Deadly Chemistry

Question 1

How are the two different types of plant structure called, that are involved in „shooting“ out chemicals

Answer 1

Lacticifers
Resin ducts

Question 2

What are Lacticifers?

Answer 2

Produce and store latex

Question 3

What is latex?

Answer 3

A water soluble emulsion containing highly polymerized terpenes as well as proteins

Question 4

What do lactifers consist of?

Answer 4

A single cell, several centimeters longwhich may be branched or unbranched

Question 5

What happens when a lactifer is damaged?

Answer 5

The latex oozes out and gets sticky bc it is exposed to air

Question 6

What are cardenolides in milkweed latex?

Answer 6

Toxins

They inhibit Na+/K+ ATPases (cation pump that is responsible for transporting NA+ out of the cell and K+ into it)

When insects feed on it they becomecataleptic

Question 7

What can lactifers be?

Answer 7

Living cells
Resin ducts
Secretory canals#

Intercellular spaces which develop through seperation or breakdown of cells

Question 8

What are Ecdysteroids?

Answer 8

Steroidal hormones present in all classes of arthropods

They regulate aspects of development, meetamorphisis and reproduction

Question 9

What are arthropods?

Answer 9

An insect

Question 10

How are insects able to produce their steroid hormones?

Answer 10

They cant produce their own steroid nucleus

To do so they need to obtain cholesterol and sitosterol from their diet

This allows moulting

Question 11

What are Brassica tissues?

Answer 11

Tissues in cabbages containg mustard oil

Question 12

Where are glucosinolates kept in brassica tissues?

Answer 12

Seperate from the enzyme responsible for breaking them down - myrosinase.

If an insects feeds on it, they contact -> isothiocyanates and nitrils get released

The mixture of those is toxic

Question 13

Are glucosinolates only released by feeding?

Answer 13

Some of them are on the leaf top

Question 14

Why are glucosinolates on the leaf surface?

Answer 14

As a first line of plant defence

Deterring non specialist insects and pathogens

Question 15

What are saponins?

Answer 15

triterpenoid compounds that are antimicrobial that also act as feeding deterrents

Question 16

What is the major glucosinolate in cabbages?

Answer 16

Sinigrin which forms mustard oil ( allyl isothiocyanate) when hydrolysed by myrosinase

Question 17

How is the formation of mustard oil by herbivores chewing called?

Answer 17

Mustard oil bomb mechanism

Question 18

What is a avirulent?

Answer 18

A microbe that is unable to cause disease

Question 19

What happens when we oculate a plant with an avirulent?

Answer 19

The plants get resistant to the virulent corresponding as well -> All the plant tissues are resisitant, not only the inoculated one

Question 20

How many phytoalexins have been identified?

Answer 20

Over 300 (2015)

Question 21

What is a phytoalexin?

Answer 21

A plant defence compound

Question 22

What distinguishes Phytoalexins from different antimicrobial compounds

Answer 22

They are only made and accumilated following attack

Question 23

What are Phytoancipins?

Answer 23

Antimicrobial compounds that are present in the plant before attack or ones made after attack but only using pre-existing constituents

Question 24

How much less phytoalexins do resistant plant accumilate?

Answer 24

Less than one third of the amount of a susceptile variety

They also accumilate faster in a resistant plant

Question 25

What are roles of serotonin in plants?

Answer 25

Senescence Flowering Plant defence (Phytoalexin)

Question 26

How does the hypersensitive response (HR) work against fungi?

Answer 26

The plant that is resistant to the fungi, kills of cells that are attacked by it, thereby killing the fungi as well

Question 27

How do fungi use the HR for their gain?

Answer 27

Only works for necrotrophs: they trigger HR in attacked cells, and feed on them

Question 28

What are hemibiotrophs?

Answer 28

Pathogens that start as biotroph but convert into a necrotoph

Question 29

What is to be said about dead cells?

Answer 29

They often contain a lot of antimicrobial compounds These chemicals are made both by the attacked cells before they die and by the surrounding cells

Question 30

Is programmed cell death only part of a defence response?

Answer 30

It is an important part of plant development occuring for example in the fomation of xylem vessels

Question 31

How do viruses multiply?

Answer 31

They hijack the plants genetic machinery, getiing it to replicate thei RNA(DNA for some viruses) During the replication, viral RNA accumilates

Question 32

What determines the specificity in the RNA silencing machanism?

Answer 32

Antisense RNA -

Question 33

How does gel electrophoresis work?

Answer 33

It seperates macromolecules (DNA, RNA and Proteins) according to size and charge Samples are placed at the bottom of the gel and an electric current is applied Negatively charged nucleic acid molecules move through the gel - shorter molecules move faster and are further up the gel than bigger ones

Question 34

How exactly does RNA silencing work?

Answer 34

1. Virus double stranded RNA is set upon by plant enzymes known as dicer proteins 2. The dicer proteins (enzymes) cut the viral double stranded DNA into specific fragments of between 21 and 24 nucleotides in lenght (siRNA) 3.These two strands of siRNA are seperated and one of these strands becomes incorporated in the RNA induced silencing complex 4.In this complex are two enzymes - one binds the RNA strand, the other one (a nuclease) degrades the RNA Using the RNA strand as a template, the binding enzymes bind the complimentary nucleotide sequence 5.The viral RNA molecules are then degraded -> this suppresses the accumilation of viral RNA

Question 35

Why is the RNA silencing mechanism in plants?

Answer 35

It is a potent defence mechanism that is effective against rapidly replicating viruses Because the complex is targeting siRNA derived from virus RNA, it is specific for viral RNA and the hosts RNAs are not affected The silencing signal is mobile, it moves with the virus so it cannot escape the silencing even when it moves

Question 36

How do viruses overcome the RNA silencing complex?

Answer 36

A suppressor from the tomato bushy stunt virus binds directly to the dsRNA molecules, preventing them to be incorporated into the RNA induced silencing complex Other viruses may disrupt RNA silencing by interfering with the function of the dicer-like enzyme

Question 37

What are siRNAs good for except virus resistance?

Answer 37

Bacterium resistance microRNA regulates plant defence

Question 38

What is the circadian rhythm?

Answer 38

The rhythm that determines the sleeping and eating patterns of an organism

Question 39

Is the circadian rhythm a response to light or temperature changes?

Answer 39

No They are capable to measure 24h intervalls

Question 40

What genes depend on the circadian rhythm?

Answer 40

Stomata opening Spore production Defence production such as jasmonic acid (during the daytime)