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Tannins: What do they represent in plant life?



Tannins were, and still are, the target of researches on their specific biological activities, especially in the role of antioxidants and anticarcinogens. Furthermore, there is ample proof of their anti-inflammatory, cicatrizant and anti-HIV functions. But, what is their real significance in plant life? When did they first appear in the evolutionary history of plants, and what ecological advantages do they bestow on these organisms? This chapter will present tannins from a 'plant point of view', in an attempt to point out their importance in plant survival, when acting against biotic herbivores, as well as pathogen and abiotic stress (air pollutants).
In: Tannins: Types, Foods Containing, and Nutrition ISBN: 978-1-61761-127-8
Editor: Georgios K. Petridis © 2010 Nova Science Publishers, Inc.
Chapter 10
Claudia Maria Furlan*, Lucimar Barbosa Motta
and Deborah Yara Alves Cursino dos Santos
Departamento de Botânica, Instituto de Biociências,
Universidade de São Paulo, São Paulo, SP, Brazil
Tannins were, and still are, the target of researches on their specific biological
activities, especially in the role of antioxidants and anticarcinogens. Furthermore, there is
ample proof of their anti-inflammatory, cicatrizant and anti-HIV functions. But, what is
their real significance in plant life? When did they first appear in the evolutionary history
of plants, and what ecological advantages do they bestow on these organisms? This
chapter will present tannins from a ‘plant point of view’, in an attempt to point out their
importance in plant survival, when acting against biotic herbivores, as well as pathogen
and abiotic stress (air pollutants).
Tannins have been the target of researches with the aim of investigating their biological
activities, especially as antioxidants and anticarcinogens. Furthermore, there is ample proof of
their anti-inflammatory, cicatrizant and anti-HIV functions. But, what is their bearing on plant
life? When did they first appear in the evolutionary history of plants, and what ecological
advantages do they bestow thereon? It is important to know about tannins from the point of
view ‘plants’, in an attempt to understand their involvement in plant-defense against biotic
and/or abiotic stress, or rather, their importance in plant survival itself.
* Corresponding author: e-mail:;;
Claudia Maria Furlan, Lucimar Barbosa Motta et al.
Tannins are chemically defined as secondary compounds synthesized through vegetal
secondary metabolism, or, for many authors, by special metabolism [Monteiro et al., 2005].
Secondary metabolites have been associated to plant-environmental interactions [Haslam,
1995]. Traditionally, tannins have been described as modulators in plant-herbivore
interactions and|or protection agents against infection, with the main function as herbivore
deterrents due to their acid taste and the property of precipitating proteins.
Khanbabaee & Ree [2001] provided a convenient classification of tannins based on their
specific structural characteristics and chemical properties, thereby avoiding the traditional
classification in hydrolyzable and non-hydrolyzable tannins. The authors classified tannins in
four groups as follows: 1. gallotannins, all those with galloyl units or derivatives bound to
diverse polyol-, catechin- or triterpenoid units; 2. ellagitanins, those in which at least two
galloyl units are C-C coupled to each other, without containing a glycosidically linked
catechin unit; 3. complex tannins, which present a catechin unit glycosidically bound to either
a gallotannin or ellagitannin unit; and 4. condensed tannins, all of which being oligomeric and
polymeric proanthocyanidins.
According to some authors, tannins can be used as chemotaxonomic markers, especially
for Angiosperm orders and families [Okuda et al., 2000; Okuda 2005]. Okuda et al. [2000]
correlated the orders, families and genera in the Cronquist system of plant classification with
the oxidative structural transformation of plant polyphenols. Accordingly, the biogenetic
transformation of hydrolyzable tannins is considered to start from gallotannins (galloyl group
in gallotannin I) to the hexahydroxydiphenoyl (HHDP) group in ellagitannin (II), continuing
with the dehydrohexahydroxydiphenoyl (DHHDP) group into dehydroellagitannin (III), and
finally transformed DHHDP groups into transformed dehydroellagitannins (IV). In their
correlation, tannins are absent in only one Cronquist subclass, the Asteridae.
It is important to point out that the Cronquist system of plant classification was accepted
and followed by many researchers until 1998, when macromolecular biology data (mainly
DNA sequences) gave rise to new insights regarding plant evolution. Nowadays, most of the
subclasses, orders and families proposed by Cronquist have been reevaluated, and angiosperm
systematics recircumscribed based on phylogenetic paradigms, thereby giving rise to a new
proposal - the Angiosperm Phylogeny Group [APG, 2009]. This new system presents a
synthesis of angiosperm phylogeny hypothesis, by emphasizing monophyletic groups based
mainly on the combination of DNA sequences (rbcL, 18S rDNA, atpB, matK). Even so, the
Asterids clade is still characterized by families with the presence of typical alkaloids and
iridoids (secoiridoids). Since this clade is mainly formed by herbaceous plants, tannins seem
not to be directly related to this form of life.
According to Agrawal [2006], the evolution of plant defense strategies is nowadays
viewed in a phylogenetic perspective: the biosynthetic machinery needed to produce plant
defense must be well-conserved and of single origin. Thus, in major classes the origin should
be monophyletic. This could be supported by the correlations between qualitative plant
defenses (alkaloids, iridoids, glucosinolates) and the absence of tannins (a quantitative
defense) [Hartman, 2008]. In other words, tannins are ubiquitous in woody plants, but almost
absent in herbaceous species [Haslam, 1988].
Although tannins are especially present and studied in flowering plants, it is important to
remember that non-hydrolysable tannins are also found in Monilophytes (mainly ferns), and
tannic substances in Phaeophyta, an algae group unrelated to Archaeplastida, a clade which
includes Glaucophyta, Rhodophyta, Chlorophyta and Land plants. Phaeophyta (brown algae)
Tannins: What Do They Represent in Plant Life 3
presents a characteristic group of polyphenols with tanning properties, the phlorotannins,
which constitute a structural class of polyketides found exclusively in these algae [Maschek
& Baker, 2008].
According to Popper & Fry [2004] and Popper [2008], and when studying the primary
cell wall composition of Lycophyta, Monilophyta (mainly ferns) and Spermatophyta
(Gymnosperm and Angiosperm), tannins may not be strictly a primary cell-wall component.
