & Julkunen-Tiitto 1995), we can assumed that the concentration of allelochemicals is higher in young leaves than in mature leaves. This also applies to S. saponaria, Grisi et al. (2012) having reported that the phytotoxicity of young leaves of this species is greater than that of mature leaves. Other studies have also shown that the inhibitory effect decreases as age increases, being highest at the early stages of plant development (Kobayashi et al. 2,008; Marchi et al. 2008). These results suggest that the maturation stage influences the production of allelochemicals and that phytochemical studies using young leaves may be more promise in the search for new substances.

There is a need for further fractionation using fraction 6 (57-70) of the ethyl acetate extract obtained from the powder of S. saponaria young leaves. Such studies should employ column chromatography, as well as purification with high-performance liquid chromatography and proton nuclear magnetic resonance, in order to identify the class of compounds responsible for the phytotoxic effect observed. However, it is important to note that bioguided fractionation is a useful and essential tool for the isolation of active compounds.

Acknowledgments

This study received financial support from the Brazilian agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Office for the Advancement of Higher Education), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, National Council for Scientific and Technological Development).

Submitted: 3 December, 2010

Accepted: 10 October, 2012

References

• Abrahim, D.; Braquini, W.L.; Kelmer-Bracht, A.M. & Ishii-Iwamoto, E.L. 2000. Effects of four monoterpenes on germination, primary root growth, and mitochondrial respiration of maize. Journal of Chemical Ecology 26(3):611-624
• Albiero, A.L.M.; Bacchi, E.M. & Mourão, K.S.M. 2001. Caracterização anatômica das folhas, frutos e sementes de Sapindus saponaria L. (Sapindaceae). Acta Scientiarum 23(2):549-560.
• An, M.; Haig, T. & Pratley, J.E. 2000. Phytotoxicity of vulpia residues: ii. separation, identification, and quantitation of allelochemicals from Vulpia myuros Journal of Chemical Ecology 26(6):1465-1476.
• Brasil. 2009. Regras para análise de sementes Brasília, Ministério da Agricultura e Reforma Agrária.
• Bryant, J.P. & Julkunen-Tiitto, R. 1995. Ontogenic development of chemical defense by seedling resin birch: energy cost of defense production. Journal of Chemical Ecology 21(7):883-895.
• Cândido, A.C.S; Schmidt, V.; Laura, V.A.; Faccenda, O.; Hess, S.C.; Simionatto, E. & Peres, M.T.L.P. 2010. Potencial alelopático da parte aérea de Senna occidentalis (L.) Link (Fabaceae, Caesalpinioideae): bioensaios em laboratório. Acta Botanica Brasilica 24(1):235-242.
• Chaves Filho, J.T. & Stacciarini-Seraphin, E. 2001. Alteração no potencial osmótico e teor de carboidratos solúveis em plantas jovens de lobeira (Solanum lycocarpum St.-Hil.) em resposta ao estresse hídrico. Revista Brasileira de Botânica 24(2):199-204.
• Croteau, R.; Kutchan, T.M. & Lewis, N.G. 2000. Natural products (secondary metabolites). Pp. 1250-1268. In: Buchanan, B.; Gruissem, W. & Jones, R. (Eds). Biochemistry & molecular biology of plants American Society of Plant Physiologists, Rockville, MD.
• Cruz-Ortega, R.; Anaya, A. L.; Hernández-Bautista, B. E. & Laguna-Hernández, G. 1998. Effects of allelochemical stress produced by Sicyos deppei on seedling root ultrastructure of Phaseolus vulgaris and Cucurbita ficifolia Journal of Chemical Ecology 24(12):2039-2057.
• Dayan, F.E. & Duke, S.O. 2006. Clues in the search for new herbicides. In: Reigosa, M.E.; Pedrol, N.& L. Gonzaléz. Allelopathy - a physyiological process with ecological implications Spring Verlag, Netherlands.
• Gatti, A.B.; Perez, S.C.J.G.A. & Lima, M.I.S. 2004. Atividade alelopática de extratos aquosos de Aristolochia esperanzae O. Kuntze na germinação e no crescimento de Lactuca sativa L. e Raphanus sativus L. Acta Botanica Brasilica 18(3):459-472.
• Gniazdowska, A. & Bogatek, R. 2005. Allelopathic interactions between plants. Multi site action of allelochemicals. Acta Physiologiae Plantarum 27(3B):395-407.
• Grisi, P.U.; Ranal, M.A.; Gualtieri, S.C.J. & Santana, D.G. 2012. Allelopathic potential of Sapindus saponaria L. leaves in the control of weeds. Acta Scientiarum Agronomy 34(1):1-9.
• Guarim Neto, G.; Santana, S.R. & Silva, J.V.B. 2000. Notas etnobotânicas de espécies de Sapindaceae Jussieu. Acta Botanica Brasilica 14(3):327-334.
• Hamburger, M. & Hostettmann, K. 1991. Bioactivity in plants: The link between phytochemistry and medicine. Phytochemistry 30(12):3864-3874.
• Iganci, J.R.V.; Bobrowski, V.L.; Heiden, G.; Stein, V.C. & Rocha, B.H.G. 2006. Efeito do extrato aquoso de diferentes espécies de boldo sobre a germinação e índice mitótico de Allium cepa L. Arquivo do Instituto Biológico 73(1):79-82.
