14.4 The Life Cycle of Flowering Plants

Biology 1001

November 28, 2005

Photoperiod and the Control of Flowering The events of the life cycle, such as flowering, seed

germination and leaf growth, need to be appropriately timed with respect to season

The environmental stimulus that plants use to detect the time of year is photoperiod, or the relative lengths of night and day

A physiological response to photoperiod, such as flowering, is called photoperiodism

The Effect of Photoperiod on Flowering On the basis of photoperiod requirement for

flowering there are three types of plants “Long-day” plants flower early in the season,

in the spring or early summer, when the days are long “Long-day” plants are really short night plants Examples include radishes and irises

“Short-day” plants flower late in the season, in late summer, fall or early winter, when the days are short “Short-day” plants are really long night plants Examples include poinsettias, chrysanthemums,

and strawberries “Day-neutral” plants flower at a certain stage

of maturity regardless of photoperiod Examples include tomatoes and dandelions

How does interrupting the dark period with a brief exposure to light affect flowering?

“Short-day” plants require a period of darkness greater than a critical period

“Long-day” plants require a period of darkness less than the critical period

A flash of light given in the night to a short-day plant inhibits flowering

A flash of light given in the night to a long-day plant promotes flowering Figure 39.22!

Phytochrome is the pigment that intercepts light

A unique characteristic of the pigment phytochrome is its reversibility in response to red and far-red light

Red light is the most effective at interrupting night

Because this effect is reversible by a flash of far-red light it is though that the pigment involved in photoperiod is phytochrome

Figure 39.23!

Figure 39.24! – Is there a flowering hormone?

It is leaves that detect photoperiod and transmit a signal to flower to buds

The flowering signal is a hormone or combination of hormones, as yet unidentified, called florigen

A bud’s meristem changes from a vegetative state to a flowering state – involves expression of a set of organ identity genes

Flowering photoperiod

Non-flowering photoperiod

Fruits Develop From Ovaries, Figure 38.9!

A fruit is a mature ovary that protects the seed and aids in its dispersal

The fruit begins to develop after pollination The wall of the ovary becomes the pericarp, the thickened

wall of the fruit

Fertilization clipFruit development clip

FRUITS

~ Some variation in fruit structure ~ ~ Some variation in fruit dispersal ~

SEEDS Seeds are mature ovules that contain the multicellular plant

embryo, the endosperm and a protective coat

SEED DORMANCY & GERMINATION As a seed matures, it dehydrates and

enters dormancy Breaking dormancy requires an

environmental stimulus such as fire, abrasion, rainfall, digestion

Dormancy increases the chances that germination occurs under ideal conditions

Germination begins with the imbibition of water which causes the seed coat to rupture and triggers the embryo tor resume growth

Enzymes digest the storage material in the endosperm

The embryonic root is the first organ to emerge, the the shoot breaks the soil surface Figure 38.10!!

Figure 30.10!,!! - The life cycle of an angiosperm

Figure 38.2!,!! – An Overview of Angiosperm Reproduction