Parasitic plant


A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant They make up about 1% of angiosperms and are in almost every biome in the world1 All parasitic plants have modified roots, named haustoria singular: haustorium, which penetrate the host plants, connecting them to the conductive system – either the xylem, the phloem, or both This provides them with the ability to extract water and nutrients from the host Parasitic plants are classified depending on where the parasitic plant latches onto the host and the amount of nutrients it requires2 Some parasitic plants are able to locate their host plants by detecting chemicals in the air or soil given off by host shoots or roots, respectively About 4,500 species of parasitic plant in approximately 20 families of flowering plants are known34

Contents

  • 1 Classification
  • 2 Evolution of parasitic behavior
  • 3 Seed germination
    • 31 Seed dispersal
  • 4 Obstacles of attaching to a host
  • 5 Host range
  • 6 Aquatic parasitic plants
  • 7 Importance
  • 8 Plants parasitic on fungi
  • 9 References
  • 10 Further reading

Classificationedit

Parasitic plants are characterized as follows:

  • 1a Obligate parasite – a parasite that cannot complete its life cycle without a host
  • 1b Facultative parasite – a parasite that can complete its life cycle independent of a host
  • 2a Stem parasite – a parasite that attaches to the host stem
  • 2b Root parasite – a parasite that attaches to the host root
  • 3a Hemiparasite – a plant that is parasitic under natural conditions and is also photosynthetic to some degree Hemiparasites may just obtain water and mineral nutrients from the host plant Many obtain at least part of their organic nutrients from the host as well
  • 3b Holoparasite - a parasitic plant that derives all of its fixed carbon from the host plant Commonly lacking chlorophyll, holoparasites are often colors other than green

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

  • Nuytsia floribunda Western Australian Christmas tree is an obligate root hemiparasite
  • Rhinanthus eg Yellow rattle is a facultative root hemiparasite
  • Mistletoe is an obligate stem hemiparasite

Holoparasites are always obligate so only two terms are needed, eg

  • Dodder is a stem holoparasite
  • Hydnora spp are root holoparasites

Plants usually considered holoparasites include broomrape, dodder, Rafflesia, and the Hydnoraceae Plants usually considered hemiparasites include Castilleja, mistletoe, Western Australian Christmas tree, and yellow rattle

Evolution of parasitic behavioredit

Parasitic behavior evolved in angiosperms roughly 12-13 times independently, a classic example of convergent evolution Roughly 1% of all angiosperm species are parasitic, with a large degree of host dependence The taxonomic family Orobanchaceae encompassing the genera Tryphysaria, Striga, and Orobanche is the only family that contains both holoparasitic and hemiparasitic species, making it a model group for studying the evolutionary rise of parasitism The remaining groups contain only hemiparasites or holoparasites5

The evolutionary event which gave rise to parasitism in plants was the development of haustoria The first, most ancestral, haustoria are thought to be similar to that of the facultative hemiparasites within Tryphysaria, 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 juvenile radicle, seen in obligate hemiparasitic species within Striga Lastly, obligate holoparasitic behavior originated with the loss of the photosynthetic process, seen in the Orobanche genus5

Seed germinationedit

Seed germination of parasitic plants occurs in a variety of ways These means 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 in close proximity to their host plants because their seeds are limited in the amount 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 use autotrophic nutrition to establish the early stages of seeding67

Root parasitic plant seeds tend to use chemical cues for germination In order for germination to occur, seeds need to be fairly close to their host plant67 For example, the seeds of the parasitic plant witchweed Striga asiatica need to be within 3 to 4 millimeters mm of its host in order to pick up chemical signals in the soil to signal germination This range is important because Striga asiatica will only grow about 4 mm after germination6 Chemical compound cues sensed by parasitic plant seeds are from host plant root exudates that are leached in close proximity from the host’s root system into 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 called strigolactones Strigolactone stimulates ethylene biosynthesis in seeds causing them to germinate67

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, orobanchol and alectrol from red clover, and 5-deoxystrigol from Lotus japonicas 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 fungus78

