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APS 276- Symbiosis > 6 + 7 : parasitic plants > Flashcards

6 + 7 : parasitic plants Flashcards

1
Q

what % of flowering plants do parasitic plants represent and species/families and how many times has it evolved within them?

A

1%
3000 species in 22 families
evolved separately at least 11 times

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2
Q

for the european/common mistletoe what is the latin name, classification and habitat?
also give 2 facts about it

A
  • viscum album
  • obligate shoot hemiparasite of xylem
  • arboreal
  • attached to stems of plants and can photosynthesise but gains resources from the host
  • spread by mistletoe thrush bird vector that eats the berries and wipes the seeds in faeces on other branches
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3
Q

for the dodder what species is it, classification and habitat?
also give 3 facts about it

A
  • cuscuta species
  • shoot holoparasite of phloem and xylem
  • canopy
  • holoparasite so no chlorophyll or photosynthesis
  • germinates and shoot above ground that rotate and curl around nearby objects/plants
  • reduced structure
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4
Q

for the monster flower what species is it, classification and habitat?
also give 4 facts about it

A
  • rafflesia species
  • endophytic root holoparasite
  • forest floor
  • largest flower in world 1m across
  • endophyte so lived within tree structure
  • attracts flies with rotting meat smell
  • reduced structure
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5
Q

what must a parasitic plant access from the host and how do they do this?

A

vascular bundle to gain resources

- withdraw C and mineral nutrients from host xylem/phloem using transfer organ HAUSTORIA

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6
Q

how does the haustoria work?

A

glued to outside of host root

penetration peg pushes through outer cortex

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7
Q

for the indian sandalwood what is the classification and habitat?
also give 2 facts about it

A
  • obligate root hemiparasite of xylem
  • semi arid areas
  • parasitize plants underground
  • visually wouldn’t know was a parasite
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8
Q

what are the 2 key strategies used by parasitic plants for nutrient abstraction

A
  1. direct xylem-xylem vascular continuity
  2. interfacial parenchyma/transfer cells associated with xylem/phloem or both (cells press against xylem/phloem to take water/minerals or sugar)
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9
Q

what is direct xylem-xylem vascular continuity?

A
  • parasite penetrates xylem of host plant forming continuous xylem stream
  • parasite abstracts resources by transpiration and the accumulation of osmotically active compounds
  • via a portal
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10
Q

what % of parasitic plants are hemi and holoparasitic and what does this mean?

A

80% hemi: chlorophyll but obtain some C from xylem fluid as well as some water and nutrients from host

20% holo: 600 species- no chlorophyll or rubisco and obtain all C from host

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11
Q

what are 2 examples of hemiparasitic plants?

A

striga hermonthica

rhinanthus minor

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12
Q

give 6 points about hemiparasites

A
  • mostly obtain host resources from host xylem
  • establish vascular continuity with xylem
  • lots of unloading needed by haustorium
  • sucks out whatever host plant gives it in xylem fluid so is unbalanced
  • often have low photosynthetic capacity
  • from variety of unusual storage compunds
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13
Q

in striga what % of C has been shown to come from the host?

A

30% or more

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14
Q

what is an example of holoparasitic species?

A

orobanche

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15
Q

give 7 points about holoparasites

A
  • unload from host xylem and phloem
  • dont form continuity with host phloem
  • unload via specialised cells closely adpressed to host phloem
  • no chlorophyll or rubisco
  • get all C from host
  • reduced form
  • form variety of unusual storage compounds
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16
Q

if a larger host range what does this mean for photosynthesis and host derived C?

A

more photosynthetically competent

less host derived C

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17
Q

what happens to coevolution with increased evolutionary complexity?

A

more coevolution

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18
Q

what is striga hermonthica’s common name and give 9 facts about it

A

giant witchweed

  • African savannah and agroecosystems
  • infect staple cereals such as maize, sorghum, millet
  • obligate root hemiparasite of xylem
  • orobanchceae family
  • constraint to African crop production with $7bn loss annually
  • mainly affects poor subsistence farmers of over 100 million
  • UN estimates it causes avg yield loss of 40%
  • 73m ha cops infested
  • can cause 100% crop failure
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19
Q

what effect does striga have on host and is this linear?

A

asymmetric
striga biomass and grain yield relationship non linear
- small amount of striga has a disproportionately large impact on host

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20
Q

what is the nitrogen assimilation pathway in plant roots to get C?

A

NO3- > NO2- > NH3

NH3 + Glutamate > Glutamine (used for transport in xylem fluid)

Glutamine > Asparagine (transport in xylem fluid)

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21
Q

if the assimilates for the N assimilation pathway are in the shoots what happens?

