phytoalexin

File:Capsidiol.svg is a phytoalexin produced by certain plants in response to pathogenic attack.]]

Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized de novo by plants that produce the compounds rapidly at sites of pathogen infection. In general phytoalexins are broad spectrum inhibitors; they are chemically diverse, and different chemical classes of compounds are characteristic of particular plant taxa. Phytoalexins tend to fall into several chemical classes, including terpenoids, glyco steroids, and alkaloids; however, the term applies to any phytochemicals that are induced by microbial infection.

Function

Phytoalexins are produced in plants to act as toxins to the attacking organism. They may puncture the cell wall, delay maturation, disrupt metabolism or prevent reproduction of the pathogen in question. Their importance in plant defense is indicated by an increase in susceptibility of plant tissue to infection when phytoalexin biosynthesis is inhibited. Mutants incapable of phytoalexin production exhibit more extensive pathogen colonization as compared to wild types. As such, host-specific pathogens capable of degrading phytoalexins are more virulent than those unable to do so.{{cite journal |last1=Glazebrook |first1=J |last2=Ausubel |first2=F M |title=Isolation of phytoalexin-deficient mutants of Arabidopsis thaliana and characterization of their interactions with bacterial pathogens |journal=PNAS |volume=91 |issue=19 |year=1994 |pages=8955–8959 |pmid=8090752 |pmc=44725 |bibcode=1994PNAS...91.8955G |doi=10.1073/pnas.91.19.8955 |doi-access=free}}

When a plant cell recognizes particles from damaged cells or particles from the pathogen, the plant launches a two-pronged resistance: a general short-term response and a delayed long-term specific response.{{citation needed|date=March 2023}}

As part of the induced resistance, the short-term response, the plant deploys reactive oxygen species such as superoxide and hydrogen peroxide to kill invading cells. In pathogen interactions, the common short-term response is the hypersensitive response, in which cells surrounding the site of infection are signaled to undergo apoptosis, or programmed cell death, in order to prevent the spread of the pathogen to the rest of the plant.{{citation needed|date=March 2023}}

Long-term resistance, or systemic acquired resistance (SAR), involves communication of the damaged tissue with the rest of the plant using plant hormones such as jasmonic acid, ethylene, abscisic acid, or salicylic acid. The reception of the signal leads to global changes within the plant, which induce expression of genes that protect from further pathogen intrusion, including enzymes involved in the production of phytoalexins. Often, if jasmonates or ethylene (both gaseous hormones) are released from the wounded tissue, neighboring plants also manufacture phytoalexins in response. For herbivores, common vectors for plant diseases, these and other wound response aromatics seem to act as a warning that the plant is no longer edible.{{citation needed|date=March 2018}} Also, in accordance with the old adage, "an enemy of my enemy is my friend", the aromatics may alert natural enemies of the plant invaders to the presence thereof.

Recent research

Allixin (3-hydroxy-5-methoxy-6-methyl-2-pentyl-4H-pyran-4-one), a non-sulfur-containing compound having a γ-pyrone skeletal structure, was the first compound isolated from garlic as a phytoalexin, a product induced in plants by continuous stress.{{cite journal |vauthors=Kodera Y, Matuura H, Yoshida S, Sumida T, Itakura Y, Fuwa T, Nishino H |journal=Chem. Pharm. Bull. |volume=37 |pages=1656–1658 |title=Allixin, a stress compound from garlic |issue=6 |year=1989 |doi=10.1248/cpb.37.1656 |doi-access=free}} This compound has been shown to have unique biological properties, such as anti-oxidative effects, anti-microbial effects, anti-tumor promoting effects,{{cite journal |vauthors=Nishino H, Nishino A, Takayama J, Iwashima A, Itakura Y, Kodera Y, Matsuura H, Fuwa T |title=Antitumor promoting activity of allixin, a stress compound produced by garlic |journal=Cancer J. |volume=3 |year=1990 |pages=20–21}} inhibition of aflatoxin B2 DNA binding,{{cite journal |author1=Yamasaki T. |author2=Teel R. W. |author3=Lau B. H. S. |title=Effect of allixin, a phytoalexin produced by garlic, on mutagenesis, DNA-binding and metabolism of aflatoxin B1 |journal=Cancer Lett. |volume=59 |issue=2 |year=1991 |pages=89–94 |pmid=1909211 |doi=10.1016/0304-3835(91)90171-D}} and neurotrophic effects. Allixin showed an anti-tumor promoting effect in vivo, inhibiting skin tumor formation by TPA in DMBA initiated mice. Herein, allixin and/or its analogs may be expected to be useful compounds for cancer prevention or chemotherapy agents for other diseases.{{cn|date=March 2023}}

