nodule formation by alisha dewangan.pptx

Nodule formation

1. Govt. J. Yoganandam Chhattisgarh Raipur ( C.G ) Msc Botany 2 nd Semester Topic – Nodule formation and nod factor Presented by : Alisha Dewangan Guided by : Mrs Namrata Dubey mam

2. Synopsis Overview Symbiotic nitrogen fixation in leguminous plants Nodule formation Nodulation factor

3. 1. OVERVIEW ‘Conversion of atmospheric nitrogen into nitrogenous compounds or salts to make available for the absorption of plants is called nitrogen fixation .’ 2. Symbiotic nitrogen fixation in leguminous plants In leguminous plants , symbiotic nitrogen fixing bacteria are found in knob like structure called root nodules . ‘ The root nodule of leguminous plants contain bacteria which lives symbiotically with plant. ’ The root nodules contain the species of symbiotic bacteria called rhizobium .

4. Rhizobium are commonly found in soil of crop field where bacteria and plant both specifically affect each other growth . Ex. of some of the symbiotic nitrogen bacteria are rhizobium ,bradyrhizobium , sinorhizobium , mesorhizobium , azorhizobium . Most of the species depend upon the plants on which they occur , such as – Pea - Rhizobium leguminosarum Soyabean - R. japonica Moong, urd , beans - R.phaseoli Alfa-alfa - R.melioti Clover - R.trifoli This bacteria fix atmospheric Nitrogen to ammonia and make available to plants and receive food from them , this type of nitrogen fixation is called symbiotic nitrogen fixation

5. 3. Nodule formation Steps involved in rhizobium nodulation process Attraction and multiplication of rhizobium Attraction to root surface Root hair curling Formation of infection thread Nodule formation

6. 1 . Attraction and multiplication of rhizobium Roots of higher plants release variety of chemical to increase microbial activities like sugar , amino acids , enzymes , vitamins etc . But the roots of leguminous plants secretes some chemical substances like polygalacturonase in the rhizosphere region which attracts and help the bacteria to multiply rapidly near the roots . Whereas , roots of leguminous plants also secrets , a secondary metabolites i.e., flavonoids , when presence of low N2 in soil . Flavonoids – it produces a chemical signals for attracting specific rhizobium species towards the roots .

7. 2. Attraction to the root surface However , some species of rhizobium posses a special adhesion protein called rhicadhesion on their surface . It is a binding protein . However , rhizobium secrets a extracellular polysaccharides slime from their body called lectins . Lectin helps to bind rhizobium cells to root hair . It moves by chemotactic movement [ movement of an organisms in response to chemical stimulation ] .

8. 3. Root hair curling These rhizobium bacteria accumulate near the root hair and attaches to root hair cell wall or either enter to soft or injured root hair tip . When the bacteria is attach to root hair cell wall , These bacteria digest the cell wall of plant root hair and penetrate inside it . Rhizobium releases a nod factor that form a root hair to get curled and deformed by the secretion of beta indole acetic acid .

9. 4. Formation of infection thread Infection thread is originate from the tip of the curled root hair portion . Then , the bacteria enter into the cell of inner layer of cortex and collectively forming a small tube called infection thread . The tubular infection thread contain mucopolysaccharides in which bacteria get embedded and start to multiply .

10. 5. Nodule formation The bacterial cells induce cortical cell to multiply which result in the formation of nodules on the surface of roots . Within nodules , bacterial cell multiply and colonize to form bacteroides . [theses are group of bacteria ] The rhizobia are differentiated either individually or a group of rhizobium called bacteroides which is enclosed by membrane called peribacteroides , it forms a structure called symbiosome . Symbiosome is the site N2 fixation . Bacteroides produces enzyme nitrogenase and pigment l eg-hemoglobin to form N2 fixation .

11. 4. Nodulation factor Many genes , protein and enzymes are responsible in the formation of root nodules in various events -- Nod factor – signaling molecule release by soil bacteria [rhizobia] in response to flavonoids exudation from plants . Nod factor inhibit the symbiotic relation between legume plant and rhizobia by inducing nodulation . Nodulin – factors or protein present in nodule Bacteriocins – factors or protein located on the surface of bacteria Nodulin genes - gene directly specific nodulation events of legume strain [rhizobium] called nod genes

12. 1. Nodulin genes – there are 10 genes that has identified in the species of nitrogen fixing bacteria [ rhizobium , bradyrhizobium , sinorhizobium , mesorhizobium , azorhizobium ] It is futher classified -- Common genes – nod A ,nod B ,nod C , found in all rhizobial strain Host specific genes – nod P, nod Q, nod H, nod E, nod F, nod L, nod J [ differ among rhizobial species Chemotactic movement of soil bacteria towards root is mediated by chemical such as flavonoids [inducer mol.] secreted by host plants cell Special adhesion protein called rhicadhesion is present on the surface of rhizobium species ,it’s a binding protein help in plant-bacteria attachment .

13. 4. Legume plants secrets signals , usually phenolics [ flavonoids and isoflavonoids ] , bacteria sense the flavonoids and induced transcription factor encoded by nod D , it is a regulatory protein . 5. Nod factor [ beta-indole acetic acid ] – induced the root hair curling process Nod factor also release chemical signals to promote cell division in nodule formation Mucopolysaccharide – help the bacteria to get embedded and multiplication Legh emoglobin – it is a red colour pigment found in the cell of cortical region of nodules [ control oxygen supply to bacteroides ] Nitrogenase enzyme – cell of nitrogen fixing organisms contain a specific enzyme called nitrogenase which is responsible for nitrogen fixation in plants .

14. Reference – Plant physiology by Dr. V.k jain Microbiology by R.P singh A textbook of microbiology by Dr. R.C Dubey and Dr. Maheshwari Source of internet Thank you For your attention