Symbiotic NItrogen Fixation

Question 1

Most common symbiotic nitrogen fixation relationship is between…? and what is this relationship considered?

Answer 1

1. Bacteria of the genus rhizobium and the root structures of legumes
   This relationship is considered symbiotic

Question 2

What does symbiotic mean?

Answer 2

Two types of organisms live together as in their mutualistic relationship benefits them from association with one another

Question 3

how does the bacteria and root structures help each other out in symbiotic nitrogen fixation?

Answer 3

1. Bacteria receives a protected environment and nutrients from the plants
2. the roots receive fixed nitrogen from the bacteria.

Question 4

What is Rhizobia?

Answer 4

bacteria that is capable to form symbiotic relationships with legumes and form root nodules

Question 5

What do rhizobia do?

Answer 5

They enter the root tissues of the plants and form nodules.

Question 6

what is the purpose of nodules?

Answer 6

they contain and protect the bacteria.

Question 7

True or false:

all species of the rhizobium genus are capable of either symbiotic relationships or root nodule formation

Answer 7

False, not all of them are

Question 8

Symbiotic relationships are specific to..?

limits to the rhizobium genus?

Answer 8

1. species
2. Host
   particular species of rhizobium are only able to form nodules on certain legumes.

Question 9

Proper farming technique since symbiotic relationships are so specific with host and speciies of rhizobium

Answer 9

1. farmers inoculate legume seeds with the right rhizobium first before planting

Question 10

What are legumes?

Answer 10

they are plants that produce seeds in pods and incluide alfalfa, clover , peas

Question 11

Characteristics of Rhizobium?

Answer 11

1. aerobic
2. Gram negative rods
3. does not produce spores
4. motile

Question 12

First requirement of nodulation? How is this achieved?

Answer 12

1. Bring bacterial strain in the soil in close proximity to the root hairs.
2. Achieved through the production of a chemical known as flavonoids

Question 13

What do flavonoids do?

Answer 13

they attract rhizobia, resulting in an accumulation of bacteria on recognition sites on the root hairs.
They activate the transcription of a family of bacterial genes that code for proteins known as the nodulation factors.

Question 14

What are nodulation factors responsible for?

Answer 14

they are responsible for the multi-step process by which the bacteria are able to infect the plant root hairs and ultimately form nodules.

Question 15

What genes does the sym plasmid carried by the rhizobium code for

Answer 15

1. Nodulation genes
2. nitrogenase genes
3. host-specificity genes

Question 16

What happens when a polysaccharide capsule of the rhizobium bind to the cell membrane of the root hair?

Answer 16

the root hair membrane invaginates (turns inside out) forming an infection thread in which the root hair appears to be growing into the root rather than projecting outwards

Question 17

what is leghemoglobin

Answer 17

it has a high affinity for free oxygen in the environment, keeping oxygen levels low enough to allow nitrogenase function but high enough to allow aerobic respiration in bacteria

Question 18

Why is a normal alfalfa root nodule pink in color?

Answer 18

sufficient quantities of the reddish-colored leghemoglobin

Question 19

Why is it important to keep oxygen concentrations low?

Answer 19

to prevent inactivation of the enzyme nitrogenase

Question 20

Importance of invagination?

Answer 20

it carries surface bound bacteria inside the infection thread resulting in the production of auxin

Question 21

what is the presence of nitrogenase specific to?

Answer 21

species that are capable of forming nodules

Question 22

Where in the plant can the ability of fixing nitrogen be utilized?

Answer 22

in the roots.

Question 23

What do auxins do?

Answer 23

plant growth regulating hormone that stimulate root cells to divide, forming a nodule around the infection thread, which in turn begins to branch further into the nodule

Question 24

where does rhizobia grow best?

Answer 24

in well-aerated soil

Question 25

how does the plant solve the issue between needing oxygen for respiration but getting rid of oxygen for nitrogenase function?

Answer 25

they produce a protective compound,
an oxygen carrying protein (therefore it oxygen binds)
called leghemoglobin