A

will be transported to roots so amino acids still in fluid

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22
Q

in the xylem where can C be found?

A

in low molecular weight nitrogenous compounds such as amino acids, glutamine, asparagine

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23
Q

what are the N assimilator concentrations in the roots and shoots?

A

root: 10 mol C m3 (woody plants)
shoot: 1 mol C m3 (fast growing annuals)

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24
Q

what concentration of aN assimilators do perennial herbs have?

A

in between root and shoot concentrations

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25
Q

in many hemiparasites what is the rate of photosynthesis and respiration like?

A

low photo

high resp

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26
Q

what is needed to deal with compounds in an unbalanced form from the host?

A

strong secondary metabolism

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27
Q

what did press et al discover for respiration?

A

over 1/2 species show higher respiration rates than photosynthesis
- must be gaining C from host to survive

28
Q

what did press et al discover about net carbon balance?

A

many hemiparasites have -ve net C balance

- long periods of light saturated photosynthesis needed to reach 0 net C gain which is unlikely

29
Q

what did press et al discover about hemiparasite transpiration rates?

A

high rates often 2-10 times that of mesophytes

  • transpire at night (normal plants close stomata at night)
  • keep them open to maximise transpiration stream and gain more xylem fluid
  • water lost is the hosts issue
30
Q

what is the measurement of C transfer to hemiparasite involving striga and δC? (9)

A
  • δC measures proportion of 13C/12C
  • C4 plants have PEP carboxylase
  • C3 plants have Rubisco
  • more 13C absorbed in C4 plants as PEP carboxylase drives stomatal CO2 conc low
  • C4: δ13C = -13
  • C3: δ13C = -31
  • striga is like C4 underground, relying on C from host but as emerges less reliant so more like C3 plant
  • underground stage about 70% reliant (= -20.5)
  • adult stage about 30% reliant on host plant (= -26.7)
31
Q

give 4 points about sorghum

A
  • panicles used to make flour
  • grow in drier areas than maize
  • sub-saharan africa
  • smaller when infected with striga
32
Q

what does the way C is partitioned affect?

A

growth - if more to the roots then less to the leaves

33
Q

does striga rely on host for photo and resp?

A

has its own photo and resp rates

34
Q

when looking at c flow in sorghum plant how can we measure:

a) striga, leaves, stem, roots
b) photosynthesis
c) respiration

A

a) dry weight
b) infra red gas analyser
c) oxygen electrode

35
Q

what does a small amount of striga infection do to sorghum growth?

A

large loss in dry weight

36
Q

what can be observed when looking at the component parts of a striga infected sorghum plant?

A
  • roots double: extra transpiration load, hemiparasite gains more water
  • stems 1/4 size of uninfected: reduce shading and competition for light, increase transpiration as tall plants have high humidity and higher leaf temp, shorter stems have more C
  • nearly no grain
  • decreased internode length
37
Q

how much does striga reduce host photosynthesis by and is root respiration affected between infected and uninfected plants?

A

by 50% per unit leaf area

- no is similar

38
Q

why may a huge loss in host photosynthesis benefit striga even though it seems counterintuitive ?

A
  • stomatal aperture regulated by photosynthesis rate
  • low rate shuts stomata
  • host shuts stomata meaning parasite gets more xylem fluid and nutrients by downregulating this photosynthesis
39
Q

give 7 features on striga gesnerioides

A
  • smaller than s.hermonthica
  • infects legume crops
  • reduced leaves small and scale like, closely adpressed to the stem
  • leaves and stem have chlorophyll
  • large primary haustorium
  • lower transpiration rate than s.hermonthica
  • intermediate to holoparasites
40
Q

in striga gesnerioides what is the net C gain and photosynthesis and respiration like? and is c exported?

A

never reaches +ve
rate of respiration larger than rate of photosynthesis so reliant on host plant
- c exported from the host for parasite respiration and growth so reduces host productivity

41
Q

in contrast to hemiparasites what is holoparasite respiration like?

A

low

42
Q

what does orobanche take from the host?

A

solutes from the host phloem

43
Q

in detail what are the 2 main ways to measure resource transfer?

A
  • SOLUTE FLOW IN XYLEM SAP: collect xylem sap from cut stems by pressuring roots
  • C FLOW: gas analyser to measure host photosynthesis, sealable pots to measure above and below ground respiration, dry weight change measured
44
Q

what flow can the parasite alter?

