January 7 ~Feb1 2013 th
Midterm date: Monday Febuary 4 2013th5-7pm
Module 2: Begins on Tuesday Feb 5 .
Total: 12 lectures
1-2: Tree of life-plants
3-4 Plant cells and plant tissues
5-6. From seed to tree
7-8. Freom tree to seed
9. Transport in plants
10. Plant nutrition and soils
11. Plant defense
12. Plant life on the edge.
Lecture 6 notes (From seed to tree)
B) From primary to secondary plant body
ii. Shoot and root primary growth.
Primary meristem: Shoot apical meristem & Root apical meristem
• Shoot apical meristem tissue from xylem (inside) to epidermis (outside): xylem> vascular
cambium> phloem>collenchyma>cortex (made up of parenchyma)>epidermis
o E.g sunflower (Helianthus)
o From pith(inside) to epidermis: pith>primary xylem>vascular cambium>primary
phloem>collenchyma>cortex(parenchyma with some collenchyma)>ground
o X-section of shoot is circle and vascular bundles around.
• Root apical meristem tissue
o During mitotic cell division: procambium>ground meristem>root apical meristem>root
o During differentiation: primary xylem>vascular cambium(replace procambium)>primary
phloem>endoderm>periccle>cortex>epidermis with root hair
Main difference between root and shoot: Root has no pith and the vascular
cambium is at the centre. Root has endoderm and pericycle.
Endoderm acts as a filter for material from root hair to vascular tissue.
o X-section of root is circle a star shaped.
• Limited maximum size with primary growth: collenchyma has ligment that strengthen plant for
• Primary to secondary growth: the girth(middle) of root/stem is increased, Vascular cambium&
cork cambium are secondary meristems that give rise to secondary tissues.
Secondary meristem: Ground meristem & Vascular Cambium. Side-branches are axillary meristem
iii. Shoot secondary growth
Secondary growth in woody eudicots
• Herbs have only primary phloem, primary xylem, vascular cambium in bundles
• Trees& shrubs have ring of vascular cambium-interfascicular.
• Cork cambium-another meristem- that grows with the phloem rays. As the vascular largens, the
epidermis rips so the cork cambium fills in the rip holes.
• Pith stays the same, vascular ring largens from year 1 to year 2.
From bark (outside) to pith(inside):
• Bark: cork>cork cambium>cortex>phloem ray> phloem
• Vascular cambium -there are no rings in phloem
• Wood: secondary xylem(includes the summer wood and spring wood=one annual ring)>primary
• Pith Diagram of primary and secondary growth of shoot
iv. Apical dominance and growth forms
why are there so many growth forms? Because of apical dominance of Shoot apical meristem
Shoot apical meristem produced hormone auxin.
Apical dominance: suppression of axillary buds. Branching pattern depends on auxin conecntration and
length of brank.
Lower the branch, lower auxin that suppresses bud growth, so more buds at lower branh.
Figure 2. these plants low auxin level because there is a lot of branching and flowers
so if there is a flower that buds=high auxin
Breakdown of apical dominance: interior & exterior factor
• If shoot apical meristem turns into a flower=end of merstem cell, no more auxin.
• Cut off the bud by: wind, bug, sun clip, desiccation. And allow the side buds (axillary meristem to
grow. Axillary meristem is used for backup once shoot apical meristem is gone)
• Removal of Shoot apical meristem>auxillary meristem grows>develop into branches with own
shoot pical meristem.
Lecture 7 notes (From tree to seed);aka sex in plants
1) plant sex organs
Generalized flower structure: 4=stamen,carpel,sepal,petal
• Male: anther + filament=stamen
• Female: stigma + style+ ovary = carpel
• Sepal(sepal covers petal)
• Protects inner flower organs before bud opens
• Frequently green
• Can be used to form tubes
• Typically colorful to attract pollinators
• Can be fused to form tube.
• E.g violet, walsteinia, bellflower
• Anther: pollen produces. Has 4 pollen sacs
• Stigma: sticky landing platform for pollen (e.g. kiwi, poppy, tulip)
• Style: connects stigma with ovary (Azalea, primrose, lily,)
• Ovary contains one to multiple ovules. Ovules contain egg cell.
o Syncarpous ovary: many ovules (e.g cucumbers)
Shoot apical meristem-generative to reproductive organs
• Turns from leaf primordium into flower primordium
• E.g arabidopsis thaliana. Is the evolution of flower originated from modified leaves?
Different genes of rings: carpel>stamen>petal>petal
Shoot apical meristem>flower primordium?
ABC model of flower development
A,B,C genes specify the four different flower organ types
• Each of these genes is active in two adjacent rings of cells
• A=sepal organ
• A+B = petals organ
• B+C=stamen organ
• C=carpel organ
2) plant sex is not as boring as animal sex
some plants can have missing sepals or petals
• E.g sarcandra: no sepal, no petal
• Chickweed: no petal
• Golden saxifrage: no sepal
• Meadow rue: no petal, no female organ.
