ArticlePDF Available

Evaluation of total phenolics, anthocyanins and antioxidant capacity in purple tomatillo (Physalis ixocarpa) genotypes

Authors:

Abstract

Purple tomatillo genotypes were evaluated for their total anthocyanin, phenolic and antioxidant capacity. The result showed that ICTS-UDG-9-224 and ICTS-UDG-9-32 had the highest amount of total phenolic compounds 10.08 and 9.6 mg GAE/g fresh weight in genotypes, respectively, followed by ICTS-UDG-1-1 and ICTS-UDG-2-2 (5.5 and 5.3 mg GAE/g fresh weight), respectively. The highest content of anthocyanins was found in the genotypes ICTS-UDG-9-32 (6.94 mg of pelargonidin 3-glucoside equivalents/g of fresh weight). In contrast, the genotypes ICTS-UDG-9-224 showed lowest values of antocyanins content. On the other hand, for total antioxidant capacity, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods showed that genotypes, ICTS-UDG-2-2 and ICTS-UDG-1-1 had the highest antioxidant capacity (approximately 80%) followed by genotypes ICTS-UDG-9-32 (55%) and ICTS-UDG-9-224 (28%), respectively. These results provide useful and important information for researchers in order to increase the antioxidant capacity and functional value of purple tomatillo for the food and nutraceutical industries.
African Journal of Biotechnology Vol. 9(32), pp. 5173-5176, 9 August, 2010
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 ©2010 Academic Journals
Full Length Research Paper
Evaluation of total phenolics, anthocyanins and
antioxidant capacity in purple tomatillo (Physalis
ixocarpa) genotypes
Daniel González-Mendoza1* Onecimo Grimaldo-Juárez1, Roberto Soto-Ortiz, Fernando
Escoboza-Garcia1 and José Francisco Santiguillo Hernández2
1Instituto de Ciencias Agrícolas -Universidad Autónoma de Baja California, Carretera Delta S/N, Ejido Nuevo León
21705, Baja California México.
2Centro Regional Occidente, Universidad Autónoma Chapingo, Chapingo, México.
Accepted 16 July, 2010
Purple tomatillo genotypes were evaluated for their total anthocyanin, phenolic and antioxidant
capacity. The result showed that ICTS-UDG-9-224 and ICTS-UDG-9-32 had the highest amount of total
phenolic compounds 10.08 and 9.6 mg GAE/g fresh weight in genotypes, respectively, followed by
ICTS-UDG-1-1 and ICTS-UDG-2-2 (5.5 and 5.3 mg GAE/g fresh weight), respectively. The highest content
of anthocyanins was found in the genotypes ICTS-UDG-9-32 (6.94 mg of pelargonidin 3-glucoside
equivalents/g of fresh weight). In contrast, the genotypes ICTS-UDG-9-224 showed lowest values of
antocyanins content. On the other hand, for total antioxidant capacity, the 2,2-diphenyl-1-picrylhydrazyl
(DPPH) methods showed that genotypes, ICTS-UDG-2-2 and ICTS-UDG-1-1 had the highest antioxidant
capacity (approximately 80%) followed by genotypes ICTS-UDG-9-32 (55%) and ICTS-UDG-9-224 (28%),
respectively. These results provide useful and important information for researchers in order to
increase the antioxidant capacity and functional value of purple tomatillo for the food and nutraceutical
industries.
Key word: Antocyanins, purple tomatillos, bioactive compounds, antioxidant capacity.
INTRODUCCION
The production of reactive oxygen species in organisms
can have a role in cell communication processes and
defense mechanisms. However, excessive production
and accumulation of these products can cause a series of
biochemical reactions that can generate various dis-
orders on the cells. For example, may oxidize nucleic
acid, proteins, lipids or DNA and can initiate a variety of
disease processes such as cancer, neurodegenerative
disorders, cardiovascular disease and arteriosclerosis
(Migliore and Coppedé, 2009). The alternatives to reduce
*Corresponding author. E-mail: daniasaf@gmail.com Tel: +52
686 5230079. Fax: +52 686 5230217.
Abbreviations: DPPH, 2,2-Diphenyl-1-picrylhydrazyl; UV,
ultraviolet; GAE, gallic acid equivalent; RSA, radical
scavenging.
the presence of reactive oxygen species in higher
organisms have suggested the consumption of fruits rich
in bioactive compounds such as anthocyanins (Salinas-
Moreno et al., 2009).
