http://www.saber.ula.ve/handle/123456789/880 Articulos, Pre-prints del Grupo de Química Ecológica 2026-04-26T22:10:06Z http://www.saber.ula.ve/handle/123456789/16805 Structure-Activity Relationships (SAR) studies of Benzoxazinones, their degradation products and analogues. Phytotoxicity on Standard Target Species (STS). Oliveros Bastidas, Alberto; Macías, Francisco A.; Marín, David; Castellano, Diego; Simonet, Ana M.; Molinillo G., José Structure-Activity Relationships (SAR) studies of Benzoxazinones, their degradation products and analogues. Phytotoxicity on Standard Target Species (STS) (Macías, Francisco A.; Marín, David; Oliveros, Alberto; Castellano, Diego; Simonet, Ana M. and Molinillo G., José M.) Abstract Benzoxazinones 2,4-dihydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIMBOA) and 2,4-dihydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA) have been considered key compounds for understanding allelopathic phenomena in Gramineae crop plants such as corn ( Zea maysL.), wheat ( Triticum aestivumL.), and rye ( Secale cerealeL.). The degradation processes in the environment observed for these compounds, in which soil microbes are directly involved, could affect potential allelopathic activity of these plants. We present in this work a complete structure-activity relationships study based on the phytotoxic effects observed for DIMBOA, DIBOA, and their main degradation products, in addition to several synthetic analogues of them. Their effects were evaluated on standard target species (STS), which include Triticum aestivumL. (wheat) and Allium cepaL. (onion) as monocots and Lepidium sativum L. (cress), Lactuca sativa L. (lettuce), and Lycopersicon esculentum Will. (tomato) as dicots. This permitted us to elucidate their ecological role and to propose new herbicide models based on their structures. The best phytotoxicity results were shown by the degradation chemical 2-aminophenoxazin-3-one (APO) and several 2-deoxy derivatives of natural benzoxazinones, including 4-acetoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (ABOA), 4-hydroxy-(2 H)-1,4-benzoxazin-3(4 H)- one (D-DIBOA), and 4-hydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (D-DIMBOA). They showed high inhibitory activity over almost all species growth. The fact that APO is a degradation product from DIBOA with high phytotoxicity and stability makes it possible to assign an important ecological role regarding plant defense mechanisms. 2-Deoxy derivatives of natural benzoxazinones display a wide range of activities that allow proposing them as new leads for natural herbicide models with a 1,4-benzoxazine skeleton. © 2005 American Chemical Society. Published on Web 01/19/2005. 2008-07-15T09:00:00Z http://www.saber.ula.ve/handle/123456789/16809 Hydrogen cyanide release during feeding of generalist and specialist lepidopteran larvae on a cyanogenic plant, Passiflora capsularis. Alonso Amelot, Miguel; Avila Nuñez, Jorge Luis; Duarte, Lisday; Oliveros Bastidas, Alberto Hydrogen cyanide release during feeding of generalist and specialist lepidopteran larvae on a cyanogenic plant, Passiflora capsularis. (Alonso Amelot, Miguel; Avila Nuñez, Jorge Luis; Duarte, Lisday y Oliveros Bastidas, Alberto) Abstract The hydrogen cyanide-based interaction of a strongly cyanogenic plant, Passiflora capsularis, and larvae of two insect herbivores, a generalist (Spodoptera frugiperda) and a specialist (Heliconius erato), is examined in terms of the combined kinetics of the feeding process and the simultaneous hydrogen cyanide (HCN) liberation, as compared with the natural kinetics of hydrogen cyanide evolution by plant-leaf tissue. There are marked differences in acceptance of P. capsularis by third-instar larvae of specialist and generalist species. The former, H. erato, display a parsimonious ingestion rate of 0.74 ± 0.15 mg (fresh weight) min-1 comprising 18% active feeding time, whereas S. frugiperda larvae show a more erratic and restrained feeding involving 4% of the time at 0.45 ± 0.14 mg min-1. These S. frugiperda larvae ingest 124.4 ± 8.3 mg (fw) of the non-cyanogeneic Spinacia oleracea leaves in 24 h compared with only 74.7 ± 20.1 mg of P. capsularis in the same period. The total hydrogen cyanide released naturally from wild specimens of P. capsularis plants