6% of angiosperms are unisexual=dioecious flowers. (one male plant, and one female plant only just as
how there is only one male, and one female)
• E.g asparagus, hemp/dioecious
17% are monoecious=both genders (one male flower and female flower organ in the same plant)
• E.g hazelnut, corn
75% complete flowers are hermaphroditism=perfect flower.= male & female on the same flower in the
• e.g trillium, rubus odoratus, blue cohosh, evening primose.
More varied plant reproduction
• In dioecy: male plant 1 + female plant 2 (one plant, one sex)
• In monoecy: -one plant 2 sex
o male plant 1 + female plant 2
o male flower plant 1 + female flower plant 1
• In hermaphroditism:-one flower 2 sex
o male plant 1 + female plant 2
o male flower plant 1 + female flower plant 1
o male flower 1 plant 1 + female flower 2 plant 1.
Why Animals are mostly dioecious. 75% plants are hermaphroditism-one flower 2 sex.?
This is because of self pollination=selfing=inbreeding.
Selfing is generally detrimental. Same plant pollinating same plant.= inbreeding depression.
Monoecious& hermaphroditic species has 94% of plants.
Dioecious species-on female plant, one male plant- has no selfing possible. Because there is no femal and
male organ in the same plant.
3) How to avoid doing it yourself
a) temporal separation-several phases separated in time
e.g Blood root: in the morning the stigma opens, anther closes. In the night, stigma closes, anther opens
asynchrony: geitonogamous selfing:between flowers
• pollination between flowers: fertilization of a flower by pollen from another flower on the same
• Monoecious, hermaphroditism.
b) spatial separation of sexual organs within flower
One plant with high anthers and short style.
Other plant with low anther and high style. e.g sage, primrose
in sage there is spatial and temporal separation. The stigma is sometimes not receptive.
c) self incompatiblilty
Lecture 8 notes (From tree to seed);aka sex in plants
3) How to avoid doing it yourself
c) self incompatiblilty
no fertilization with own pollen because there is biochemical self recognization.
Stigma change biochemical surface, rejects its own pollen, if pollen gets into pollen tube, a plug is
produced to prevent inbred offspring.
e.g fruit trees such as apple trees, chrry, pear.
4) Sex slaves of the plant kingdom.
Flowers: ingenious solution of angiosperms: non-directed or directed moblilty of pollen to seek egg.
Triassic, Jurassic, Cretaceous, Cenozoic era. – angiosperms.
Insects involved in angiosperms from smallest to largest influence: Diptera, Lepidoptera, hymenoptera,
Forces behind the evolution of flowers;
• Assurance of seed set: sheer mechanisms, bring female and male gametes together ot at least
replace the two parents
• Inbreeding avoidance: create high quaility offspring.
Pollination syndromes: direct and indirect moblility of pollen to seek egg
• Specialization of floral architecture, attraction, food requirements, rewards
• Abiotic pollination- indirect. Water&wind. Most water plants produce above water
o 10% of all plants are wind-pollinated
o 18% of plants have wind-pollinated species in them
o wind pollination found in high lattitdue/alititude, dry environments, open vegetation,
o E.g orchard grass, awneless brome grass., willow, alder, manitoba maple
o All grass are wind-pollinated
o Wind pollinated plants are: small inconspicious flowers, no special flower, no nectar,
long filaments, long styles. Produce a lot of pollen.
• Biotic pollination-direct. Animals, mammals. Can control which animals come.
o Pollinator needs reward (pollen, nectar)
o Specialized organ construction
o Often only a restricted set of polinators can take rewards=adaptation to specialized
Specialist plants rely on more narrow group of polinators. Extreme co-
evolution=one pollinator one plant. Exclusive relationship
Generalist flowering plants attract wide range of pollinators (e.g elderberry,
goldenrod, Queen Anne’s lace, Coltsfoot). None-specialized food; pollen and
nectar. Flowers make platform for insects of different size to roam.
o BEE polination: most important pollinator group
Originate 80 million years=diversified along with the evolutionary radiation of
Adult bees live on nectar (3-~35% sugar)
Larvae (juveniels) live on pollen-rich in protein Bee strongest in color spectrium is yellow, blue, green, UV.
E.g hepatica, dog violet, trout lily, downy yellow violet, marsh marigold, blue-
Bee are colorblind (relized by charlock)
Plants have nectar guides (leaf lines that points straight into to the plant into the
Hidden nectar: some plants only allow bee access (bee land on plant platform,
bee open nectar). E.g dog violet, dwarf snapdragon, bird’s trefoil.