Nevertheless, the authors often came across tannins associated with primary cell-wall-rich
material, and some even deposited within the primary cell-wall itself. They also reported the
presence of non-hydrolyzable tannins (proanthocyanidins) in the alcohol-insoluble residue of
some of the analyzed monilophytes, although they were absent from lycophyte alcohol-
Vascular plants (or Tracheophytes) form a well-supported, monophyletic group, this
including the Lycophytes, Monilophytes and Spermatophytes [APG, 2009]. Ferns are the
earliest diverging plants in which proanthocyanidins began to predominate over flavonols [De
Bruyne et al., 1999]. Proanthocyanidins remained important in early diverging Angiosperms,
although their synthesis decreased in more advanced orders [De Bruyne et al., 1999], prior to
the Asterids forming the most divergent group of Angiosperms. It seems likely that the
production of proanthocyanidins evolved simultaneously in the monilophytes, contrary to
Bate-Smith [1977], who believed that these compounds appeared later on in plant
evolutionary history, rather than in the vascular condition.
Recent studies involve the search for connections between ecosystem processes and
genetic mechanisms. Schweitzer et al. [2008] assayed, not only the role of condensed tannins
in herbivore defense in a Populus, model-system, but also the presence of these compounds in
a genetic context. The authors pointed out that condensed tannins (complex flavonoid
polymers) occur across phylogenetically diverse plant groups, as well as in various
ecosystems (from Arctic to tropical). This wide distribution suggests a profound evolutionary
history. Variation in the production of condensed tannin has a clear genetic basis. The
possibility of a lack or even reduced synthesis of these compounds in knockout mutant
production is the key to clarifying the specific roles of tannins at individual and ecosystem
levels. A further observation was the importance of ‘underground’ condensed tannin in
regulating nutrient dynamics, a new view of tannins, outside traditional herbivore/pathogen
Almeida et al. [2005] studied the medicinal flora of the Caatinga, an arid Brazilian
biome, so as to verify whether the theory of ecological apparentness could explain choice and
ethnobotanical plant use. Five classes of chemical compounds (tannins, alkaloids, phenols,
quinines and triterpenes) were analyzed. Phenols and tannins were outstanding in all plant
species and habitats, possibly through their widespread distribution, especially among
lignified plants, common in the Caatinga environment. The authors pointed out that the
phenols have been related to several biological activities (antiviral, antioxidant, diuretic,
antirheumatic and others) [Grassmann et al., 2002]. On the other hand, tannins are used
against diarrhea, as antiseptics, vasoconstrictors, antimicrobial and antifungal, due to their
astringent activity [Gutiérrez et al., 2008; Falleh et al., 2008; Brandelli et al., 2009].
Claudia Maria Furlan, Lucimar Barbosa Motta et al.
Tannins vs. Biotic Stress: Herbivory and Allelopathy
Tannins are present in the leaves, bark, fruits and seeds of many plants. The main
function of these compounds is to provide protection against microbial pathogens, harmful
insects and other herbivores. The storage of proanthocyanidins in the endothelial layer of the
seed coat in many species may be seen as a classic example of a pre-formed protective barrier
[Lattanzio et al., 2004; Panjehkeh et al., 2009]. Aziz et al. [2004] suggested that the
proanthocyanidins present in glandular trichomes of alfalfa (Medicago sativa L.) act as a first
line of defense against insect predation. Coffee varieties that are susceptible to the fungal
pathogen Hemileia sp have lower levels of proanthocyanidins than those resistant. These
compounds, when isolated from pulp or leaves, inhibit fungal germination in vitro [Gonzalez
de Colmenares et al., 1998]. A strong negative correlation correlativeness was found between
the concentration of procyanidin, a condensed tannin, in leaf-bud petioles in seven genotypes
of groundnuts (Arachis hypogaea), and fecundity of the aphid Aphis craccivora on the same
genotypes [Grayer et al., 1992].
Developing seeds of Sesbania drummondii are attacked by nymphs and adults of the bug
Hyalymenus tarsatus (Heteroptera: Alydidae), which kill some and weaken others. Parasitism
by this piercing-sucking insect reduces the resources of future seedlings and affects seed
physiology, this including dormancy and the exudation of allelochemicals by imbibing seeds.
There is evidence that inducible proanthocyanidin accumulation, also present in leaves re-
acting against mammalian and insect herbivores, may represent a defense mechanism of some
seeds against piercing–sucking insects [Ceballos et al., 2002].
Condensed tannins are also considered to be an important inducible defense form against
mammalian herbivores. Ward & Young [2002] observed differences in condensed tannin
defense in Acacia drepanolobium submitted to distinct large mammalian herbivore
treatments. Contrary to expectations, tannin concentration in trees was higher in the upper
canopy, where there was little mammal induced damage.
Nevertheless, not all effects of proanthocyanidins are beneficial at the expense of
microorganisms and insects. For example, in the bark of Pinus densiflora, these tannins
function as oviposition stimulants for the cerambycid beetle Monochamus alternatus [Allison
et al., 1999].
Furthermore, hydrolysable tannins are believed to induce reduced insect performance.
Barbehein et al. [2009a] tested the hypothesis that higher foliar tannin levels also produce
higher concentrations of semiquinone radicals (from tannin oxidation) in the caterpillar mid-
gut, and radical enhancement could be associated with increased oxidative stress in mid-gut
tissues, with a consequential negative impact on larval performance. By testing various
concentrations of hydrolyzable tannins from hybrid poplars (Populus tremula x P. alba), the
authors observed that there was no measurable amount of semiquinone radicals in the mid-gut
of the larvae of Lymantria dispar caterpillars that ingested control leaves, whereas the levels
of these radicals greatly increased in those that ingested 15% tannin. Contrary to expectations,
larval growth rates were alike, whereby the surmise that tannins act as ‘‘quantitative
defenses’’, since high levels appear to be necessary for increasing levels of semiquinone
According to Barbehein et al. [2009b], hydrolysable tannins are much more active as pro-
oxidants in caterpillar gut than condensed tannins. On studying the resistance of red oak
(Quercus rubra L.), a species that produces high levels of condensed tannins, and sugar
Tannins: What Do They Represent in Plant Life 5
maple (Acer saccharum Marsh.) which produces high levels of hydrolysable tannins, the
authors observed that when Lymantria dispar L. caterpillars ingested oak leaves coated with
hydrolysable tannins, levels of hydrolysable tannin oxidation increased in their mid-gut
contents. Once again, the emphasis on high levels of hydrolysable tannins being important for
producing oxidative stress, but that increased tree resistance to caterpillars depends on
additional factors, such as those producing nutritional stress.
