Download Lecture 2 Plant growth

TYPE OF PLANT
GROWTH AND
DEVELOPMENT,
MECHANISM OF PLANT
PSF 602S
LECTURER : Zivuku.M
Objectives
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Define the term plant growth
Differentiate between plant growth and plant development
Discuss the functions of leaves
Explain how growth and development occurs in leaves, roots,
stems
WHAT IS PLANT GROWTH?
Plant growth is the process by which a plant increases in the
number ,size and length of leaves, stems, roots and tubers.
WHAT IS PLANT DEVELOPMENT?
Plant development by which plant structures originate
and mature as a plant grows.
LEAVES
STEMS
TYPE OF PLANT
GROWTH AND
DEVELOPMENT
ROOTS
TUBERS
LEAVES
WHAT ARE THE FUNCTIONS OF LEAVES?
Absorb sunlight to manufacture plant sugars through a process
called photosynthesis.
The cuticle is part of the epidermis.
It produces a waxy layer called cutin, which protects the leaf from
dehydration and disease.
Special epidermal cells called guard cells regulate the passage of
water, oxygen, and carbon dioxide into and out of the leaf through
tiny openings called stomata.
The Growth and Development of Leaves
The first leaves to develop are the unifoliolate leaves.
Two of these single leaves appear directly opposite one
another above the cotyledons.
All subsequent leaves are
trifoliolates
comprised of
3 leaflets.
THE GROWTH AND DEVELOPMENT
OF RICE LEAVES
A leaf primordium is differentiated from a little
below the shoot apical meristem (SAM).
 As it develops, it elongates and forms a coneshaped structure around the SAM.
Soon after, smaller veins start to form on both sides
of its base, and later in between larger veins.
When the primordium has grown to about 8 mm, a cavity develops
at its base.
The auricles and the ligule will be differentiated from this location,
which will be differentiated into the collar.
The collar separates the blade and the sheath.
After the cavity has formed, the meristem that is responsible for
elongation is activated and the blade starts to elongate.
Now the blade has grown to its full size, and its cells have stopped
dividing, the blade is ready to emerge.
As the blade emerges, it unrolls from its tip down to the base.
As it unrolls, cells in the blade expand to reach a larger size.
This is why an older leaf is wider and longer that a newly emerged
leaf not because it has more cells, but because its cells have grown
larger.
As soon as the blade starts to expand, the leaf sheath starts to
elongate.
The sheath completes its elongation when the blade has fully
expanded.
ROOTS
WHAT ARE THE FUNCTIONS OF
ROOT
Anchor the plant in the soil.
Store food.
Absorb water and mineral salts

from the soil.
Form a passage way for water and dissolved substances from the
root into the stem and also for foods from the stem down into the
root.
The Growth and Development of Root
Early root growth is one of the functions of the apical
meristem located near the tip of the root.
The meristem cells more or less continuously divide,
producing more meristem, root cap cells and undifferentiated
root cells.
The latter become the primary tissues of the root, first undergoing
elongation, a process that pushes the root tip forward in the
growing medium.
Gradually these cells differentiate and mature into specialized cells
of the root tissues.
Growth from apical meristems is known as primary growth, which
encompasses all elongation.
Secondary growth encompasses all growth in diameter, a major
component of woody plant tissues and many nonwoody plants.
For example, storage roots of sweet potato have secondary growth
but are not woody.
Secondary growth occurs at the lateral meristems, namely the
vascular cambium and cork cambium.
THE GROWTH AND DEVELOPMENT
OF SOYBEN ROOT
As soybean seed takes on the water and
swells, the radical is the first part of embryo to
penetrate the seed coat .
It develops rapidly into a root which must
become firmly anchored for seedling to
develop enough leverage to force its way to
the soil surface.
Lateral roots are formed soon after the radical or primary
root begins to elongate.
Root hair appear on the primary root within 4 or 5 days after
germination and on the lateral roots soon after they are
formed .
These hair are the main absorbing surface of the root system.
They are very small nearly invisible without a lens and might
be extensions of single epidermal cells.
They are actively growing part of the root just behind the
growing point.
What condition did root grow?
Roots will generally grow in any direction where the correct
environment of air, mineral nutrients and water exists to
meet the plant's needs.
Roots will not grow in dry soil.
At germination, roots grow downward due to gravitropism.
STEM
What are the functions of stem ?
 serves as mechanical support for leaves and buds.
 Water and food storage.
 Reproduction
 Photosynthesis
 New growth
Types of growth and
development
in
stem
Primary stem growth :o begins at the tip of the terminal bud in the area called the apical
meristem.
o The cell divisions on the apical meristem are responsible for the
stem's growth in length.
