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Parasitic plant

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Cuscuta,a stem holoparasite, on anAcaciatree inPakistan

Aparasitic plantis aplantthat derives some or all of its nutritional requirements from another living plant. They make up about 1% ofangiospermsand are found in almost everybiome.Allparasiticplants develop a specialized organ called thehaustorium,which penetrates the host plant, connecting them to the host vasculature – either thexylem,phloem,or both.[1]For example, plants likeStrigaorRhinanthusconnect only to the xylem, via xylem bridges (xylem-feeding). Alternately,plantslikeCuscutaand some members ofOrobancheconnect to both the xylem and phloem of the host.[1][2][3]This provides them with the ability to extract resources from the host. These resources can include water, nitrogen, carbon and/or sugars.[4]Parasitic plants are classified depending on the location where the parasitic plant latches onto the host (root or stem), the amount of nutrients it requires, and their photosynthetic capability.[5]Some parasitic plants can locate theirhostplants by detecting volatilechemicalsin the air or soil given off by hostshootsorroots,respectively. About 4,500speciesof parasitic plants in approximately 20 families offlowering plantsare known.[5][6]

There is a wide range of effects that may occur to a host plant due to the presence of a parasitic plant. Often there is a pattern of stunted growth in hosts especially in hemi-parasitic cases, but may also result in higher mortality rates in host plant species following introduction of larger parasitic plant populations.[7]

Classification

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Parasitic plants occur in multiple plant families, indicating that the evolution ispolyphyletic.Some families consist mostly of parasitic representatives such asBalanophoraceae,while other families have only a few representatives. One example is the North AmericanMonotropa uniflora(Indian pipe or corpse plant) which is a member of the heath family,Ericaceae,better known for its member blueberries, cranberries, andrhododendrons.

Parasitic plants are characterized as follows:[5]

1 a Obligate An obligate parasite cannot complete its life cycle without a host.
b Facultative A facultative parasite can complete its life cycle independent of a host.
2 a Stem A stem parasite attaches to the host stem.
b Root A root parasite attaches to the host root.
3 a Hemi- A hemiparasitic plant lives as a parasite under natural conditions, but remainsphotosyntheticto at least some degree. Hemiparasites may obtain only water and mineral nutrients from the host plant, or many also obtain a part of their organic nutrients from the host.
b Holo- A holoparasitic plant derives all of its fixed carbon from the host plant. Commonly lacking chlorophyll, holoparasites are often colors that are not green.
Mistletoe,an obligate stem hemiparasite

For hemiparasites, one from each of the three sets of terms can be applied to the same species, e.g.

Holoparasites are always obligate so only two terms are needed, e.g.

  • Dodderis a stem holoparasite.
  • Hydnoraspp. are root holoparasites.

Plants usually considered holoparasites includebroomrape,dodder,Rafflesia,and theHydnoraceae.Plants usually considered hemiparasites includeCastilleja,mistletoe,Western Australian Christmas tree,andyellow rattle.

Evolution of parasitism

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Strigawitchweeds (white, center, attached to roots of the host) are economically important pests of the crop plants that they parasitize.

Parasitic behavior evolved in angiosperms roughly 12-13 times independently, a classic example ofconvergent evolution.Roughly 1% of all angiosperm species are parasitic, with a large degree of host dependence. The taxonomic familyOrobanchaceae(encompassing the generaTriphysaria,Striga,andOrobanche) is the only family that contains both holoparasitic and hemiparasitic species, making it a model group for studying the evolutionary rise ofparasitism.The remaining groups contain only hemiparasites or holoparasites.[8]

The evolutionary event which gave rise to parasitism in plants was the development ofhaustoria.The first, most ancestral, haustoria are thought to be similar to that of the facultative hemiparasites withinTriphysaria,lateral haustoria develop along the surface of the roots in these species. Later evolution led to the development of terminal or primary haustoria at the tip of the juvenileradicle,seen in obligate hemiparasitic species withinStriga.Lastly, holoparasitic plants, always forms of obligate parasites, evolved over the loss of photosynthesis, seen in the genusOrobanche.[8]The most specialized forms of holoparasitic plants are the four familiesRafflesiaceae,Cytinaceae,MitrastemonaceaeandApodanthaceae,lineages which independently has evolved further into endoparasites that, except for the flowers, spend their entire life cycle within the tissue of their host.[9]