Low-molecular-weight phenols (LMWP) and tannins have traditionally been studied in
their defensive role against plant herbivores and pathogens [Rooke & Bergström, 2001;
Barbehenn et al., 2009a, 2009b], as UV screens and anti-oxidants [Hässing et al., 1999;
Feldman, 2005; Falleh et al., 2008], and also as allelopathic agents [Rawat et al., 1998].
Esterified flavan-3-ols, such as (–)-epigallocatechin gallate, as well as oligomeric
proanthocyanidins, accumulate at very high levels in tea-plant leaves. The interest in tea
polyphenols is now mainly concentrated on their potential health-benefits [Khana & Mukhtar,
2007], although high levels of monomeric flavan-3-ols, such as (–)-epicatechin have also
been linked with plant resistance against fungal attack [Punyasiri et al., 2005]. Catechin was
recently described as a powerful allelochemical, responsible for the adaptive advantage of the
invasive species spotted knapweed (Centaurea stoebe) in North America [Chobot et al.,
2009]. (–). Catechin appears to induce oxygen production and a calcium-signaling cascade
that leads to root-death in susceptible species [Bais et al., 2003].
Prunus armeniaca is an important agro-forest tree planted on the boundaries of farm
land. Its negative influence on several crops is infered. Retardation in germination, growth
and yield were detected in wheat (Triticum aestivum) plants growing nearby [Rawat et al.,
1998]. The authors demonstrated that the effects on Triticum aestivum of light petroleum and
ethyl acetate extracts of Prunus armeniaca was higher than those of aqueous extracts. Among
the isolated compounds, proanthocyanidins displayed the maximum inhibition of wheat-
growth and germination in lab tests. Nevertheless, further recent studies, mostly under field
conditions, have shown that the allelopathic role of phenolic compounds might be
misunderstood. Authors have suggested that these compounds are more important in shaping
the soil nutrient environment for plants, than directly acting as growth inhibitors [Inderjit,
Phenolic compounds may affect the plant nutrient environment by distinct mechanisms,
due to their chemical reactivity. While low-molecular-weight-phenols (LMWP) reduce soil-
nutrient availability by stimulating soil respiration and the immobilization of N in the
microbial biomass, tannins bind to proteins and N-rich soil organic matter, mostly acting on
lowering gross soil-N mineralization and nitrification rates by binding to microbial enzymes
or enzyme substrates [Meier & Bowman, 2008]. Phenolic-rich plants may therefore
negatively modify neighboring plant growth by restricting N supply. Since phenolic
compounds may complexly affect soil nutrient availability for plants, some authors suggested
that the allelopathic influence of these compounds should be better addressed through field
experiments [Inderjit & Foy, 2001]. For these authors, laboratory bioassays can demonstrate
the possibility of an allelopathic relationship, and are only suitable for a partial understanding
of the process.
Nonetheless, Inderjit & Foy [2001] demonstrated that the inhibitive effect of mugwort
(Artemisia vulgaris L.) on red clover (Trifolium pratense L.) growth is directly attributable to
the phenolic compounds released by the former into the soil. It was observed that this
Claudia Maria Furlan, Lucimar Barbosa Motta et al.
inhibition was overcome by adding activated charcoal, which absorbed organic molecules
(e.g., phenols), not the case with nitrogen-based fertilizers.
By using two species that co-dominate alpine moist meadows as a model system (the
phenol-rich forb Geum rossii,and the fast-growing grass Deschampsia caespitosa), Meier et
al. [2009] demonstrated that phenol-rich root inputs could be an unappreciated factor
structuring plant communities, especially in N-limited systems dominated by phenol-rich
species themselves. In semi-arid environments, agro-forestry has the means of enhancing
agricultural production and buffer rural livelihood against drought. However, the
misapplication of phenol-rich plants in locations where soil nutrients are limited possibly
engenders economical problems [Nakafeero et al., 2007].
The understanding of how tannins function in plant-herbivore interactions depends to a
large extent, not only on our knowledge of the chemistry of these compounds, but also of
herbivore strategies when dealing with these substances.
Tannins vs. Abiotic Stress: Air Pollutants
There are changes in plant morphology, physiology, biochemistry and growth rate,
brought about by air pollutants [Iqbal et al., 1996; Viskari et al., 2000; Moraes et al., 2002].
Criteria for assessing this impact include analyzing visible injury [Oksanen & Holopainen,
2001] and the accumulation of toxic substances, as well as evaluating biochemical and
physiological pollutant-induced changes in parameters related to photosynthesis, respiration,
enzyme activities, and the syntheses of lipids, proteins and other metabolites, etc. [Viskari et
al., 2000; Calatayud & Barreno, 2001; Herbinger et al., 2002]. Air pollution can also induce
qualitative and quantitative changes in secondary metabolite composition [Kanoun et al.,
2001; Lopanen et al., 2001; Furlan et al, 1999, 2010].
In the late 1980’s, the study of secondary metabolites, when investigating plant pollution
stress, became more popular. Air pollution has been demonstrated as a potential cause of
qualitative and quantitative changes in many compounds from secondary metabolism. Katoh
et al. [1989a] were among the first to report a decrease in the levels of tannins in Cryptomeria
japonica growing near a steam-power station. They found a negative correlation between the
levels of foliar soluble sulphate and tannin content, thereby implying an association between
air pollution and inhibition of the shikimate pathway. The reduction in the amount of tannin
seemed to be related to an increase in feeding rate of Dasychira abietis argentata on C.
japonica. At the same time, the authors reported decreased amounts of soluble phenols in C.
japonica exposed to ozone, correlated to lower levels of glucose [Katoh et al., 1989b].
Later, Kainulainen et al. [1995] observed the same results, i.e., decreased levels of
glucose, frutose and soluble phenols, in needles of Pinus sylvestris and Picea abies exposed
to SO2, thereby infering the effect of air pollution on photosynthesis and carbohydrate
metabolism, with the consequential decrease in both carbon gain and the rate of synthesis of
secondary metabolites, especially those derived from the shikimic acid pathway.
In an open-top experiment using Phaseolus vulgaris L. cv. Nerina, Kanoun et al. [2001]
detected a significant decrease in the accumulation of a hydroxycinnamic acid derivative in
plants exposed to ozone fumigation at 65–85 ppb. These findings infer that ozone exposition
might alter plant–pathogen interactions. On the other hand, as cinnamic derivatives are
Tannins: What Do They Represent in Plant Life 7
important precursors of flavonoid synthesis, enhanced isoflavonoid composition was noted.
