Lecture 25 - Plant Growth & Development (part 2) Flashcards
What does secondary growth do?
increases the diameter of a plant
Secondary growth
increases the plants girth (diameter) through the activity of lateral meristems
Where does secondary growth occur in?
- Occurs in all Gymnosperms, most Eudicots and a select few Monocot species
- Occurs in roots and shoots, never leaves
Secondary growth occurs simultaneously with…
primary growth in woody plants
What does primary growth & secondary growth do?
• Primary growth adds leaves, increases height
• Secondary growth increases girth in the older regions
- increases the diameter of a plant
Primary Growth (process)
- Apical cells in the root/shoot tips are undifferentiated
- When they divide, some daughter cells will remain in the meristematic region
- Other daughter cells become partially differentiated into primary meristem cells (protoderm, ground, procambium)
- Daughter cells from those will differentiate into cells in mature tissues
What is the direction of primary growth?
vertical, downward
What is the direction of vascular cambium secondary growth?
both directions
What are the 2 lateral meristems of secondary growth?
- vascular cambium
- cork cambium
What happens at the very beginning of secondary growth?
Primary growth from the activity of the apical meristem is nearing completion and the vascular cambium has just formed
Where does primary growth continue?
in the apical bud
Where does secondary growth occur?
along the vascular cambium
What do some of the initials of the vascular cambium give rise to?
vascular rays
What are vascular rays?
files of parenchyma cells that CONNECT secondary xylem and phloem & TRANSPORTS water B/T them
- aids in wound repair, and stores carbohydrates
What do vascular rays aid in?
aids in wound repair, and stores carbohydrates
What happens when girth increases the first time?
secondary phloem can’t keep up with filling in the gaps
- Eventually the epidermis ruptures and falls off
- A cork cambium develops from the cortex parenchyma cells, producing cork cells
• Cork will replace the epidermis
Where does the cork cambium develop from?
develops from the cortex parenchyma cells
What does the cork cambium produce?
cork cells
What does cork replace?
the epidermis
What happens in year 2 of secondary growth?
the vascular cambium produces more secondary xylem and phloem
- The cork cambium produces more cork cells
What happens when girth increases the second time?
the outermost cork cells get sloughed off (just like the epidermis did)
What happens if cork cambium is lost during secondary growth?
another one will form deeper in the cortex tissue to make more cork cells
What happens if the cortex is eventually sloughed off?
the cork cambium will arise from the secondary phloem tissue
What forms a layer of periderm?
Each cork cambium and the tissues is produces (cork)
What is bark composed of?
all the tissues exterior to the vascular cambium
What does the vascular cambium produce?
secondary xylem and secondary phloem
What appears as a ring of meristematic cells?
- Secondary xylem
* Secondary phloem
Secondary xylem
towards INSIDE of stem/root
What is secondary xylem composed of?
tracheids, vessel elements, fibres
Secondary phloem
towards OUTSIDE of stem/root
What is secondary phloem composed of?
Still composed of sieve-tube elements and companion cells
What does secondary growth colloquially produce?
“wood”
What are the 2 types of “wood”?
- Early wood
* Late wood
Early wood
spring wood, xylem cells are large, with thin walls
Late wood
summer wood, xylem cells smaller, thicker cell walls
Growth ring
can be seen between the previous year’s late wood and the new year’s early wood
What are the 2 types of growth rings?
- Thick rings
* Thin rings
Thick rings
= warms years, good climate
Thin rings
= less favourable climate
What happens as secondary xylem becomes older?
it loses its transport function
What are the 2 types of secondary xylem?
- Heartwood
* Sapwood
Heartwood
innermost secondary xylem, darker
Sapwood
outmost (younger) secondary xylem, still does transport of water
What does the epidermis get replaced by?
Gets replaced by the periderm
What is the periderm composed of?
Composed of the cork cambium + cork cells
Bark =
periderm + secondary phloem
What happens if you remove a ring of bark from a tree?
the plant will die since it cannot transport photosynthates from the shoot to the root
Lenticels
allow for gas exchange in the stems that have secondary growth
What are the 3 Primary Meristems?
- Protoderm
- Procambium
- Ground Meristem
What are the 4 Primary Tissues?
- Epidermis
- Primary Phloem
- Primary Xylem
- Ground Tissue (Pith, Cortex)
What does Ground Tissue include?
Pith & Cortex
What are the 2 Lateral Meristems?
- Vascular Cambium
2. Cork Cambium
What are 3 Secondary Tissues?
- Secondary Phloem
- Secondary Xylem
- Cork
What makes up periderm?
Cork Cambium & Cork
What are apart of Dermal Meristem/Tissue?
- Protoderm
- Epidermis
- Cork Cambium
- Cork
- Periderm
What is apart of Ground Meristem/Tissue?
- Ground Meristem
- Ground Tissue (Pith, Cortex)
What is apart of Vascular Meristem/Tissue?
- Procambium
- Primary Phloem & Xylem
- Vascular Cambium
- Secondary Phloem & Xylem
What does development of the plant body include?
the production of cells from meristems, forming tissues, to forming organs
Genetically controlled
one genotype can result in many phenotypes depending on different environments
What is an example of genetically controlled?
Ex. Cabomba caroliniana forms two leaf types depending if it submerged or on the surface of water
What are the 3 stages of development in the plant body?
1) Growth
2) Morphogenesis
3) Differentiation
Describe the growth stage of the plant body development
irreversible change in size
Describe the morphogenesis stage of plant body development
gives tissues, organs, bodies their shape and cell positions
Describe the differentiation stage of plant body development
cells become different from one another
Arabidopsis thaliana
is a plant model organism
• It is small, reproduces quickly, produces lots of seeds
• It has a relatively small genome (27,000 protein-coding genes), with 5 chromosomes
• Wide range of habitat types
• Result in different phenotypes, which can be studied
What does flowering do?
shifts the plant from vegetative growth to reproductive growth
Meristem identity genes
regulates floral formation when on
What is genetic control of flowering trigged by?
- Environment (light, temperature)
* Hormones
What is the ABC model of flower formation?
- A genes -> outer 2 whorls
- B genes -> middle 2 whorls
- C genes -> inner 2 whorls
Sepals =
A
Petals =
A + B
Stamens =
B + C
Carpels =
C