Stem parasitic plants, unlike most root parasitic plants, germinate using the resources inside their endosperms and are able to survive for a small amount of time An example, Dodder Cuscuta spp is a parasitic plant whose seed falls to the ground and may remain dormant for up to five years before it is able to sense a host plants nearby Using the resources in the seed endosperm, dodder is able to germinate Once germinated, the plant has 6 days to find and establish a connection with its host plant before its resources run out6 Dodder seeds germinate above ground and 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 is able to pick up its host plant’s scent whereby it then is able to orient itself in the direction of its host Scientists used volatiles from tomato plants α-pinene, β-myrcene, and β-phellandrene to test the reaction of C pentagona and found that the stem will oriented itself in the direction of the odor7 Some studies suggest that by using light reflecting from nearby plants dodders are able to select host with higher sugar because of the levels of chlorophyll in the leaves9 Once the dodder finds its host, it wraps itself around the host plants stem Using adventitious roots, the dodder taps into the host plant’s stem with a haustorium, an absorptive organ within the host plant vascular tissue Dodder makes several of these connections with the host as it moves up the plant679

Seed dispersaledit

There are several ways of seed dispersal, but all the strategies aim towards the same goal of putting the seed in direct contact to or within a critical distance to the host

  1. The Cuscuta seedling can live for 3-7 weeks and extend out 35 cm in search of the host before it dies This is because the Cuscuta seed is large and has stored nutrients to sustain its life This is also useful for seeds that get digested by animals and excreted out10
  2. Mistletoe use a sticky seed for dispersal The seed sticks to nearby animals and birds and then come into direct contact with the host11
  3. Arceuthobium seeds have a similarly sticky seed as the mistletoe but they do not rely on animals and birds, they mainly disperse by fruit explosiveness Once the seed makes contact with the host rain water can help position the seed into a suitable position12
  4. Some seeds detect and respond to chemical stimulations produced in the host’s roots and start to grow towards the host13

Obstacles of attaching to a hostedit

The parasitic plant has many obstacles to overcome in order to attach to the host Distance from the host and stored nutrients are only some of the problems, the host's defenses are an obstacle to overcome itself The first hurdle is penetrating the host, the host has systems to reinforce the cell wall by protein cross-linking so that it stops the parasitic progress at the cortex of the host's roots The second hurdle is the host's ability to secrete germination inhibitors This prevents germination of the parasitic seed The third hurdle is the host's ability to create a toxic environment for where the parasitic plant attaches to The host secretes phenolic compounds into the apoplast the creates a toxic environment for the parasitic plant eventually killing it The fourth hurdle is the host's ability to ruin the tubercle using gums and gels or injecting toxins into the tubercle14

Host rangeedit

Some parasitic plants are generalists and parasitize many different species, even several different species at once Dodder Cassytha spp, Cuscuta spp and red rattle Odontites vernus are generalist parasites Other parasitic plants are specialists that parasitize a few or even just one species Beech drops Epifagus virginiana is a root holoparasite only on American beech Fagus grandifolia Rafflesia is a holoparasite on the vine Tetrastigma Plants such as Pterospora become parasites of mycorrhizal fungi There is evidence that parasites also practice self-discrimination, species of Tryphysaria experience reduced haustorium development in the presence of other Tryphysaria Although, the mechanism for self-discrimination in parasites is not yet known5

Aquatic parasitic plantsedit

Parasitism also evolved within aquatic species of plants and algae Parasitic marine plants are described as benthic, 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 designation epiphytic epilithic is 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, endophytic plants and algae grow inside their host plant, these have a wide range of host dependence from obligate holoparasites to facultative hemiparasites15

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 as kelp and other macroscopic brown algae are generally restricted to temperate areas Roughly 75% of parasitic red algae infect hosts in the same taxonomic family as themselves, these are given the designation adelphoparasites Other marine parasites, deemed endozoic, are parasites of marine invertebrates molluscs, flatworms, sponges and can be either holoparasitic or hemiparasitic, some retaining the ability to photosynthesize after infection15

Importanceedit

Species within Orobanchaceae are some of the most economically destructive species on Earth Species of Striga alone are estimated to cost billions of dollars a year in crop yield loss annually, infesting over 50 million hectares of cultivated land within Sub-Saharan Africa alone Striga can infect both grasses and grains, including corn, rice and Sorghum, undoubtedly some of the most important food crops Orobanche also threatens a wide range of important crops, including peas, chickpeas, tomatoes, carrots, and varieties of the genus Brassica eg cabbage, lettuce, and broccoli Yield loss from Orobanche can 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 of Orobanche and Striga species, which are even more devastating in developing areas of the world, though no method has been found to be entirely successful5