• Inoue, M.H.; Santana, D.C.; Vilhena, K.S.S.; Souza Filho, A.P.S.; Guilhon, G.M.S.P.; Possamai, A.C.S.; Silva, L.E. & Dallacort, R. 2010. Avaliação do potencial alelopático de substâncias isoladas em sementes de araticum (Annona crassiflora). Planta Daninha 28(4):735-741.
• Kobayashi, S.; Asai, T.; Fujimoto, Y & Kohshima, S. 2008. Anti-herbivore structures of Palouwnia tomentosa: Morphology, distribution, chemical constituents and changes during shoot and leaf development. Annals of Botany 101(7):1035-1047.
• Köppen, W. 1948. Climatologia com um estúdio de los climas de la tierra (traduzido por. P.R.H. Pérez). México, Fondo de Cultura Econômica.
• Macías, F.A.; Galindo, J.L.G.; Varela, R.M.; Torres, A.; Molinillo, J.M.G. & Fronczek, F.R. 2006. Heliespirones B and C: Two New Plant Heliespiranes with a Novel Spiro Heterocyclic Sesquiterpene Skeleton. Organic Letters 8(20):4513-4516.
• Macías, F.A.; Lacret, R.; Varela, R.M.; Nogueiras, C. & Molinillo, J.M.G. 2010. Isolation and phytotoxicity of terpenes from Tectona grandis Journal of Chemical Ecology 36(4):396-404.
• Maraschin-Silva, F. & Aqüila, M.E.A. 2005. Potencial alelopático de Dodonaea viscosa (L.) Jacq. Iheringia 60(1):91-98.
• Marchi, G.; Marchi, E.; Wang, G. & Mcgiffen, M. 2008. Effect of age of a sorgum-sudangrass hibrid on its allelopathic action. Planta Daninha 26(4):707-716.
• Marzinek, J.; De-Paula, O.C. & Oliveira, D.M.T. 2008. Cypsela or achene? Refining terminology by considering anatomical and historical factors. Revista Brasileira de Botânica 31(3):549-553.
• Murgu, M. & Rodrigues-Filho, E. 2006. Dereplication of Glycosides from Sapindus saponaria using Liquid Chromatography-Mass Spectrometry. Journal of Brazilian Chemical Society 17(7):1281-1290.
• Pelegrini, D.D.; Tsuzuki, J.K.; Amado, C.A.B.; Cortez, D.A.G. & Ferreira, I.C.P. 2008. Biological activity and isolated compounds in Sapindus saponaria L. and other plants of the genus Sapindus Latin American Journal of Pharmacy 27(6):922-927.
• Povh, J.A.; Pinto, D.D.; Corrêa, M.O.G. & Ono, E.O. 2007. Atividade alelopática de Machaerium acutifolium Vog. na germinação de Lactuca sativa L. Revista Brasileira de Biociências 5(2):447-449.
• Ranal, M.A. & Santana, D.G. 2006. How and why to measure the germination process? Revista Brasileira de Botanica 29(1):1-11.
• Rizvi, S.J.H. & Rizvi, V. 1992. Exploration of allelochemicals in improving crop productivity. Pp. 443-472. In: Rizvi, S.J.H. & Rizvi, V. (Eds.). Allelopathy: basic and applied aspects London, Chapman and Hall.
• Scrivanti, L.R. 2010. Allelopathic potential of Bothriochloa laguroides var. laguroides (DC.) Herter (Poaceae: Andropogoneae). Flora 205(5):302-305.
• Singh, A.; Singh, D. & Singh, N.B. 2009. Allelochemical stress produced by aqueous leachate of Nicotiana plumbaginifolia Viv. Plant Growth Regulation 58(2):163-171.
• Souza, F.M.; Gandol, S.; Perez, S.C.J.G.A. & Rodrigues, R.R. 2010. Allelopathic potential of bark and leaves of Esenbeckia leiocarpa Engl. (Rutaceae). Acta Botanica Brasilica 24(1):169-174.
• Souza Filho, A.P.S.; Rodrigues, L.R.A. & Rodrigues, T.J.D. 1996. Efeitos de extratos aquosos de assa-peixe sobre a germinação de três espécies de braquiária. Planta Daninha 14(2):93-101.
• Souza Filho, A.P.S.; Santos, R.A.; Santos, L.S.; Guilhom, G.M.P.; Santos, A.S.; Arruda, M.S.P.; Muller, A.H. & Arruda, A.C. 2006. Potencial alelopático de Myrcia guianensis. Planta Daninha 24(4):649-656.
• Sparg, S.G.; Light, M.E. & Van Staden, J. 2004. Biological activities and distribution of plant saponins. Journal of Ethnopharmacology 94(2-3):219-243.
• Teerarak, M.; Laosinwattana, C. & Charoenying, P. 2010. Evaluation of allelopathic, decomposition and cytogenetic activities of Jasminum officinale L. f. var. grandiflorum (L.) Kob. on bioassay plants. Bioresource Technology 101(14):5677-5684.
• Villela, F.A.; Doni Filho, L. & Sequeira, E.L. 1991. Tabela de potencial osmótico em função da concentração de polietileno glicol 6000 e da temperatura. Pesquisa Agropecuária Brasileira 26:1957-1968.
• Vyvyan, J.R. 2002. Allelochemicals as leads for new herbicides and agrochemicals. Tetrahedron 58(9):1631-164.
• Wandscheer, A.C.D. & Pastorini, L.H. 2008. Interferência alelopática de Raphanus raphanistrum L. sobre a germinação de Lactuca sativa L. e Solanum lycopersicon L. Ciência Rural 38(4):949-953.
• Weston, L.A.; Harmon, R. & Mueller, S. 1989 Allelopathic potential of sorghum-sudangrass hybrid (sudex). Journal of Chemical Ecology 15(6):1855-1865.

Publication Dates

• Publication in this collection
  08 May 2013
• Date of issue
  Mar 2013

History

• Received
  03 Dec 2010
• Accepted
  10 Oct 2012