A

host C flow

45
Q

give 6 points on Tobacco that is and isn’t infected with orobanche cernua found by Hibberd et al

A
  • causes crop loss
  • flux vector width proportional to C flow into leaves by photosynthesis
  • when infected is a 20% increase in C fixed by parasitised hosts and delayed senescence
  • infected have an 84% increase in C directed to roots
  • less than 1% C via xylem
  • parasite provides a strong sink for C so no downregulation
46
Q

compare what hibberd et al found with an infected Nicotiana plant

A
  • uninfected had a large N cycling around the plant
  • infected had more N input from roots
  • infected had smaller root system so 127% increase in N inflow so more efficient at obtaining N from the soil
47
Q

what are the basic stages of striga life cycle?

A

seed production > seed dispersal > germination > haustorial initiation > attachment > below ground growth > emergence > flowering >

48
Q

a) how long is the striga life cycle
b) how big are the seeds and how many are produced per adult?
c) what is their dispersal like?
d) why is it able to have such small seed

A

a) 90-120 days
b) 0.2mm long, 100,000-200,000 seeds
c) easy: air, animals, people, dust, water, other crop plants
d) little seed resource needed as can take resources from host and small seed aids dispersal

49
Q

for how long and when is the striga seed dormant?

A

decade or 20 years so very resilient

- dry season

50
Q

when will it only germinate and what happens once it has germinated?

A

if detects root exudates from host

  • uses chemotaxis up concentration gradient towards host root
  • grabs host root and produces enzymes to push into it
  • attaches and forms haustorium and secondary haustoria
  • decreases host photosynthesis
51
Q

what are the 6 main problems needed to be overcome for striga control?

A
  1. long term viablity in soil
  2. changes in cultural practices
  3. high seed numbers
  4. high dispersal ability
  5. damage pre-emergence
  6. high impact on host
52
Q

what are 5 examples of cultural and physical methods used to aim for striga control?

A
  1. crop rotation (but need large plot to still grow crops for family)
  2. land preparation (striga stays at the surface)
  3. fertiliser addition (poor farmers cant afford fertiliser so low N soil where striga thrives)
  4. mixed/intercropping (increase N in soil to suppress striga using a legume and will increase shading but will decrease overall productivity)
  5. hand weeding (4-5 yrs to reduce soil seed bank to return to normal productivity, very labour intensive, whole village needed to avoid spread)
53
Q

what are 4 chemical methods used to combat striga?

A
  1. fumigants (ethylene gas)
  2. germination stimulants (cause suicidal germination bu too quick)
  3. antitranspirants (spray to block stomata but does not sufficiently suppress growth)
  4. herbicides
54
Q

what are 2 biological methods used to combat striga?

A
  • fungi

- insects

55
Q

what is the difference between a tolerable and resistant variety of host plants against striga?

A

resistant: striga can from viable connections
tolerable: when host infected with striga has small impact on yield

56
Q

what are some mechanisms host plants use against striga? (8)

A
  • low production of germination stimulant (but striga may respond with hypersensitive seeds- red queen)
  • mechanical barriers (cell wall lignification)
  • inhibition of germ tube exoenzymes by root exudates
  • phytoalexin synthesis
  • post attachment hypersensitive reactions
  • unfavourable phytohormone supplied by host
  • insensitivity to striga toxin (tolerance)
  • avoidance through root growth habit by having fewer roots in shallow soil
57
Q

what are phytoalexins?

A

low molecular weight secondary metabolites acting as a self defence mechanism for the host plants, produced in response to pathogen attack

58
Q

are there any resistant or tolerant varieties of maize, millet, sorghum or rice available to african farmers

A

no

59
Q

desmodium produces a mixture of chemicals- what do these do?

A
  • cause germination of striga

- inhibit root growth

60
Q

give 3 points about what Khan et al 2008 did in a PPT smallholder economics trial to address subsistence farmer economic problem?

A
  • 10 farmers recruited from each 6 districts W Kenya
  • each planted 3 plots: maize monocrop, maize bean intercrop, maize desmodium pennisetum push pull technology
  • looked at economic costs and yields over several years in each system
61
Q

what were the results found from Khan et al 2008 study?

A
  • all 3 plots have labour and non labour costs but the push pull technology had the most outputs
  • big increase in maize productivity when using PPT in every case in different districts but more costs and outputs
  • huge increase in dollar output across districts for PPT
62
Q

what is total gross benefit?

A

total revenue-total variable costs

63
Q

in the Khan et al 2008 study what is the push and what is the pull?

A

desmodium repels stemborer moths that are the push and these are attracted to napier grass which is the pull

64
Q

in the Khan et al 2008 study how does PPT compare to the other two systems and what makes it a viable option?

A

more profitable

enhances productivity and diversification for smallholder farmers who depend on limited land resource

65
Q

in the Khan et al 2008 study what should be done to help the farmers?

A

enhance their access to less costly planting material and promote education and training to use PPT technology

APS 276- Symbiosis (29 decks)

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