Bio 102 Chapter 33 Control Systems

slide show by Kim Foglia modified by A Darlak One last thing for 32

• Water Transport Clip • http://media.pearsoncmg.com/bc/bc_0med ia_bio/bioflix/bioflix.htm?cc7water

• What Are the Health Benefits of Soy? – Soy protein • Is one of the few plant proteins that contains all the essential amino acids

PLANT HORMONES • Experiments on how turn toward light led to the discovery of a plant hormone – Plants exhibit • The growth of shoots in response to light

Figure 33.1A – Microscopic observations of plants • Indicate that a cellular mechanism underlies phototropism

Shaded side of shoot

Light

Illuminated side of shoot

Figure 33.1B • Showing That Light Is Detected by the Shoot Tip – Charles Darwin (late 1800s) showed that the tip of a grass seedling detects light • And transmits a signal down to the growing region of a shoot

Light

Control Tip Tip covered by Tip covered Base covered removed opaque cap by trans- by opaque parent cap shield Figure 33.1C

Darwin and Darwin (1880) • Showing that tip needs to be continuous with stem – Boysen-Jensen cut the tips off oat coleoptiles, they did not bend. When put these tips back on, these coleoptiles bent toward the light. – Then separated tip with porous and non porous

Light

Control Tip Tip covered by Tip covered Base covered Tip separated Tip separated removed opaque cap by trans- by opaque by gelatin by mica parent cap shield block

Figure 33.1C Darwin and Darwin (1880) Boysen-Jensen (1913) • Isolating the Chemical Signal- (Frits Went 1926) – The hormone Auxin • Was determined to affect phototropism • Promotes faster cell elongation on the shaded site of the shoot

Shoot tip placed on agar block. Chemical (later called auxin) diffuses from shoot tip into agar. Agar

Block with Other controls: chemical Offset blocks with Blocks with no stimulates chemical stimulate chemical have growth. Control curved growth. no effect.

No light

Figure 33.1D HORMONE = chemical messenger

• produced by one part of the plant

CELL CYTOPLASM • translocatedWALL to other parts where it triggers a response 1 Reception 2 Transduction 3 Response • ALLOWS plant to react/adjust to external

conditions w/o a nervous system Activation of cellular Relay molecules responses

Receptor

Hormone or environmental stimulus Plasma membrane Plant Hormones

• Growth promoters: Auxins, Cytokinins, Gibberellins • Growth inhibitors: Ethylene gas, Abscisic aci Growth promoters

• Hormones can promote plant growth in two ways: – Stimulating cell division in meristems to produce new cells. – Stimulating elongation in cells. 1. Auxin (IAA- Indole Acetic Acid)

• Effects – Stimulates or inhibits the elongation of shoots and roots – controls cell division & differentiation – Fruit growth – Phototropism – – apical dominance • stimulates proton pumps; acid weakens cell wall so cells can expand 3 Wedge-shaped expansins, activated by low pH, separate cellulose microfibrils from Cell wall cross-linking polysaccharides. The exposed cross-linking enzymes polysaccharides are now more accessible to cell wall enzymes. Cross-linking Expansin cell wall 4 The enzymatic cleaving of the cross-linking polysaccharides CELL WALL polysaccharides allows the microfibrils to slide. The extensibility of the Microfibril cell wall is increased. Turgor causes the cell to expand.

H2O Cell H+ Plasma wall H+ membrane 2 The cell wall becomes more H+ acidic. H+ H+ H+ H+ H+

1 Auxin increases the Nucleus Cytoplasm activity of Vacuole proton pumps. ATP + Plasma membrane H 5 With the cellulose loosened, the cell can elongate. Cytoplasm = hormone induced growth response toward/away from stimulus

• PHOTOTROPISM-response to light (Positive- grow toward light; Negative grow away from light) – Differential rate of cell elongation; Shoot bends toward light due to asymmetrical distribution of auxins – Light stimulates movement of auxin to dark side so cells on dark side elongate faster than cells on light side

PHOTOTROPISM

http://media.pearsoncmg.com/bc/bc_campbell _essentials_3/videos/Phototropism-V.html GRAVITROPISM • (AKA Geotropism) • respond to gravity • Roots grow down, shoots grow up due to asymmetrical distribution of auxins

http://media.pearsoncmg.com/bc/bc_campbell_e ssentials_3/videos/Gravitropism-V.html • Plants may detect gravity by the settling of statoliths (specialized plastids containing dense starch grains)

Statoliths 20 m

(a) (b) THIGOMOTROPISM • respond to touch • EX: vines curl around supports

• Rubbing the stems of young plants a couple of times daily – Results in plants that are shorter than controls Apical dominance • Auxins are released from the shoot tip. These stimulate cell elongation in the stem, but suppress the lateral buds.

