Download Plant Growth and Development

Plant Growth and Development
Plant Physiology 3(2-1)
15-02-2012
From germination to senescence!!
Zygote
Embryo
Seedling
How do new plant structures arise from
preexisting structures?
How do plant tissues grow in a particular
pattern?
What are the basic principles that govern plant
growth and development?
Embryogenesis
Sperm+Egg
Zygote
During embryogenesis:
•Single-celled zygote is transformed into multicellular, microscopic plant
(embryo) that has the complete body plan of a mature plant present in a
rudimentary form
•It occurs within the Embryo sac of the ovule
•Ovule and Endosperm are parts of a seed
Wheat
endosperm?
Small
Egg
Surrounds embryo and
provides nutrition in the
form of starch
Angiosperms: Flowering plants whose ovules are produced within ovary and whose seeds
occur within a fruit that develops from the ovary
Gymnosperms: ovules not enclosed in ovary and seeds not enclosed in fruits
Monocots: Embryo with single cotyledons
Dicots: Embryo with two cotyledons
The outline of a mature plant!
Arabidopsis thaliana
Embryogenesis and plant development:
Axial patterning
Radial patterning
Primary meristems
Shoot apical meristem
Cytoplasmic
Large vacuole
Root apical meristem
Axial
Patterning
First division of zygote
Apical cell: receives more cytoplasm
•Divides vertically
•Generates globular (octant) embryo
Basal cell: receives large vacuole
•Horizontal division
•Suspensor cells 6-9 cells that attach
the embryo to the vascular system
•Hypophysis derivative of basal cell
that contributes to embryo
development and forms Columella
(central part of root cap)
Three axial regions develop before the embryo reaches
the Heart stage;
Apical region: gives rise to cotyledons and shoot apical
meristem
Middle Region: gives rise to hypocotyl, root and most of
the root meristem
Hypophysis: gives rise to the rest of root meristem
Radial Patterning
•Visible at Globular Stage
•Radially arranged three regions
•Protoderm:
•Cortex:
•Endodermis:
•Vascular tissues:
•Pericycle:
Primary meristems
Protoderm
Procambium
Ground meristem
Epidermis
Primary vascular
tissues and
vascular cambium
Cortex and
endodermis
Vascular Tissues: The tissue in vascular
plants that circulates fluid and nutrients.
Comprise of;
1- Xylem conducts water and nutrients up
from the roots
2-Phloem distributes food from the leaves
to other parts of the plant
Embryo development in Arabidopsis
Embryo goes
through divisions,
generating an
eight-cell (octant)
embryo after 30
hrs of fertilization
Cell elongation
throughout
embryo axis and
further
development of
cotyledons
Seed Dormancy: growth,
development and
metabolic activities stop..
Why?
Globular
stage
Heart
stage
Cell division in
apical regions that
later form
cotyledons
Torpedo
stage
Maturation
stage
Last stage, embryo
and seed lose
water to enter
dormancy
Seed Dormancy
Arrested plant growth
Survival strategy against different external threats
Controlled by biological clock that tells plant when to
produce soft tissues to survive against harsh winters or other
factros-----Intersting????
When a mature seed is placed under favorable conditions and fails to germinate, it
is said to be dormant. Seed dormancy is referred to as embryo dormancy or
internal dormancy and is caused by endogenous characteristics of the embryo that
prevent germination. The oldest seed that has been germinated into a viable plant
was an approximately 1,300-year-old lotus fruit recovered from a dry lakebed in
northeastern China.
Seed Coat Dormancy: External dormancy or hardseededness, which is caused by
the presence of a hard seed covering or seed coat that prevents water and oxygen
from reaching and activating the embryo. It is a physical barrier to germination, not
a true form of dormancy.
Genes involved in Embryogenesis
Plays role in Axial Patterning
No root and cotyledons
GNOM gene
MONOPTEROS gene
No hypocotyl and root
SHORT ROOT and SCARECROW genes
HOBBIT gene
Both take part in Radial Patterning
Defective root meristem development
SHOOTMERISTEMLESS gene
Mutants fail to form shoot meristem
HOBBIT gene
Columella (COL):
Lateral Root Cap (LRC):
Quiscent Center (QC):
Slowly dividing root
meristematic cells that
regulate the
differentiation of
neighboring cells
Role of HOBBIT gene in root meristem development
•Marker of root meristem identity
•hbt mutant shows abnormality in two- or four-cell stage
•Hypophyseal precursor divides vertically instead of horizontally
•Root without Hypophysis fails to form Quiescent Center and Columella
•Consequently hbt mutants are unable to form lateral roots
Acknowledgement
•Plant Physiology by Taiz and Zeiger
•Wikipedia