Anthocyanins are plant secondary metabolites, res-
ponsible for most of the red, blue and purple pigmen-
tation found in flowers, fruits and leaves (Harborne and
Williams, 2000). They are involved in plant resistance
against ultraviolet (UV) light and in animal attraction for
pollination and seed dissemination (Archetti, 2000;
Manetas, 2006). The major sources of anthocyanins in
edible plants include the families Vitaceae (grape) and
Rosaceae (blackberry, apple, peach, etc.). Other plant
families which contain anthocyanin pigments are
Solanaceae (tomato and eggplant) and Cruciferae (red
cabbage) (Lohachoompol et al., 2004). Among the plants
of the Solanaceae family, are the peel tomato (Tomatillo)
whose fruits, especially green color, are consumed in
different regions of Mexico, USA and Central America
5174 Afr. J. Biotechnol.
(Mulato-Brito and Peña-Lomeli, 2007). In contrast,
consumption of the fruit, purple tomatillo, is limited mainly
to the western region of Mexico (Santiaguillo et al., 1994).
Therefore, information on the functional properties of this
fruit would be helpful in increasing the awareness of the
consumers regarding the level of beneficial phyto-
chemicals present in this nutritious vegetable.
Thus, the current study was undertaken to determine
the content of bioactive compounds such as phenolic
compounds, anthocyanins and antioxidant activity present
in the fruit pericarp of purple tomatillo.
MATERIALS AND METHODS
Collection of fruits from plant materials
Fresh fruits of four selected purple tomatillo (Physalys ixocarpa)
genotypes from different regions of Jalisco, Mexico were collected
in June 2009 from a cultivated green house at the Institute of
Agronomy Sciences of the Autonomous University of Baja, Cali-
fornia (UABC). Immediately after harvesting, fruits were frozen and
stored at -20°C until analysis.
Sample preparation
A ground freeze-dried sample of 300 mg of each genotypes were
weighted and phenols and anthocyanins were extracted with 3 ml
80% aqueous solution of HCl-methanol (1%) at C and then
homogenates were centrifuged at 3000 rpm for 10 min; super-
natants were subjected to further analysis.
Quantitative determination of total phenolic content
The total phenolic content of the crude acidified methanol extract
was determined by using a modified Folin-Ciocalteu method with
gallic acid (Sigma Chemical Co.) as a standard. Folin Ciocalteu
reagent (600 µl, Fluka) was added for methanolic extract solution
(120 µl), then 1 N aqueous sodium carbonate solution (360 µl) was
added and the tube was vortexed and then incubated for 40 min.
A blue color appeared and the absorbance was measured at 725
nm with a Beckman DU-50 spectrophotometer. All measurements
were made in triplicates and the results expressed as milligrams of
gallic acid equivalent (GAE) per g of fresh weight.
Anthocyanin extraction and determination
The extracts were freshly prepared from frozen fruit and did not
undergo extensive processing or significant browning; a pH differential
method for determination anthocyanin content was considered
unnecessary. Therefore, the total anthocianin of the acidified
methanol extract from 10 selected purple tomatillo (P. ixocarpa)
genotypes was measured at 535 nm using a Beckman DU-50
spectrophotometer. All measurements were made in triplicates and
the results expressed as milligrams of pelargonidin 3-glucoside
equivalents per gram of fresh weight.
Determination of DPPH scavenging activity
A methanolic solution (60 µl) of sample extract was added to 1200
µl (0.025 g L-1) of DPPH solution. The mixture was shaken
vigorously and allowed to stand at room temperature for 30 min.
The absorbance was measured at 517 nm by a spectrophotometer
using methanol as a blank. Lower absorbance of the reaction mixture
indicates higher free radical scavenging activity. The percentage of
2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging (RSA) was
calculated using the equation:
Initial absorbance - Final absorbance
%DPPH RSA = x 100
Initial absorbance
Statistical analysis
Data were analyzed with analyses of variance (ANOVA), and mean
of comparison test (Tukey’s = 0.05) was performed (Statistical
Package version 5.5, Statsoft, USA). Significant differences were
accepted if p < 0.05 and data was expressed as mean ± standard
error.
