plant cell & tissue biology - biologicalsciences.leeds.ac.uk

BLGY1115

Prof. Paul Knox

j.p.knox@leeds.ac.uk

Plant cell & tissue

biology

Books

• BIOLOGY

Campbell et al., 10th Global edition,

Pearson Publishers

• Chapter 35 (p 816).

Plant Structure & Growth

Also Chapters 36-39

a source of food………..

…….. and drink!

Plants………...

major source of

biomass on Earth …..

• 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 post-

embryonically 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

Angiosperms Dicotyledons

Monocotyledons

Gymnosperms Conifers

Cycads

Ginkgo

Ferns (Pteridophytes)

Horsetails & club mosses

Mosses & liverworts (Bryophytes)

Green algae

Red algae

Brown algae

# species

300,000

65,000

550

100

1

12,000

1,000

16,000

7,000

4,000

1,500

Seed

Seedless

Algae

Vascula

r

Non-

vasc.

Dicotyledon leaf Monocotyledon

leaves

Monocots & Dicots

• 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

Characteristic DICOTYLEDONS MONOCOTYLEDONS

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 zygote

proembryo

suspensor

Protoderm is now defined

- anticlinal divisions

Globular stage

embryo

Further precisely

determined divisions

suspensor

Heart-shaped

stage embryo

procambium

cotyledons forming

Mature

embryo

future shoot apical meristem

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

Zygote

Endosperm nucleus

Seed coat

(testa)

Endosperm

Cotyledon

Pea

Carrot

Embryogenesis

in context of

developing

seeds

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

Fig. 38-9 Two common types

of seed germination

(a) Common garden bean

Seed coat

Radicle

Hypocotyl

Hypocotyl

Cotyledon

Cotyledon

Cotyledon

Hypocotyl

Epicotyl

Foliage leaves

(b) Maize

Radicle

Foliage leaves

Coleoptile Coleoptile

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

GROUND

VASCULAR

Leaf

Shoot Root

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

x x

x x

x

Meristem

initial

Cell that leaves

meristem and

differentiates

The basis of

meristem

activity

• 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

RAM

SAM – shoot apical meristem

RAM – root apical meristem

These are not the only meristems: during development

new meristems arise in shoot and root structures