Botany Lecture (ROOTS)
Main functions of roots: Typically shallower and more horizontal than a
1. Anchor the plant; taproot system that allows roots to quickly obtain
2. Absorb & conduct water and minerals; and water before it evaporates.
3. Produce hormones and other substances that regulate Monocotyledonous plants (corn, rice, “one seed
plant’s development & structure. leaf”) have fibrous root systems.
Two main patterns of root growth: In ivies, this aids in climbing, appearing along the
1. Taproot system – has a large main root known as aerial stems
taproot. In certain plants with specialized stams (rhizomes,
Taproot develops directly from the radicle (root-like; corns, bulbs) only a.r. are produces.
a part of embryo or immature plantlet within the Finer; the growth is more lateral
seed that grows out and develops into the firs root)
and produces branch roots called lateral roots. Root structures:
Radicle may develop into a thick taproot, from which 1. Root cap – composed of a thimble-shaped mass of
thinner branch roots arise, or many adventitious parenchyma cells covering the tip of each root.
roots may arise from the stem, which is attached to Quite obvious in some, others nearly invisible
the radicle and continuous with it. Function: to protect from damage the delicate tissue
Taproot penetrates deeply and are therefore well behind it as the young root tip pushes through open
suited for plants that become larger (e.g.: trees). angular and abrasive soil particles.
Most dicotyledonous plants (peas, carrots, “two seed The root cap has no equivalent in stems.
leaves”) have taproot systems The dictyosome (golgi bodies) of root cap’s outer
with one, or occasionally more, cells secrete and release a slimy substance
primary roots from which (mucigel) that lodges in the walls and eventually
secondary roots develop. passes to the outside.
Thick (more volume to absorb The cells, which are replaced from the inside,
water); the growth is more constantly slough off, forming a slimy lubricant that
vertical – goes deeper facilitates the root tip’s movement through the soil.
2. Fibrous root system (adventitious It also provides a medium favorable to the growth of
roots) beneficial bacteria (rhizobium that enters the roots
(Adventitious roots) those that through a root hair called infection thread) that add
do not develop from another root but develop to the nitrogen supplies available to the plant.
instead from a stem, lead or another plant part. Root cap’s cells have an average life of less than a
(Fibrous root system) may have large numbers of week, a new root cap is produced.
fine roots of similar diameter , then develops from
the adventitious roots.
Root cap also functions in the perception of gravity The cells become several times their original length
(amyloplasts, the plastid containing starch grains, and wider.
act as gravity sensors – collecting on the sides of Tiny vacuoles are formed that merge and grow until
root cap cells facing the direction of gravitational one or two large vacuoles, occupying up to 90% or
force) – the root begins to grow downward [again] more of the volume of each cell.
within 30 mins. to few h.; Calcium ions influence the Where most growth of root takes place as the cell
distribution of growth hormones in cells lengthen, the process that actually extends the root
(amyloplasts). farther into the soil.
2. Region of cell division – composed of an apical Only the root cap and apical meristem are pushing
meristem in the center of root tip, producing the through the soil, since no further increase in cell size
surrounding root cp. takes place above the region of elongation.
Inverted cup-shaped zone located a short distance The usually extensive remainder of each root
behind the actual base of the meristem. remains stationary for the life of the plant. If a
Cells divide every 12-36 hrs (usually towards noon & cambium is present, however, there normally is a
midnight). gradual increase in girth through the addition of
Cells are mostly cubical with relatively large, more secondary tissues produced by the cambium.
or less centrally located nuclei and a few very small 4. Region of maturation – cells begin specializing in
vacuoles. structure and function into different cell types, such as
Apical meristem subdivides into three meristematic epidermal cells and conducting cells.
areas: Region of differentiation or root hair zone: region
(a) Protoderm (epidermis): develops from the where most of the cells mature or differentiate into
outside portion various distinctive cell types of primary tissues
(b) Ground meristem (ground tissue, parenchyma Root hair zone (large numbers of hairlike, delicate
cells of the cortex): inside the protoderm protuberances that develop from many of epidermal
(c) Procambium (vascular tissue: xylem & phloem): cells.
solid cylinder in the center of root Root hairs: protuberances (projections) which absorb
Pith: a parenchyma tissue which originates from the water and minerals, adhere slightly to soil particles
ground meristem, is generally present in stems but with the aid of microscopic fibers they produce and
is absent in most dicot roots. (grass roots & greatly increase the total absorptive surface of the
monocots) root.