According to Kanoun et al. [2001], the production of ozone-induced phenolics seemed to be
closely related to leaf necrosis injury. Pollutants such as sulfur dioxide and ozone may
increase the amounts of leaf nitrogen [Viskari et al., 2000], hence stimulating herbivore
Furlan et al. [1999, 2004] observed a correlation between the increased percentage of leaf
loss due to herbivority, as observed in Tibouchina pulchra grown in the more polluted areas
of Cubatão (São Paulo, Brazil), and the increased leaf nitrogen content resulting from the
decrease in total soluble phenols and tannins. They suggested that, in addition to pollution
stress, plants growing in polluted areas underwent a further stress, viz., increased herbivorous
Tannins have long been related to herbivore feeding, since the classic experiment of
Feeny in the late 1960´s. At the time, Feeny proposed that the deleterious tannin effects on
Operophtera brumata larvae feeding was the ability of these compounds to bind and
precipitate proteins. Tannins have been characterized as a form of quantitative defense against
insect herbivores [Moilanen & Salminen, 2008]. Later, in 1993, Appel postulated that
surfactants in insect-gut fluids inhibit tannin-protein interactions. The author observed that
most lepdopteran larvae have basic-gut (pH 9-12), which ionizes tannins and results in a loss
of hydrogen-binding capacity [Appel, 1993]. Hypothetically, tannin oxidative activity is
considered to be the real origin of their anti-herbivore function. Products of tannin oxidation
can deplete insect herbivore nutrients or produce cytotoxic effects [Appel, 1993, Hagerman et
al., 2003].
On the other hand, air pollutants tend to acidify intracellular pH or, the case of ozone,
cause leaf oxidative burst in sensitive species. According to Wohlgemuth et al. [2002], this
generates superoxide anion radicals and hydrogen peroxide. Reactive oxygen species (ROS)
not only provide protection against pathogens, but also induce an array of protective genes by
the oxidation of cell wall components and plasma membranes. Recently, ROS formation from
air pollution, UV-radiation or other abiotic stress factors has been shown to act as a signaling
pathway that overlaps hypersensitive response (HR), typical of plant infection by pathogens
[Rao et al. 2000; Langebartels et al. 2002].
Barbehenn et al. [2006] showed that the oxidative activity of tannins tended to
progressively diminish, group by group, from proanthocyanidins (condensed tannins),
through gallotannins and galloylglucoses to ellagitannins. However, many authors contest this
result, through ellagitannins having been the least studied. Moilanen & Salminen [2008], on
investigating 115 ecological tannin papers from 1985-2002, encountered 52 studies of total
phenols, 41 of proanthocyanidins, 13 of gallotannnins and only three related to ellagitannins.
The identification and characterization of leaf injury in well-adapted plant species are
crucial factors for realistically assessing risks by air pollution. Furthermore, bio-indicator
organisms react to atmospheric pollution and other biotic or abiotic stress. Field surveys have
recorded O3-like injury symptoms in numerous tree, shrub and forb species in Europe and
North America [Van der Heyden et al., 2001; Sans et al., 2002; Orendovici et al., 2003]. More
recently, Psidium guajava (the guava plant) was characterized as an ozone bio-indicator in
tropical regions [Furlan et al., 2007]. Visible foliar symptoms, in the form of dark-colored
(reddish) stippling among veins on the upper surface of older leaves, were highly correlated
with accumulated doses of ozone exposure (AOT40) [Furlan et al., 2007; Pina & Moraes,
2007]. Latter, Rezende & Furlan [2009] noted the higher incidence of anthocyanins and total
Claudia Maria Furlan, Lucimar Barbosa Motta et al.
tannins on Psidium guajava ozone fumigated plants, thereby indicating the cause of the
characteristic ozone leaf-injuries observed. This is of consequence, when contemplating the
less efficient traditional antioxidant system. Nonetheless, Dias et al. [2007] observed no
difference in the concentration of ascorbic acid and the activity of enzymes superoxide
dismutase (SOD) and peroxidase (POD) in leaves of P. guajava exposed to ozone in a
contaminated area of São Paulo, although according to Chalker-Scott [1999] there is a strong
relationship between the incidence of red leaves and stressful environments, when other
energy dissipation systems and free-radical scavenging have been exceeded, thereby
emphasizing its importance as part of the antioxidant pool.
When studying Psidium guajava exposed to high ozone concentration in São Paulo (the
city), using histochemical methods, Tresmondi [2010], observed that symptomatic and non-
symptomatic leaves accumulated phenol compounds, mainly anthocyanins and condensed
tannins, in upper layer mesophyll cells. Furthermore, the accumulation of H2O2 in mesophyll
cells as a result of oxidative stress was noted, thereby denoting the correlation between ozone
concentration and H2O2 content. Phenol accumulated on symptomatic leaves prior to the
appearance of leaf injury, thereby inferring their importance in chemical defense (mainly as
antioxidants) against ozone oxidative stress.
Tannins have also been related to environmental extremes, such as high altitude,
temperature and sunlight. Alonso-Amelot et al. [2007] observed an induced chemical
adaptive response in non-adapted plants growing at high altitudes. On comparing sun-exposed
and self-shaded fronds in Pteridium arachnoideum (fern), an accumulation of higher amounts
of phenols and tannins was noted, with the increase in altitude. Dry season water-stress also
caused an increase in phenols and tannins, thereby the conclusion that UV-B radiation and
water availability are important factors in non-adapted plant acclimation response to stress at
altitudinal gradients.
Tannins are undesirable compounds when plant-parts are consumed as food. On the other
hand, and from an agricultural view-point, they are useful as a protection from biotic-stress.
Tannins are also important in reinforcing plant tissues, their evolutionary presence pointing to
the emergence of Tracheophytes (Vascular Plants). This is especially patent in
proanthocyanidin-free mutant seeds of snapbeans, which proved to be more sensitive to
mechanical and water stress than seeds from the original cultivars.
It was also clear that phenols and tannins are synthesized in plants not only through
genetic determinants, physiological demands and evolution-controlled defense needs, but also
by the influence of environmental stress such as drought, UV-B radiation and atmospheric
pollution. Comprehending tannin functions in plant- interactions depends, to a large extent,
on our knowledge, not only of the chemistry of these compounds, but also of the strategies
that herbivores possess for dealing with these substances. This knowledge is also important
for finding tannin-rich species, or even producing mutants, which could increase the amount
of a particular biologically active metabolite.