Role of natural phenols in the plant defense against fungal pathogens

Polyphenols, especially isoflavonoids and related substances, play a role in the plant defense against fungal and other microbial pathogens.

In Vitis vinifera grape, trans-resveratrol is a phytoalexin produced against the growth of fungal pathogens such as Botrytis cinerea{{cite journal |title=The role of grape polyphenols on trans-resveratrol activity against Botrytis cinerea and of fungal laccase on the solubility of putative grape PR proteins |author1=F. Favaron |author2=M. Lucchetta |author3=S. Odorizzi |author4=A.T. Pais da Cunha |author5=L. Sella |journal=Journal of Plant Pathology |year=2009 |volume=91 |issue=3 |pages=579–588 |url=https://www.sipav.org/main/jpp/volumes/0309/030909.pdf |access-date=2011-01-22}} and delta-viniferin is another grapevine phytoalexin produced following fungal infection by Plasmopara viticola.{{cite journal |title=Production of the phytoalexins trans-resveratrol and delta-viniferin in two economy-relevant grape cultivars upon infection with Botrytis cinerea in field conditions |last1=Timperio |first1=Anna Maria |last2=d’Alessandro |first2=Angelo |last3=Fagioni |first3=Marco |last4=Magro |first4=Paolo; Lello Zolla |journal=Plant Physiology and Biochemistry |volume=50 |issue=1 |year=2012 |pages=65–71 |pmid=21821423|doi=10.1016/j.plaphy.2011.07.008}} Pinosylvin is a pre-infectious stilbenoid toxin (i.e. synthesized prior to infection), contrary to phytoalexins which are synthesized during infection. It is present in the heartwood of Pinaceae.{{cite journal |title=Screening Analyses of Pinosylvin Stilbenes, Resin Acids and Lignans in Norwegian Conifers |last1=Hovelstad |first1=Hanne |last2=Leirset |first2=Ingebjorg |last3=Oyaas |first3=Karin |last4=Fiksdahl |first4=Anne |journal=Molecules |volume=11 |issue=1 |year=2006 |pages=103–14 |pmid=17962750 |pmc=6148674 |doi=10.3390/11010103 |doi-access=free}} It is a fungitoxin protecting the wood from fungal infection.{{cite journal |title=Antibacterial and antifungal activity of pinosylvin, a constituent of pine |last1=Lee |first1=S.K. |last2=Lee |first2=H.J. |last3=Min |first3=H.Y. |last4=Park |first4=E.J. |last5=Lee |first5=K.M. |last6=Ahn |first6=Y.H. |last7=Cho |first7=Y.J. |last8=Pyee |first8=J.H. |journal=Fitoterapia |volume=76 |issue=2 |year=2005 |pages=258–60 |pmid=15752644 |doi=10.1016/j.fitote.2004.12.004}}