3. Region of elongation – where the derivatives stop When a seedling or plant is removes, many of the
dividing and begin to grow in length. delicate root hairs are torn off or die within seconds
Merges with the apical meristem, usually extending if exposed to the sun, thereby greatly reducing the
about 1 cm (0.4 in) or less from the tip of root. plant’s capacity to absorb water and minerals in
solution. (this is why plants should be watered,
shaded, and pruned after transplanting until new 2. Pneumatophores – spongy roots which extend above
root hairs have formed). the water’s surface and enhance gas exchange
The life of average root hair is not more than a few between the atmosphere and the subsurface roots to
days, although a few lives for a max. of perhaps which they are connected.
three weeks. - Mangrove, bald cypress tree
The cuticle (epidermis) which may be relatively thick 3. Propagative roots (fruit-bearing) – many plants
on the epidermal cells of stems and leaves, is thin produce adventitious buds (buds appearing in places
enough on the root hairs and epidermal cell of roots other than stems) along the roots that grow near the
in the region of maturation to allow water to be surface of ground. The buds develop into aerial stems
absorbed but still sufficient to protect against are called suckers (shoots up from the roots; produce
invasion by rootlets from primary roots), which have additional
bacteria and rootlets at their bases. Cherries, apples, pears, and
fungi. other fruit trees produce suckers.
In some roots, the 4. Aerial roots – velamen roots (absorb moisture) of
epidermis, cortex, orchids, prop roots of corn and banyan trees,
and endodermis adventitious roots of ivies, and photosynthetic roots of
(regulates the certain orchids are among the various kinds of aerial
flow of substances roots.
between cortex - Often occur in epiphytes, plants that grow on
and vascular other plants for support but nourish themselves
tissue) are 5. Contractile roots – some herbaceous dicots &
sloughed off as monocots have contractile roots that pull the plant
their girth increases, but in those roots where the deeper into the soil. Many lily bulbs are pulled a little
endodermis is retained, the inner walls of the deeper into the soil each year as new sets of
endodermal cells eventually become thickened by contractile roots are developed.
the addition of alternating layers of suberin and wax. - Roots contain minerals; when used up as energy,
Later, cellulose and sometimes lignin are deposited. it contracts
Specialized roots 6. Buttress roots – flared roots that extends from tree
1. Food-storage roots – store large quantities of starch trunks, contributing to stability.
(amyloplasts) and other carbohydrates for extensive - Fig tree: large roots for large tree (specially
growth. (carrots, beets, turnips, and radishes – the f.s. designed for support, not for water)
tissues are usually a combination of root and stem). - Strong hold or support
- Approximately two centimeters at the top of ave. 7. Parasitic roots – contains haustoria which penetrates
carrot is derived from stem tissue that merges the stems and roots of other plants to obtain water,
with root tissue below. minerals and organic molecules
- Sucks out through xylem and phloem - Considered as antioxidant
- Mycorrhizae (fungi) is necessary for phosphate
absorption in plants. It lives in root hairs.
- Saprophytic: host is dead plant
Phytomediation – plants that detoxify soil from metal
poisoning (Au, Ag, Pb, Pt, Hg, Cd, Cs (mining)
Kamoteng kahoy - Manihot esculenta (Euphorbiaceae) –
tapioca plant or cassava
- Leaves: yield saponins, flavonoids, and vitamin C
- Contains cyanoglycoside (toxic) linamarin
Tugi – Dioscorea tugui or Discorea esculenta (Dioscoreaceae) –
lesser/Asiatic/Chinese yam
- World’s best source of steroids
Gabi – Colocasia esculenta (Araceae) – taro, taro potato
- Contains predominant lactobacilli (in amt. greater
than in yogurt)
Kamote – Ipomea batatas (Convulvolaceae) – sweet potato