To maximize resources, many parasitic plants have evolved 'self-incompatibility', to avoid parasitizing themselves. Others such asTriphysariausually avoid parasitizing other members of their species, but some parasitic plants have no such limits.[8]Thealbino redwoodis a mutantSequoia sempervirensthat produces no chlorophyll; they live on sugars from neighbouring trees, usually the parent tree from which they have grown (via a somatic mutation).[10][11][12]

Seed germination

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Parasitic plantsgerminatein several methods. These can either be chemical or mechanical and the means used by seeds often depends on whether or not the parasites are root parasites or stem parasites. Most parasitic plants need to germinate near their host plants because their seeds are limited in the number of resources necessary to survive without nutrients from their host plants. Resources are limited due in part to the fact that most parasitic plants are not able to useautotrophicnutrition to establish the early stages of seeding.[13][14]

Root parasitic plant seeds tend to use chemical cues for germination. For germination to occur, seeds need to be quite close to the host plant.[13][14]For example, the seeds of witchweed (Striga asiatica) need to be within 3 to 4 millimeters (mm) of its host to receive chemical signals in the soil to trigger germination. This range is important becauseStriga Asiaticawill only grow about 4 mm after germination.[13]Chemical compound cues sensed by parasitic plant seeds are from host plant root exudates that are leached nearby from the host'sroot systeminto the surrounding soil. These chemical cues are a variety of compounds that are unstable and rapidly degraded in soil and are present within a radius of a few meters of the plant exuding them. Parasitic plants germinate and follow a concentration gradient of these compounds in the soil toward the host plants if close enough. These compounds are calledstrigolactones.Strigolactone stimulatesethylene biosynthesisin seeds causing them to germinate.[13][14]

There are a variety of chemical germination stimulants. Strigol was the first of the germination stimulants to be isolated. It was isolated from a non-host cotton plant and has been found in true host plants such as corn and millets. The stimulants are usually plant-specific, examples of other germination stimulants include sorgolactone from sorghum, Orobanche and electoral from red clover, and 5-deoxystrigol fromLotus japonicus.Strigolactones are apocarotenoids that are produced via the carotenoid pathway of plants. Strigolactones and mycorrhizal fungi have a relationship in which Strigolactone also cues the growth of mycorrhizal fungus.[14][15]

Stem parasitic plants, unlike most root parasites, germinate using the resources inside their endosperms and can survive for some time. For example,the dodders (Cuscutaspp.)drop their seeds to the ground. These may remaindormantfor up to five years before they find a host plant. Using the resources in the seedendosperm,the dodder can germinate. Once germinated, the plant has 6 days to find and establish a connection with its host plant before its resources are exhausted.[13]Dodder seeds germinate above ground, then the plant sends out stems in search of its host plant reaching up to 6 cm before it dies. It is believed that the plant uses two methods of finding a host. The stem detects its host plant's scent and orients itself in that direction. Scientists used volatiles fromtomatoplants (α-pinene,β-myrcene,andβ-phellandrene) to test the reaction ofC. pentagonaand found that the stem orients itself in the direction of the odor.[14]Some studies suggest that by using light reflecting from nearby plants dodders can select hosts with higher sugar because of the levels ofchlorophyllin the leaves.[16]Once the dodder finds its host, it wraps itself around the host plant's stem. Using adventitious roots, the dodder taps into the host plant's stem with ahaustorium,an absorptive organ within the host plantvascular tissue.Dodder makes several of these connections with the host as it moves up the plant.[13][14][16]

Seed dispersal

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There are several methods of seed dispersal, but all the strategies aim to put the seed in direct contact with, or within a critical distance of, the host.

  1. TheCuscutaseedlingcan live for 3–7 days and extend out 35 cm in search of the host before it dies. This is because theCuscutaseed is large and has stored nutrients to sustain its life. This is also useful for seeds that get digested by animals and are excreted.[5]
  2. Mistletoeuse a sticky seed for dispersal. The seed sticks to nearby animals and birds and then comes into direct contact with the host.[5]
  3. Arceuthobiumseeds have a similarly sticky seed as the mistletoe but they do not rely on animals and birds, they mainly disperse by fruitexplosiveness.Once the seed makes contact with the host, rainwater can help position the seed in a suitable position.[5]
  4. Some seeds detect and respond tochemical stimulationsproduced in the host's roots and start to grow towards the host.[5]