Tannins: What Do They Represent in Plant Life 9
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... There are some exceptions such as the Acacia sp. and Terminalia sp. species, which are an important source of condensed and hydrolysable tannins, and a few dicotyledons species (Furlan et al., 2010). ...
... Tannins in plants occupy up to 20% of the dry weight (DW), ranking them after cellulose, hemicellulose and lignin. The synthesis of tannins in plants is often associated with defence responses against microbial pathogens, harmful insects, herbivores (Furlan et al., 2010) and UV-A or UV-B radiation. Polyphenols are stored in vacuoles and cell walls (Fraga-Corral et al., 2020). ...
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Tannins are a group of polyphenolic compounds synthesized and accumulated by higher plants as secondary metabolites. They are divided into hydrolysable tannins and proanthocyanidins and are found in many plant tissues in which they occur in diverse structures and amounts. This review provides a brief background on tannin distribution in plants, and summarizes the current literature on tannins in strawberries, raspberries, blueberries, currently the most commonly cultivated and consumed berries, and chokeberries, which have become popular in the last decades. The effects of processing and storage on tannin composition and levels in processed products are also provided.
... Flavonoids are also capable of absorbing harmful UV radiation (Takahashi and Ohnishi, 2004) and are responsible for flower colours (Yao et al., 2004;Griesbach, 2005). Tannins are often found in roots, bark, stems, leaves (Porter, 1988), fruits and seeds of many plants (Furlan et al., 2010). The concentration of tannins in leaves of forest trees is dependent on the developmental stage, tissue and environmental conditions (Barbehenn and Constabel, 2011). ...
... There is considerable genotype-specific variation in tannin concentration within 'Magnolia' species (Osier and Lindroth, 2006). The main function of tannins is to provide protection against microbial pathogens, harmful insects and herbivores (Furlan at al., 2010). It is possible that the antimicrobial effect of flavonoids and tannins is responsible for the positive relationship between the concentration of these compounds and efficiency of primary culture initiation, because bacterial contamination is a major problem in this stage of micropropagation. ...
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The influence of basal media composition, concentration of plant growth regulators (PGRs), and the developmental stage of primary explants (dormancy, stage of bud opening and fruit ripening) on the initiation phase of nine Magnolia genotypes, including M. stellata /Sieb. & Zucc./Maxim., M. × soulangeana ‘Rustica Rubra’, M. denudata Desr., M. × soulangeana ‘Alexandrina’, M. liliiflora Desr., M. officinalis var. biloba Rehd. & Wils., M. salicifolia Maxim., M. × soulangeana ‘Lennei’, and M. kobus DC, was evaluated. The highest efficiency of primary culture initiation of seven Magnolia genotypes (except for M. liliiflora and M. salicifolia ) was achieved from primary explants collected in the bud opening stage. A high positive correlation was found between total tannins and efficiency of the primary culture initiation at the fruit ripening stage (r = 0.833). Standardi and Catalano medium (S 2 ) with 0.5 mg l ⁻¹ of 6-benzylaminopurine (BAP) was the most appropriate for multiplication of M . × soulangeana ‘Alexandrina’, whereas tissue cultures of M . × soulangeana ‘Lennei’ proliferated and grew better on S 2 medium with 1.0 mg l ⁻¹ of BAP and 1.0 g l ⁻¹ of polyvinylpyrrolidone. The requirements for the composition of basal media and concentration of PGRs in the initiation and multiplication stages of micropropagation of various Magnolia species and cultivars are genotype-specific.
... The overall TPAC changing patterns were found to decrease remarkably from D9 to D12 and then uprose gradually (p < 0.05) on basis of MANOVA. The previous studies revealed that condensed tannins (proanthocyanins) were ubiquitous in ligneous pants but almost absent in herbaceous species (59), which was in accordance with this study results. It was known from the MANOVA results that the seedling age significantly affected the TPAC (p < 0.05) while abiotic treatments did the little effect on the content. ...
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The wheat seedlings of 6 days old were daily subjected to ultraviolet irradiation (irradiating for 5, 10, 20, 40, and 60 min/day, respectively), Polyethylene glycol 6000 (5, 10, 15, 20, 25% in 1/2 Hoagland solution, respectively), and salinity solution (10, 25, 50, 100, 200 mM in 1/2 Hoagland solution, respectively), while the control group (CK) was supplied only with the Hoagland solution. The wheatgrass was harvested regularly seven times and the total soluble polysaccharides, ascorbic acid, chlorophyll, total polyphenol, total triterpene, total flavonoid, and proanthocyanins content were tested. The antioxidant capacity was evaluated through 2,2′-azino-bis (3-ethylbenzthia-zoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability, and ferric ion reducing power. Technique for order preference by similarity to ideal solution (TOPSIS) mathematical model was adopted to comprehensively assess the functional phytochemicals of the different treatments. The results showed that the accumulation patterns of phytochemicals under abiotic stress were complex and not always upregulated or downregulated. The antioxidant activity and functional phytochemicals content of wheatgrass were significantly affected by both the stress treatments and seedling age, while the latter affected the chemicals more efficiently. The top five highest functional phytochemicals were observed in the 200 mM NaCl treated group on the 21st and 27th day, 25% PEG treated group on the 24th day, 200 mM NaCl treated group on the 24th day, and the group of 40 min/day ultraviolet exposure on 27th day.
... Eichler (Combretaceae), a widely distributed deciduous species of Caatinga, locally known as "vaqueta", contains high concentration of tannins that are considered toxic for the cattle consuming large amounts of its leaves in the beginning of the rainy season, during when leaf regrowth happens in this species (Itakura et al. 1987;Oliveira 2012;Almeida et al. 2017;Helayel et al. 2017) and is a delayed greening species (Coley and Kursar 1996). Tannins are compounds resulting from the plant secondary metabolism which are ubiquitous in ligneous plants (Haslam 1988) and might have negative effects on herbivores (Nichols-Orians 1991) depending on their concentration (Hartmann 2008;Furlan et al. 2011). Despite its toxicity, leaves of T. glaucocarpa were among the most frequent leaf material collected by workers of Atta sexdens L. (Hymenoptera, Formicidae) in a Caatinga area in the state of Bahia, Brazil (Oliveira 2012;Cruz et al. 2020). ...
