parasitic plants

Question 1

what is the Raffelsia arnoldii

Answer 1

The largest individual flower on earth which is endemic to Indonesia with no stems, leaves or observable roots
A holoparasitic endophyte which smells like rotting flesh so attract its fly pollinator

Question 2

outline some characteristics of parasitic plants

Answer 2

derive all their nutrition from other plants
comprise of 1% of angiosperms but found in every biome in the world

• modified roots known as haustoria (plural) haustorium (single)
• extract water nutrients directly from the host (trophic relationship)
• dont photosynthesis as they derive nutrients from host so often lack green colourings

Question 3

what is a haustorium

Answer 3

a modified root found in parasitic plants which taps into host xylem and phloem to derive nutrients

Question 4

how are parasitic plants classified

Answer 4

1) according to where the parasite attaches on to the host (stem or root)

2) the amount of nutrients required or taken from the host

Question 5

what are the four different types of parasite under classification one (where the parasite attaches)

Answer 5

1) obligate = a parasite which cant complete its life cycle without a host

2) facultative = a parasite that can complete its lifecycle independent of the host

3) stem parasite = a parasite which attaches to the host stem

4) root parasite = a parasite that attaches to the host root

Question 6

what are the two types of parasites which come under classification two (how much nutrients are needed/taken from the host)

Answer 6

1) hemiparasite = a plant that is parasitic under normal conditions and is also photosynthetic to some degree. They may obtain water and mineral nutrients from the host plant but many obtain at least part of their organic nutrients from the host as well (can be obligate and faculative)

2) Holoparasite = a parasitic plant that derives all of its fixed carbon from the host plant; totally lacking chlorophyll, they are often colours other than green (always obligate)

Question 7

why are parasitic plants considered an example of convergent evolution

Answer 7

parasitism in angiosperms evolved 13 times independently with niche availability driving adaptations rather than taxonomy

Question 8

outline the striga species e.g. S.asiatica, S.gesnerioides and S. hermonthica

Answer 8

Genus of obligate hemi parasitic flowering plants of crop roots
- found in semi-arid areas of Africa, Asia and Australia
- require a living host for germination and initial development
- decimate crops causing stunted growth, wilting and chlorosis (economic impact)

Question 9

outline the lifecycle of striga species

Answer 9

1) each plant produces up to 500 k seeds a year which can remain dormant in the soil for over 10 years

2) seeds germinate in the presence of host root exudate and tap into the root of host plants

3) free living stringa plant then producing more seeds

Question 10

outline how striga species penetrate host xylem and phloem

Answer 10

1) rapid cell division wedges the host cell open and they penetrate host root cortex

2) the osculum on the haustorium penetrates the host xylem through pits

3) striga sieves tubes develop and approach the host phloem

4) cotyledons emerge within 24h of tapping xylem/ phloem

Question 11

outline the evolution of plant parasitism

Answer 11

parasitism has evolved multiple times in angiosperms

about 4000 species are parasitic with 3 lineages solely being hemi parasitic and 8 holoparasitic

Question 12

what are the different steps of parasitic plant evolution

Answer 12

1) the evolution of the haustorium
2) Host specificity
= ability to distinguish self from nonself to prevent parasitism of siblings
3) Haustorial compatibility with host roots
= parasite must maintain a union with the host and counter act resistance
4) Germination signals
= increased sophistication in mechanisms to locate host, seeds respond to chemical trigger
5) consequences
= relaxation of evolutionary pressure for photosynthesis

Question 13

outline characteristics of dodder (cuscuta spp.)

Answer 13

A holoparasite of a wide range of plants e.g. clover, potatoes and various ornamentals

• seeds able to germinate without a host but must attach to one within three days
• if the host is suitable haustoria growth is stimulated and the basal part of the parasite shrivels with no soil contact

Question 14

how can dodder be controlled

Answer 14

planting a non-host crop known as trap crops which attract the parasitic plant away from economically valuable one

Question 15

outline the parasitic plant mistletoe

Answer 15

oblgate hemiparasite species
- transmitted to branches via bird droppings
- seeds germinate independent on the host
- commonly kills the distal portion of the branch it grows on

Question 16

how is mistletoe a keystone species even though its parasitic

Answer 16

• trophic relationship with birds
• increases biodiversity in forest patches as animals are reliant on the berries as a winter food source
• kills branches of host creating dead wood which increases niches

Question 17

outline the parasitic plant Rhinanthus minor aka yellow rattle and how it is used in habitat management

Answer 17

facultative hemiparasite of roots in grassland species in the UK

selects which ever species is dominant in the habitat e.g. restricts grass growth allowing other species to flourish
= useful in habitat management