Cyanobacteria

Question 1

How were plant cells created?

Answer 1

Endosymbiosis with cyanobacteria created plant cells, and cyanobacterial cells became chloroplasts

Question 2

Tell me about cyanobacteria toxins

Answer 2

some cyanobacteria produce toxins:
- cyanotoxins, cytotoxins, neurotoxins etc
this effects feeding organisms via bioaccumulation

Question 3

Tell me about cyanobacteria thylakoid
- clue word: perforation

Answer 3

Cyanobacteria are able to photosynthesise because they have thylakoid membrane situated in concentric cells
The thylakoid has perforations to allow cytoplasm through

Question 4

Describe the carboxisome

Answer 4

CO2 fixation occurs in the carboxysome. They are organelles with a protein shell (no membrane) that contain RuBisCO and work to concentrate CO2 around it

Question 5

What’s involved in differentiation into a heterocyst

Answer 5

initialised by N deprivation:
- synthesis of the nitrogenase enzyme
- degradation of PSII
- formation of thick external polysacciride layers that minimise diffusion - N2 is provided by adjacent cells

Question 6

What form can cyanobacteria populations be in?

Answer 6

• Unicellular
• In colonies
• Filamentous gelatinous mass (from microscopic to wall nut size)

Question 7

Tell me about Nostoc genus

Answer 7

cyanobacteria that are part of nostoc genus are able to form symbiosis with plants:
undergoing differentiation and becoming Akinetes, Hormogonia and Heterocysts

Question 8

What is an akinete?

Answer 8

Akinetes are formed under stressed conditions, are enlarged/resistant cells and can withstand dark and dry conditions.
They germinate once conditions have returned favourable

Question 9

What is a hormogina?

Answer 9

Hormogina are essential to plant symbiosis. SIgnalling attracts them to plants, where they differentiate back into vegetative cells. However 1/10 differentiates into a heterocyst

Question 10

What is a heterocyst?

Answer 10

heterocyst is formed when N is scarce. They connect to adjacent cells via channels, and cannot revert back to vegetative cells

Question 11

briefly describe the physiological processes inside a heterocyst

Answer 11

• N2 is provided from adjacent cell
• ATP is synthesised by PSI
• NADPH is provided by adjacent cell as glucose, yielding NADPH through pentose phosphate pathway

Question 12

what happens to the resulting reduced N from fixation in a heterocyst?

Answer 12

reduced nitrogen (NO3-) is converted into glutamine for amino acid metabolism inside the heterocyst. Any remaining is released into medium (plant) and converted into NH4+

Question 13

Where does colonisation occur in the special symbioses with sphagnum mosses and cyanobacteria

Answer 13

Colonisation occurs in the hyalocytes (dead hyaline cells that are connected to the environment, allowing water and storage exchange)

Question 14

Tell me about the special symbiosis between Azolla ferns and Trichormus azollae

Answer 14

Trichormus cyanobacteria is held in cavities, and doesn’t need to recolonise after plant dies.
Reproduction is via spores in sporocarp structure. When the plant is ready to germinate, Hormogonia is produced and differentiates into akinetes, which travel with spores.

Question 15

How could you describe the relationship between Azolla ferns and Trichormus azollae

Answer 15

It is a guaranteed perpetual symbiosis through germination of resting Akinetes alongside the plant

Question 16

Tell me about Cyanobacteria colonisation in gymnosperms

Answer 16

If conditions are favourable in Cycads (the only gymnosperm that establishes symbiosis), cyanobacteria colonises the intercellular space in the root cortex

Question 17

tell me about cyanobacteria symbiosis with Angiosperms

Answer 17

Only seen in epidermal cells of rice and Gunnera genus, where anthocyanin-rich stem glands attract nostoc (glands produce viscous carb rich mucilage that creates a suitable microenvironment for nostoc)

Question 18

What is the second requirement for symbiosis? (other than Hormogonia)

Answer 18

Signalling pathways:
NOD factors (i.e. lipochistoligasacharides) activate symbiotic signalling pathway, causing transcriptional reprogramming and symbiosis establishment

Question 19

Why is cyanobacteria important in agriculture?

Answer 19

It supports plant growth via:
- fixating N2
- phylohormone and siderophore production
- mineral solubilisation
- improve soil structure (via biofilms)

Question 20

how is cyanobacteria used in rice cultivation?

Answer 20

Either through direct symbiosis, or populations of azolla fern (Biofertilizer), cyanobacteria contributes 20-30kg/ha of N through fixation

Question 21

What holistic environmental benefits does cyanobacteria provide?

Answer 21

BMF minimises pollution (doesn’t require fossil fuels) and fixed N is less susceptible to denitrification, leaching and volatilisation as it is directly absorbed