Plants and symbiosis Flashcards
What biotic stresses do plants face?
Bacteria
Fungi
Viruses
Insects
What are the two main ways in which plants defend themselves?
Physical barriers like wax or spines
Toxins and anti feedants like secondary metabolites, protease inhibitors and lectins (chemical warfare)
When would a plant use a secondary metabolism?
When the plant detects a change in its environment so it responds and changes its metabolism often to affect the other organism
What are the two types of defence mechanisms?
Constitutive or induced
When would an induced response be used?
Requires recognition of change in the environment and signalling
Describe the responses a plant might take against microbial pathogens
Oxidative burst that releases a reactive oxygen species.
Programmed cell death that creates necrotic lesions.
Produce lignin/callose for structural support.
Release antimicrobial enzymes.
How are invading fungi and bacteria recognised?
Elicitors found on a pathogen cell wall.
Some bacteria make elicitors which are recognised inside the cells.
What is meant by systematic acquired resistance?
Pathogen attacks one leaf and produces hypersensitive response. Salicylic acid is produced and is transported to the rest of the plant once signal is given using methyl salicylate. Defence responses are now induced to prevent further attack.
What is the induced response to herbivores?
Wound damage and detection of elicitors increases jasmonic acid synthesis which will then signal the synthesis of proteinase inhibitors using methyl jasmonate
How do pathogens fight back from plant defence mechanisms?
Evolve new proteins that aren’t recognised by plants or by making plant hormones like auxin that will alter the pathways of jasmonic and salicylic acid.
Give an example of a symbiotic relationship between pathogens and plants
Nitrogen fixing rhizobia live as symbionts in root nodules of legumes
How do rhizobia have a symbiotic relationship with legumes?
Host roots release chemicals that attract rhizobia and switch on expression of nod genes. Nod factors induce differentation of host celles into nodules which contain leghaemoglobin which keeps the level of oxygen low. The rhizobia grow into these nodules and host signals induce development of bacteroids.