RESULTS AND DISCUSSION
The phenolic compounds (one of the most important
antioxidant plant components) are widely investigated on
plants and fruits (Djeridane et al., 2006). These com-
pounds might interfere in several of the steps that lead to
the development of malignant tumors, inactivating
carcinogens, inhibiting the expression of mutant genes
and the activity of enzymes involved in the activation of
procarcinogens and activating enzymatic systems involved
in the detoxification of xenobiotics. In the present study,
significant variations were observed in the content of total
phenolic compounds from different genotypes of selected
purple tomatillo genotypes (Figure 1). The maximum
values of total phenolic compounds per geno-types were
10.08, 8.34 and 7.31 mg GAE/g fresh weight in
genotypes ICTS-UDG-9-224, ICTS-UDG-9-32 and ICTS-
UDG-13-52, respectively. While minimum values were
recorded from ICTS-UDG-1-1 and ICTS-UDG-2-2 (5.5
and 5.3 mg GAE/g fresh weight, respectively).
On the other hand, the presence of anthocyanins in
plant-derived food is very important because their intake
in the human diet is associated with protection against
coronary heart disease and an improvement in sight. In
this study, our results showed that anthocyanin content in
purple tomatillo genotypes were slightly different (Figure
2).
The highest content of anthocyanins was found in the
genotypes ICTS-UDG-9-32 (6.94 mg of pelargonidin 3-
glucoside equivalents / g of fresh weight). In contrast, the
genotypes ICTS-UDG-2-2 and ICTS-UDG-1-1 did not
show significant difference in antocyanins content. On the
other hand, the genotypes ICTS-UDG-9-224 showed the
lowest values of antocyanins content (Figure 2). To the
best of our knowledge, there are no reports on total phenolic
and anthocyanin content from purple tomatillo genotypes,
thus preventing a direct comparison. How-ever, our
findings are in accordance with those reported on black
Soybean Cikuray variety (Astadi et al., 2009) and
strawberry (Tulipani et al., 2008). In this sense, we found
González-Mendoza et al 5175
Figure 1. Total soluble compounds phenolics of four different genotypes of purple tomatillo. Means ± standard error; n = 3.
Figure 2. Values of total anthocyanin of four different genotypes of purple tomatillo. Means ± standard error; n = 3.
similar values on phenolic and anthocyanin content. On the
other hand, for total antioxidant capacity, the DPPH
methods showed that genotypes, ICTS-UDG-2-2 and
ICTS-UDG-1-1 had the highest antioxidant capa-city
(90% approximately) followed by genotypes ICTS-UDG-
9-32 (55%) and ICTS-UDG-9-224 (28%), respectively
(Figure 3). Similar values have been observed in different
plants such as roselle of Hibiscus sabdariffa (Galicia-
Flores et al., 2008) and Camellia sinensis Linn (Khalaf et
al., 2008). Finally, these results provide useful and
important information for researchers in order to increase
the antioxidant capacity and functional value of purple
5176 Afr. J. Biotechnol.
% inhibition of DFFH radical
Figure 3. Antioxidant capacity of four different genotypes of purple tomatillo. Means ± standard error. n = 3.
tomatillo for the food and nutraceutical industries.
Conclusion
In the present study, selected purple tomatillo (P.
ixocarpa) genotypes appear to be good and safe source
of antioxidants. The fruits of this plant could be used for
direct consumption as salads or as extracts to increase
the nutritional value of different foods and diets. Future
studies include identification of the remaining antioxidant
constituents in the semi purified aqueous fractions and
study of the anticancer effects of these aqueous extracts.
ACKNOWLEDGEMENTS
We thank Ph.D. José Sánchez Martínez for excellent
technical assistance and Red de Tomate de Cascara for
helping us obtain the seeds used in the studyand
Programa de Mejoramiento del Profesorado (PROMEP)
convocatoria 2008, incorporacion de Nuevos Profesores
de Tiempo Completo.
REFERENCES
Archetti M (2000). The origin of autumn colours by coevolution. J.
Theor. Biol. 205: 625-630
Astadi Ignasius R, Astuti M, Santoso U, Nugraheni P (2009). In vitro
antioxidant activity of anthocyanins of black soybean seed coat in
human low density lipoprotein (LDL). Food Chem. 112:659-663.
Galicia-Flores L, Salinas-Moreno Y, Espinoza-García BM, Sánchez-
Feria C (2008). Physicochemical characterization and antioxidant
activity of roselle extracts (Hibiscus sabdariffa L.) national and
imported. Revista Chapingo Serie Horticult. 14: 121-125
Harborne JB, Williams CA (2000). Advances in flavonoid research since
1992. Phytochemistry, 55: 481-504.
Khalaf N A, Shakya AK, Al-Othman A, El-Agbar Z, Farah H (2008).