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Thiloa glaucocarpa is a toxic plant as a food item for bovine cattle. However, dry leaves are frequently collected to cultivate the symbiotic fungi of several colonies of Atta sexdens throughout the Caatinga Seasonally Dry Tropical Forest biome in Brazil and such behavior is not clear. In this study, we analyzed the removal of T. glaucocarpa leaves for A. sexdens and tested the hypothesis that the preference for removal of dry leaf material over fresh leaves may be related to the decay of chemical defenses. Dried leaf discs of T. glaucocarpa were offered to laboratory-raised colonies of A. sexdens. Overall, there was a lower consumption of T. glaucocarpa than the previous report, but it is possible to observe a preference for mature and fresh leaves removal, contradicting initial predictions. Probably, the removal of dried leaves is a specific solution learned by natural colonies to reduce the number of secondary compounds and guarantee diet availability in a highly seasonal and food-poor environment. The preference for mature leaves is not usual and is probably the result of a higher production of secondary compounds in young leaves, which could guarantee protection for leaves against herbivory in early rains and improve the productivity of T. glaucocarpa at the beginning of the rainy season.
... Promising results have been achieved by supplementation of boar s diet with a variety of feed additives such as chicory root or inulin [27][28][29][30][31][32][33][34][35][36], raw potato starch [24,[37][38][39], sugar beet pulp [40], Jerusalem artichoke [41], oligofructose and fructooligosaccharides [31,42], and tannins [18,19,43]. The last one is the group of natural astringent polyphenolic compounds widely distributed in many species of plants, where they play a role in protection from predation and help in regulating plant growth [44,45]. ...
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The slaughtering of entire males increases the probability of incidence of tainted pork due to the presence two main compounds—androstenone and skatole. If a surgical castration of young entire male pigs is stopped in the EU countries, fattening of boars is likely to become one of the most commonly used systems in pig farming. Since skatole production and accumulation in fat tissue can be controlled by dietary approaches, several studies have investigated various feed additives to reduce this compound of boar taint. Ones of the most promising is tannins. The aim of this study was to determine the effect of different dietary tannin level supplementation on carcass, pork quality, chemical, amino and fatty acid composition. as well as perception of boar taint and accumulation of skatole and androstenone in adipose tissue. Eighty entire males were randomly distributed to control (T0) and four experimental groups. Control pigs received standard feed mixture (16.8% CP, 13.9 MJ ME) without any tannin supplementation. Experimental pigs received the same diet with administration of 1% (T1), 2% (T2), 3% (T3) and 4% (T4)—sweet chestnut extract rich in hydrolysable tannins for 40 days (from average live weight of 80 kg until slaughter at average weight 122.28 kg ± 5.63 kg). Dietary tannins supplementation did not show any significant effect on chemical composition, cholesterol content, and amino acid composition of muscle as well as fatty acid composition and androstenone accumulation in adipose tissue. A slight or small effect was observed on carcass and meat quality, respectively. Pigs in groups T4 and/or T3-T4 had higher electrical conductivity in semimembranosus muscle and cooking loss value compared to T1, T2 or T0, T1, and T2 groups (p < 0.05). Tannins in the pig’s diet greatly affected fatty acid profile in meat of entire males. The highest tannin levels (4%) increased concentrations of lauric, myristic, vaccenic, linoleic, total PUFA, and n-6 PUFA in muscle compared to the control. Similar results were found in group T3 except for vaccenic, linoleic, and total PUFA. On the contrary, concentrations of heptadecanoic and oleic acids in groups T3 and T4 were lower than those in T1 and T2 groups. Perception of boar taint using „hot iron“ method (insertion a hot iron tip of soldering iron into adipose tissue) tended to decrease in T2 group compared with control. Skatole accumulation in fat tissue was reduced in groups T2-T4 at significance level (p = 0.052–0.055) compared to the control pigs. In summary, tannins supplementation had no effect on chemical and amino acid composition as well as fatty acid profile in adipose tissue, and only slight on carcass value. However, 4% concentration of tannins significantly increased content of some fatty acids compared to control group.
... Furlan et al. [58], reported that tannins have been the focus of researches as their biological activities, especially as anti-carcinogens and anti-oxidants, anti-inflammatory, and anti-HIV functions. This result shows the ample proof the importance of tannins in S. platensis and its vital value. ...
Full-text available
Algae are used as one of important medical sources for its therapeutic properties; and edible algae are acknowledged as complete foods which provide right balance of proteins, carbohydrates, vitamins, mineral salts, carotenoids, and antioxidants. The aim of the current study was to evaluate hot-water extracts of different marine microalgae species (Spirulina platensis, Anabaena oryzae, Scenedesmus obliquus and Chlorella vulgaris) in vitro for their cholesterol-lowering activity, individually or in combinations. The algal extracts (AEs) were prepared from different marine microalgae species and their in vitro anti-cholesterol activities were assessed spectrophotometrically. The algal growth and their bioactive constituents (polyphenol content, antioxidant capacity and tannin content) were quantified using Folin-Ciocalteu, DPPH, vanillin-HCl assays, respectively. The highest value of the biomass concentration (1.367 g) was recorded for S. platensis in 1000 mL of culture media after 21 days. Increasing anti-cholesterol activity by S. platensis extract was observed up to 60 min at a concentration of 15 mg/mL and a highest inhibition was found as 76.01% value (p < 0.05). The combined extracts from S. platensis with C. vulgaris showed maximum cholesterol-lowering effect (77.95%) value (p < 0.05), after the same incubation period. The phytochemical screening indicated the presence of tannins in all algal extracts, with highest tannin contents in S. platensis (4.66 μg TAE/g DW), followed by A. oryzae with (2.99 μg/g) and S. obliquus (2.13 μg/g), A. oryzae extract contained the highest concentration of phenolic compounds (503.67 μg GAE/g). The highest antioxidant activity was obtained by S. platensis extract (92.66%) value (p < 0.05) at 15 mg/mL, while the least one was observed by S. obliquus (16.81%). The extract of S. platensis, used individually or combined with C. vulgaris extract, is recommended as natural bioactive source, with anti-cholesterol and antioxidant potentialities. Graphical abstract
... These compounds, as the name suggests, are hydrolyzed by weak acids, and can be divided into gallotannins, which provide sugar and gallic acid, and ellagitannins, which, in addition, yield ellagic acid after hydrolysis [53]. The main function of these compounds in plants is to provide protection against microbial pathogens, harmful insects, and other herbivores [52], but as summarized by Furlan et al. [54] they are synthesized in plants in response to the influence of environmental stressors such as drought, UV-B radiation, and atmospheric pollution. These effects result from the ability of tannins to bind proteins, to act as antioxidants or pro-oxidants, and to chelate iron and other metals [55]. ...
