Final Exam: Plants

they have stem cells that continue to exist into adult life, which allow them to grow throughout their lifetime

only have stem cells in the embryo

get rid of it and see the effect on the organism

• dark: long hypocotyl because it is trying to find the light
• light: short hypocotyl

therapeutics for gene regulation -- if you make too much of a bad protein, you can suppress it by using small RNA

• Cell Division
• Self-Renewal

• asymmetric cell divisions create two daughter cells with different cell fates
• One daughter cell goes on to form a specialized cell
• Other daughter remains a stem cell (self-renewal)

• animal stem cells are totipotent only in early embryo
• all plant cells are totipotent

In meristems found in the 16 cell embryo

where stem cells are maintained undifferentiated by short-range diffusible signals

the daughter cells that are placed outside the reach of the signal begin to differentiate

primary growth of roots and shoots, enabling indeterminate growth (make it longer)

primary shoot growth

primary root growth

• zone of differentiation
• zone of elongation
• zone of cell division

dome-shaped mass of actively dividing cells at the shoot tip

meristematic cells left at the basses of leaf primordia

secondary growth (make it wider)

cylinder of meristematic cells one cell thick that gives rise to secondary vascular tissue (xylem and phloem)

• - Apical Meristems: (primary growth) -- Located at the tips of roots and in the buds of shoots
• Lateral Meristems: (secondary growth)

• cell division: increases the potential for plant growth
• cell expansion: accounts for actual increase in plant size

water uptake

orientation of cellulose microfibrils in the cell wall, which is dictated by the microtubules in the cytoplasm

• Smallest plant genome (28,000 genes)
• Small stature
• Brief life cycle (6-10 weeks)
• Self-pollinates (can isolate homozygous mutations)
• Can be out-crossed (can do genetics)
• Can isolate mutants in development
• Can map the mutations to the genome to identify genes controlling plant development

• Shoot/root polarity
• big basal cell (roots) vs. small apical cell (shoots)

by short-range diffusible signals from localized source cells

floral meristem, from which the floral organs are derived

stem cells move away from the apical meristem and form a new meristem

• Order of emergence determines organ fate
• 1. sepal
• 2. petal
• 3. stamen
• 4. carpel

Carpel

asymmetric division

• Wild-type: stomata are separated from each other by at least one pavement cell
• Scream mutant: all epidermal cells are stomata

Gain-of-function

• the first asymmetrical division of zygote
• division is symmetric so plant doesn't know which side is shoot vs. root

controls polar auxin transport (via PIN1 auxin transporter) that establishes the shoot-root axis in the early embryo

Involved in determining where, when, and how body segments develop

• animals: In flies, homeotic mutants result in legs growing in place of antennae
• plants: flower homeotic mutants show abnormal numbers of floral parts

• 1. Each gene acts in two whorls
• 2. Combination of gene products determine organ identity
• 3. Gene A and C are mutually exclusive

carpel, stamen, stamen, carpel

sepal, sepal, carpel, carpel

sepal, petal, petal, sepal

flowers composed of leaves

• normally suppresses gene B activity in 4th whorl
• but in superman mutant, gene B is expressed in the 4th whorl, so it becomes a stamen instead of a carpel

Clark Kent

enclose the flower

brightly colored, attract pollinators

petals and sepals

• male reproductive organ
• produce pollen, anther + filament

• female reproductive organs
• produce ovules, stigma + style + ovary

pollen grain, which is what fertilizes the egg

• pollen lands on sigma
• pollen grain grows down pollen tube into the ovary and discharges two sperm cells near the embryo sac

• sperm 1: fertilizes the egg to make zygote (2n)
• sperm 2: combines with polar nuclei -> endosperm (3n)

becomes food source for the embryo

to coordinate developmental timing between the embryo and its food stores

• First mitotic division of embryo is asymmetric
• Large basal cell forms suspensor cell
• Terminal apical cell divides several times to form spherical pro-embryo
• Cotyledon appear at either side of apical meristem
• After germination, apical and root meristems sustain primary growth of seedling

can be alive for 100s of years before germination

when the embryo is alive but not growing, seed is desiccated yet protects embryo from drying out