• Cytokinins, produced in the roots, can stimulate lateral buds if the shoot tip is removed. Adventitious roots

• Adventitious roots are those growing out of places where roots don’t normally grow. • Auxins stimulate root growth on the end of a houseplant cutting. Fruit growth

• Developing seeds produce auxins that stimulate growth of the plant ovary into a fruit.

• Removal of seeds from a strawberry prevents the fruit from growing, but add auxin and will grow.

• How could this be used in commercial agriculture? 2. CYTOKININS

• Promote growth of lateral buds when auxin concentrations are low. • Promote cell division in meristems. • Stimulate fruit and seed development. • Delays senescence of plant parts. Plants become bushier

“Stump” after removal of apical bud

Lateral branches Test it!

• http://media.pearsoncmg.com/bc/bc_camp bell_concepts_7/process/39A/index.html

3. Gibberellins • Promote seed/bud germination; leaf growth; stimulate flowering/fruit development • Stimulate stem elongation (INTERNODES); loosen cell walls so cells can expand • Many “dwarf” varieties don’t have working gibberellins plump grapes in grocery stores have been treated with gibberellin hormones while on the vine Foolish rice seedlings

• Gibberellins were discovered when Japanese scientists were investigating bakanae, or “foolish rice seedling” disease, that caused seedlings to grow excessively tall, then fall over. Commercial Uses

• On the left are ordinary green grapes with seeds. On the right is a cluster of Thompson seedless grapes. These both came from the same variety of grapevine. How can this be? 4. Abscisic acid (ABA)

• Often antagonistic to other hormones • Slows growth/promotes seed dormancy • LEAF______ABSCISSION – leaves die and fall off – Prevents deciduous trees from desiccation during winter when roots cannot absorb water from frozen ground – Stimulus is shortening days and cooler temperatures – Signals closing of stomata in leaves under water stress to save water

– http://media.pearsoncmg.com/bc/bc_campbell_concepts_6/activi ties/c6eLib/activities/H39/H3901/st01/frame.html Functions of Abscisic Acid • Controls seed and bud dormancy. • Inhibits gibberellins. • Promotes senescence in plants.

NO ABA 5. Ethylene “gas” • Controls senescence (aging) - leaf fall, withering of flowers – Role in APOPTOSIS = programmed cell death – Promotes RIPENING OF FRUIT – Inhibits cell elongation

One bad apple spoils the whole bunch… Gaseous discoveries

• In ancient China, people placed pears or oranges in rooms with burning incense to make them ripen faster. • For centuries, people assumed heat or light was responsible for fruit ripening. In the 19th century, fruit ripening sheds were built using gas or kerosene heaters. When these were replaced with electric heaters, fruit didn’t ripen as fast. “Illuminating gas”

• In the 1800’s, gas lighting was first installed in cities. People noticed that houseplants growing near gas light fixtures grew abnormally. Cut flowers aged and wilted quickly. • Physiologist Dimitry Neljubow analyzed natural gas and found that one component, ethylene gas, was responsible for the effects.

Apoptosis in Plants

What is the • Many events in plants involve evolutionary advantage of apoptosis loss of leaves – response to hormones in autumn? • ethylene • auxin – death of annual plant after flowering • senescence – differentiation of xylem vessels • loss of cytoplasm – shedding of autumn leaves Promotes Fruit Ripening • Example of positive feedback system – ethylene triggers ripening – ripening stimulates more ethylene production • Adaptation – hard, tart fruit protects developing seed from herbivores – ripe, sweet, soft fruit attracts animals to disperse seed • Mechanism – triggers ripening process • breakdown of cell wall-softening • conversion of starch to sugar-sweetening PHOTOPERIODISM

= physiological response to day length

• detect time of year by PHOTOPERIOD (relative length of night and day) • Circadian rhythm/ubiquitous to all eukaryotes • synchronized with the Earth's light-dark cycle

Short Day/Long Night or Long Day/Short Night?