Antioxidant Activity of Some Common Plants Turk. J. Biol. 32: 51-55.
Lohachoompol V, Srzednicki G, Craske J. 2004. The Change of Total
Anthocyanins in Blueberries and Their Antioxidant Effect After Drying
and Freezing. J. Biomed. Biotechnol. 5: 248-252
Manetas Y (2006). Why some leaves are anthocyanic and why most
anthocyanic leaves are red? Flora, 201: 163-177.
Migliore L, Coppedè F (2009).Oxidative Stress and mechanisms of
environmental toxicity. Mutat. Res. 31: 73-74.
Mulato-Brito J, Pena-Lomeli A (2007). Germplasm evaluation of
tomatillo (Physalis ixocarpa Brot.) cropped under Ontario, Canada
and Chapingo, Mexico environmental conditions. Vegetable Crops
Res. Bull. 66: 117-127.
Salinas-Moreno Y, Almaguer-Vargas G, Peña-Varela G, Ríos-Sánchez
R (2009). Ellagic acid and anthocyanin profiles in fruits of raspberry
(Rubus idaeus L.) in different ripening stages. Revista Chapingo
Serie Horticult. 15: 97-101.
Santiaguillo HJF, López RM, Peña AL, Cuevas JASYJ, Sahagún C
(1994). Distribución, colecta y conservación de germoplasma de
tomate de cáscara (Physalis ixocarpa Brot.). Revista Chapingo Serie
Horticult. 2: 125-129.
Tulipani S, Mezzetti B, Capocasa F, Bompadre S, Beekwilder J, Ric De
Vos CH, Capanoglu E, Bovy A, Battino M (2008). Antioxidants,
phenolic compounds, and nutritional quality of different strawberry
genotypes. J. Agric. Food Chem. 56: 696-704.
Article
Full-text available
The aim of this study, which involved a field experiment conducted in north-eastern Poland, is to evaluate the phytometric parameters, yield, and biological value of fruit of three tomatillo cultivars grown in soil mulched with black PE (polyethylene) film and covered with PE film and non-woven PP (polypropylene) fabric. A two-factor field experiment was conducted in 2015 and 2017–2018 in the Agricultural Experiment Station owned by the University of Warmia and Mazury in Olsztyn. In the control treatment, tomatillo plants were grown without protective covers or mulch. Tomatillo fruits were harvested gradually, upon physiological maturity, which was determined based on changes in the color of the peel and calyx, and the aroma. The growth and development of tomatillos were evaluated based on plant measurements performed in the field. The chemical composition of tomatillo fruits was analyzed at the stage of full fruiting. During the three-year study, the weight, vertical diameter, and horizonal diameter of fruit were highest in cv. ‘Rio Grande Verde’ and lowest in cv. ‘Purple’. The combined use of mulch and plant covers accelerated fruit ripening. The total and marketable yields of tomatillo fruit were highest in cv. ‘Rio Grande Verde’ and lowest in cv. ‘Purple’. The fruit of cv. ‘Purple’ had the highest content of dry matter, total sugars, extract, β-carotene, and total polyphenols.
Article
Tomatillo (Physalis philadelphica and Physalis ixocarpa) are native fruits to Mexico and Central America. However, the tomatillo plant grows in tropical and subtropical regions around the world. The tomatillo fruit is also called husk tomato. The growth conditions may modify, as for another vegetable, the yield and composition of fruits and seeds. Pests and some microorganisms (transmitted by insects) generate some diseases to the plant. Plants and fruits of tomatillo contains vitamins, minerals, phenolic compounds, and steroidal lactones such as physalins, having antimicrobials and antinarcotic effects. This is why plants and fruits are widely used in traditional medicine to relieve some discomforts: fever, cough, amygdalitis, gastrointestinal disorders or diabetes and as food ingredient in the Mexican and Guatemalan cuisines. The aim of this review was to compile in a single manuscript the whole information about the plant and fruits of tomatillo, considering fruit origin, botanical aspects, cultivation characteristics, components, and health benefits as well as the main uses of fruits and parts of the plant.
