Light and Temperature Interaction

Fall Leaf Color• cool temps - very bright days

Orange• yellow, reds, purples and

browns

• chlorophyll cells die as temperatures get cooler

Yellow• carotenoids

• after chlorophyll dies you see the other pigments that are always present

Red-Purple• anthocyanins

• not always present

• synthesized in cooler temps

• made from sugar molecules

Brown• tanins

• mask or show up more once chlorophyll dies

• produced in the leaves

Leaf Fall• need an abscission layer

• leaf can no longer translocate carbohydrates out of the leaf

Bright Days• lots of carbohydrates in the

leaf

• anthocyanins get brighter color

The Key……• cool, short days

Greenhouse Effect• short, high energy wave

lengths of light from sun enters house

• absorbed by structures and plants

Greenhouse Effect• plants re-radiate green light

in longer waves

• long waves do not have as much energy as the short waves

Greenhouse Effect• longer waves do not have

enough energy to escape from the house

• result is heat

Greenhouse Effect• this is how the earth is heated

• long waves cannot escape through the clouds

• cloudy nights are warmer

Light• energy - electromagnetic

radiation

• wavelengths - distance from peak to peak

• measured in nanometers “NM”

Far Red• color plants use

Infra Red• heat energy

Visible light• light quality - color

• quantity - intensity, how bright

• duration - photoperiod

Quality• blue - 400-510 NM

• cell elongation

• photosynthesis - chlorophyll absorbs red and blue light

Quality• phototropism - plant tends to

grow or bend toward a light source

Red• photosynthesis

• stimulates branching

• encourage growth of axillary buds

Red• phytochrome - light

absorbing pigment

• seed germination in photoblastic seeds

Red• flowering responses

• photoperiod

Far Red• filters through leaf• inhibits branchingphytochromereactions - inhibitsgermination ofphotoblastic seeds

Far red• promotes stem elongation

Yellow - Green• does not effect plants

Intensity• measured in foot candles

• amount per unit area on plant

Plants• shade loving

• too much sun - leaf burn

• dehydrate

• kill chlorophyll

Plants• sun loving

• low light, pale color

• new leaves are small

• lack vigor

Plants• don’t flower properly if at all

Light• Light Compensation Point

-”LCP”

• light intensity where rate of photosynthesis = the rate of respiration

LCP• Lowest intensity you can

grow a plat at

• If a plant is grown below this level, respiration will be greater than photosynthesis

LCP• plant will die

• for a plant to grow photosynthesis must be greater than respiration

Acclimitization• preparing plant for lower

light intensity conditions

• expose to lower light intensity

Artificial Lights• Incandescent

• far red, red - elongation

• low blue

• 80% of emitted radiation is heat

Incandescent• 20% visible light

• 12% utilized by plant

Flourescent• red, blue

• 36% heat energy

• 22% light used by plant

• spectral flexibility

Flourescent• can change the quality of the

light by changing the coating on inside of bulbs

• Cool White - Ca Halophosphate

“Gro-Lux”• coated with Mg

Fluorogerminate

• not as long life as cool white, 30X more expensive

Metal Halide• increase light intensity

Low Pressure Sodium• yellow glow

• energy efficient

• yellow - orange light

High Pressure Sodium• red, blue light

• energy efficient

Photoperiod• length or duration of the light

period

• biological measurement of relative length of light and dark periods

Photoperiod• effects

• flowering

• leaf abscision

• dormancy - acclimate for winter

Effects…..• Sex expression

• runner formation

• tuber formation

• bulb formation

Short Day Plants• flower when day length is

shorter

• the dark period is critical

• it’s dark longer than it is light

Short Day Plants• examples

• Chrysanthemum

• Christmas Cactus

• Poinsettia

Long Day Plants• flower when days are long

and nights are short

• example: lettuce, radish, petunias

Facilitative Long Day• flower any period

• if long day - flowering is enhanced

• examples - tomato, begonia

Day Neutral• flower under long or short

day lengths

• example: African Violet

Poinsettias• use night interrupted lighting

• turn on artificial lights from 10 p.m. to 2 a.m.

• splits up the dark period

Poinsettias• cyclic lighting from 10 p.m.

to 2 a.m.

• lights on for 6 minutes and off for 24 minutes