is in the range 326 - 3901 µ g g-1. Hydrogen cyanide evo lution from macerated P. capsularis leaves takes place along a hyperbolic function with time and initial velocities of cyanide evolution are a linear function of total hydrogen cyanide. When feeding on P. capsularis leaves, H. erato releases only a minor fraction relative to total hydrogen cyanide (0.09%) and to the anticipated cyanide from the initial velocity (7%). By contrast, S. frugiperda evokes 5.8-fold more than the anticipated hydrogen cyanide release from the plant. The findings are interpreted as diverging strategies by generalist and specialist insects in the utilization of hydrogen cyanide in cyanogenic plants. 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16817 Phenolics and condensed tannins of high altitude Pteridium arachnoideum in relation to sunlight exposure, elevation, and rain regime. Alonso Amelot, Miguel; Oliveros Bastidas, Alberto; Calcagno P., María Pía Phenolics and condensed tannins of high altitude Pteridium arachnoideum in relation to sunlight exposure, elevation, and rain regime. (Alonso Amelot, Miguel; Oliveros Bastidas, Alberto y Calcagno P., María Pía) Abstract Non-adapted plants growing in high altitude such as bracken fern Pteridium arachnoideum are exposed to environmental extremes that may induce a chemical adaptive response. Here we show that there is a non-uniform distribution of low (LMP) and high molecular weight (HMP) phenolics in the frond parts of P. arachnoideum growing at high elevation. LMPeHMP levels were measured in sun-exposed (E) and self shaded (SS) pinnae between 2100 and 3190 m in the tropical Andes, during dry and rainy seasons. While there was no difference in E vs. SS contents of LMP at 2100 m, E accumulated greater LMPeHMP concentrations relative to SS as altitude increased. This difference was increased during the dry season. Linear correlations between the position of each pinnae relative to the ground level and LMPeHMP occurred along a 2570e3190 m transect. Water restriction in the dry season also caused increase of LMP and HMP.We conclude that excess UV-B radiation and water availability are important modelers of the non-adapted plant acclimation response to stress in tropical high mountain habitats. 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16816 Allelopathy as a new strategy for sustainable ecosystems development. Macías, Francisco A.; Marín, David; Oliveros Bastidas, Alberto; Varela, Rosa E.; Simonet, Ana M.; Carrera, Ceferino; Molinillo G., José Allelopathy as a new strategy for sustainable ecosystems development. (Macías, Francisco A.; Marín, David; Oliveros Bastidas, Alberto; Varela, Rosa E.; Simonet, Ana M.; Carrera, Ceferino y Molinillo G., José) Abstract Natural products involved in plant-plant and plant-microorganism ecological interaction (Allelochemicals) are an important potential source for alternative agrochemicals and pharmaceuticals, in order to solve the many problems derived from inadequate culture practices and abuse of synthetic herbicides. Isolation, structural determination, bioassay techniques and applicability for these compounds in crop protection and pharmaceutical research are discussed, and future trends on Allelochemicals applications are examined. The new strategies for sustainable ecosystem controlled by allelochemicals offer a particular interest for the development of human bases in space, since these products can stimulate or inhibit plant germination and growth, and permit to develop crops with low residue amounts in water, facilitating wastewater treatment and recycling. 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16810 Effects of Minthostachys mollis essential oil and volatiles on seedlings of lettuce, tomato, cucumbre and Bidens pilosa. Alonso Amelot, Miguel; Usubillaga, Alfredo; Avila Nuñez, Jorge Luis; Oliveros Bastidas, Alberto; Avendaño Meza, Marisabel Effects of Minthostachys mollis essential oil and volatiles on seedlings of lettuce, tomato, cucumbre and Bidens pilosa. (Alonso Amelot, Miguel; Usubillaga, Alfredo; Avila Nuñez, Jorge Luis; Oliveros Bastidas, Alberto y Avendaño Meza, Mairsabel) Abstract The extraction and chemical composition of essential oil of Minthostachys mollis (Kunth) Griseb (Lamiaceae) and its inhibitory effects on germation