Nitrogen fixation in Plants

A presentation on Nitrogen Fixation, the process in Detail.Office 2010 is highly recommended.

1. NITROGEN FIXATION Presented by- Utpal Mallick

2. CONTENTS What is Nitrogen? Why is it important? Nitrogen fixation and its types Process of Nitrogen fixation

3. Why is Nitrogen fixation important? The nitrogen cycle is more complex than other biogeochemical cycles because most organisms cannot use the nitrogen found in the atmosphere - even though almost 80% of the air is nitrogen! In order for plants and humans to get the nitrogen they need, the nitrogen must be converted into ammonia - NH3.

4. The conversion of this atmospheric nitrogen to the usable form of ammonia is known as nitrogen fixation.  Nitrogen fixation  can be defined as the process of creating ammonia from atmospheric nitrogen. Without this process, most plants and animals would not have the nitrogen needed to live.

5. NON- BIOLOGICAL It is brought about by ionizing phenomena such as cosmic radiations , meteor trails ,lightning, thunderstorms , volcanic eruptions etc . • These provides high energy for breaking N≡N & also for the formation of free N₂ with oxygen or hydrogen (H ₂ 0).

6. Industrial N2 fixation Accomplished by Haber -Bosch process . Developed in Germany 1914 by Fritz H aber & Karl B osch. Process- N2 and H2 react with each other in presence of Industrial catalyst( nickel / iron) High temperature about 500 ͦ c High pressure – 200 atm To form NH3

7. Biological Nitrogen Fixation Biological nitrogen fixation was discovered by the German agronomist Hermann Hellriegel and Dutch microbiologist Martinus Beijerinck . Biological nitrogen fixation ( BNF ) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase . The reaction for BNF is : N2 + 16ATP + 8H+ + 8 e− → 2 NH3 + H2 + 16ADP + 16Pi

8. BNF is mostly accomplished by microorganisms called diazotrophs or N₂ fixers. They include some species of bacteria, fungi,blue green algae,lichens etc . Fixation of atmospheric Nitrogen into nitrogenous salts with the help of MICRO_ORGANISMS. Two types of Nitrogen fixation Symbiotic Non-symbiotic

9. NON-SYMBIOTIC FIXATION Fixation is carried out by free living micro-organism. They inhabit both terrestrial and aquatic habitat. They can be Aerobic, Anaerobic or Blue green algae.

10. SYMBIOTIC FIXATION Fixation of free nitrogen by micro-organisms living in soil symbiotically inside the plants ‘ Symbiosis’ – coined by DeBary . Three categories Nodule formation in leguminous plants Nodule formation in non- leguminous plants Non nodulation

11. Nodule formation Root nodules formed due to infection of Rhizobium . Free living bacteria growing , near the root of legumes are unable to fix nitrogen in free conditions. Roots of the legumes secrete some growth factors that helps in fast multiplication of bacteria. (E.g.) Pisum sativum secretes homo serine & also carbohydrate containing protein Lectins over their surface.

12. Structure and function of nodule Outermost layer of nodule- bacteriod zone-enclosed by cortical cells. Rate of N- fixation of nodule directly proportional to the volume of the nodule. Nodules are small-contain leghaemoglobin . Leghaemoglobin Effective nodules are larger- pink in colour -due to the presence of red coloured leghaemoglobin . This pigment is similar to haemoglobin of blood. Found in nodules between bacteriods & membrane envelops , enclosing them.

13. It is heme protein. Contain heme moiety attached to a peptide chain represent globin part. The amount of leghaemoglobin in nodules has direct relationship between amount of atm N fixed by legumes . MW-16,000-17,000 daltons .

14. Pathway of nitrogen fixation in root nodules Glucose-6-phosphate acts as a electron donor. Glucose-6-phosphate is converted to phosphogluconic acid. Glucose-6-phosphate + NADP+ + H2O 6phosphogluconic acid + NADPH + H+ NADPH donates electrons to ferrodoxin . Proton is released and ferrodoxin is reduced. Reduced ferrodoxin acts as electron carrier. Donate electron to Fe-protein to reduce it. Electrons released from ferrodoxin thus oxidized

15. Reduced Fe-protein combines with ATP in the presence of Mg + 2 . Second sub unit is activated and reduced. It donates electrons to N2 to NH3 Enzyme set free after complete reduction of N2 to NH3 .

16. Thank you! Any queries?