MACROSCALEMACROSCALE: : EVAPOTRANSPIRATION

THIS WEEKS LAB: UP AGAINST GRAVITY !THIS WEEKS LAB: UP AGAINST GRAVITY !

HOW DOES WATER GET TO THE TOP OF A PLANT?HOW DOES WATER GET TO THE TOP OF A PLANT?

MICROSCALEMICROSCALE

1 meter 39.37 inches

1 millimeter (1mm) = .001 m

1 micron (1 um) = .001 mm

1 nanometer (1 nm) = .001 um = 1 x 10-9 m

(1 billionth of a meter)

Stomata & guard cells !Stomata & guard cells !

Rooted in one spot………...no eyes…….. no ears…….. no nose……no brain….

DO PLANTS “SENSE” AND “RESPOND” TO THEIR ENVIRONMENT? HOW?

WHAT WOULD IT BE IMPORTANT FOR PLANTS TO SENSE?

LIGHT?

GRAVITY?

WIND/TOUCH?

PATHOGENS

PLANTS SENSE THEIR ENVIRONMENT, AND THEY RESPOND BY:

ANIMALS SENSE THEIR ENVIRONMENT, AND THEY OFTEN RESPOND BY: ACTION OR MOVEMENT

…..………….CHANGING THEIR GROWTH PATTERN

INDETERMINATE GROWTH !

DO PLANTS SENSE LIGHT? IF SO, HOW?

What do plants respond to?

• Light – phototropism

• Water – hydrotropism

• Gravity - geotropism• Chemicals –

chemitropism– Plant growth

substances

SUNLIGHT

Is made up of different wavelengths of light.

When combined, they look white to the eye.

When refracted by different amounts, we see different colors which represent the different wavelengths.

prism

LIGHT IS COMPRISED OF MANY WAVELENGTHS

EACH COLOR HAS ITS OWN WAVELENGTH

High Energy

Low Energy

Electromagnetic spectrum

PLANTS USE PARTICULAR WAVELENGHS OF LIGHT FOR PHOTOSYNTHESIS

CHLOROPHYLL A & B: absorb blue light (450 nm),

absorb red light (680-700)

reflects green light (plants appear green to the eye)

Infrared far red

PLANTS ABSORB LIGHT FOR PHOTOSYNTHESIS

BUT HOW DO THEY SENSE IT?

COLEOPTILE

•IN MONOCOTS (GRASS, CORN)

•HOLLOW, CYLINDRICAL STRUCTURE

•PROTECTS PRIMARY LEAF

•AS IT PUSHES THROUGH THE SOIL

primary root

HOW CAN WE STUDY LIGHT PERCEPTION IN PLANTS?

Coleoptiles have been used in experiments to learn about how plants sense light.

Darwin’s coleoptiles 1881

Blue light (450 nm) Coleoptile bends

FULL LIGHT SPECTRUM

PHOTOTROPISM IS A RESPONSE TO BLUE LIGHT !!

WHAT DO PLANTS SEE?

PHOTOTROPISM – a directed movement in response to light

positive = towards light negative = away from light

no response for others

BLUE LIGHT IS ALSO USED IN PHOTOSYNTHESIS

PLANTS SENSE BLUE LIGHT AND BEND TOWARD IT

Test different wavelengths of light

SIMPLE APPARATUS FOR STUDYING COLEOPTILES

CAMERA COLEOPTILES GO IN HERE & LIGHT FILTERS

SOME PLANTS PREFER SHADE

SOME PLANTS PREFER FULL SUN

WHAT OTHER RESPONSES DO PLANTS HAVE TO LIGHT ?

SHADE HAS MORE FAR-RED LIGHT ----WHY?

More red light (660-700 nm)

Far red light = 720-780 nm, more in shade Red light = 600-690 nm, more in sun

HOW DO PLANTS RESPOND TO FAR-RED LIGHT (indicates shade)?

MORGAN & SMITH EXPERIMENTS

Light wavelengths for photosynthesis were constant

HOW WILL PLANTS RESPOND?

H0: sun and shade plants respond the same Ha: sun and shade plants respond differently

What should we measure? Stem growth?

WHAT DO THESE RESULTS TELL US ?

RESPONSE OF SHADE PLANTS ?RESPONSE OF SUN PLANTS?

• AT LEAST SOME PLANTS CAN SENSE FAR RED LIGHT

• SUN PLANTS RESPOND BY ELONGATING THEIR STEMS FASTER

DATA INTERPRETATION

CONCLUSIONS?

SUN PLANTS SHADE PLANTS

BEANS ARE SUN PLANTS

“ESSENTIALLY GROWING OUT OF THE SHADE”

How do plants know when to Flower?

CAN PLANTS TELL THE LENGTH OF A DAY OR NIGHT?

Spring Summer Fall Winter

PHOTOPERIODISM – a response based on relative day and night length

bloom in summer

bloom in fall

Plants appear to sense the length of the NIGHT

How could we test this?

HOW DO FAR-RED (735 nm) & RED LIGHT (660 nm) AFFECT FLOWERING?

The Red/Far Red Switch

RED has an effect

FAR RED turns off effect

How do RED light and FAR-RED light affect the germination of lettuce seeds?

Experiment: lettuce seeds need light to germinate. Good test system !

Red light promotes germination (ON)

Far-red light inhibits germination (OFF)

Last wavelength determines response

ON-OFF SWITCH !

Red

Far-red

In nature, FAR RED tells the plant it is in the SHADE!

WHAT’S THE MECHANISM ? HOW DO PLANTS SENSE LIGHT?

THERE IS A LIGHT SENSING MOLECULE = PHYTOCHROME THAT CHANGES ITS SHAPE = PHOTOREVERSIBLE !

not chlorophyll !

conformation

RED: ON! GO!FAR RED: OFF! STOP!More Pr inhibits More Pfr stimulates

In sunlight, red dominates & is absorbed by the seed

Weed/lettuce seeds germinate in light.

Red light

Far-red light

Lettuce seeds don’t germinate in the shade

OFF SWITCH !

Relative amounts of: red: far-red

THE HUNT FOR PHYTOCHROME

BUTLER 1959

CORN STEMS ELONGATE IN FAR-RED LIGHT

Scientists ISOLATED PROTEINS

ONE WAS PHOTO-REVERSIBLE !

PHYTOCHROME WAS DISCOVERED !

Chlorophyll Absorbs blue and red light for photosynthesis

Phytochrome senses red or far-red light & can affect:

flowering

seed germination

stem elongation

stomata opening?

Phototropins

in cell membrane of shoots

sunlight detector

Responds to blue light

phototropism

(by phosphorylation)

Many other pigments in plants absorb other wavelengths of light & plant responds

Pigment wavelength

Senses shade

Photoperiodism

in chloroplasts

PLANTS ARE CREATURES OF LIGHT………………………

NEW

HOW DOES THIS TRANSLATES INTO A PLANT RESPONSE?

A “HOT TOPIC” OF INVESTIGATION NOW !

1. SIGNAL -- BLUE LIGHT

2. NPH1 PROTEIN CHANGES

3. PO42- ADDED

(PHOSPHORYLATION) (get activation)

4. CELL RESPONSE

PHOTOTROPINS: SENSE BLUE LIGHT

THEN WHAT?

PLANTS ARE CREATURES OF LIGHT, GRAVITY, AND FORM……..

WE WILL DISCUSS GRAVITY NEXT !