Bot-Lec (Sem-1) - Chapter 13: Roots

roots

the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body

taproot system; fibrous root system

two kinds of root systems

taproot system

a root system with a large taproot and smaller branch roots; observed in conifers and dicots; a modified fleshy feature of sugar beets and carrots

Beta vulgaris

scientific name of sugar beet; with taproot

radicle/primary root; taproot; branch roots

parts of a taproot system

radicle/primary root

part of the taproot system; first to emerge from a seed

taproot

part of the taproot system; enlarged radicle in dicots that persist throughout its life

branch roots

part of the taproot system; smaller roots that grow from the taproot

fibrous root system

a type of root system; an extensive mass of evenly sized roots; commonly observed in monocots; radicle is replaced by a mass of adventitious roots

adventitious roots

form on other organs like stems; begin growing soon after seed germination in monocots; observed in monocots, rhizomes of ferns, club mosses, and horsetails; form in leaves, petioles, and stems; controlled by the hormone auxin; similar in structure and functions with primary roots

auxin

a plant hormone that encourages the elongation of shoot cells in plants; controls the growth of adventitious roots

anchorage; storage; absorption; conduction

four primary functions of roots

root cap/tip

part of a root; thimble-shaped and found at root tips; peripheral cells secrete a considerable amount of mucigel

mucigel

slimy substance secreted by dictyosomes

protection; lubrication; water absorption; nutrient absorption

four functions of mucigel

quiescent center

part of the root; located behind the root cap; consists of 500-1000 seemingly inactive cells; cells are in the G1 phase of the cell cycle

quiescent cells

not necessarily quiescent; replace damaged meristem cells; organizes patters of primary growth in roots

cellular division; cellular elongation; maturation

three zones of the subapical region

zone of cellular division

root apical meristem

zone of cellular elongation

region where cells start to elongate

zone of maturation

where cell differentiation is completed

diarch; triarch; tetrarch; polyarch

four arrangements of xylem in roots

modified roots

roots with special features for specific functions

starch

what beets, turnips, radish, and cassava store

sucrose

what sweet potatoes store

water

what desert plants store more than 70 kg of

suckers

modified roots that produce aerial shoots, like cherry, pear, apple, and teak; become new individuals when separated from parent plant; common means of propagation

pneumatophores

modified roots for aeration, like mangroves; import oxygen from the atmosphere; oxygen diffuses to submerged roots

contractile roots

modified roots for movement, like lily, ginseng, and dandelion; can shrink more than 50% in only a few weeks; pull a plant to more stable environment

parasitism; mycorrhizae; nodules

three forms of nutrition in modified roots

parasitism

causes great losses in important crops; e.g. witchweed, broomrape, Cuscuta

mycorrhizae

mutualistic associations between a root and a fungus; improves the plant’s tolerance to stress

nodules

localized swellings in the roots of legumes; cells are often infected with Rhizobium; mutualistic relationship between plant roots and bacteria

Rhizobium

nitrogen-fixing bacterium

aerial roots

adventitious roots formed by aboveground structures like stems; functions include water retention, photosynthesis, and support

water retention; photosynthesis; support

three functions of aerial roots

velamen

multiple epidermis of roots of some epiphytic orchids (aerial plants); almost impermeable to water; mechanical protection and water retention

photosynthesis

a function unique to aerial and aquatic plant roots; sometimes turns the roots flat and green, like shoots; observed in vanilla orchid, Philodendron, Vanilla planifolia, Microcoelia smithii

Philodendron

aroids; an example of plants with photosynthetic roots

Vanilla plantifolia

vanilla orchid; contains high contents of vanillin; an example of plants with photosynthetic roots

Microcoelia smithii

pinhead orchids; an example of plants with photosynthetic roots

prop roots

supportive aerial roots that grow into the soil

buttress root

found at the base of the trunks of shallow-rooted tropical trees; plant-like roots that are often more than 4 m high

food; drugs

economic importance of roots

aconite

root drug for poison

ipecac

root drug that causes vomiting

ginseng

root drug for herbal supplement

reserpine

root drug for tranquilizing

protoveratrine

root drug for heart relaxant