and shoot/root elongation of lettuce, tomato, cucumber and Bidens pilosa (L.) var pilosa described. Hydrodistillation gave 2.9% (v/w) of essential oil (97.8% of terpenoids). Pulegone (83.6%), menthone (7.6%), limonene (2.0%) linaloo (1.2%), and isomenthone (0.8%) were the major components of essential oil. This oil was applied at 1.0, 2.5 and 5.0 ul on filter paper disks for bioassay. The seed germination of all test spp was completely inhibited even with the lowest dose. Five days-old transplants of seedlings (7 days for B. pilosa) exposed to 5, 10 and 20 ppm of oil in the vapour phase inhibited the elongation of shoot more than root and its inhibitions was concentration dependent B. pilosa was inhibited at 20 ppm with necrosis of hypocotyls. 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16814 Allelopathy. Macías, Francisco A.; Molinillo G., José; Oliveros Bastidas, Alberto; Marín, David; Chinchilla, Nuria 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16807 Optimization of Benzoxazinones as natural herbicide models by Lipophilicity enhancement. Macías, Francisco A.; Marín, David; Oliveros Bastidas, Alberto; Molinillo G., José Optimization of Benzoxazinones as natural herbicide models by Lipophilicity Enhancement. (Macías, Francisco A.; Marín, David; Oliveros Bastidas, Alberto y Molinillo G., José Abstract Benzoxazinones are plant allelochemicals well-known for their phytotoxic activity and for taking part in the defense strategies of Gramineae, Ranunculaceae, and Scrophulariceae plants. These properties, in addition to the recently optimized methodologies for their large-scale isolation and synthesis, have made some derivatives of natural products, 2,4-dihydroxy-(2H)-1,4-benzoxazin-3-(4H)-one (DIBOA) and its 7-methoxy analogue (DIMBOA), successful templates in the search for natural herbicide models. These new chemicals should be part of integrated methodologies for weed control. In ongoing research about the structure-activity relationships of benzoxazinones and the structural requirements for their phytotoxicity enhancement and after characterization of the optimal structural features, a new generation of chemicals with enhanced lipophilicity was developed. They were tested on selected standard target species and weeds in the search for the optimal aqueous solubility-lipophilicity rate for phytotoxicity. This physical parameter is known to be crucial in modern drug and agrochemical design strategies. The new compounds obtained in this way had interesting phytotoxicity profiles, empowering the phytotoxic effect of the starting benzoxazinone template in some cases. Quantitative structure-activity relationships were obtained by bioactivity-molecular parameters correlations. Because optimal lipophilicity values for phytotoxicity vary with the tested plant, these new derivatives constitute a more selective way to take advantage of benzoxazinone phytotoxic capabilities. 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16803 Structure-Activity Relationship (SAR) studies of benzoxazinones, their degradation products, and analogues. Macías, Francisco A.; Marín, David; Oliveros Bastidas, Alberto; Castellano, Diego; Simonet, Ana M.; Molinillo G., José Structure-activity relationship (SAR) studies of benzoxazinones, their degradation products, and analogues. Phytotoxicity on problematic weeds Avena fatua L. and Lolium rigidum Gaud. (Macías, Francisco A.; Marín, David; Oliveros Bastidas, Alberto; Castellano, Diego; Simonet, Ana M. y Molinillo G., José Abstract Avena fatua L. (wild oat) and Lolium rigidum Gaud. (rigid ryegrass) are highly problematic weeds affecting a wide variety of cereal crops worldwide. The fact that both of these weeds have developed resistance to several herbicide groups made them optimal candidates as target organisms for ongoing research about the potential application of allelochemicals and analogue compounds as natural herbicide models. Benzoxazinones, a family of natural allelochemicals present in corn, wheat, and rye, including 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one, together with some degradation products, found in crop soils as well as in other systems, and some synthetic analogues of them were tested on wild oat and rigid ryegrass seeds; the results were statistically treated, and some structure-activity relationships, useful in further development of natural herbicide models, were elucidated. The most active compounds were the synthetic benzoxazinone 2-acetoxy-(2H)-1,4-benzoxazin-3(4H)-one and the degradation product 2-aminophenoxazin-3-one, with highly significant inhibition on the development of both weeds. The ecological role of these compounds is discussed by considering both degradability and phytotoxicity. The bioactivity of aminophenoxazines has been correlated by their aqueous solubility-lipophilicity predicted by means of computational methods. 