Obstacles to host attachment

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A parasitic plant has many obstacles to overcome to attach to a host. Distance from the host and stored nutrients are some of the problems, and the host's defenses are an obstacle to overcome. The first hurdle is penetrating the host since the host has systems to reinforce the cell wall byprotein cross-linkingso that it stops the parasitic progress at thecortexof the host's roots. The second hurdle is the host's ability tosecretegermination inhibitors. This preventsgerminationof the parasitic seed. The third hurdle is the host's ability to create atoxicenvironment at the location where the parasitic plant attaches. The host secretesphenoliccompounds into theapoplast.This creates a toxic environment for the parasitic plant, eventually killing it. The fourth hurdle is the host's ability to ruin thetubercleusing gums and gels or injecting toxins into thetubercle.[17]

Host range

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Some parasitic plants are generalists and parasitize many different species, even several different species at once.[18]Dodder (Cuscutaspp.) and red rattle (Odontites vernus) are generalist parasites. Other parasitic plants are specialists that parasitize a few or just one species. Beech drops (Epifagus virginiana) is a root holoparasite only on American beech (Fagus grandifolia).Rafflesiais a holoparasite on the vineTetrastigma.Plants such asPterosporabecome parasites ofmycorrhizalfungi. There is evidence that parasites also practice self-discrimination, species ofTriphysariaexperience reduced haustorium development in the presence of otherTriphysaria.The mechanism for self-discrimination in parasites is not yet known.[8]

Aquatic parasitic plants

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Parasitism also evolved within aquatic species of plants and algae. Parasitic marine plants are described asbenthic,meaning that they are sedentary or attached to another structure. Plants and algae that grow on the host plant, using it as an attachment point are given the designationepiphytic(epilithicis the name given to plants/algae that use rocks or boulders for attachment), while not necessarily parasitic, some species occur in high correlation with a certain host species, suggesting that they rely on the host plant in some way or another. In contrast,endophyticplants and algae grow inside their host plant, these have a wide range of host dependence from obligate holoparasites to facultative hemiparasites.[19]

Marine parasites occur as a higher proportion of marine flora in temperate rather than tropical waters. While no full explanation for this is available, many of the potential host plants such askelpand other macroscopicbrown algaeare generally restricted to temperate areas. Roughly 75% of parasiticred algaeinfect hosts in the same taxonomic family as themselves, these are given the designation adelphoparasites. Other marine parasites, deemed endozoic, are parasites of marine invertebrates (mollusks,flatworms,sponges) and can be either holoparasitic or hemiparasitic, some retaining the ability to photosynthesize after infection. These are the only parasitic plants that parasitize animal hosts.[19]

Importance

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Species withinOrobanchaceaeare some of the most economically destructive species on Earth. Species ofStrigaalone are estimated to cost billions of dollars a year in crop yield loss annually, infesting over 50 million hectares of cultivated land withinsub-Saharan Africaalone.Strigacan infest both grasses and grains, includingcorn,riceandsorghum,some of the most important food crops.Orobanchealso threatens a wide range of important crops, including peas,chickpeas,tomatoes,carrots,lettuce,[20]and varieties of the genusBrassica(e.g. cabbage and broccoli). Yield loss fromOrobanchecan reach 100% and has caused farmers in some regions of the world to abandon certain staple crops and begin importing others as an alternative. Much research has been devoted to the control ofOrobancheandStrigaspecies, which are even more devastating in developing areas of the world, though no method has been found to be entirely successful.[8]

  • Mistletoes cause economic damage to forests and ornamental trees.
  • Rafflesia arnoldiiproduces the world's largest flowers at about one meter in diameter. It is a tourist attraction in its native habitat.
  • Sandalwoodtrees (Santalumspecies) have many important cultural uses and their fragrant oils have high commercial value.
  • Indian paintbrush (Castilleja linariaefolia) is the state flower ofWyoming.
  • The oak mistletoe (Phoradendron serotinum) is the floral emblem ofOklahoma.
  • A few other parasitic plants are occasionally cultivated for their attractive flowers, such asNuytsiaandbroomrape.
  • Parasitic plants are important in research, especially on the loss of photosynthesis and the co-dependency of functional, genetic and lifestyle changes.[21][22][23][24]
  • A few dozen parasitic plants have occasionally been used as food by people.[25]
  • Western Australian Christmas tree (Nuytsia floribunda) sometimes damages underground cables. It mistakes the cables for host roots and tries to parasitize them using itssclerenchymaticguillotine.[26]

Some parasitic plants are destructive while some have positive influences in theircommunities.Some parasitic plants damageinvasive speciesmore thannative species.This results in the reduced damage ofinvasive speciesin the community.[27]Parasitic plants are major shapers of their community, affecting not just the host species but indirectly affecting others. Competition amongst host species will change due to the parasitic plant.[28]Plant parasitism have been shown to keep invasive species under control and become keystone species in an ecosystem.[29]