  • Mistletoes cause economic damage to forest and ornamental trees
  • Rafflesia arnoldii produces the world's largest flowers at about one meter in diameter It is a tourist attraction in its native habitat
  • Sandalwood trees Santalum species have many important cultural uses and their fragrant oils have high commercial value
  • Indian paintbrush Castilleja linariaefolia is the state flower of Wyoming
  • The Oak Mistletoe Phoradendron serotinum is the floral emblem of Oklahoma
  • A few other parasitic plants are occasionally cultivated for their attractive flowers, such as Nutysia and broomrape
  • Parasitic plants are important in research, especially on the loss of photosynthesis during evolution
  • A few dozen parasitic plants have occasionally been used as food by people16
  • Western Australian Christmas tree Nuytsia floribunda sometimes damages underground cables It mistakes the cables for host roots and tries to parasitize them using its sclerenchymatic guillotine17

Some parasitic plants are destructive while some have positive influences in their communities Some parasitic plants damage invasive species more than native species This results in the reduced damage of invasive species in the community18

Newly emergent snow plant Sarcodes sanguinea, a fungus parasite

In many regions, including the Nepal Eastern Himalayas, parasitic plants are used for medicinal and ritual purposes 19

Plants parasitic on fungiedit

About 400 species of flowering plants, plus one gymnosperm Parasitaxus usta, 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 termed myco-heterotrophs rather than parasitic plants 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 family Ericaceae, known for extensive mycorrhizal relationships, there are the Monotropoids The Monotropoids include the genera Monotropa, Monotropsis, and Pterospora among others Myco-heterotrophic behavior is commonly accompanied by the loss of chlorophyll20

Referencesedit

  1. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  2. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  3. ^ Nickrent, D L and Musselman, L J 2004 Introduction to Parasitic Flowering Plants The Plant Health Instructor doi:101094/PHI-I-2004-0330-01 1
  4. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  5. ^ a b c d Westwood, James H, John I Yoder, Michael P Timko and Claude W Depamphilis "The Evolution of Parasitism in Plants" Trends in Plant Science 154 2010 227-35 Web
  6. ^ a b c d e f Scott, P 2008 Physiology and behavior of plants: parasitic plants John Wiley & sons pp 103–112
  7. ^ a b c d e f Runyon, 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
  8. ^ 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
  9. ^ a b Lesica, P 2010 Dodder: Hardly Doddering Kelseya Newsletter of Montana Native Plant Society Vol 23 2, 6
  10. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  11. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  12. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  13. ^ Heide-Jørgensen, H, & Heide-J²rgensen, Henning S 2008 Parasitic flowering plants Leiden: BRILL
  14. ^ Walters, D 2010 Plant Defense Warding off attack by pathogens, herbivores and parasitic plants Hoboken: Wiley
  15. ^ a b Dring, M J The Biology of Marine Plants London: E Arnold, 1982 Print
  16. ^ Parasitic Angiosperms Used for Food
  17. ^ Sclerenchymatic guillotine in the haustorium of Nuytsia floribunda
  18. ^ Li J, Jin Z, Song W 2012 Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts An Implication for Biocontrol PLoS ONE 74: e34577 https://doiorg/101371/journalpone0034577
  19. ^ 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 doi:101186/s13002-016-0086-y Retrieved 2017-05-11 
  20. ^ Judd, Walter S, Christopher Campbell, and Elizabeth A Kellogg Plant Systematics: A Phylogenetic Approach Sunderland, MA: Sinauer Associates, 2008 Print

Further readingedit

  • Joel DM et al Eds2013 Parasitic Orobanchaceae: Parasitic Mechanisms and Control Strategies Springer, Heidelberg
  • Digital Atlas of Cuscuta Convolvulaceae
  • The Parasitic Plant Connection
  • The Strange and Wonderful Myco-heterotrophs
  • Parasitic Flowering Plants
  • The Mistletoe Center
  • Parasitic Plants Biology Study Guide
  • Nickrent, Daniel L 2002 Parasitic plants of the world
  • Calladine, Ainsley and Pate, John S 2000 Haustorial structure and functioning of the root hemiparastic tree Nuytsia floribunda Labill RBr and water relationships with its hosts Annals of Botany 85: 723-731
  • Milius, Susan 2000 Botany under the mistletoe: Twisters, spitters, and other flowery thoughts for romantic moments Science News 158: 411
  • Hibberd, Julian M and Jeschke, W Dieter 2001 Solute flux into parasitic plants Journal of Experimental Botany 52: 2043-2049


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