Bee do not see red
Subgroup plants that are built for bee but do not provide reward for bee. This
limit cost of reproduction. Flower mimic female bee ot fool male bee into the
plant. (e.g orchids-ophrys. Orchid pretend to be female bee in smell, touch, to
have the male bee onto the flower)-coevolution!-one pollinator one plant
o Fly pollination
Eastern skunk cabbage- attracts flies to thinking it is flesh
Largest angiosperm is the amorphophallus titanium for flies.
Flowers are: dull, white/red, putrid smell, flowers=trap
o Butterfly pollination
Flower are red/orange
Narrow tubes for proboscis(beak?) of butterflies so that only butterfly gain
o Moth pollination
E.g soapwort, dame’s rocket, white campion.
Since moths are only active at night. Flowers are white/dull color, small smell,
long narrow floral tube.
Moth plants similar to butterfly plants
o Humming birds:-attracted to red/yellow. Have bad sense of smell
Take in liquid nectar (less concentrated than bee nectar) because humming bird
lap nectar with tonge(corolla tubular).
E.g Glaucous honeysuckle, red columbine. Lecture 9 notes Transport in plants
Basic plant needs: sugar=carbon dioxide + light +water, water, oxygen, minerals
A) Water transport through xylem
i) Hypotheses on mechanisms of water transport.
How does water move through xylem?
Answer: 3 hypotheses: capillary action, root osmotic push, transpiration.
1] capillary action- travels 1 m up xylem
water move upward xylem through adhesion (water & tube walls) and cohesion (water & water
Adhesion is stronger than cohesion.
Capillary action is not strong enough for trees because it travels for 1 meter!
2) Root osmotic push- travels 3 m up xylem
Osmosis (osmotic pressure) is where water diffusion through semipermeable membrane such as the cell
wall from a low concentration to a high concentration until both concentration are equal.
Plant actively pump ions into root cells with ATP . water moves into cells by osmosis when oot hair have
greater osmotic pressure (high ion_ than surrounding soil.
But his only pushes the xylem by 3meters!
3) Transpiration-travels 100 +m up xylem.
Use of cohesion.
Sun turns liquid water into gas > gas moves from parenchyma into intercellular leaf space> cohesion pulls
water from veins into parenchyma>gas diffuse out of stomata.
ii) Synthesis, total plant water transport
soil to root hair; osmosis
into xylem: osmosis & transpiration pull (from leaves)
up xylem between root and stem: transpiration
root to leaves: cohesion
angiosperms have more efficient trachieds and vessel elements-have perforation holes
entering of water into roots:
• Apoplastic transport:water flows through cell walls, more rapid, faster, less resistant to water flow
• Symplastic transport: water flows through cell and pits of parenchymas.
• Casparian strip: waxy layer that makes apoplastic transport impassable.
• So it’s: root hair> epidermis>cortex> endodermis> Casparian strip> stele.(middle/vascular
cambium)>xylem parenchyma>xylem vessels
o Endodermis: control layer to what substances can enter xylem.
o So when apoplastic cannot pass, they active transport into symplastic transport to upload
water. When symplastic-through cells transport passes endodermis, water active transport
back into apoplast transport-thorugh cell wall..
iii) Control of water transport
Stoma: two bordering guard cells (specialized epidermis cells).
• 90% water transported through xylem: lost to transpiration through stomata.
• 200L of water/day transpiration
• photosynthesis high=carbon dioxide high=transpiration high=cooling and nutrient flux=stomata
• photosynthesis low=carbon dioxide low=water saving mode=danger of overheating&low nutrient
flux. =stomata open
Factors affecting stomata to open:
• water-open when a lot of water,
• temperature-close when too hot/cold,
• light-close when dark except CAM photosynthesis,
• carbon dioxide concentration-open when low in carbon dioxide.
How stoma opens & close • osmosis through active regulation of potassium concentration (ATP-driven pumps)
• stoma opens when K pump into guard cell which cause water to flow into guard cell, dilating
• Increase K in cell, increase water intake.
B) Sugar transport through phloem
Xylem absorbs in roots: water, oxygen, minerals. Xylem releases water, oxygen in leaves.
Phloem absorbs in leaves carbon dioxide, sugar. Phloem releases carbon dioxide in roots
/figure 1. Xylem red arrow . Phloem blue arrow
Sugars move from sources to sinks
• Source of sugar: tissue or organs that make/store food. Seed endosperm, leaves, roots
• Sink of sugar: tissue or organs that require metabolites for energy and for biosynthesis. Shoot/ root
meristem, developing seed, flowers, roots.
Xylem has no sugar.
Xylem one direction route.
• No end walls between cells
• Water and minerals
Phloems have a 2-way flow (not a the same time)
• Have end walls between cells.
• Water and food
Phloem movement: pressure-flow model.