Plants obtain nitrogen, crucial for protein synthesis, primarily through two methods: absorption from the soil and symbiotic relationships with nitrogen-fixing bacteria.
Nitrogen Uptake from the Soil
Plants absorb nitrogen from the soil in the form of inorganic compounds:
- Nitrates (NO3-): This is the most common form of nitrogen absorbed by plants.
- Nitrites (NO2-): Absorbed in smaller quantities and converted to ammonium within the plant.
- Ammonium (NH4+): Can be directly absorbed, but is less mobile in the soil than nitrates.
These nitrogen compounds are transported through the plant's roots to the leaves and other tissues where they are incorporated into amino acids, the building blocks of proteins. The availability of these compounds in the soil is often dependent on the activity of soil microorganisms that break down organic matter or convert atmospheric nitrogen.
Symbiotic Nitrogen Fixation
Many plants, particularly legumes (like beans, peas, and lentils), have a symbiotic relationship with nitrogen-fixing bacteria, especially Rhizobium species. This relationship allows the plant to obtain nitrogen directly from the atmosphere.
- Process:
- Rhizobium bacteria infect the roots of the plant.
- The plant forms specialized structures called nodules on its roots.
- Within these nodules, the bacteria convert atmospheric nitrogen (N2) into ammonia (NH3).
- The plant then uses the ammonia to synthesize amino acids and proteins.
This symbiotic relationship is mutually beneficial; the plant provides the bacteria with carbohydrates (energy) and a protected environment, while the bacteria provide the plant with a usable form of nitrogen.
In summary, plants acquire nitrogen for protein synthesis either directly from the soil in the form of nitrates, nitrites, or ammonium, or through symbiotic relationships with nitrogen-fixing bacteria that convert atmospheric nitrogen into usable forms.
