Lecture 11- Plant growth Flashcards
What are nutrients?
The major ingredients for macromolecules: hydrogen, oxygen, carbon, nitrogen
How does carbon enter the living world?
Photosynthesis using carbon dioxide from the air
How does hydrogen and oxygen enter plants?
Mainly as water
What mineral nutrients do plants need?
Phosphorus, magnesium, iron, sulfur
Where are mineral nutrients found?
In soil solution
What is phosphorus used for in plants?
Used in nucleic acids, ATP, phospholipids
What is sulfur used for in plants?
Proteins, coenzymes
What is magnesium used in within plants?
Chlorophll, ribosomes, enzymes
What is iron used in within plants?
Chromocytes, chlorophyll synthesis
In what form do plants take up mineral nutrients from the soil?
Iron form
What are autotrophs?
Organisms that make their own organic compounds from simple inorganic compounds
How do microenvironments direct a plants growth?
Encourages or discourages proliferation of a root system to direct plant growth
How do plants obtain more nutrients given that they are sessile?
Growth: extension of root system to mine new sources of mineral nutrients and water
Leaves and stem growth provides more oxygen and carbon
What happens to the roots of a plant as they grow?
They encounter a variable environment
What effect may animal droppings have on a plants roots?
Local high concentration of nitrogen
What may cause a tiny alkaline area?
Calcium carbonate particles in the soil
How does dead organic matter change the soil for a root?
Makes the area acidic
With the exception of nitrogen, where are mineral elements required by plants derived from?
Rocks
What is the criterion for calling something an essential element?
It is required for the plant to complete its life cycle (cannot be replaced)
What concentration of macronutrients is required?
1g per kg dry matter
What concentration of micronutrients is required?
less than 100milligrams per kg of dry matter
What is plant development?
The series of progressive changes that take place throughout its life
What are the 4 factors that regulate plant growth?
- Environmental cues
- Hormones (mediate environmental cues)
- Receptors (sense environmental cues)
- Genome (enzymes for development)
What plant is used as a model organism?
Arabidopsis thaliana- a weed in the Mustard family
Why is Arabidopsis thaliana a good model organism?
- Small genome
- Small body and seeds
- Flowers and seeds quickly
- Genes can be inserted or deleted
What are hormones?
Regulatory compounds that act at low concentrations, often at sites distant to where they were produced
What is the difference between hormones in plants and in animals?
In plants, many different cell types produce hormones
What other molecules are involved in plant development?
Photoreceptors (pigment molecules associated with proteins)
By what mechanism does light effect the development of a plant?
Light act on photoreceptors which regulate the processes of development
What determines the limit of a plants development?
The plant’s genome
What is a signal transduction pathway?
A sequence of biochemical reactions by which a cell generates a response to a stimulus
What amplifies a response to signals in plants?
Protein kinase (molecules which modifies mostly proteins by mostly phosphorylation)
What does it mean for a seed to be dormant?
Developmental activity is suspended (does not divide, expand or differentiate)
What does it mean for a seed to germinate?
To develop into a seedling
How does a germinating plant obtain nutrition?
Monomers are obtained by digesting polysaccharides, fat and proteins stored in the seed
How do some plants mobilize the reserves of nutrients in the seed?
Using hormones
When is germination complete?
When the radicle (embryonic root) emerges from the seed coat
What is the seed called after germination?
Seedling
How is development controlled after a seed germinates underground?
A series of photoreceptors
What is flowering?
The formation of reproductive organs
Describe early root development in monocots (such as corn)
Coleoptile projects from early shoot as it grows to the soil surface
What is the first step in seed germination?
Imbibition (uptake of water) due to differences in water potential- can exert tremendous force
What metabolic changes occur as a seed uptakes water?
enzymes are activated, RNA and proteins are synthesised, cellular respiration increases, metabolic pathways are activated
In many seeds, what is growth the result of?