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16801 Allelpathic studies in sostainable agriculture: development of new agrochemicals. Macías, Francisco A.; Molinillo G., José; Oliveros Bastidas, Alberto; Marín, David; Chinchilla, Nuria 2007-04-09T09:00:00Z http://www.saber.ula.ve/handle/123456789/16802 A method for the practical quantification and Kinetic evaluation of Cyanogenesis in plant material. application to Pteridium aquilinum and Passiflora capsularis. Oliveros Bastidas, Alberto; Alonso Amelot, Miguel A method for the practical quantification and Kinetic evaluation of Cyanogenesis in plant material. application to Pteridium aquilinum and Passiflora capsularis (Alonso Amelot, Miguel and Oliveros, Alberto) Abstract A procedure for the quantitative determination of hydrogen cyanide (HCN) released by plants has been developed based on the UV-vis spectrum of the sodium picrate-cyanide complex. Fresh plant tissue mixed with toluene was placed in a gas flow system designed to carry the evolved HCN through 2,4- dinitrophenylhydrazine solution in acidic water:ethanol to trap interfering volatile carbonyl derivatives, and then into an alkaline solution of sodium picrate. After 18 h of gas flow at a rate of 6 mL/min, the absorbance of the solution was measured at 500 nm and the concentration of HCN was determined by calibration in the range 10-3 - 10-5 M. The molar absorptivity coefficient (1.385 L/cm M) yielded a detection limit of 2.6 x 10-6 mol/L and a 92.6 ± 2.6% recovery yield of HCN. The method was applied to determine the cyanide release capacity of Passiflora capsularis (up to 3.34 mg of HCN/g fresh plant tissue), and of croziers of Pteridium aquilinum var arachnoideum (10.4-61.3 mg of prunasin/g fresh plant tissue), and its rate of HCN production (K = 2.20 ± 0.01 x 10-4/s). Cymbopogon citratum, known to release large quantities of volatile, potentially interfering, monoterpene ketones and aldehydes, gave a negative reaction. Copyright © 2000 John Wiley & Sons, Ltd. This article was published on Phytochemical Analysis Phytochem. Anal. 11, 309-316 (2000) 2006-02-24T09:00:00Z http://www.saber.ula.ve/handle/123456789/16818 Degradation Studies on Benzoxazinoids. Soil Degradation Dynamics of 2,4-Dihydroxy-7-methoxy- (2 H)-1,4-benzoxazin-3(4 H)-one (DIMBOA) and Its Degradation Products, Phytotoxic Allelochemicals from Gramineae. Oliveros Bastidas, Alberto; Macías, Francisco A.; Marín, David; Castellano, Diego; Simonet, Ana M.; Molinillo G., José Degradation Studies on Benzoxazinoids. Soil Degradation Dynamics of 2,4-Dihydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIMBOA) and Its Degradation Products, Phytotoxic Allelochemicals from Gramineae (Macías, Francisco A.; Oliveros, Alberto; Marín, David; Castellano, Diego; Simonet, Ana M. and Molinillo G., José M.) Abstract Benzoxazinoids have been described as important allelochemicals from Gramineae as well as Acanthaceae, Rannunculaceae, and Scrophulariaceae plants. Several bioactivities have been described and evaluated for these compounds, including fungistatic, antifeedant, and phytotoxic. In ongoing studies about allelochemicals as natural herbicide models, the description of soil dynamics in phytotoxic agents has high importance, because the possible biotransformations developed by soil microorganisms could yield compounds with modified biological properties, affecting the overall allelopathic capability of the producer plant in a direct manner. Thus, a complete degradation study has been carried out for 2,4-dihydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIMBOA) and 6-methoxybenzoxazolin-2 (3 H)-one (MBOA) in two soils cultivated with Triticum aestivumL. Varieties (cv. Astron