BIOL 410 - Photoperiod

What does the biological clock of plants do?

Internal timing mechanism that allows plants to adjust physiologically to cause responses.

What are two advantages of plants having a biological clock?

1. allows plants to flower when environmental conditions are best

2. allows flowering times to match the timing of pollinator hatching

What is photoperiod?

The length of the day at night.

What is photoperiodism?

Flowering in response to photoperiod.

What are the three classes of plant responses to photoperiod?

1. long day plants

2. short day plants

3. day neutral plants

Long day plants LDP traits:

• flower in spring or summer

• flower when the dark periods (nights) are shorter than a critical night length CNL

Short day plants SDP traits:

• flower in fall or winter

• flower when the dark periods (nights) are longer than a critical night length CNL

What are some SDP examples?

Poinsettia, Chrysanthemum, Cannabis

true or false: For LDPs and SDPs, CNL must be reached for flowering.

true.

What is a day neutral plant?

Day neutral plants do NOT respond to photoperiod. Responds to age, nutrient levels, and temperatures.

What are some examples of day neutral plants?

• sunflower

• tobacco

• rice

• cucumber

• tomato

How was photoperiodism discovered?

1920s: farmers planted soybeans for 2 months. All the soybeans flowered at the same time. For initial experiments, scientists tested light, temperature and nutrients. Results indicated that plants were responding to light. Not accurate!

What organ in plants receives the photoperiod?

The leaf.

What happened once the CNL was reached?

A flowering signal (FtmRNA) moves from the leaf to the A.M. to cause flowering.

The FtmRNA stimulates genes in the A.M. to shift A.M. from what?

Vegetative to Flowering.

The A.M. stops making what?

• leaves

• buds

• stems

The A.M. starts making what?

• sepals

• petals

• stamens

• carpel

In what plant was FtmRNA first discovered?

Arabidopsis. Tiny mustard plant which is the main experimental plant for genetic studies.

Why is arabidopsis used for genetic studies?

• short life cycle

• fast reproduction

• small genome

• large sample size

• cost efficient

• easy to keep