Expansion of small, preformed cells (cell division does not occur during early stages of germination)
DNA synthesis occurs after the radicle ruptures the seed coat.
How does an embryo obtain nutrition?
Uses the reserves of energy/raw material stored in the seed coat
Where are nutrition and energy reserves found within an embryonic plant?
Cotyledon and endosperm (specialised nutritive tissue)
What is the typical activity of the hormone abscisic acid in plants?
Maintains seed dormancy and winter dormancy, closes stomata
What is the typical activity of auxins in plants?
Promote stem elongation, adventitious root initiation, fruit growth
Inhibit auxillary bud outgrowth
What is the typical activity of cytokinins in plants?
Inhibit leaf senescence, promote cell division and auxillary bud outgrowth, affect root growth
When is formation of reproductive organs initiated?
Flower formation begins when a plant reaches a certain size
How do some plants flower at certain times of the year?
They distinguish between seasons
How do plants distinguish between seasons?
Photoreceptors absorb light to measure time
Hormones trigger flowering
What are perennials? Give some examples.
Plants that continue to grow year after year, such as iris and elm
What are annuals? Give some examples.
Plants which complete their life cycle in one year, then senesce and die. For example, petunia and marigold
What does senesce mean?
Deterioration due to ageing
What causes senescence?
Signals from the environment causes hormones such as ethylene to begin senescence
Why does senescence occur?
Adaptation for producing more offspring
Other than in annuals, where is senescence seen?
Perennials leaves at the end of the growing season- regulated by ethylene and auxin
When might seeds remain dormant?
- During unfavorable years
- Not before a certain period of time
- Not unless in specific environments
What environments might cause a seed to germinate?
Digestive tracts, abrasive surfaces, soil microorganisms, fire, leaching
Before a plant can photosynthesis, where does it obtain nutrition?
Food reserves in the cotyledon or endosperm
What is the endosperm?
Tissue that surrounds the embryo
How do angiosperms reproduce?
Sexually and asexually
What is the advantage of sexual reproduction?
Genetic recombination gives diverse phenotypes
What type of angiosperm reproduction is important in agriculture?
Both sexual and asexual
What crops come from sexual reproduction?
-Annual crops grown from seeds:
Grains (wheat, rice, corn)
Soybeans
What crops come from asexual reproduction?
Navel oranges, strawberries
How did Navel oranges arise?
- Single Brazilian Navel orange tree
- Seedless
- Propagated asexually
- Aberrant flowers- part aborts and results in seedless fruit
Why are strawberries propagated asexually?
They are highly heterozygous/ not true breeding
Propagated asexually to ensure desirable genotype
What are the 4 groups of organs and what are they derived from?
Derived from modified leaves
- Carpels
- Stamens
- Petals
- Stepals
What are the female and male sex organs?
Carpels- female
Stamen- male (staMEN- men are male)
What is a pistil?
A structure composed of one or more carpels
What is the base of the pistil called?
The ovary
What does the ovary contain?
One or more ovules
What do ovules contain?
A megasporangium- in which, the female gametophyte may develop.
What is in the stamen?
A filaments with a two-lobed anther
What does the anther consist of?
4 microsporangia fused together
Where do male gametophytes begin their development?
Within the microsporangia.
How are petals and sepals arranged?
Whorls (circles) or spirals around the carpels and stamens
What do the petals constitute?
The corolla
What do the sepals constitute?
The calyx
What do all the flower parts attach to?
The stem tip called the receptacle
What is alternation of generations in flowering plants?
Multicellular diploid generation alternates with multicellular haploid generation
In angiosperms, which generation is the larger, more conspicuous one?
The diploid sporophyte generation
Which generations produces flowers?
Diploid sporophyte generation
What produces haploid spores?
The flowers of the diploid sporophyte generation
What is produced in the megasporangia?
Megagametophytes (female gametophytes) called embryo sacs
What is produced in the microsporgangia?
