Roots & Plant Nutrition

Roots

plant organ that functions in anchorage and absorption; most are produced below ground

critical to most plants for absorption of water and minerals

can also help to anchor soil in place and therefore prevent erosion

Rootless Plants

mosses; Spanish moss; some aquatic and tropical plants can absorb enough moisture through their leaves

Root Uses for Foods

foods and flavorings: root vegetables are good source of carbohydrates and low in fat; carrots and sweet potatoes high in beta-carotene

ex: carrots, rutabagas, yams, beets, parsnips

Root Uses for Non-Foods

mandrake roots: to help induce sleep

rotenone: fish poison and insecticide

nicotine: produced in roots of tobacco plant and carried by xylem to leaves

spruce roots: used by Native Americans to make canoes, baskets, etc

Hormones & Secondary Compounds

cytokinin and gibberellin are produced in roots and carried by xylem to shoots where they affect growth/development

rotenone, nicotine, and other secondary compounds are produced in roots for plant defense 

Prop Roots

supports stems and branches; helps support tall non-woody plants

ex: corn

Buttress Roots

helps support tall tropical trees growing on thin soils

Aerial Roots

roots formed above the ground; grow down from branches of banyan trees and help support long, heavy branches

Pneumatophores

grow into stems and can take in air through lenticels (groups of cells that permit gas exchange between plant interior and external atmosphere)

Aerenchyma

spaces in internal root structure which can be filled with air

oxygen diffuses from here to submerged roots to support respirations and ATP synthesis 

Contractile Roots

roots shorten by collapsing some cells and can pull plant back into warmer soil on cold days

ex: dandelions

Haustorial Roots

produce root-like organs that penetrate host stems and obtain water and nutrients from host; parasitic to other plants

ex: dodder and mistletoe 

Epiphytic Roots

exposed to air and may absorb moisture from humid air and from available pockets of water

ex: orchids, pitcher plants

Taproots

single main root from which many branch roots grow out

found in gymnosperms and eudicot angiosperms

Fibrous Roots

primary root from the seed; lives for a short time; replaced by many roots developing from the stem; no single root is predominant; shallower than taproot

found in monocot flowering plants

Adventitious Roots

roots that develop along stems or from leaves

ex: tomato

Feeder Roots

fine peripheral roots active in absorbing water and minerals; found near soil surface and extend outward

produced from taproots and fibrous roots

Root Structure

lateral branch roots: extend from main root; youngest branch roots are nearest to the root tip

root hairs: fingerlike extensions of some root epidermal cells; main site of absorption of water and minerals with the aid of ATP to power carrier proteins

Root Apical Meristem (RAM)

area of rapidly dividing cells in roots; protected by a root cap made of mucigel (Golgi secretion made of viscous polysaccharides); root cap cells slough off after 4-5 days

Amyloplasts

may indicate direction of gravity to the root; supports positive gravitropism (tissues growing with gravity)

Root Cap

thimble-shaped mass of cells at the tip of growing root; functions primarily in protection of RAM

Root Meristem

produces primary tissues (protoderm, ground meristem, and procambium)

Region of Maturation

differentiation starts in this region; higher on the root;

Cortex

primary tissue composed mainly of parenchyma and stores starch; air spaces between cells to allow diffusion of oxygen through root; usually extends between the epidermis and the vascular tissue

Endodermis

innermost cortex layer; closely packed and has waterproof layer that forms barrier between the cortex and the root core

How Water & Minerals Pass Into Endodermis

water: diffuse through the endodermal cells to the core

minerals: can only pass into and through the endodermal cells via transporter proteins

Casparian Strip

band of suberin around the radial and transverse walls of endodermal cell

Pericycle

tissue sandwiched between the endodermis and phloem of a root; the site of branch root (lateral root) formation

Mineral Absorption Types

symplastic: transport of minerals through root via plasmodesmata

apoplastic: transports of minerals from root hair to endodermis through cell walls and intercellular spaces; requires active transport

Acidic Soils

aluminum becomes dissolved in soil water and may damage plant root growth

Essential Macronutrient Elements for Plants

taken from water/air: H hydrogen; C carbon (from carbon fixation CO2); O oxygen

taken from soil: N nitrogen; Mg magnesium; P phosphorous; S sulfur; K potassium; Ca calcium

Essential Micronutrient Elements for Plants

B boron; Cl chlorine; Mn manganese; Fe iron; Cu copper; Zn zinc; Mo molybdenum

all found in soil; all used for enzyme function other than B

Hydroponics

growth of plants in greenhouses in a mineral nutrient solution without the use of soil

ex: lettuce crop