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BLGY1115
Plant cell & tissue
biology
Prof. Paul Knox
[email protected]
Books
• BIOLOGY
Campbell et al., 10th Global edition,
Pearson Publishers
• Chapter 35 (p 816).
Plant Structure & Growth
Also Chapters 36-39
Plants………...
major source of
biomass on Earth …..
a source of food………..
…….. and drink!
• Special features of plant growth &
development
• Embryogenesis. Meristems
• Primary and secondary growth.
Wood formation
• Plant cell walls
• Plant tissues and cell types
• Plasticity and plant development
Plants are complex multi-cellular organisms
Distinctive features of
plant development
• Post-embryonic development
• Plant cells do not migrate
• Plant cells are totipotent &
have developmental plasticity
Post-embryonic
development
• The plant embryo has a simplified body plan
• Most of the plant body is produced postembryonically by the activity of meristems
• Morphogenesis occurs continuously
throughout the life of a plant
• Plants can respond to the environment
with changes in growth and development
Development of a
human embryo
Late stage
plant embryo
future SAM
future RAM
SAM – shoot apical meristem
RAM – root apical meristem
Plant cells cannot migrate because of the cell wall
• The relative positions of cells in the
plant body is always important
• Cellular processes must be highly
co-ordinated in both space and time
• CELL DIVISION: timing and orientation
• CELL EXPANSION: extent and direction
• CELL DIFFERENTIATION: spatial relationships
of cell types important
The plant kingdom & plant diversity
• The flowering plants (Angiosperms) are
an extremely widespread, successful &
diverse group of organsims
• They are structurally the most complex
plants & have evolved from structurally less
complex plants
• The table shows a summary of the major
extant groups of the plant kingdom
Division/Class
# species
Angiosperms
300,000
65,000
Gymnosperms
Seed
Conifers
Cycads
Ginkgo
Ferns (Pteridophytes)
Horsetails & club mosses
Mosses & liverworts
550
100
1
12,000
1,000
16,000
Seedless
(Bryophytes)
Green algae
Red algae
Brown algae
7,000
4,000
1,500
Algae
Vascular
Dicotyledons
Monocotyledons
Nonvasc.
Dicotyledon leaf
Monocotyledon
leaves
Monocots & Dicots
Characteristic
DICOTYLEDONS
MONOCOTYLEDONS
• Number of cotyledons
Two
One
• Leaf structure
Petiole
Sheath
• Leaf venation
Network
Parallel
• Stem vascular bundles
Circular pattern Scattered
• Root system
Tap root
Fibrous
• Root protoxylem poles
Small number
Large number
• Secondary growth
Present
Absent
• Adventitious roots
Absent
Present
• Flower parts
Multiples of 2 or 5
Multiples of 3
Arabidopsis
thaliana
Thale cress
Arabidopsis
• Arabidopsis thaliana
• Angiosperm belonging to the
cabbage/mustard family Brassicaceae
• A very important plant in
modern plant biology
• It has become the preeminent
model system for plant
molecular genetics and the
study of the mechanisms of
growth and development
Arabidopsis
• It is small enough to be grown in sterile
containers in the lab.
• Prolific seed production
• Has a short life cycle (c. 6 - 8 weeks)
• Easy transformation (introduction of DNA)
• It has a small genome (115 Mb DNA - 5
chromosomes)
• Large numbers of mutant lines - available
from stock centers
• Arabidopsis - first plant
genome to be fully
sequenced (2000) in a
programme comparable to
the human genome
sequencing project
• Indicating that it has c.
25,000 genes
• Arabidopsis has
considerable genetic
resources/stock centres to
support its study.
Development of
plant structures
Embryogenesis
Embryogenesis
• Fertilisation of the egg cell induces cell
divisions, cell expansions and cell
differentiation resulting in the formation of
an embryo
• Development of three tissue systems &
the root and shoot apical meristems
• Highly regulated cell processes leading to
defined cell patterns
Dicotyledon embryogenesis
Egg
proembryo
suspensor
zygote
Further precisely
determined divisions
Protoderm is now defined
- anticlinal divisions
Globular stage
embryo
suspensor
cotyledons forming
Heart-shaped
stage embryo
procambium
future shoot apical meristem
Mature
embryo
future root apical meristem
Monocot embryo development
• Similar to dicot - a single cell zygote
develops into a multicellular embryo
• One cotyledon (scutellum)- a notch forms at
globular stage and embryonic axis forms at
one side
• Meristems more developed
• Shoot meristem enclosed in a sheath coleoptile
• Several root meristems may form directly in
embryo
Embryo sac
Embryogenesis
in context of
developing
seeds
Endosperm nucleus
Zygote
Endosperm
Cotyledon
Pea
Seed coat
(testa)
Carrot
Flowering plant
(Angiosperm)
life cycle
Double
fertilisation
event
What is known of the cellular &
molecular mechanisms that
underpin development events?
Plant embryogenesis initiates with the
establishment of an apical-basal axis
Molecular mechanisms of this event
unclear.
Recent work has shown that a small
cysteine-rich peptide is required for
formation of the zygotic basal cell lineage
and proembryo patterning in Arabidopsis.
Peptides accumulate before
fertilization in central cell gametes and
thereafter in the endosperm cells.
Costa et al. (2014) Science 344, 168-172
Seed germination
Grass sprouting on left
(a monocot), showing
hypogeal germination
(the cotyledon remains
underground and is not visible)
Compare to a dicot (right)
with epigeal germination
Two common types
of seed germination
Fig. 38-9
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
Foliage leaves
Coleoptile
Coleoptile
Radicle
(b) Maize
3 tissue systems
• Protoderm  dermal tissue
– EPIDERMIS
• Procambium  vascular tissues
– XYLEM, PHLOEM
• in between
ground (or fundamental) tissues
– PITH, CORTEX PARENCHYMA
Three tissue systems set up in the embryo
are elaborated into distinct spatial
arrangements by the activity of meristems
DERMAL
VASCULAR
GROUND
Root
Shoot
Leaf
Development of
plant structures
Meristems
• Meristem development is different
to embryogenesis
• Embryogenesis: whole group of
cells undergoes changes in form
e.g. transition from globular to
heart-shaped embryo
• Meristem: a set of cells undergoing
repetitive processes
–iterative development
• Meristems: regions of plants that
remain embryonic with the capacity to
produce new cells
• Cells that are continually dividing and
adding to the population of cells are
known as initials
• When an initial divides the two daughter
cells have differing fates:
– One cell: divides again
– One cell: differentiates
• In this way an initial can produce a
file of cells
– a line of attached cells
• As a cell moves relatively further
away from an initial it differentiates
The development of a file of cells
x
x
x
Meristem
initial
x
x
x
x
x
The basis of
meristem
activity
Cell that leaves
meristem and
differentiates
• Most of the plant body is produced by
the iterative activity of meristems
• Meristems are complex with 50 to 100
initials. (Ferns have one initial cell)
• Meristem activity can be
– determinate: limited development to give
rise to a specific structure e.g. flower - has
an endpoint
– indeterminate: continuous production of
organs e.g. leaves - no developmental
endpoint
In plants, a meristem gives rise to all cell
types - no separate stem cells for each
cell type
Root and shoot apical meristems have
very different structures: different spatial
organisations of cell divisions and
expansions
Meristems develop from embryos
.
SAM – shoot apical meristem
RAM – root apical meristem
SAM
RAM
These are not the only meristems: during development
new meristems arise in shoot and root structures