Nitrogen Flashcards
Why is it beneficial that N is less electronegative than oxygen?
The hydrogen bonds it participates in are weaker and easily separated (e.g., DNA)
What type of molecules is nitrogen found in?
All amino acids, all nucleotides, pigments (e.g., chlorophyll), plant hormones, secondary metabolites.
Why is nitrogen the most limiting nutrient?
Atmospheric N2 is extremely stable and cannot be broken by plants. -H and N_O bonds are more easily broken.
What are usable forms of nitrogen?
Ammonium, nitratte
How is N2 broken up for plants?
By bacteria
What is an issue with nitrate and nitrite?
Negatively charged, just like temperate soils. They are not retained well by soil and are often leached.
How is the triple bond in N2 broken down to be used by plants?
By the enzyme nitrogenase
What is an issue with nitrogenase?
O2 inhibits nitrogenase, thus requires anaerobic conditions
How many ATP molecules are required to fix one molecule of nitrogen?
16
How do plants attract free-living microbes to get N?
Deposit carbs from sloughed-off root cap cells and mucilage, which support bacterial growth. Produce N which is made available to plants by amoebae and fungi that feed on bacteria and organic matter.
How do plants maximize SA for N uptake?
Lateral root outgrowth responsive to nitrate or ammonium
Roots grow continuously
Thus, more growth where nitrogen signals are received
What specifically increases the SA for N uptake? How do they take in nitrogen?
Root hairs. Their cell membrane is covered in uptake transporters for nutrients such as nitrate.
What is a con for using root hairs to increase N uptake?
Increase in energy used for carriers and moving against concentration gradient
What are the benefits of mycorrhizae?
Fungi use extensive hypahe to scavenge nutrients over a much greater surface area/volume of soil than can be achieved by the root.
What are the different ways fungi can interact with roots?
Grow over surface = ecto
Enter root = endo
Enter cells = vam
What are nodules?
Complex structures with meristematic region and vascular connection
How do legumes take in nitrogen?
Form symbiotic relationship with N-fixing bacteria. Nodule provides an anaerobic environment where bacteria can fix N.
What does nodule formation require?
Coordinated exchange of signals between the plant and bacteria
How do signals cause nodule formation?
Root hairs receive signals, they then curl around the bacteria, forming an infection thread, which bacteria then use to enter cells.
What genes regulate the communication between legumes and bacteria?
NOD genes
How does legum-rhizobium symbiosis benefit legumes?
Gets organic nitrogen
How does legum-rhizobium symbiosis benefit legumes?
Gets organic nitrogen
What is a cost of legume-rhizobium symbiosis to legumes?
Very costly in terms of energy. 16 ATP/N2. about 20% of photosynthate goes to this.
How does legum-rhizobium symbiosis benefit bacteria?
Gets fixed carbon, energy from plants.