and cv. Ritmo). The main purpose was to identify degradation products and to elucidate biotransformation dynamics. Results show DIMBOA to degrade rapidly, yielding MBOA in both studied soils at different doses ( t1/2 ) 31 ( 1 h, n) 12) and reaching high conversions (80 ( 4 h, n) 42). MBOA, an intermediate in the degradation pathway from DIMBOA to 2-amino-7-methoxy-3 Hphenoxazin-3-one (AMPO), was more resistant toward biodegradation ( t1/2 ) 5 ( 1 days, n) 6). MBOA showed maximum conversions at a dose of 250 mg/kg of soil (36 ( 3 days, n ) 6). Soil belonging to T. aestivum cv. Ritmo crops showed higher degradation capacity than cv. Astron soil. AMPO was the final degradation product observed for DIMBOA in the soils and experimental conditions selected. Consequences for activity and stability of these compounds in relation to allelopathy are discussed. © 2004 American Chemical Society Published on: Journal of Agricultural and Food Chemistry 2004, 52, 6402-6413. 2005-07-27T09:00:00Z http://www.saber.ula.ve/handle/123456789/16811 Degradation Studies on Benzoxazinoids. Soil Degradation Dynamics of (2 R)-2-O-B-D- Glucopyranosyl-4-hydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA-Glc) and Its Degradation Products, Phytotoxic Allelochemicals from Gramineae. Oliveros Bastidas, Alberto; Macías, Francisco A.; Marín, David; Castellano, Diego; Simonet, Ana M.; Molinillo G., José Degradation Studies on Benzoxazinoids. Soil Degradation Dynamics of (2 R)-2-O-B-D-Glucopyranosy l-4-hydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA-Glc) and Its Degradation Products, Phytotoxic Allelochemicals from Gramineae (Macías, Francisco A.; Oliveros, Alberto; Marín, David; Castellano, Diego; Simonet, Ana M. and Molinillo G., José M.) Abstract Wheat (Triticum aestivumL.) has been found to possess allelopathic potential and studies have been conduced to apply wheat allelopathy for biological weed control. 2,4-Dihydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA) is a common product found in wheat, corn, and rye exudates and it can be released to the environment by that way. In this report, the stability of DIBOA is studied in two soils from crop lands of wheat cv. Astron and cv. Ritmo. These varieties were selected by their concentrations of DIBOA and 2,4-dihydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIMBOA) from aerial parts and by the bioactivities of their aqueous extracts in the growth of wheat coleoptiles sections. The degradation rate of DIBOA in these soils was measured in laboratory tests during 90 h by high-pressure liquid chromatography methods. These analyses demonstrate that DIBOA was transformed primarily into 2-benzoxazolinone (BOA). This transformation was similar in both soil types with an average half-life of 43 h. The degradation studies for BOA show its biotransformation to 2-aminophenoxazin-3-one (APO) with a half-life of 2.5 days. Therefore, BOA is an intermediate product in the biotransformation from DIBOA to APO in these wheat crop soils and is consistent with previous findings. APO was not degraded after three months in soil, suggesting that its degradation rate in soil is very slow. Published on: Journal of Agricultural and Food Chemistry 2005, 53, 554-561. 2005-07-27T09:00:00Z http://www.saber.ula.ve/handle/123456789/16815 Structure-Activity Relationship Studies of Benzoxazinones and Related Compounds. Phytotoxicity on Echinochloa crus-galli (L.) P. Beauv. Chinchilla, Nuria; Oliveros Bastidas, Alberto; Macías, Francisco A.; Marín, David; Molinillo G., José; Varela, Rosa E. Structure-Activity Relationship Studies of Benzoxazinones and Related Compounds. Phytotoxicity on Echinochloa crus-galli (L.) P. Beauv (Macías, Francisco A.; Chinchilla, Nuria; Varela, Rosa M.; Oliveros, Alberto; Marín, David; and Molinillo G., José M.) Abstract Echinochloa crus-galli ( E. crus-galli; barnyardgrass) is a weed widely distributed. It constitutes a serious weed problem in 42 countries and has been found in at least 27 more. It is the world's main weed of rice affecting up to 36 crops worldwide. Several biotypes of this plant, with resistance to herbicides with different modes of action have evolved. In our ongoing studies regarding the potential application of benzoxazinones and their soil degradation products for