Microgametophytes (male gametophytes) called pollen grains
What happens within the megasporangium inside the ovule to produce megaspores?
The megasporocyte divides meiotically to produce 4 haploid megaspores
What happens after 4 megaspores have been produced/
?
All but 1 degenerate
What happens to the surviving megaspore?
It undergoes three mitotic divisions to produce 8 haploid nuclei contained within a single cell- 3 nuclei at one end, 3 at the other and 2 in the middle
What happens after the megaspore contains 8 nuclei in one cell?
Each develops a cell wall to make an eliptical, 8 celled megametophyte with 8 nuclei
What is at the end of the megagametophyte?
Three cells- egg and 2 synergids
What do synergids do?
Attract the pollen tube and receive the sperm nuclei
What is at the opposite end of the megagametophyte?
3 antipodal cells which degenerate
What is in the central cell of the megagametophyte?
Two polar nulcei which combine with one sperm nucleus
What is the embryo sac?
The entire megagametophyte structure
How does the microsporocyte developing into the microgametophyte within the anther?
The microsporocyte undergoes meiosis to produce 4 haploid microspores
Each microspore develops a cell wall and divides by mitosis to form two haploid cells in each pollen grain (microgametophyte)
What are the two cells that make up the microgametophyte?
The generative cells and the tube cell
What is pollination?
The transfer of pollen from anther to stigma
How is self-pollination achieved in some plants?
Pollination occurs before the flower opens, such as in peas
What is cross-pollination?
When pollen is transferred to a different individual
What are common ways pollen is transported?
Wind, water, animals (insects, birds, bats)
What are some characteristic features in plants that are wind pollinated?
- Sticky or feather-like stigmas
- Many pollen grains
What is self-incompatibility?
When plants reject pollen from their own flowers
Why do some plants have self-incompatibility?
To promote out-crossing between different genotypes
What gene is responsible for self-incompatibility?
The S gene
How does the S gene determine compatibility?
If the S allele in pollen matches the S allele in the pistil, the pollen grain fails to grow
What does the pollen tube do?
Deliver sperm cells to the embryo sac
What is germination of a pollen grain?
The development of a pollen tube after a pollen grain lands on the stigma of a compatible pistil
Why does pollen from other species not lead to germination?
Cell-cell signaling between pollen and stigma from the same species binds the pollen to the stigma
Foreign pollen drops off or fails to germinate
In what ways does the pollen tube grow?
Grows through the style to reach the ovule
How is downward growth of the pollen tube guided?
By chemical signals released by the synergids
What happens after the pollen tube grows through the megasprogangium and reaches the embryo sac?
The generative cell undergoes one mitotic division to produce two haploid sperm cells
What happens after two haploid sperm cells are produced?
Both sperm enter the synergid which degenerates and releases the sperm cells- one fertilises the egg to form a zygote, the other unites with the polar nuclei to form a triploid nucleus
What happens after the sperm fuses with the egg cell?
The diploid zygote divides mitotically to produce the sporocyte embryo
What does the triploid nucleus do next?
Divides by mitosis to form the nutritive endosperm
What is the result of the first mitotic division of the zygote?
Asymmetric division of the cytoplasm
What happens to the asymmetric zygote?
One daughter cell becomes the embryo, the other becomes a supporting structure called the suspensor
What does the suspensor do?
Pushes the embryo against the endosperm to provide route for nutrients
What does the embryo develop into in eudicots?
A heart stage as the cotyledons begin to form
What happens to a eudicot embryo after the heart stage?
Further elongation leads to torpedo stage
What is the structure of a eudicot embryo?
Shoot apex forms between cotyledons
Root apex forms from other end
Both contain meristematic cells
What can happen in later stages of embryo development?
The seed loses water and becomes dormant
What are integuments?
Tissues which surround the megasporangium and develop into the seed coat
What does the carpel become?
The wall of the fruit that surrounds the seed.