Sakuranetin is a flavanone, a type of flavonoid. It can be found in Polymnia fruticosa{{cite web |title=Structure and Data for Sakuranetin (NSC 407228) |website=home.ncifcrf.gov |url=http://home.ncifcrf.gov/mtdp/Catalog/compounds/407228.html |access-date=2012-04-13 |url-status=dead |archive-url=https://web.archive.org/web/20181203010928/https://home.ncifcrf.gov/mtdp/Catalog/compounds/407228.html |archive-date=2018-12-03}} and rice, where it acts as a phytoalexin against spore germination of Pyricularia oryzae.{{cite journal | doi=10.1016/S0031-9422(00)97532-0 | title=Sakuranetin, a flavanone phytoalexin from ultraviolet-irradiated rice leaves | year=1992 | last1=Kodama | first1=Osamu | last2=Miyakawa | first2=Junichi | last3=Akatsuka | first3=Tadami | last4=Kiyosawa | first4=Shigehisa | journal=Phytochemistry | volume=31 | issue=11 | pages=3807–3809 | bibcode=1992PChem..31.3807K }} In Sorghum, the SbF3'H2 gene, encoding a flavonoid 3'-hydroxylase, seems to be expressed in pathogen-specific 3-deoxyanthocyanidin phytoalexin synthesis,{{cite journal |title=Differential Expression of Two Flavonoid 3'-Hydroxylase cDNAs Involved in Biosynthesis of Anthocyanin Pigments and 3-Deoxyanthocyanidin Phytoalexins in Sorghum |author1=Chun-Hat Shih |author2=Ivan K. Chu |author3=Wing Kin Yip |author4=Clive Lo |journal=Plant and Cell Physiology |year=2006 |volume=47 |issue=10 |pages=1412–1419 |doi=10.1093/pcp/pcl003 |pmid=16943219 |url=https://academic.oup.com/pcp/article/47/10/1412/2279020|doi-access=free }} for example in Sorghum-Colletotrichum interactions.{{cite web |title=Biosynthesis and regulation of 3-deoxyanthocyanidin phytoalexins induced during Sorghum-Colletotrichum interaction: Heterologous expression in maize. |author1=Chopra, Surinder |author2=Gaffoor, Iffa |author3=Ibraheem, Farag |url=http://abstracts.aspb.org/pb2009/public/P48/P48067.html |url-status=dead |archive-url=https://web.archive.org/web/20110725021532/http://abstracts.aspb.org/pb2009/public/P48/P48067.html |archive-date=2011-07-25}}

6-Methoxymellein is a dihydroisocoumarin and a phytoalexin induced in carrot slices by UV-C,{{cite journal |title=Induction of 6-Methoxymellein and Resistance to Storage Pathogens in Carrot Slices by UV-C |last1=Mercier |first1=J. |last2=Arul |first2=J. |last3=Ponnampalam |first3=R. |last4=Boulet |first4=M. |journal=Journal of Phytopathology |volume=137 |year=1993 |pages=44–54 |doi=10.1111/j.1439-0434.1993.tb01324.x}} that allows resistance to Botrytis cinerea{{cite journal |title=Cell death, 6-methoxymellein accumulation, and induced resistance to Botrytis cinerea in carrot root slices |last1=Hoffman |first1=R. |last2=Heale |first2=J.B. |journal=Physiological and Molecular Plant Pathology |volume=30 |year=1987 |pages=67–75 |doi=10.1016/0885-5765(87)90083-X}} and other microorganisms.{{cite journal |title=Isolation and antimicrobial activity of the phytoalexin 6-methoxymellein from cultured carrot cells |last1=Kurosaki |first1=Fumiya |last2=Nishi |first2=Arasuke |journal=Phytochemistry |volume=22 |issue=3 |year=1983 |pages=669 |doi=10.1016/S0031-9422(00)86959-9|bibcode=1983PChem..22..669K }}