weed control, a complete structure-activity relationships (SARs) study was made by using barnyardgrass as the target plant. Compounds used in this study were previously tested on a wide variety of standard target species (STS), and they include natural allelochemicals 2- O-â-D-glucopyranosyl-4-hydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA-Glc), 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and 2,4-dihydroxy- (2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA), together with some degradation derivatives found in wheat crop soil and some synthetic analogues. Their phytotoxicity on E. crus-galliis discussed and compared with the results obtained from previous screening. This work constitutes the next step in the search for natural herbicide models based on benzoxazinones and their degradation products. The most active compounds were the degradation product 2-aminophenol (APH) and the synthetic analogue 4-hydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (D-DIBOA). Their activities confirm the direction proposed in our previous SAR study, which establishes D-DIBOA to be the best lead for natural herbicide model development with benzoxazinone structure. Published on: Journal Agricultural and Food Chemistry 2005-07-27T09:00:00Z http://www.saber.ula.ve/handle/123456789/16813 Phenolics and condensed tannins in relation to altitude in neotropical Pteridium spp. Oliveros Bastidas, Alberto; Alonso Amelot, Miguel; Calcagno P., María Pía Phenolics and condensed tannins in relation to altitude in neotropical Pteridium spp. A field study in the Venezuelan Andes (Alonso Amelot, Miguel; Oliveros, Alberto and Calcagno Pisarelli, María Pía) Abstract Two species of neotropical bracken, Pteridium caudatum (L.) Maxon (P.c.) and P. arachnoideum (Kaulf.) (P.a.), thrive dominantly in habitats extending from near the sea level to the Andean alpine zone around 3000 m altitude. The scope of sources of stress associated with elevation has three main components: plant competition for resources, activity of herbivores/ pathogens, and climate. The contribution of each component varies greatly from place to place and bracken must respond with considerable physiological/genetic plasticity to maintain its dominant status in all these habitats. Phenolic compounds have a number of properties for plant adaptation to evolutionary selective forces of biotic and climatic nature, in particular with reference to their protective role against excessive solar radiation. We have examined the second of these properties by studying the dynamics of low (LMP) and high (HMP) molecular weight phenolics in neotropical bracken ferns in two groups of field experiments: (1) their variation during the phenologic development of blades in sympatric populations of both bracken species to examine the synthesis and allocation of these materials under similar conditions of competition, predation and solar UV-B radiation; (2) the contents of LMP and HMP in six bracken populations of P.c. along its typical altitudinal range [1180-2140 m above sea level (asl)] and six additional populations of P.a. (1880-3190 m asl), which grows at higher elevations in the western Andes of Venezuela, to investigate the phenolics' response to the ecological gradients associated with elevation in these plants. From series (1), we recorded the progressive accumulation of both types of phenolics with frond expansion, and hence increased surface of lamina exposed to sunlight, in P.c. and P.a. However, phenolics in mature blades of P.a. were 1.6 (LMP) and 3.26 (HMP) greater in amount than in P.c. From series (2), synthesis and accumulation of LMP was found to be independent of altitude, except forthe subalpine population of P.a. at 3190 m asl, where a 167% increment of the average contents was recorded. By contrast, the levels of HMP correlated positively with elevation in both bracken species. The independent response of both types of phenolics to solar radiation may be interpreted as either more effective and metabolically cost-effective protection of HMP against UV-B light than LMP or differential light activation of key steps in the biosynthesis of HMP and LMP in bracken. © 2004 Elsevier Ltd. All rights reserved Published on: Biochemical Systematics and Ecology 32 (2004) 969-981 