Botany - Roots

• root - part of the plant axis whcih normally develops below the surface of the soils
• 3 major types of root system : taproot, fibrous, adventitious
• taproot - originates from the seed radicle and consists of one main root, generally growing straightforward with smaller lateral or branch roots
• taproot - dicots plants generally have this type of root system
• primary root system : primary root, secondary root, tertiary root, quaternary root, root hairs
• fibrous root - also originates in the seed radicle which consists of fine numerous root similar in dm
• monocot plants generally have this type of root system (fibrous)
• adventitious root - the root that grow from any part of the plant other than the radicle
• adventittious may develope from a base of stems, nodes, internode and in some cases from leaves
• root cap - composed of a thimble-shaped mass of parenchyma cells covering the tip of each root
• root cap - functions to protect the delicate tissues behind it from damage as the young root tip pushes through often angular and abrasive soil particles
• root cap - secrete and realease a slimy substance forming a slimy lubricant that facilitates the root tips' movement throught the soil
• mucilaginous lubricant - provides a medium favorable for the growth of beneficial bacteria that adds nitrogen supply in the soil
• root cap - also functions in the perception of gravity
• amyloplast - plastids containing starcg grains act as a gravity sensors, collecting on the sides of root-cap cells facing the direction of gravitational force
• according to the starch-statolith-concept, gravity-dependent sedimentation of amyloplasts in statocytes of the columella (calyptra) provide directional cues and elicits the bending response
• region of cell division is also called meristematic region
• region of cell division - growing apex of the root
• cells in region of cell division are small, cube-shaped, thin-walled, and have a large centrally located nuclei
• apical meristem soon subdivides into 3 meristematic areas: protoderm, ground meristem, procambium
• protoderm - gives rise to an outer layer of cells (epidermis)
• ground meristem - produces parenchyma cells of the cortex
• procambium - produces the primary xylem and primary phloem
• pith - generally present in stems but not in most dicot roots, present in most monocot
• parenchyma meristem originates from ground meristem
• region of elongation - found above the meristematic region
• region of elongation - cells elongate several times their original length and push the root tip through soil
• region of elongation - cells starts developing their specialized functions
• region of maturation - lies above the region of elongation and extends upwards
• region of maturation - responsible for the increase in lenth of the root into various distinctive cell types
• region of maturation is also called region of differentiation/root hair zone
• cells in region of maturation are already mature and perform specific functions like protective covering, transport and support
• root hairs are not separate cells, rather they are tubular extension of specialized epidermal cells
• root hairs are so numerous that they appear as a fluffly mass to the nake eye, typically numbering more than 38,000 cm2 of SA
• the presence of root hairs here absorb water and minerals from the soil particlaes, adhere tightly to root particles and greatly increase the total absorptive surface of the root
• intermal morphology of dicot

  • epidermal region
  • cortex
  • endodermis
  • stele/vascular cylinder
  • pericycle
• epidermal region -- outermost layer of cells which is only one cell thick. most of the cells here have extensions and form root hairs
• (dicot )cortex consists of many thin-walled parenchyma cells w/ intercellular spaces.
• cortex functions primarily for food storage
• endodermis - innermost layer of the cortex, consisting cylinder of compactly arranged cells whose walls are impregnated with lignin and suberin