Secondary stem growth :o Also known as secondary thickening or lateral growth arises
from secondary meristems.
o Secondary xylem and secondary phloem are formed.
o Stems are tend to thickening.
o Cambium is developed at the outer part of the stem.
o More stronger than primary stem.
Stem terminology
Shoot
(a young stem [1 years old or
less] with leaves)
twig (A young stem [1 year old or less] that
is in the dormant winter stage with
no leaves.)
branch (A stem that is more than 1 year old,
typically with lateral stems radiating from
it)
trunk
(A woody plant's main stem)
Types of stems:
Specialize above ground stems:
o Crowns ( strawberries)
o Spurs (apple, cherry trees)
o Stolons ( strawberry runners)
Specialized below-ground stems
o Rhizome
o Bulb
 Tunicate - thin, papery covering; protection to the bulb from damaging and
drying during digged out from the soil.
 Nontunicate – do not have papery cover.
o Corm
o Tuberous stem
What are the functions of tubers?
 food storage
reproduction
Types of growth and
development in tubers
Stem tubers
 are formed from the thickening of rhizomes or stolons.
Exp:- potato tubers are developed from thickened stolons or
known as propagation.
Root tubers
Enlargement of modified lateral roots and budding.
Types of tubers:
There are 2 types of tubers:
i.
Stem tubers
ii.
Root tubers
MECHANISM OF
GROWTH
MECHANISM OF GROWTH
• Seed germination
• Photosynthesis
• Plant hormones
MECHANISM OF GROWTH
SEED GERMINATION
• Germination is the process in which a plant or fungus
emerges from a seed or spore and begins growth.
• example of germination is the sprouting of a seedling from a
seed of an angiosperm or gymnosperm.
• of a sporeling from a spore, for example the growth of hyphae
from fungal spores, is also germination.
MECHANISM OF GROWTH
PHOTOSYNTHESIS
• a process that converts carbon dioxide into organic
compounds, especially sugars, using the energy from sunlight.
• the process always begins when energy from light is absorbed
by proteins called photosynthetic reaction centers that contain
chlorophylls.
MECHANISM OF GROWTH
also known as plant growth regulators (PGRs) or phytohormones,
are chemicals that regulate plant growth.
Plant hormones are often not transported to other parts of the
plant and production is not limited to specific locations.
occur in extremely low concentrations
Plants lack glands that produce and secrete hormones, instead
each cell is capable of producing hormones.
affect gene expression and transcription levels, cellular division,
and growth.
Auxin (IAA)
Cytokinins
Gibberellins
Brassinosteroids
Abscisic Acid (ABA)
Ethylene
Auxin (IAA)
are class of plant growth substance and morphology (often
called phytohormone or plant hormone)
On the molecular level, auxins have an aromatic ring and a
carboxylic acid group
Function:
Primary site of synthesis in shoot apical meristem and young
leaves.
influence cell enlargement, bud formation and root initiation.
in conjunction with cytokinins, they control the growth of stems,
roots, and fruits, and convert stems into flowers.
Stimulate stem elongation and promotes the formation of lateral
and adventitious roots.
Regulates development of fruit.
Cytokinins
Synthesized primarily in the roots and transported to other organs.
-promote cell division and organ development, but impede
senescence.
influence cell division and shoot formation.
Modify apical dominance and promote lateral bud growth.
Promote movement of nutrients into sink tissues.
Stimulate seed germination.
Delay leaf senescence.
Gibberellins
Site for production in meristems of apical buds and roots, young
leaves and developing seeds.
Stimulates stem elongation, pollen development, pollen tube
growth, fruit growth, and seed development and germination.
Regulate sex determination and the transition from juvenile to
adult phases.
control cell expansion,
Brassinosteroids
Present in all plant tissue at different intermediates predominate in
different organs.
Promotes cell expansion and cell division in shoot, at low
concentration promote root growth.
Promote xylem differentiation but inhibit phloem differentiation.
Promote seed germination and pollen tube elongation.
Abscisic Acid (ABA)
Almost all plant cell can synthesize ABA.
Inhibit growth.
Promotes stomatal closure during drought stress.
Promotes seed dormancy and inhibit early germination.
Promotes leaf senescence and desiccation tolerence.
Ethylene
Can be produce by almost all plant parts.
Promotes ripening of many types of fruit, leaf abscission and the
triple response in seedlings (inhibition of stem elongation,
promotion of lateral expansion and horizontal growth).
Enhances the rate of senescence.
Promotes root and root hair formation.
LEAF
SENESCENCE
LEAF ABSCISSION
DESICCATION TOLERENCE