plant defense repsonse

Do plants have an immune system?- Plants do not have an immune system comparable to animals but they have developed and array of structural, chemical, and protein-based defenses designed to detect invading organisms and stop them before they are able to cause extensive damage.

Plants do not have an immune system comparable to animals but they have developed and array of structural, chemical, and protein-based defenses designed to detect invading organisms and stop them before they are able to cause extensive damage.

plants are not passive

they are able to respond rapidly to pathogen attacks

passive defenses

Protection from a pathogen’s initial invasion is achieved via

physical barriers

• Wax

• Cuticle • Cell wall

• Stomata

• Callose deposition

chemical barriers

• Toxins (cyanide)

• Ricin

• Alkaloids (caffeine, cocaine, nicotine, and morphine)

• Allelopathy

Dermal covering

- made up of epidermal tissues

- secretes a waxy substance called cutin or cuticle

- helps plants conserve water and prevents attack

rhizobium

nitrogen fixing bacterium that make the soil more fertile by turning nitrogen into nitrates which the plants can use

rhizobacterium

- lives around the roots of plants, benefit from root saps or exudates

- Provide substances such as hormones needed for plant growth

cyanogenic glycoside

- cyanide-containing compounds that break down into cyanide when ingested

- cyanide can stop cellular respiration by blocking the electron transport chain that can kill attacking organisms

neurotoxin

- hemlock plant, Conium maculatum, highly poisonous plant that could kill a person from 20 minutes to 3 hrs after ingestion of its extract

ricin

- an alkaloid found in castor beans, Ricinus communis, six times more lethal than cyanide and is twice as lethal as the venom of cobra

secondary metabolites

affeine, cocaine, nicotine, and morphine- affect cellular processes

Why then are plants not poisoned by the toxins that they produced?

These secondary metabolites are enclosed in membrane-bound organelles which are separated from the rest of the cytoplasm so that they do not get involved in cellular metabolism. The toxins they produce are not harmful unless metabolized by the consumer.

allelopathy

• plants poison other plants

- chemicals released into the environment where it affects the development and growth of neighboring plants

- minimizes shading and overcrowding among plants