2005-07-01T09:00:00Z http://www.saber.ula.ve/handle/123456789/16799 Kinetics of the natural evolution of hydrogen cyanide in plants in neotropical Pteridium Arachnoideum and its ecological significance. Oliveros Bastidas, Alberto; Alonso Amelot, Miguel Kinetics of the natural evolution of hydrogen cyanide in plants in neotropical Pteridium Arachnoideum and its ecological significance (Alonso Amelot, Miguel and Oliveros, Alberto) Abstract The time-dependent natural release of hydrogen cyanide (HCN) was studied quantitatively using young croziers of the neotropical bracken fern Pteridium arachnoideum. HCN production was quantified in crushed tissue using a flow reactor at 30.0 ± 0.1?C. Released HCN was carried into appropriate traps with a moist air flow. Aliquots were drawn from the traps at fixed time intervals, and the HCN concentration was evaluated spectroscopically. All available prunasin (Pru), the only cyanogenic glycoside present, underwent decomposition into HCN in less than 1200 min. Fiddleheads (N = 76) contained 1.84-107.70 mg Pru g-1 dw in a continuous fashion suggesting genetic polymorphism. Acyanogenic morphs were rare (1/77). From the kinetics of the samples with Pru content near the median histographic distribution (N = 46), accumulated HCN formation as a function of time, initial velocities, average HCN production rate, and corresponding rate equations were obtained. Initial and average velocities correlated well with total Pru content. The yield of cyanide liberation varied widely between 0.51 and 47.86 µg HCN min-1 g-1 dw and was a linear function of [Pru]t. However, the ß-glucosidase enzyme involved in this reaction was not rate limiting and occurs in excess in the natural system. Enzyme activity was found to be independent of [Pru]t . The contribution of HCN as an allomone-upon-request against herbivores was assessed quantitatively. Bracken fiddleheads produced a pulse of HCN soon after tissue injury that waned rapidly, leaving a large portion of intact prunasin to decompose more slowly in the herbivore's lumen. The balance between the external and internal courses was found to depend on the concentration of prunasin in the plant, the amount of crozier eaten, and the time used to consume it. Journal of Chemical Ecology, Vol. 31, No. 2, February 2005 (©2005) DOI: 10.1007/s10886-005-1343-z 2005-07-01T09:00:00Z http://www.saber.ula.ve/handle/123456789/16806 Bracken adaptation mechanisms and xenobiotic chemistry. Oliveros Bastidas, Alberto; Alonso Amelot, Miguel; Calcagno P., María Pía; Arellano, Elida Bracken adaptation mechanisms and xenobiotic chemistry (Alonso Amelot, Miguel; Oliveros, Alberto; Calcagno Pisarelli, María Pía and Arellano, Elida) Abstract As opposed to animals, plants have to cope with the resources, environmental restrictions, herbivores, and pathogens they find in the particular spot where they are bound to grow. Hence, resource sequestration, predation and competition relationships, and adaptation to various sources of other environmental stresses and their seasonal variation must be flexible enough to ensure survival and successful reproduction. Plants express this fitness by a combination of biological traits and chemical arsenals which operate under the reign of a genome of considerable plasticity. For the great majority of plants it is either the biological characters or the chemical composition that are explored independently to understand their fitness. But only in a few instances is the combination of these two avenues examined jointly. The extensive studies on the ecology, chemistry, and toxicology of bracken (Pteridium aquilinum) make this fern one of the few examples where a reasonable explanation for its extraordinary success is beginning to emerge by the combined perception of these two most important aspects of plant life. It is the purpose of this article to briefly review how the sum of biological and chemical traits cooperates to make of bracken one of the five most pernicious weeds in the world today. © 2001 IUPAC Pure Appl. Chem., Vol. 73, No. 3, pp. 549-553, 2001 Lecture presented at the 22nd IUPAC International Symposium on the Chemistry of Natural Products, São Carlos, Brazil, 3-8, September 2000. Other presentations are published in this issue, pp. 549-626. 2005-07-01T09:00:00Z