Plant Lec: Parasitic Plants

Parasitic plant

-When a plant attaches to and derives nutrients from another plant

-Form of parasitism

-Some parasitic plants attach to the roots of other plants (the host)

Holoparasitism

-Complete parasites (can’t live on their own)

-Most extreme form of plant parasitism

-Lack chlorophyll, leaves, stomata, and are usually small, just a stalk with flowers

-Highly modified roots

Myco-heterotrophs

-Rather than attach directly to plant roots, often a fungi (mycorrhizae) that bridges the gap between the plants

-Host plant ‘leaks’ organic compounds into the soil

• Parasitic plant seeds detect these compounds (called strigolactones) to know when to germinate

• The seedlings modified roots, called haustoria, attach to the mycorrhizae on the host roots

-Parasite absorbs sugars, amino acids, and other useful solutes (called photoassimilates) from the plant’s phloem and water from the xylem (via the mycorrhizae)

Dodder

-Holoparasite that attaches to the stem of host plants (not roots)

-No mycorrhizae involved when the parasite attaches above the ground

-Can sense chemical gradients and grow toward its host

-Roots of these parasites are highly modified. Called haustoria

Hemiparasites

-Plants that obtain nutrients from other plants, but have chlorophyll and leaves, so they can photosynthesize

-Also obligate because it cannot live on its own (mistletoe)

Mistletoe

-Obligate Hemiparasites

-Infect the branches of many woody plants, including oaks

-Birds eat berries of mistletoe and poop out seeds

• Sticky mucus around seed and causes attachment to stems

• Seed germinates and the root penetrates the bark

• The root (haustoria) spreads through the phloem and xylem of the host

-High levels of mistletoe concentration can kill trees

-Dwarf mistletoe infects pines

• Ballistically dispersed

Dwarf mistletoe life cycle

Striga

-important pest on the roots of crop plants like corn in Africa

-Reduces crop yields and costs millions of dollars per year

-Life cycle image

Strigolactones

-Plants release these hormones to attract VAM (arbuscular mycorrhizae)

-Parasitic plants also sense the presence of host plants using strigolactones

-If plants successfully inoculate with VAM mycorrhizae, they are less likely to be infected by parasitic plants

-Mycorrhizae helps to protect the plant from its parasites and makes the plant more productive (more fruits and leaves)

Facultative Hemiparasites

-Plant that can photosynthesize (chlorophyll and leaves) and can live on its own

• Indian paintbrush will attach to sagebrush if given opportunity

Evolution of an obligate holoparasite must have followed this sequence

Are epiphytes parasites?

-No, they do not extract nutrients from their host

-However, they can become so numerous that they can cause problems for the plant they rest upon

-Needs a substrate, but doesn’t have to be a tree

-Too dry in temperate forests for many

-Can find small epiphytes in subtropical sites

-Tropical forests can have large bromeliads

-Many cacti live on other plants in rain forests

-Loads can weight many tons

Tree fall gaps

-Very important in ecology of rainforests, where canopy is typically closed

-Epiphyte Loads are one of the main causes of tree falls.

-Gaps allow for different types of plants to colonize and fill in the gap

-Allows for greater plant diversity and greater diversity of animals

Strangler fig

-Epiphyte that becomes a parasite