Newly emergentsnow plant(Sarcodes sanguinea), a flowering plant parasitic onmycorrhizalfungi

In many regions, including theNepalEastern Himalayas,parasitic plants are used for medicinal and ritual purposes.[30]

Plants parasitic on fungi

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About 400 species of flowering plants, plus onegymnosperm(Parasitaxus usta) and onebryophyte(theliverwortAneura mirabilis), are parasitic on mycorrhizal fungi. This effectively gives these plants the ability to become associated with many of the other plants around them. They are termedmyco-heterotrophs.Some myco-heterotrophs are Indian pipe (Monotropa uniflora), snow plant (Sarcodes sanguinea), underground orchid (Rhizanthella gardneri), bird's nest orchid (Neottia nidus-avis), and sugarstick (Allotropa virgata). Within the taxonomic familyEricaceae,known for extensive mycorrhizal relationships, there are the Monotropoids. The Monotropoids include the generaMonotropa,Monotropsis,andPterosporaamong others. Myco-heterotrophic behavior is commonly accompanied by the loss of chlorophyll.[31]

See also

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References

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  1. ^abKokla, Anna; Melnyk, Charles W. (2018-10-01). "Developing a thief: Haustoria formation in parasitic plants".Developmental Biology.442(1): 53–59.doi:10.1016/j.ydbio.2018.06.013.ISSN0012-1606.PMID29935146.S2CID49394142.
  2. ^Kuijt, Job(1969).The biology of parasitic flowering plants.Berkeley: University of California Press.ISBN0-520-01490-1.OCLC85341.
  3. ^Heide-Jørgensen, Henning (2008).Parasitic flowering plants.BRILL.doi:10.1163/ej.9789004167506.i-438.ISBN9789047433590.
  4. ^Smith, David (January 2000). "The Population Dynamics and Community Ecology of Root Hemiparasitic Plants".The American Naturalist.155(1): 13–23.doi:10.1086/303294.PMID10657173.S2CID4437738.
  5. ^abcdefgHeide-Jørgensen, Henning S. (2008).Parasitic flowering plants.Leiden: Brill.ISBN978-9004167506.
  6. ^Nickrent, D. L. and Musselman, L. J. 2004. Introduction to Parasitic Flowering Plants.The Plant Health Instructor.doi:10.1094/PHI-I-2004-0330-01[1]Archived2016-10-05 at theWayback Machine
  7. ^Smith, David (January 2000)."The Population Dynamics and Community Ecology of Root Hemiparasitic Plants".The American Naturalist.155(1): 13–23.doi:10.1086/303294.ISSN0003-0147.PMID10657173.S2CID4437738.
  8. ^abcdeWestwood, James H.; Yoder, John I.; Timko, Michael P.; dePamphilis, Claude W. (2010). "The evolution of parasitism in plants".Trends in Plant Science.15(4). Elsevier BV: 227–235.Bibcode:2010TPS....15..227W.doi:10.1016/j.tplants.2010.01.004.ISSN1360-1385.PMID20153240.
  9. ^Endoparasitic plants and fungi show evolutionary convergence across phylogenetic divisions
  10. ^Stienstra, T. (11 October 2007)."It's no snow job - handful of redwoods are rare albinos".San Francisco Chronicle.RetrievedDecember 6,2010.
  11. ^Krieger, L. M. (2010-11-28)."Albino redwoods hold scientific mystery".San Jose Mercury News.Retrieved2012-11-23.
  12. ^"A Creepy Monster of the Forest: The Albino, Vampiric Redwood Tree".Discover Magazine Discoblog. Archived fromthe originalon 2019-09-06.Retrieved2012-11-23.{{cite magazine}}:Cite magazine requires|magazine=(help)
  13. ^abcdefScott, P. 2008. Physiology and behavior of plants: parasitic plants. John Wiley & sons pp. 103–112.
  14. ^abcdefRunyon, J. Tooker, J. Mescher, M. De Moraes, C. 2009. Parasitic plants in agriculture: Chemical ecology of germination and host-plant location as targets for sustainable control: A review. Sustainable Agriculture Reviews 1. pp. 123-136.
