lec 28- plant defenses against biotic stressors

Question 1

what are plants attacked by?

Answer 1

-herbivores: insects, large animals
-pathogens: viruses, bacteria, fungi

Question 2

what is the plant defense against pathogens?

Answer 2

the waxy cuticle covering epidermal cells is an effective barrier to many pathogens

Question 3

what are plant defenses against herbivores?

Answer 3

bark, thorns, spines, and trichomes protect leaves and stems from damage by herbivores

Question 4

how do pathogens cause a disease in a plant?

Answer 4

they enter the plant after getting past its surface, mostly through the stomata or wounds

Question 5

what defenses do plants have even when eaten?

Answer 5

chemical defenses

Question 6

what are plant tissues protected by?

Answer 6

secondary metabolites which can repel insects, hinder metabolsim, disrupt the nervous system etc.

Question 7

are plant defenses effective but costly to produce?

Answer 7

yes

Question 8

what are inducible defenses?

Answer 8

defenses that are triggered once a threat occurs

Question 9

explain the coevolutions that occurred during the arms race between pathogens and plants?

Answer 9

-plant detection of pathogen leads to responses and resistance
-pathogen escapes detection and responses leading to sensitive plants
-pathogen releasing plant degrading toxin
-plant releasing pathogen degrading toxin

Question 10

what is plant evolved pattern triggered immunity (PTI)?

Answer 10

sequence patterns (PAMPs) in bacterial protein recognized by binding to a surface receptor, triggering immune signalling to cause immune response like release of pathogen toxins

Question 11

what is a pathogen evolved bacterial effectors?

Answer 11

pathogen secretes bacterial effectors that are secreted into plants cells to inhibit the immune signalling

Question 12

what is gene for gene resistance and S and R plants?

Answer 12

when pathogen and plants are evolving to beat one another, S plants are susceptible to pathogens and R plants are resistant

Question 13

what is the hypersensitive response (HR)?

Answer 13

a plant defense where cells surrounding the site of infection rapidly die to starve the pathogen

Question 14

what are the 4 steps to the Hypersensitive response?

Answer 14

1. stomata closes, keeping out pathogens
2. toxins targeting pathogens are produced
3. cell walls are reinforced to prevent pathogen movement
4. cells in the infected area are rapidly dying by suicide

Question 15

what is released after the HR?

Answer 15

a hormone known as methyl salicylate (MeSA) produced at the site of infection triggers a set of events called the systemic acquired resistance (SAR)

Question 16

what does SAR do?

Answer 16

releases a SAR signal that expresses PR genes that help in protecting roots and shoots from further infection

Question 17

what type of inhibitors do plants contain to make herbivores sick?

Answer 17

proteinase inhibitors, they block proteinase enzymes in the mouth and stomachs

Question 18

what induces the production of proteinase inhibitors?

Answer 18

systemin

Question 19

what is the signal transduction pathway of systemin?

Answer 19

1. systemin is released from damaged cells
2. the hormone travels through phloem and binds to membrane receptors on cells
3. activated membrane receptors triggers a series of chemical reactions that make jasmonic acid
4. jasmonic acid triggers a signalling pathway that produced proteinase inhibitors

Question 20

how do trees eavesdrop?

Answer 20

when an insect eats a plant, it causes the release of volatile compounds into the air, other plants sense these compounds and boost their own defenses.

Question 21

how do plants primarily defend themselves?

Answer 21

with secondary metabolites that repel and are toxic to herbivores and pathogens

Question 22

what is the difference between primary and secondary metabolites?

Answer 22

primary:
-function in essential metabolic processes
-found in all plants
-direct function in growth
secondary:
-function in non-essential metabolic processes
-not found in all plants
-no direct function in growth

Question 23

what are secondary metabolite functions?

Answer 23

-defend against herbivores and pathogens
-attract pollinators and dispersing animals
-inhibit growth of near by plants

Question 24

where are secondary metabolites found in plants?

Answer 24

mostly everywhere in many cell types

Question 25

what are the three types of secondary metabolites?

Answer 25

-phenolics
-nitrogen containing compounds
-terpenoids

Question 26

what are examples of phenolic compounds?

Answer 26

-flavonoids: toxic to insects, mammals, microbes, and fish
-tannins: inactivate digestive enzymes, condensed form of flavonoids

Question 27

what are examples of nitrogen containing compounds?

Answer 27

-Alkaloids: defend against mammals, interfere with CNS (e.g. morphine, caffeine, nicotine)
-cyanogenic glycosides: releases toxic HCN when plant damaged

Question 28

what are terpenes?

Answer 28

-5 carbon compound, smell bad and are sticky
-used in perfumes
-attract pollinators