24 Darkness

Flash of light

Critical night length night Critical Time (hr) Time

Light

0

Short-day (long-night) plants Long-day (short-night) plants http://media.pearsoncmg.com/bc/bc_campbell_concepts_6/activities/c7eLi b/c6e/H39/H3902/st01/frame.html DAY LENGTH & FLOWERING • SHORT-DAY: flower in late summer/early fall/winter when daylight is decreasing • daylight < a critical length • Really should be called LONG NIGHT PLANTS • if dark interrupted by flash of light . . . no flowers.

• LONG-DAY : flower in late spring/early summer when daylight is increasing • daylight > a critical length • SHORT NIGHT PLANTS- if dark interrupted by flash of light. . . it flowers • EX: lettuce

NIGHT LENGTH = CRITICAL

Short day plants (= really need LONG NIGHT) don’t flower if dark time is interrupted by short burst of light • DAY-NEUTRAL: flowering unaffected by day length

PHYTOCHROME • Light-absorbing protein responsible for plant's response to photoperiod • Switching between forms controls various plant events

Pr (absorbs red light) ←→Pfr (absorbs far red light)

• Pfr is biologically active form- triggers many plant responses to light

• Phytochromes have two photoreversible states

– With conversion of Pr to Pfr triggering many developmental responses

Pr Pfr Red light Responses: Synthesis seed germination, control of flowering, etc. Far-red light

Slow conversion Enzymatic in darkness destruction (some plants) RESPONSE TO LIGHT • Synchronizes biological clock to the environment • PHYTOCHROME SYSTEM & BIOLOGICAL CLOCK allow plants to assess amount of daylight/season

• Ex: Pr = no germination Pfr = germination EXPERIMENT During the 1930s, USDA scientists briefly exposed batches of lettuce seeds to red light or far-red light to test the effects on germination. After the light exposure, the seeds were placed in the dark, and the results were compared with control seeds that were not exposed to light.

Dark (control)

Red Dark Red Far-red Dark

Red Far-red Red Dark Red Far-red Red Far-red

CONCLUSION Red light stimulated germination, and far-red light inhibited germination. The final exposure was the determining factor. The effects of red and far-red light were reversible. Plant Communication

• Plants communicate chemically. • Injured plants send out chemical signals that may – signal other plants to prepare for an attack. – attract other insects that eat the insects that are attacking the plant. • Defenses Against Herbivores

– Some plants recruit predatory animals • To help defend them against certain herbivores

4 5

Recruitment of wasp

Wasp lays

eggs

Based Based Signals:

1997 1997 American

–

 (1997), p. (1997), 912. Synthesis and release of 3chemical

attractants Science 276 276 Science

Damage to1 plant Plant cell and chemical in 2 caterpillar saliva Signal transduction

pathway

Adapted from Edward Farmer, “Plant Biology: New Fatty Acid “Plant New Biology: Farmer,Edward Adapted from the Lesson World”fromAPlant for the Advancement ofAssociation Science. Figure 33.14A SIGNAL TRANSDUCTION PATHWAY

Receptors are sensitive to very weak environmental and chemical signals

2nd messengers - small, internally produced chemicals transfer and amplify the signal from the receptor to other proteins that cause the response

EX: cGMP, cAMP SIGNAL TRANSDUCTION PATHWAY

Ca++ and cGMP = 2nd messengers that activate protein kinases

Both pathways turn Light signal is detected on genes that by phytochrome receptor produce proteins that produce response which activates 2 signal transduction pathways Nastic Movements

Nastic movement in the sensitive plant (Mimosa pudica)

http://media.pearsoncmg.com/bc/bc _campbell_essentials_3/videos/Mi mosaLeaf-V.html

Hinge control in Venus Fly Trap - Nastic movement Movies

• Sensitive Plant: http://www.youtube.com/watch?v=BV U1YuDjwd8 • Venus Fly Trap: http://www.youtube.com/watch?v=ktI GVtKdgwo&feature=related

How it works

• Nastic movements are rapid, reversible movements in a plant. • Electrical potentials across cell membranes, similar to those in our nerve cells, signal plant cells at the base of the Mimosa leaf to rapidly lose water. This causes the leaf to droop.