  15. ^Schneeweiss, G. 2007. Correlated evolution of life history and host range in the nonphotosynthetic parasitic flowering plants Orobanche and Phelipanche (Orobanchaceae). Journal Compilation. European Society for Evolutionary Biology. 20 471-478.
  16. ^abLesica, P. 2010. Dodder: Hardly Doddering. Kelsey Newsletter of Montana Native Plant Society. Vol 23. 2, 6
  17. ^Walters, D. (2010). Plant Defense Warding off an attack by pathogens, herbivores, and parasitic plants. Hoboken: Wiley.
  18. ^Marvier, Michelle A. (1998)."Parasite Impacts on Host Communities: Plant Parasitism in a California Coastal Prairie".Ecology.79(8): 2616–2623.Bibcode:1998Ecol...79.2616M.doi:10.2307/176505.ISSN0012-9658.JSTOR176505.
  19. ^abDring, M. J. (1982).The Biology of Marine Plants.London: E. Arnold.ISBN0-7131-2860-7.
  20. ^Landa, B. B.; Navas-Cortés, J. A.; Castillo, P.; Vovlas, N.; Pujadas-Salvà, A. J.; Jiménez-Díaz, R. M. (2006-08-01). "First Report of Broomrape (Orobanche crenata) Infecting Lettuce in Southern Spain".Plant Disease.90(8): 1112.doi:10.1094/PD-90-1112B.ISSN0191-2917.PMID30781327.
  21. ^Yang, Z.; Wafula, E.K.; Honaas, L.A.; et, al. (2015)."Comparative transcriptome analyses reveal core parasitism genes and suggest gene duplication and repurposing as sources of structural novelty".Mol. Biol. Evol.32(3): 767–790.doi:10.1093/molbev/msu343.PMC4327159.PMID25534030.
  22. ^Wicke, S.; Müller, K.F.; dePamphilis, C.W.; Quandt, D.; Bellot, S.; Schneeweiss, G.M. (2016)."Mechanistic model of evolutionary rate variation en route to a nonphotosynthetic lifestyle in plants".Proc. Natl. Acad. Sci. U.S.A.113(32): 1091–6490.Bibcode:2016PNAS..113.9045W.doi:10.1073/pnas.1607576113.PMC4987836.PMID27450087.
  23. ^Wicke, S.; Naumann, J. (2018)."Molecular evolution of plastid genomes in parasitic flowering plants".Advances in Botanical Research.85(1): 315–347.doi:10.1016/bs.abr.2017.11.014.
  24. ^Chen, X.; Fang, D.; Wu, C.; et, al. (2020)."Comparative plastome analysis of root- and stem-feeding parasites of Santalales untangle the footprints of feeding mode and lifestyle transitions".Genome Biol. Evol.12(1): 3663–3676.doi:10.1093/gbe/evz271.PMC6953812.PMID31845987.
  25. ^"Parasitic Plant Food".parasiticplants.siu.edu.
  26. ^Sclerenchymatic guillotine in the haustorium ofNuytsia floribundaArchived2006-07-26 at theWayback Machine
  27. ^Song, Wenjing; Jin, Zexin; Li, Junmin (April 6, 2012)."Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts? An Implication for Biocontrol".PLOS ONE.7(4): e34577.Bibcode:2012PLoSO...734577L.doi:10.1371/journal.pone.0034577.PMC3321012.PMID22493703.
  28. ^Pennings, Steven C.; Callaway, Ragan M. (2002-05-01)."Parasitic plants: parallels and contrasts with herbivores".Oecologia.131(4): 479–489.Bibcode:2002Oecol.131..479P.doi:10.1007/s00442-002-0923-7.ISSN1432-1939.PMID28547541.S2CID6496538.
  29. ^Těšitel, Jakub; Li, Ai-Rong; Knotková, Kateřina; McLellan, Richard; Bandaranayake, Pradeepa C G; Watson, David M (April 2021)."The bright side of parasitic plants: what are they good for?".Plant Physiology.185(4): 1309–1324.doi:10.1093/plphys/kiaa069.PMC8133642.PMID33793868– via Oxford Academic.
  30. ^O'Neill, Alexander; Rana, Santosh (2017-07-16)."An ethnobotanical analysis of parasitic plants (Parijibi) in the Nepal Himalaya".Journal of Ethnobiology and Ethnomedicine.12(14): 14.doi:10.1186/s13002-016-0086-y.PMC4765049.PMID26912113.
  31. ^Judd, Walter S., Christopher Campbell, and Elizabeth A. Kellogg.Plant Systematics: A Phylogenetic Approach.Sunderland, MA: Sinauer Associates, 2008. Print.
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