The gametophytes produce: Fertilization? zygotes (2n),

Transcription

1 1 Chapter 38: Flowering Plant Reproduction and Biotechnology I. Introduction to Plant Reproduction Fitness of an organism is measured by its: Flowering plant reproduction: Sexual: Asexual: II. Sexual Reproduction and Alternation of generations in plants The haploid (n) and diploid (2n) generations: Sporophyte (2n),? These spores divide by mitosis,? The gametophytes produce: Fertilization? zygotes (2n), A. Seeds In angiosperms, sporophyte generation is dominant: produces flowers that contain gametophytes.

2 2 B. Flower structures 1. Flowers: Unlike the indeterminate growth of vegetative shoots, flowers are determinate shoots 2. The four kinds of floral organs are the sepals, petals, stamens, and carpals. Their site of attachment to the stem = 3. Sepals and petals are non-reproductive organs. Sepals i. ii. Petals i. often brightly colored 4. Stamens and carpels (pistils) are the male and female reproductive organs, respectively. Stamen structure Carpel structure Carpel number per flower

3 3 The stamens and carpels of flowers contain sporangia, within which the spores and then gametophytes develop. i. The male gametophytes: ii. The female gametophytes: 5. Complete flowers ; incomplete flowers ; Bisexual flower (formerly perfect flower): A unisexual flower: Numerous floral variations have evolved during the 130 million years of angiosperm history 6. A monoecious plant: E.g., maize and other corn varieties: 7. A dioecious species: C. Pollination brings male and female gametophytes together 1. The male gametophyte begins its develop within the sporangia (pollen sacs) of the anther.

4 4 2. The female gametophyte begins to develop within the ovules of the ovary. i. An ovule: only one megaspore usually survives ii. Megaspore: iii. membranes partition this mass into a multicellular female gametophyte - the egg sac 2 synergid cells: 2 polar nuclei: 3 antipodal cells The development of angiosperm gametophytes involves meiosis and mitosis Flowers have many variations in size, shape, and color. Much of this diversity represents coevolutionary adaptations with animal pollinators. pollen grain? travels via wind or animals? lands on stigma? pollen tube grows toward embryo? sperm through style? sperm to ovary? sperm into the embryo sac? egg fertilized? zygote? embryo ovule develops into entire ovary develops into Fruits carried by wind or by animals disperse seeds away from the source plant where the seed germinates.

5 5 D. Mechanisms to prevent self-fertilization 1. Dioecious plants: 2. Monoecious plants: 3. self-incompatibility (analogous to the immune response of animals) a. biochemical block: b. genes for self-incompatibility: c. matching alleles between pollen grain and the carpel s stigma prevent E. Fruit development 1. The wall of the ovary becomes: 2. Other floral parts: 3. The fruit usually ripens about the same time as its seeds are completing their development. F. Seed germination 1. As a seed matures: 2. Conditions required to break dormancy and resume growth and development vary between species. a. Some seeds:

6 6 b. Others: 3. Seed germination depends on imbibition, a. seed coat ruptures: b. Enzymes: c. The radicle, the embryonic root, emerges 1 st d. Next, the shoot tip must break through the soil surface. 4. In many dicots, a hook forms in the hypocotyl, and growth pushes it aboveground. 5. Monocots use a different method for breaking ground when they germinate. III. Asexual reproduction A. Many plants clone themselves by asexual reproduction, also called vegetative reproduction. B. Asexual reproduction is an extension of the capacity of plants for indeterminate growth.

7 7 C. Types of asexual reproduction 1. Fragmentation: 2. Apomixes: D. Sexual and asexual reproduction are often complementary Many plants capable of both each offers advantages in certain situations. 1. Advantages of sexual reproduction: 2. Advantages of asexual reproduction: E. Vegetative propagation of plants is common in agriculture 1. Various methods have been developed for the asexual propagation of crop plants, orchards, and ornamental plants. 2. Plant tissue culture and genetic engineering of plants. 3. One method that researchers use to insert foreign DNA into plant cells is by firing DNAcoated pellets into cultured plant cells. 4. Another approach combines protoplast fusion

8 8 IV. Introduction to Issues Related to Plant Biotechnology A. Plant biotechnology -- two meanings B. Selective breeding and domestication by humans 1. Plants attractive to human harvest/cultivation originally exploited 2. Humans selected certain traits and created plants that could not survive for long in the wild. E.g., maize cannot spread its seeds naturally. 3. Further, intensive artificial selection has occurred in common food crops C. Modern plant biotechnologists, through genetic engineering, are not limited to transferring genes between closely related species or varieties of the same species. 1. This has transformed agricultural productivity in a variety of ways. 2. Examples: D. Plant biotechnology has incited much public debate 1. Some are political, economic, or ethical debates 2. The most fundamental debate centers on the extent to which GM organisms are an unknown risk that could potentially cause harm to human health (e.g. allergens) or to the environment (e.g. non-target species).