Full-text available
Abiotic stressors such as extreme temperatures, drought, flood, light, salt, and heavy metals alter biological diversity and crop production worldwide. Therefore, it is important to know the mechanisms by which plants cope with stress conditions. Polyphenols, which are the largest group of plant-specialized metabolites, are generally recognized as molecules involved in stress protection in plants. This diverse group of metabolites contains various structures, from simple forms consisting of one aromatic ring to more complex ones consisting of large number of polymerized molecules. Consequently, all these molecules, depending on their structure, may show different roles in plant growth, development, and stress protection. In the present review, we aimed to summarize data on how different polyphenol structures influence their biological activity and their roles in abiotic stress responses. We focused our review on phenolic acids, flavonoids, stilbenoids, and lignans.
... Besides their multiple applications for human health and agriculture, ellagitannins have also impor tant functions for plant physiology, indeed they can offer protection against biotic stresses (Furlan et al., 2011). Lastly, the concentration of ellagic acid deriva tives seems to increase under salinity stress (BorochovNeori et al., 2014), probably because of the ability of these compounds to alleviate osmotic stress as previously reported in other species (El Souda et al., 2013). ...
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The demand for pomegranate (Punica granatum L.) juices is increas ing worldwide due to its documented healthpromoting effects which likely derive from phenolic compounds. This study reports the phenolic composition of the juices obtained from eight wildgrowing pomegranate accessions collect ed in eight areas of Azerbaijan, characterized by different climate and soil com position. The anthocyanins found in all the accessions were cyaniding deriva tives and pelargonidin derivatives, while only two accessions contained also delphinidin3,5Odiglucoside. The main hydrolysable tannins contained in the juices were punicalagin and ellagic acid derivatives. These bioactive metabo lites found in the juices varied qualitatively and quantitatively among the eight accessions, thus constituting specific traits for selecting promising accessions that can be used as a nutritious food source. The different phenolic profiles might be determined both by genotype and the growing environmental condi tions, or by their interaction. Our results suggest that some of the studied wild growing pomegranate accessions might have a commercial value because of their richness in bioactive metabolites and might constitute a suitable source of genes for breeding programs.
The evaluation of genetic variability is essential to support the conservation of economically important plant species such as Chrysobalanus icaco, a medicinal plant. In Brazil, this species occurs in endangered sandbank areas along the Atlantic coast raising considerable concern over C. icaco diversity conservation. Therefore, research in population structure is needed and can be carried out using single-nucleotide polymorphisms. The aim of this study was to optimize high-quality DNA extraction based on the CTAB method.
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A revised and updated classification for the families of flowering plants is provided. Many recent studies have yielded increasingly detailed evidence for the positions of formerly unplaced families, resulting in a number of newly adopted orders, including Amborellales, Berberidopsidales, Bruniales, Buxales, Chloranthales, Escalloniales, Huerteales, Nymphaeales, Paracryphiales, Petrosaviales, Picramniales, Trochodendrales, Vitales and Zygophyllales. A number of previously unplaced genera and families are included here in orders, greatly reducing the number of unplaced taxa; these include Hydatellaceae (Nymphaeales), Haptanthaceae (Buxales), Peridiscaceae (Saxifragales), Huaceae (Oxalidales), Centroplacaceae and Rafflesiaceae (both Malpighiales), Aphloiaceae, Geissolomataceae and Strasburgeriaceae (all Crossosomatales), Picramniaceae (Picramniales), Dipentodontaceae and Gerrardinaceae (both Huerteales), Cytinaceae (Malvales), Balanophoraceae (Santalales), Mitrastemonaceae (Ericales) and Boraginaceae (now at least known to be a member of lamiid clade). Newly segregated families for genera previously understood to be in other APG-recognized families include Petermanniaceae (Liliales), Calophyllaceae (Malpighiales), Capparaceae and Cleomaceae (both Brassicales), Schoepfiaceae (Santalales), Anacampserotaceae, Limeaceae, Lophiocarpaceae, Montiaceae and Talinaceae (all Caryophyllales) and Linderniaceae and Thomandersiaceae (both Lamiales). Use of bracketed families is abandoned because of its unpopularity, and in most cases the broader circumscriptions are retained; these include Amaryllidaceae, Asparagaceace and Xanthorrheaceae (all Asparagales), Passifloraceae (Malpighiales), Primulaceae (Ericales) and several other smaller families. Separate papers in this same volume deal with a new linear order for APG, subfamilial names that can be used for more accurate communication in Amaryllidaceae s.l., Asparagaceace s.l. and Xanthorrheaceae s.l. (all Asparagales) and a formal supraordinal classification for the flowering plants.
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Psidium guajava 'Paluma' is sensitive to ozone, to which reacts with characteristic visible foliar injuries. The concentration of ascorbic acid (AA) and the activity of enzymes superoxide dismutase (SOD) and peroxidase (POD) had been evaluated in new and old leaves of plants exposed (n = 13) to ozone in a contaminated area (Ibirapuera, São Paulo, SP) and in a controlled environment (glasshouse with filtered air) to assess the occurrence of latent injuries (alteration in AA, SOD and/or POD) and if the occurrence of these differed between leaves with or without visible injuries. The AA concentration was higher in plants of Ibirapuera, without difference between new or old and with or without visible injuries. The activity of SOD and POD differed between new and old leaves, but not with relation to the site of exposition and the presence or absence of foliar injuries. There was no significant decrease in biomass in plants exposed in Ibirapuera. We conclude that in P. guajava 'Paluma' SOD and POD are not related to the protection against visible foliar injuries and that the AA is a indicator of latent injury.
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The ecological activities of plant phenolics are diverse and highly variable. Although some variation is attributable to differences in concentration, structure, and evolutionary history of association with target organisms, much of it is unexplained, making it difficult to predict when and where phenolics will be active. I suggest that our understanding is limited by a failure to appreciate the importance of oxidative activation and the conditions that influence it. I summarize examples of oxidative activation of phenolics in ecological interactions, and argue that physicochemical conditions of the environment that control phenolic oxidation generate variation in ecological activity. Finally, I suggest that measurements of oxidative conditions can improve our predictions of phenolic activity and that experiments must be designed with conditions appropriate to the biochemical mode of phenolic action.
