14.4 The Life Cycle of Flowering Plants

1. 14.4 The Life Cycle of Flowering Plants Biology 1001 November 28, 2005

2. 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

3. 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

5. 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!

6. 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!

7. Figure 39.24! – Is there a flowering hormone? Flowering photoperiod Non-flowering photoperiod • 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

8. 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 clip Fruit development clip

9. FRUITS ~ Some variation in fruit structure ~ ~ Some variation in fruit dispersal ~

10. SEEDS • Seeds are mature ovules that contain the multicellular plant embryo, the endosperm and a protective coat

11. 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!!

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

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