in the first four days after fertilization

• Transverse microtubule band = anti-clinal division (vertical)
• Radial microtubule band = peri-clinal division (horizontal)

embryo, adult life

• auxin mediates phototropism
• extracted chemical messenger into agar block, when agar was put on top of tip, it still bent

hormone that makes cells elongate

• auxin content of cell
• cell where this protein is expressed appear blue, promoted by DR5, which is stimulated by Auxin

accumulates on dark side, making them elongate, which makes the plant bend

• Are small diffusible molecules
• Are produced in very low concentrations
• Minute amount of hormone can have a profound effect on the growth and development
• Hormones are transported- plant hormones are made in one location and transported to another
• Hormones are perceived by receptors and signals transduced to effect changes in gene expression

• auxin (cell elongation)
• cytokinin (cell division)
• Brassinosteroid (cell division and elongation of stems)
• Gibberllin (promotes seed germination)

• Abscisic acid (promotes dormancy of embryo)
• Ethylene (promotes senescence and fruit ripening)

causes cell wall to break down and become softer and makes starch become glucose (sweeter)

• auxin transport across a cell wall causes cell expansion
• 1. transport of auxin stimulates plasma membrane proton pumps
• 2. lowering the pH in the cell wall
• 3. which activates expansin enzyme that breaks down carbs/proteins in cell wall
• 4. pressure potential exerted by cell wall decreases, causing osmotic uptake of water into cell
• 5. uptake of water elongates the cell

shoot apex, roots via phloem

roots, up to shoots via xylem

shoot vs. root development

roots

shoots

callus (undifferentiated mass of cells)

used in horticulture to stimulate roots from leaf cuttings

Brassinosteroid

• add that hormone, if it does not grow you know that the plant is defective in the receptor or signal transduction part
• if hormone starts to be created, then synthesis is not defective

embryo is germinating while it is still on the ear

• ABA: promotes seed dormancy
• GA: promotes germination

ABA levels are high, which induce production of special proteins that help it survive

• promotes conversion of starch into glucose, which is what feeds the growing embryo
• so embryo starts to grow

• slowing of stem elongation
• stem thickening
• curvature to enable horizontal growth

• allows a growing shoot to avoid obstacles (rocks in soil) as it elongates
• releases ethylene to grow around it

they grow straight

mutants that can be rescued by adding hormone or blocking hormone synthesis, are defective in hormone production

cannot be rescued by adding back the hormone (or blocking its production) are defective in either hormone perception (ex: receptor) or signal transduction component

• precocious germination
• because ABA cannot transduce its signal to inhibit growth of embryo

• relative response of a process to different wavelengths
• tells which light quality affects a process

• phototropins
• crytochromes
• phytochromes

is a protein that is covalently bound to a chromophore (a non protein pigment) that can absorb light of a particular wavelength

• crytochromes: blue light, light inhibition of hypocotyl elongation
• phytochromes: red/fr light, flowering time regulation

red/blue light perception or signal transduction

• 1: photoreceptor activity
• 2: kinase activity

• red: activates phytochrome, induces germination
• far-red: inactivates phytochrome

• circadian clock
• level of constans fluctuates throughout the day, which helps them keep track of length of day and night

When the plant senses long days

mobile signal that goes up to shoot apical meristem and activates ABC genes to make plant flower

evolve embryo protection

a vascular system, can't transport over long distances

• evolve leaves and a vascular system
• have a dominant sporophyte generation

prevents exposed zygotes from drying out

• alternation of generations and multicellular embryos
• multicellular organs that produce gametes
• walled spores produced in sporangia to aid in dispersal of spores
• apical meristems

• food supply- provided by endosperm inside seed
• desiccation- protects embryo from drying out
• seed dispersal- used to transport embryo to new environment
• viable but dormant embryo

• Cycadophyta
• Gingkophyta
• Gnetophyta
• Coniferophyta

• thrived during mesozoic
• large cones, plam-like leaves

high tolerance to air pollution

600 species, forests

• 1. reduced gametophytes
• 2. heterospory (male/female)
• 3. ovules
• 4. pollen
• 5. seeds

• naked seeds not enclosed in ovaries
• they are exposed on modified leaves

• fruits aid in seed dispersal
• help attract pollinators

the seed coat