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Saplings of Psidium guajava (guava, Myrtaceae), a tropical tree species, were exposed to industrial air pollutants at Cubatão, the largest industrial complex of Latin America, along two periods, each one comprising one-year: period I, July/2000 - June/2001; period II, December/2000 - November/2001. Saplings were exposed in two experimental sites: Pilões River Valley (PV), reference site, with low contamination by air pollutants; and Mogi River Valley (MV), a site severely affected by pollutants from chemical, fertilizer, ceramic, iron and steel industries. At both sites, the main flavonoids found were guaijaverin, quercitrin and two quercetin diglycosides. No interactions among factors were found as well as no significant differences were found among periods and among sites. However, total foliar flavonoid amounts showed the tendency of decrease after 12 months of experimentation. Cubatão industrial air pollution, with high concentrations of NO2, SO2 and particulate matter, plus climatic conditions of the initial months of exposure seem that does not influence flavonoid composition and quantities.
Many of the hypotheses adumbrated to rationalize the role of natural products in plant-herbivore interactions have focused attention on plant polyphenols (syn., vegetable tannins). Contemporary interpretations of the importance of plant polyphenols rest largely on the assumption that they act via their capacity to bind to proteins. The central proposition of plant-herbivore interactions, namely that plants, as a response to environmental pressures, have evolved the strategem of a chemical armory appropriate to the challenges they face, is examined in the context of plant polyphenols-their ability to complex to protein and their possible function as structural polymers.
Decreased levels of foliar tannin was observed with Japanese Cedars growing in the surroundings of a steam power station. Tannin content of the leaves was negatively corrrelated with the levels of foliar soluble sulphate, and a causal association was suggested between air pollution and inhibition of the shikimate pathway. Preliminary observation on predation damage of the Japanese Cedars indicates that increased feeding rate by larvae of a herbivorous moth, Dasychira abietis argentata, was associated with low foliar tannin content and the vicinity of the sampling sites to the power station. Considering the physiological function of tannins, e.g. as a defensive factor against insect predation and fungal degradation, it seems that decrease of foliar tannin levels of Japanese Cedars in the polluted areas has relevance to their high susceptibility to air pollution in field conditions.
Soil is the major player in deciding allelopathic activities. A study was designed to examine experimental complexities in determining the allelopathic behavior of soil amended with water-soluble leachates from Chenopodium murale. Chenopodium murale interferes with the growth and establishment of crop seedlings. The present study examined the role of water-soluble organic substances, if any, in the shoot growth suppression of rice (Oryza sativa L.). Rice seeds were grown on C. murale leaf leachate-amended soil to investigate the phytotoxic effects of C. murale leachates. Any modification of C. murale phytotoxic activities was studied through using abiotic soil, activated charcoal and nitrogen (N) fertilization. Chemical and microbiological analysis of C. murale-amended soil was made to evaluate the role of soil components in C. murale phytotoxicity. Significant inhibition in the shoot growth of rice was observed when abiotic or biotic soil was amended with full-strength leaf leachate (T1) of C. murale compared to unamended soils. The inhibitory effect of T1 is maintained when rice seeds were placed on T1-amended soil after 0, 24 or 48h; however, the inhibitory effects were eliminated when seeds were placed on amended soil after 72, 96h or 1 wk of incubating soil with T1. Activated charcoal (1, 2 or 4g) could not eliminate the inhibitory effects of T1-amended soil to the shoot length of rice. The phytotoxic effects of T1-amended soil to the shoot length of rice, however, were largely eliminated after the addition of N fertilization. Interference of C. murale leaf leachate to rice shoot growth could be due to number of effects that could be misconstrued as allelopathy effects.
Allelopathy has been suggested as a mechanism of interference in several weed species. Allelochemicals released from certain weed species influence the growth and yield of crop species. Several laboratory studies present circumstantial evidence of the occurrence of allelopathy as a causative agent in weed-crop agroecosystems. Field evidence, however, is still lacking. In this paper, the significance of field studies is argued in terms of a multifaceted approach to allelopathy, and mugwort is used as an example. Previous research demonstrated the allelopathic potential of mugwort; however, experiments were not carried out in a natural environment. Inderjit and Foy (1999) have demonstrated that chemical characteristics (pH, inorganic ions, and phenolics) of soil amended with mugwort leaf leachate were altered when compared to unamended soil. We have analyzed the mugwort-infested field soil and compared its chemical characteristics with those of amended soils. No definite trend, in terms of influence of mugwort on soil chemistry, was observed. Results indicate the importance of field studies in order to obtain ecologically relevant data from laboratory studies. Field situations are often complex in terms of the presence of interfering flora. Cyanobacteria, for example, play an important role in weed-crop interactions in rice paddy soils. Allelochernicals released from weed species present in the paddy field may influence nitrogen-fixing cyanobacteria in addition to their phytotoxic effects to the paddy crop. Significance of phytotoxic effects of weed species on crop growth, and N-2-fixing potential of cyanobacteria in paddy soils is discussed.
All 25 species of Acer examined contain condensed (proanthocyanidins) and hydrolysable (gallo- and/or ellagi-) tannins, but each of these varies ov
Reduced flower pigmentation in the legume Swainsona formosa is associated with increased susceptibility to Phytophthora cinnamomi and other soil-borne pathogens. This study aimed to identify the mechanism for these differences in susceptibility. Chemical analyses of stem tissues that had been previously inoculated with P. cinnamomi revealed that neither anthocyanin nor total phenolic content increased with infection. Such results suggested that observed differences in susceptibility, as indicated by flower colour, were related to preformed rather than induced stem chemistry. Acetone extracts from healthy, uninfected stem tissues of a red-flowered line were highly toxic to the fungus, while extracts from a white-flowered line were non-toxic and those from a pink-flowered line were intermediate in toxicity and this was correlated with the total phenolic and proanthocyanidin concentration of the extracts. Precipitation of proanthocyanidins with bovine serum albumen removed the toxicity of the extracts. It was concluded that differences in the proanthocyanidin content of tissues contributed to the differences in disease susceptibility of plants with different flower colours.