Chapter
A number of crops defined in culinary terms as vegetables are by botanical definition fruits. In most cases they belong in two families: Solanaceae (tomato, Capsicum spp., eggplant/aubergine) and Cucurbitaceae (pumpkin, squash, gourds, vegetable melons). Vegetable fruits offer great diversity in phytochemical composition; carotenoids are often present but they also contain phenolics and other bioactives. Within this group of fruits tomatoes have the largest body of scientific evidence for health benefits, with a link between tomato/lycopene consumption and prevention of prostate cancer well documented from in vitro to human studies. There is also good evidence for bioactives in tomato having benefits for heart health and growing evidence to support a role in skin, bone and eye health. Capsicum species have received considerable attention, with health effects from anticancer to weight management attributed to capsaicin and capsinoids. The weight of scientific evidence supports the use of vegetable fruits in the development of functional foods.
Article
Full-text available
The exploitation of exotic genetic resources in plant breeding is necessary to enhance diversity of cultivars. Purple color is an exceptional character in sesame and monitored rarely in stems, capsules and leaves. The purple sesame is suitable for commercial production with high antioxidant capacity. For understanding of its genetic behaviour, inheritance study was carried out for four years (2008-2011) by crossing Muganli-�� �Ƃ� and ACS ���ƃ��0XJDQOL-57 parent had green color in canopy while ACS 70 was purple. All the plants in the F1 generation were purple colored. In F2 population, 3:1 segregation ratio showed that purple color character was controlled by a single dominant gene. F2 progenies were sown to single rows separately, either purple or green plants. The green plants in F2 were also green colored in F3 with no segregation while the purple plants obtained from F2 indicated purple and green colors in F3 with a segregation ratio of 3:1. These segregations demonstrated that purple color in sesame was under the control of a single gene and this unique color was dominant over traditional green color. This accession (ACS 70) is a valuable genetic resource by providing a unique color character in sesame. The result presenting in this study would be of importance for further improvement of high antioxidant capacity in sesame.
Article
Full-text available
The aim of the present work was to determine the commercial quality of roselle samples of Hibiscus sabdariffa L. from Sudan, China and México (Guerrero), as well as the antioxidant activity of the beverage prepared with them, in order to find out if there exists any differences among samples that could help to give a special place in the national market to the mexican Hibiscus sabdariffa L roselles. The variables evaluated include color of the roselles and their extracts, pH, acidity, and anthocyanin profiles. The beverages prepared with the roselles from China and México showed a deep-red color, while that from Sudan was brown-redness. The mexican roselles had the highest acidity and the lowest pH values, although China roselles presented the highest anthocyanin contents. The anthocyanin profiles obtained by HPLC of the roselles from the three countries were the same. According to the quality parameters evaluated, the roselles from México and China have better quality than that from Sudan. The roselle extracts from México had the highest antioxidant activity; this means that they possessed better nutraceutical properties than the extracts from China and Sudan, characteristic that could be useful to give an added value to mexican Hibiscus sabdariffa L. roselles.
Article
Full-text available
The content of free ellagic acid (FEA) and the anthocyanin profile were determined in "Autumn Bliss" variety red raspberry fruits (Rubus idaeus L) in different ripening stages and grown in two locations. The FEA and anthocyanins were analyzed by reverse phase High Performance Liquid Chromatography (RP-HPLC). Rripening stage and growth location affected FEA. The fruits with deep red color (degree 3 ripening) from San Mateo Acatitlán, Mexico, had the highest FEA content, with a value of 5.38 mg·kg -1 of fresh fruit. the anthocyanin profile was more complex as fruits advanced in maturity. In the inmature fruits only four anthocyanins were observed, while in the completely mature fruits there were eight. In the completely mature fruits the anthocyanins with the highest relative percentages were: cianidin 3-soforoside (46.2 %) and cianidin 3-(2-glucosyl rutinoside) (25.9 %). The maximum levels of FEA and the highest number of anthocyanins were present in the completely mature raspberry fruits, this stage is characterized by the deep red color of the fruits, and is when its consumption is recommended.
Article
Full-text available
The methanolic crude extracts of some commonly used medicinal plants were screened for their free radical scavenging properties using ascorbic acid as standard antioxidant. Free radical scavenging activity was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical. The overall antioxidant activity of green tea (Camellia sinensis Linn.) was the strongest, followed in descending order by black tea (Camellia sinensis Linn.), Eugenia caryophyllus (Spreng.) Bullock and Harrison, Piper cubeba Linn., Zingiber officinale Roscoe and Piper nigrum Linn. Trigonella foenum graecum Linn. and Elettaria cardamomum (Linn.) Maton showed weak free radical scavenging activity with the DPPH method. All the methanolic extracts exhibited antioxidant activity significantly. The IC50 of the methanolic extracts ranged between 6.7 ± 0.1 and 681.5 ± 8.4 μg/ml and that of ascorbic acid was 8.9 ± 0.1 μg/ml. The study reveals that the consumption of these spices would exert several beneficial effects by virtue of their antioxidant activity.
