Lecture 19

Question 1

Stage 1 in development of the nascent light organ

Answer 1

• Upon contact with peptidoglycan, the young squid secretes mucus from the developing light organ
• Mucus is the first level of specificity, as it leads to the aggregation of Gram negative but not Gram positive bacteria

Question 2

Stage 2 in development of the nascent light organ

Answer 2

A. fischeri may be in low numbers in the aggregate but somehow outcompete the other Gram negative bacteria to eventually for a near monoculture

Question 3

Stage 3 in development of the nascent light organ

Answer 3

• Highly motile A. fischeri then migrate into the duct
• Once in the light organ they lose their flagella and become non-motile
• A. fischeri divide to form a dense population

Question 4

Role for nitric oxide (NO)

Answer 4

• well known defense response of animals to attack by bacterial pathogens
• Cells of the host duct and crypt produce high concentrations of NO synthase (NOS)

Question 5

rhizobia

Answer 5

The bacterial symbionts are collectively referred to as rhizobia, they are all members of the alpha proteobacteria

Question 6

Root nodules

Answer 6

• Infection of the root of a legume with a rhizobia leads to the formation of root nodules
• Nitrogen fixation occurs in the root nodule

Question 7

Cross-inoculation group

Answer 7

a group of related legumes that can be infected by a particular group of rhizobia

Question 8

Mycorrhizae

Answer 8

mutualistic associations between plant

roots and fungi

Question 9

Ectomycorrhizae

Answer 9

predominant in temperate forests, fungal partner remains outside the plant cell

Question 10

Endomycorrhizae

Answer 10

part of the fungal hyphae are inside the plant cell

Question 11

Arbuscular mycorrhizae (AM)

Answer 11

form of endomycorrhizae
• AM is probably the most widespread terrestrial symbiont, formed by 70-90% of land plant species
• Unlike many soil fungi, AM do not metabolize cellulose and leaf litter

Question 12

Arbuscular Mycorrhizae (AM) function

Answer 12

1. To elevate the phosphate uptake by the plant
2. To increase nitrogen acquisition by the plant
3. To provide a carbon source to the fungal partner

Question 13

Carbon:

Answer 13

1. Sucrose is transported into the apoplast, then cleaved to hexoses
2. Hexoses are converted to glycogen and TAG lipid droplets, which are suitable for travel to the outer hyphae

Question 14

Phosphate:

Answer 14

1. Imported by fungal phosphate transporters
2. Transported towards the root as polyphosphate granules, within
   vesicles
3. Phosphate is released from polyphosphate within the plant

Question 15

Nitrogen:

Answer 15

1. N is taken up by ammonium or nitrate transporters
2. N is mainly transported as Arg (+), within polyphosphate granules (-) 3. N is released from Arg as urea and either transported directly to
   plant cell or after cleavage to ammonium