CHAPTER 38 Reproduction in Flowering Plants

Chapter 38: Reproduction in Flowering Plants Many Ways to Reproduce Sexual Reproduction The Transition to the Flowering State

Chapter 38: Reproduction in Flowering Plants Photoperiodic Control of Flowering Vernalization and Flowering Asexual Reproduction

Many Ways to Reproduce Almost all flowering plants reproduce sexually, and many also reproduce asexually. 4

Many Ways to Reproduce Both sexual and asexual reproduction are important in agriculture. 5

Sexual Reproduction Sexual reproduction promotes genetic diversity in a population, which may give the population an advantage under changing environmental conditions. 6

Sexual Reproduction The flower is an angiosperm’s device for sexual reproduction. 7

Sexual Reproduction Flowering plants have microscopic gametophytes that develop in flowers of the sporophytes. The megagametophyte is the embryo sac, which typically contains eight nuclei in seven cells. The microgametophyte is the pollen grain, which delivers two sperm cells to the megagametophyte via a long pollen tube. Review Figure 38.1 8

figure 38-01.jpg Figure 38.1 Figure 38.1

Sexual Reproduction Pollination enables fertilization in the absence of liquid water. 10

Sexual Reproduction In self-incompatible species, the stigma rejects pollen from the same plant. Review Figure 38.4 11

figure 38-04.jpg Figure 38.4 Figure 38.4

Sexual Reproduction Angiosperms perform double fertilization: One sperm nucleus fertilizes the egg, forming a zygote The other unites with the two polar nuclei to form a triploid endosperm nucleus. Review Figure 38.6 12

figure 38-06.jpg Figure 38.6 Figure 38.6

Sexual Reproduction The zygote develops into an embryo, remaining quiescent in the seed until conditions are right for germination. The endosperm is the nutritive reserve upon which the embryo depends at germination. Review Figures 38.7, 38.8 15

figure 38-07.jpg Figure 38.7 Figure 38.7

figure 38-08.jpg Figure 38.8 Figure 38.8

Sexual Reproduction Flowers develop into seed-containing fruits, which often play important roles in the dispersal of the species. 18

The Transition to the Flowering State For a vegetatively growing plant to flower, an apical meristem in the shoot system must become an inflorescence meristem, which gives rise to bracts and more meristems. These new meristems may become floral meristems or additional inflorescence meristems. Review Figure 38.10 19

figure 38-10.jpg Figure 38.10 Figure 38.10

The Transition to the Flowering State Flowering results from a cascade of gene expression. Organ identity genes are expressed in floral meristems that give rise to sepals, petals, stamens, and carpels. 21

Photoperiodic Control of Flowering Photoperiodic plants regulate flowering by measuring length of light and dark periods. 22

Photoperiodic Control of Flowering Short-day plants flower when days are shorter than a species-specific critical day length; long-day plants flower when days are longer than a critical day length. Review Figure 38.11 23

figure 38-11.jpg Figure 38.11 Figure 38.11

Photoperiodic Control of Flowering Some angiosperms have more complex photoperiodic requirements than short-day or long-day plants, but most are day-neutral. 24

Photoperiodic Control of Flowering The length of the night is what actually determines whether a photoperiodic plant will flower. Review Figure 38.12 26

figure 38-12.jpg Figure 38.12 Figure 38.12

Photoperiodic Control of Flowering Interruption of the nightly dark period by a brief exposure to light undoes the effect of a long night. Review Figure 38.13 28

figure 38-13a.jpg Figure 38.13 – Part 1 Figure 38.13 – Part 1

figure 38-13b.jpg Figure 38.13 – Part 2 Figure 38.13 – Part 2

Photoperiodic Control of Flowering The mechanism of photoperiodic control involves a biological clock and phytochromes. Review Figures 38.14, 38.15 31

figure 38-14.jpg Figure 38.14 Figure 38.14

figure 38-15.jpg Figure 38.15 Figure 38.15

Photoperiodic Control of Flowering Evidence suggests there is a flowering hormone, called florigen, but it has yet to be isolated from any plant. Review Figure 38.16 34

figure 38-16a.jpg Figure 38.16 – Part 1 Figure 38.16 – Part 1

figure 38-16b.jpg Figure 38.16 – Part 2 Figure 38.16 – Part 2

Vernalization and Flowering In some plant species, exposure to low temperatures—vernalization—is required for flowering. 37

Asexual Reproduction Asexual reproduction allows rapid multiplication of organisms well suited to their environment. 38

Asexual Reproduction Stolons (horizontal stems w/roots) Vegetative reproduction involves modification of a vegetative organ for reproduction. Stolons (horizontal stems w/roots) Rhizomes(underground hor. stems) Bulbs – lilies, onions Corms - disc-like underground stems Suckers – shoots produced by roots 39

Asexual Reproduction Some plant species produce seeds asexually by apomixis (female gametophyte produces seeds without pollen fertilization). 40

Asexual Reproduction Agriculturalists use natural and artificial techniques of asexual reproduction to reproduce desirable plants. 41

Asexual Reproduction Horticulturists often graft different plants together to take advantage of favorable properties of both stock(root bearing) and scion(upper graft). Review Figure 38.18 42

figure 38-18.jpg Figure 38.18 Figure 38.18

Asexual Reproduction Tissue culture techniques, based on the totipotency of many plant cells, are used to propagate plants asexually, produce virus-free clones of crop plants, and manipulate plants by recombinant DNA technology. 44