Article
The adaptive significance of leaf reddening, as it occurs during specific developmental stages or after stress, has puzzled biologists for more than a century. Theoretically, the accumulation of a non-photosynthetic pigment competing with chlorophylls for photon capture would impose a photosynthetic cost, which should be paid off by the benefits afforded by anthocyanins under some circumstances. Hence, the proposed hypotheses presume protective functions against excess light, UV-B radiation, reactive oxygen species, water stress (osmoregulation) and herbivory. The existing arguments in favor of an anti-oxidant, anti-UV-B and osmoregulatory role are confounded by the co-occurrence in leaves of other compounds having the same properties, not absorbing visible light, attaining much higher concentrations and, in some cases, having a more appropriate location to fulfill the ascribed functions. Moreover, the excess light hypothesis should take into account that anthocyanins mainly absorb green photons, which are used photosynthetically in deeper cell layers needing less photoprotection. The more ecological, anti-herbivore hypotheses, consider red leaf color as a signal denoting high defensive commitment, as a camouflage obscuring the green reflectance indicative of a healthy leaf and/or as a device undermining the folivorous insects camouflage. The anti-herbivore hypotheses have not been thoroughly tested, yet they are compatible with the known optical preferences of insects and their underlying physiology. Overall, although a multiplicity of potential roles can be argued, the primary role may depend on the reference system, i.e. species, developmental stage or specific biotic and abiotic stressors.
Article
The objectives of this study were to determine the phenolic and anthocyanin contents in black soybean Mallika and Cikuray variety seed coat extract and to examine antioxidant activity of extract against DPPH radical and LDL oxidation. Black soybean seed coat of Mallika (M) and Cikuray (C) was extracted using methanol-1%HCl. The phenolic and anthocyanin contents were determined with Folin–Ciocalteu and pH differential methods, respectively. Individual anthocyanidins were identified with HPLCdiode array detector, and antioxidant activity was examined, using DPPH and TBARS assay with LDL as the oxidation substrate. BHT and rutin were used as antioxidant references. The phenolic content in M and C were 8.15 ± 0.23 and 6.46 ± 0.11 g GAE/100 g, respectively. The anthocyanin contents were 11.36 ± 0.12 and 1.45 ± 0.13 g/100 g, respectively. Cyanidin, delphinidin, and pelargonidin were found as individual anthocyanidins. The optimum DPPH radical scavenging capacity (%) of M and C were 92.78% and 91.50%, respectively, BHT and rutin were 77.0% and 91.94%, respectively. The optimum inhibition of TBARS formation from M and C were 37.10 and 30.37 nmol MDA equivalents/g LDL protein, respectively, and rutin were 30.10 nmol MDA equivalents/g LDL protein, respectively. These results suggest that black soybean seed coat has high levels of phenolic and anthocyanin, and also demonstrated considerable antioxidant activity of black soybean seed coat.
Article
We lack an adaptive explanation for a striking phenomenon, that of bright colours displayed in autumn by the leaves of many deciduous trees. The usual explanation is that it is simply a non-adaptive secondary effect of leaf senescence. A game-theoretic model of biological signalling provides an adaptive hypothesis for autumn colours showing that they can be the result of a process of coevolution between insects and trees: if leaf colour acts as a warning indicator of the tree's vigour to autumn parasite insects, trees can gain advantage from the reduction of parasite load and insects can gain advantage from location of the most profitable hosts to lay their eggs. The results of the model are consistent with Zahavi's handicap principle. Possible explanations for the origin of the system and evidence from natural history are discussed.
Article
Some of the recent advances in flavonoid research are reviewed. The role of anthocyanins and flavones in providing stable blue flower colours in the angiosperms is outlined. The contribution of leaf flavonoids to UV-B protection in plants is critically discussed. Advances in understanding the part played by flavonoids in warding off microbial infection and protecting plants from herbivory are described. The biological properties of flavonoids are considered in an evaluation of the medicinal and nutritional values of these compounds.