Light Relations

Light Waves

Amplitude =Intensity foot-candles	10,000 fc sum/noon 1000 fc winter 100 fc house
		Wave Length = Color

400 500 600 700 nm Wavelength
UV purple blue green yellow red IR
---------------VISIBLE SPECTRUM---------------

RAINBOW often wrong in ART.

Colors of flowers, fruits, leaves, etc.

White = all colors of rainbow at once

Pigment in object absorbs all but color reflected to us

Green = absorbs purple/blue and yellow/red
...reflects green to our eye

Blue light causes phototropism:

Light also causes changeover in genetic programs:

Etiolated
(Dark)

Photosynthesis: (review)

CO₂ + H₂O

light
---------->
chlorophyll

CH₂O
sugar

+ O₂

It is really a complex set of reactions, NOT one step.
Can be divided into two separate reaction systems:

Light-Dependent Reactions:

H₂O light
---------->
chlorophyll O₂ + ATP + NADPH₂

Light-Independent Reactions

ATP + NADPH₂ + CO₂ ----------> CH₂O
sugar

Note: Light-Independent Reactions are dependent on the products of the light-dependent reactions...so they only occur in the light!!

What color of light is needed for Photosynthesis?

(Hint: Chlorophyll is green!)

What intensity of light is needed for Photosynthesis?

How long should the lights be on?

Photoperiodism - light duration process

		chrysanthemum poinsettia	lettuce spinach
One 24-hr Day of a sequence:		SDP=LNP	LDP=SNP
16 hr Day = LD	8 hr Night = SN	vegetative	flowering

Here are conditions as found in the short days of fall (or spring):

chrysanthemum
poinsettia lettuce
spinach
One 24-hr Day of a sequence: SDP=LNP LDP=SNP
8 hr Day = SD 16 hr Night = LN flowering vegetative

	chrysanthemum poinsettia	lettuce spinach
One 24-hr Day of a sequence:	SDP=LNP	LDP=SNP
8 hr Day = SD	16 hr Night = LN	flowering	vegetative

Are the plants measuring the length of the day or the length of the night?

Interrupting the night...

chrysanthemum
poinsettia lettuce
spinach
One 24-hr Day of a sequence: SDP=LNP LDP=SNP
8 hr Day = SD 8 hr Night = SN Light
10 sec 8 hr Night = SN vegetative flowering
Compare the results with the fall results above...note that the night interruption has changed the results!

	chrysanthemum poinsettia	lettuce spinach
One 24-hr Day of a sequence:	SDP=LNP	LDP=SNP
8 hr Day = SD	8 hr Night = SN	Light 10 sec	8 hr Night = SN	vegetative	flowering

Interrupting the day...

chrysanthemum
poinsettia lettuce
spinach
One 24-hr Day of a sequence: SDP=LNP LDP=SNP
8 hr Day = SD Dark
10 sec 8 hr Day = SD 8 hr Night = SN vegetative flowering
Compare the results with the summer results above...note that the day interruption has not changed the results.

	chrysanthemum poinsettia	lettuce spinach
One 24-hr Day of a sequence:	SDP=LNP	LDP=SNP
8 hr Day = SD	Dark 10 sec	8 hr Day = SD	8 hr Night = SN	vegetative	flowering

Notice that it is the length of night that is critical!!

What pigments does this? (Hint: wavelength tells!)

Using a red-light interruption:

chrysanthemum
poinsettia lettuce
spinach
One 24-hr Day of a sequence: SDP=LNP LDP=SNP
8 hr Day = SD 8 hr Night = SN Red
10 sec 8 hr Night = SN vegetative flowering
Note: red light interrupts the night successfully...SDP(LNP) flowering is prevented.

	chrysanthemum poinsettia	lettuce spinach
One 24-hr Day of a sequence:	SDP=LNP	LDP=SNP
8 hr Day = SD	8 hr Night = SN	Red 10 sec	8 hr Night = SN	vegetative	flowering

Using far-red light interruption:

chrysanthemum
poinsettia lettuce
spinach
One 24-hr Day of a sequence: SDP=LNP LDP=SNP
8 hr Day = SD 8 hr Night = SN Far-red
10 sec 8 hr Night = SN flowering vegetative
Note: far-red light does not interrupt the night...SDP(LNP) flowering is not prevented.

	chrysanthemum poinsettia	lettuce spinach
One 24-hr Day of a sequence:	SDP=LNP	LDP=SNP
8 hr Day = SD	8 hr Night = SN	Far-red 10 sec	8 hr Night = SN	flowering	vegetative

Interrupting flashes can be a sequence of several:

SDP(LNP) LDP(SNP)
Interrupting sequences ending in RED vegetative flowering

Interrupting sequences ending in FAR-RED flowering vegetative

	SDP(LNP)	LDP(SNP)
Interrupting sequences ending in RED	vegetative	flowering
Interrupting sequences ending in FAR-RED	flowering	vegetative

Conclusion: the light-detecting pigment is Phytochrome

Recall: Similar R/FR relationship applies to lettuce seeds!

Photoperiodism Flowering Examples

Chrysanthemum Story with Driveway-What is the solution?
Poinsettia Story inside house-what is solution?
Lettuce Bolting Problem in garden-what is solution?

Non-flowering Examples

Tuberization: SDP (Long Nights Too):

Potato, Jerusalem Artichoke, Dahlia Tubers

Onions...need long season to make large bulbs!

Bermuda: forms bulbs when day 11 hours or longer

planted in early spring to grow bulbs in CT
day already longer than 11 hours....bulbs form right away...tiny

planted in fall in TX days short, weather mild, large plant
day gets longer than 11 hours in summer, large bulbs form

Spanish: forms bulbs when day 15-16 hours or longer

planted in early spring to grow bulbs in CT
plant gets large before bulbs begin to grow...large bulbs in CT

night day never gets to 15-16 hours...no bulbs ever in TX

Light Around the House

Shade Lovers:

Inside: Ferns, African Violets, Philodendron, Dieffenbachia
Outside: Ferns, Hosta, Astilbe, Begonia, Impatiens

Artificial Lighting

Duration: 16 hours (use a timer)
Intensity:
Incandescent = hot, red, dry
Fluorescent = incomplete blue, dim
GrowLux = more complete, dim
(use many tubes, close together)
Metal Halide/Sodium Mercury Vapor: bright, complete, HOT, expensive
Cops will make a house call (DEA)

Go back to the Course Schedule.