chapter 36 vegetative plant development
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Chapter 36 Vegetative plant development. 36.1. Plant Embryo Development Establishes a Basic Body Plan. 36.1 – establishing the root-shoot axis. In plants, 3D shape and form arise by regulating the amount and pattern of cell division - PowerPoint PPT PresentationTRANSCRIPT
CHAPTER 36 VEGETATIVE PLANT
DEVELOPMENT
36.1Plant Embryo Development Establishes a Basic Body Plan
36.1 – establishing the root-shoot axis
In plants, 3D shape and form arise by regulating the amount and pattern of cell division
As plant development proceeds, cells with multiple potentials are mainly restricted to meristem regions
Meristem – tissue in all plants consisting of undifferentiated cells Many meristems have been established by the time embryogenesis
ends and the seed becomes dormant Apical meristems establish the root shoot axis 3 basic tissue systems are established: dermal, ground, and
vascular While the embryo is developing, a food supply that will support the
embryo during germination is established, and ovule tissue differentiates to form a hard, protective covering around the embryo
Seed enters dormant phase, signaling the end of embryogenesis
36.1 – establishing the root-shoot axis – early cell division and patterning
The 1st division of the zygote in a flowering plant generates cells with 2 different fates: Daughter cell is small
with dense cytoplasm and becomes an embryo
Daughter cell is larger, forms elongated structure called a suspensor – links the embryo to the nutrient tissue of the seed
36.1 – establishing the root-shoot axis – early cell division and patterning
Investigating mechanisms for establishing asymmetry in plant embryo development is difficult. One approach has been to use fucus as a model system
Genetic approaches make it possible to explore asymmetric development in angiosperms and to study mutants
36.1 – Establishing 3 Tissue Systems
3 tissues differentiate while the plant embryo is still in the globular stage (b)
Dermal tissue Produces cells that protect the
plant from desiccation Formed from photoderm
Ground tissue Function in food and water
storage Formed from a ground meristem
Vascular tissue Responsible for water and
nutrient transport Formed from procambium
36.1 – Establishing 3 tissue systems – root and shoot formation
Root-shoot axis is established during the globular stage
Both the shoot and the root meristems are apical meristems but their formation is controlled independently
36.1 – establishing 3 tissue systems - morphogenesis
Globular stage gives rise to a heart-shaped embryo with 2 bulges – dicots and monocots These bulges are cotyledons Produced by embryonic cells Process is called morphogenesis
The position of the cell plate determines the direction of division
Microtubules guide cellulose deposition as the cell wall forms around the outside of a new cell Determines the cell’s final shape
36.1 – establishing 3 tissue systems – food storage
Throughout embryogenesis, starch, lipids, and proteins are produced
The sporophyte transfers nutrient via the suspensor in angiosperms
Seeds have stored nutrients to aid in germination until the growing sporophyte can photosynthesize
36.2The seed protects the dormant embryo form water loss
36.2 – how seeds form Development of the embryo is stopped
soon after the meristems and cotyledons differentiate
The integuments (outer cell layers of the ovule) develop into a seed coat which ecloses the seed with its dormant embryo and stored food
36.2 – how seeds form – adaptive importance of seeds
Seeds are important adaptively in 4 ways: Seeds maintain dormancy under unfavorable
conditions and postpone development until better conditions arise
Seeds afford maximum protection to the young plant at its most vulnerable stage of development
Seeds contain stored food that permits a young plant to develop before photosynthetic activity begins
Seeds are adapted for dispersal, facilitating the migration of plant genotypes into new habitats
36.3Fruit formation enhances the dispersal of seeds
36.3 – how fruits form Fruits that contain seeds are defined as
mature ovaries Fruits form in many ways and exhibit a
wide array of adaptations for dispersal 3 layers of ovary wall can have distinct
fates, which account for the diversity of fruit types
Fruits contain 3 genotypes in one package
36.3 – how fruits form – the dispersal of fruits
Fruits exhibit a wide array of specialized dispersal methods Fruits with fleshy coverings normally are
dispersed by birds or other vertebrates Fruits with hooked spines are often
disseminated by mammals Other fruits such as maples have wings that
aid in their distribution by the wind Coconuts and other beach plants are regularly
spread throughout a region either by water or African swallow
36.4Germination initiates post-seed development
36.4 – mechanisms of germination
Germination – the emergence of the radicle (first root) through the seed coat The sporophyte pushes through the seed coat, root grows
down, shoot grows up The shoot becomes photosynthetic and the postembryonic
phase of growth and development begins Germination begins when a seed absorbs water and its
metabolism resumes Many seeds will not germinate unless they have been
stratified – held for periods of time at low temperatures Germination can occur over a wide temperature range (5
to 30 degrees celcius) In some species, a significant fraction of a season’s
seeds remain dormant
36.4 – mechanisms of germination - utilization of reserves
Germination requires the utilization of metabolic reserves stored in the starch grains of amyloplasts (colorless plastids that store starch) and protein bodies
Fats and oils produce glycerol and fatty acids which yield energy through cellular respiration
Embryo produces gibberellic acid, a hormone, that signals the outer later of the endosperm called the aleurone to produce amylase Enzyme breaks down the endospermic starch into sugars
Abscisic acid, another hormone, can inhibit starch breakdown Emergence of the embryonic root and shoot from the seed
during germination varies widely In most plants, the root emerges before the shoot appears and
anchors the young seedling in the soil
Shoot development for (a) a eudicot, the common bean and (b) a monocot, corn
Hormonal regulation of seedling growth