Roots System

Roots structure and functions

1. ROOT SYSTEM Structure , Modifications, Storage, Respiration and Reproduction

2. Characteristics of the Root Root forms the descending portion of the plant Non green ,brownish in color Nodes , inter nodes ,leaves and buds are absent No lateral branches Root tip covered by a root cap called calyptra Roots are positively hydrotropic , negatively phototropic, Positively geotropic Vascular bundles are radial , and xylem is exarch Unicellular root hairs near the tip for water absorption

3. Root System Two types of Root Systems; Tap Root and Adventitious Root Systems

4. Root System Tap root system : Originates from the radicle Single deep seated main root , thick at the base tapers towards the apex Secondary and tertiary roots arise from the tap root Adventitious root system: Many roots of equal length, surface feeder Arise from the stem or leaf hypocotyl Underground or aerial and green or non green Root cap and root hairs are absent

5. Differences

6. Parts of a typical Root

7. Parts of a Typical Root 5parts Root cap(Calyptra)- Cap like, at the apex ,multicellular , parenchymatous protects the growing point against friction of the soil particles rich in starch, help in graviperception rich in golgi bodies, outer cells secrete mucous and lubricate. Hydrophytes like Eichhornia , Pistia,Lemna replaced by root pockets help in balancing. Multiple root caps in stilt roots of Pandanus . Orchid roots are parasites and epiphytes, M ychorrhizae roots are capless

8. Parts of a Typical Root Growing Point(Meristematic zone)- Root apex,1mm in length Zone of cell division 2 types of cells- towards the apex develop into Calyptrogen , second towards base forms histogen Zone of elongation- 4-8mm in length, helps in growth,cells elongate due to vacuolisation , power of cell division lost,helps in absorption of water and minerals Root hair zone( piliferous region)- Temporary zone, moves forward along with the growth of the root tip, root hairs are unicellular and ephemeral at maturity root hairs shrivel and become non functional, absent in plants where root cap is absent like Eichhornia Zone of maturation- Above the root hair zone, forms the bulk,cells thick walled, no water absorption, lateral roots arise from this area , secondary growth takes place

9. Functions of Roots Secondary functions: Storage of food-carrot , Raddish Extra mechanical support: Banyan,Maize Perennation - Aeration- Mangrooves Reproduction- Dahlia Floating- Jussaea Photosynthesi s- Tinospora Levelling- Nitrogen fixation- Pea Absorption of food from the host - Cuscutta,Water -Vanda Climbing- Pothos Absorption of phosphates- Mycorrhizal roots Plantless roots - Podostemum Green roots - Trapa

10. Structural and Anatomical Modifications of Root Systems

11. Structural Modifications of Tap Root for Storage Tap root becomes swollen and fleshy due to the storage of food Reserve food utilized at the time of flowering and fruiting Secondary roots remain thin Stem is reduced , discoid and bears radical leaves Types of Storage roots a)Conical B)Fusiform C) Napiform D)Tuberous

12. Structural Modifications of Tap Root for Storage Conical Tap root -Cone shaped , swollen at the base Leaves are radical gradually tapering towards the apex Stem is reduced Reasons- Arises from radicle , arises singly, cone shaped Example-Carrot Fusiform Tap root- Spindle shaped , thick in the middle , tapering at the base and apex Hypocotyl forms 2/3 of the fleshy part , terminal part formed by the tap root Secondary roots in the apical part Stem reduced ,leaves radical Reasons -Arises fro radicle Arises singlyLower swollen part is true tap root bearing secondary roots Example-Radish Napiform roots- Swollen at the base , almost spherical suddenly thins towards the apex Swollen part formed by hypocotyl Thin secondary roots at the base forms tap root Leaves are radical, stem reduced Reason- Arises from radicle, singly, bears secondary roots Example-Turnip Tuberous roots- Arise singly ,get swollen , no definite shape Example- Mirabillis

13. Structural Modifications of Adventitious roots for storage Tuberous roots- fleshy ,no definite shape , arising singly at each node, store food in the form of starch Reason- Arises from node of the stem , root cap absent Function -food storage Example- Sweet potato Fasiculated roots -Definite shape, arise in clusters from the lower node Of the erect stem, store food Example- Dahlia , store food in the form of inulin Moniliform roots -Beaded roots- Portulaca Nodulose roots- Apical portions swollen- Curcuma amada Annulated roots- Swellings as series of ring like outgrowths- Psychotria Stilt roots- Arise from lower nodes of the stem- Sugarcane Palmate roots- Like the palms of a human hand- Orchis

14. Root modification for Respiration Roots show modifications in the plants growing in coastal salt water wetlands like Mangrooves which are halophytes Habitat has excess of salts and water which gives a difficulty in anchoring , aeration and seed germination Supporting roots-stilt roots in Rhizophora Pneumatophores, vivipary Pneumatophores are respiratory roots in Mangrooves , growing in oxygen deficient areas Produce negatively geotropic aerial branches, bear lenticelsnear the tip for exchange of gases like Avicennia,Sonnertia Nature-Modified secondary roots Functions- Gaseous exchange

15. Adaptions for Respiration Pneumatophores in Mangrooves Stilt roots in Rhizophora

16. Root Modifications for Reproduction

17. Interaction of roots with microbes Rhizosphere - Area of soil in which the plants exudes some vitamins , hormones etc which promote the growth of microbes in the soil Microbes influence the growth and metabolism of the root Rhizoplane - A microhabitat formed by association of microbes and the root surface Bacteria in the rhizosphere is rhozobacteria ,promoting the growth of the plants called PGRR(plant growth promoting rhizobacteria ) 4 types of interactions: Mycorrhiza Reciprocal symbiosis in nodules Associative symbiosis. Mycotrophy

18. Microbe Interactions Mycorrhiza : Symbiotic association of saprophytic fungus with the roots of higher plants. The roots of the plant are shallow, root cap and root hairs absent,root hairs replaced by fungal hyphae which function as root hairs like roots of Pinus . Two types: Ectotrophic mycorrhiza : The bulk of the fungus lives outside the root surface, forming a thick wooly sheath like in Pinus ,Eucalyptus ,oak Endotrophic mycorrhiza - Bulk of the fungus occurs internal to the root tissue ,within the cells of the cortex forming vesicles which store lipids or finger like arbuscules which transfer nutrients from fungus to the roots common in orchids, crop ,plants grasses, fungal patner belongs to zygomycetes like Armillaria , common type of endomycorrhiza is VAM(vesicular arbuscular mycorrhiza ) which help in phosphate absorption

19. Mychorrhiza and its types Ectomycorrhiza Endmycorrhiza

20. Microbe Interactions Mycotrophy - Angiosperms growing on decayed organic matter as saprophytes, also called as humus plants Non green ,scale leaves like Wullschleigelia aphylla Root- rhizobium reciprocal symbiosis in root nodules -Mutualism Associative symbiosis -Bacteria in close contact with roots of cereals