The document summarizes root systems, their structure, modifications, functions, and interactions with microbes. It describes the key parts of a typical root including the root cap, growing point, elongation zone, root hair zone, and maturation zone. It discusses structural modifications of taproots and adventitious roots for food storage. Respiratory modifications in mangrove roots like pneumatophores are outlined. Interactions between plant roots and microbes like mycorrhizal associations and nitrogen-fixing root nodules are summarized.
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
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
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,
• Mychorrhizae 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
• Photosynthesis- 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
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
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
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