Danielone is a phytoalexin found in the papaya fruit. This compound showed high antifungal activity against Colletotrichum gloesporioides, a pathogenic fungus of papaya.{{cite journal | doi=10.1016/S0031-9422(96)00418-9 | title=Danielone, a phytoalexin from papaya fruit | year=1997 | last1=Echeverri | first1=Fernando | last2=Torres | first2=Fernando | last3=Quiñones | first3=Winston | last4=Cardona | first4=Gloria | last5=Archbold | first5=Rosendo | last6=Roldan | first6=Javier | last7=Brito | first7=Ivan | last8=Luis | first8=Javier G. | last9=Lahlou | first9=El-Hassane | journal=Phytochemistry | volume=44 | issue=2 | pages=255–256 | pmid=9004541 | bibcode=1997PChem..44..255E }}

Stilbenes are produced in Eucalyptus sideroxylon in case of pathogen attacks. Such compounds can be implied in the hypersensitive response of plants. High levels of polyphenols in some woods can explain their natural preservation against rot.{{cite journal |title=Inhibition of wood-rotting fungi by stilbenes and other polyphenols in Eucalyptus sideroxylon |first1=John H. |last1=Hart |first2=W. E. |last2=Hillis |journal=Phytopathology |volume=64 |issue=7 |pages=939–48 |year=1974 |doi=10.1094/Phyto-64-939}}

Avenanthramides are phytoalexins produced by Avena sativa in its response to Puccinia coronata var. avenae f. sp. avenae, the oat crown rust. (Avenanthramides were formerly called avenalumins.)

References

{{reflist|refs=

{{cite journal |last1=Mayama |first1=S. |last2=Bordin |first2=A.P.A. |last3=Morikawa |first3=T. |last4=Tanpo |first4=H. |last5=Kato |first5=H. |title=Association of avenalumin accumulation with co-segregation of victorin sensitivity and crown rust resistance in oat lines carrying the Pc-2 gene |journal=Physiological and Molecular Plant Pathology |volume=46 |issue=4 |year=1995 |pages=263–274 |s2cid=82948086 |doi=10.1006/pmpp.1995.1021}}

{{cite journal |last=Hammerschmidt |first=Ray |title=Phytoalexins: What Have We Learned After 60 Years? |journal=Annual Review of Phytopathology |volume=37 |issue=1 |year=1999 |pages=285–306 |pmid=11701825 |doi=10.1146/annurev.phyto.37.1.285}}

{{cite journal |last1=Mayama |first1=S. |last2=Matsuura |first2=Y. |last3=Iida |first3=H. |last4=Tani |first4=T. |title=The role of avenalumin in the resistance of oat to crown rust, Puccinia coronata f. sp. avenae |journal=Physiological Plant Pathology |volume=20 |issue=2 |year=1982 |pages=189–199 |doi=10.1016/0048-4059(82)90084-4}}

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External links

[https://web.archive.org/web/20110604234827/http://www.lancs.ac.uk/staff/robertmr/downloads/mrr-crips.pdf Signals Regulating Multiple Responses to Wounding and Herbivores] Guy L. de Bruxelles and Michael R Roberts
[https://web.archive.org/web/20040609070225/http://www.cepceb.ucr.edu/resources/pdf/walling/Walling-2000-JPGR.pdf The Myriad Plant Responses to Herbivores] Linda L. Walling
[https://www.uky.edu/~garose/link100.htm The Chemical Defenses of Higher Plants] Gerald A. Rosenthal
[https://web.archive.org/web/20041012013705/http://aob.oupjournals.org/cgi/content/full/89/5/503 Induced Systemic Resistance (ISR) Against Pathogens in the Context of Induced Plant Defences] Martin Heil
[https://academic.oup.com/plphys/article/127/3/727/6110169?login=false Notes from the Underground] Donald R. Strong and Donald A. Phillips
[https://web.archive.org/web/20040813200322/http://www.colostate.edu/Depts/Entomology/courses/en570/papers_2000/mannix.html Relationships Among Plants, Insect Herbivores, Pathogens, and Parasitoids Expressed by Secondary Metabolites] Loretta L. Mannix