1. Angiosperm Reproduction
Chapter 38
Angiosperm Reproduction

2. What you need to know: The relationship between seed and fruit.
How temperature and moisture determine seed germination.
How different modes of plant reproduction affect their genetic diversity.

3. Angiosperms have 3 unique Features:
Flowers
Fruits
Double Fertilization
Angiosperm: the diploid sporophyte is the dominant generation/ largest, most conspicuous, and longest lasting.

6. Flower Structure Reproductive shoots Flower organs:
Sepal – leaflike, protect flower bud
Petal – modified leaves, attract pollinators
Stamen – ♂ reproductive organ
anther + filament
Carpel – ♀ reproductive organ
stigma + style + ovary
Flower attached to stem at receptacle
Pollination by wind, insects, birds

7. Pollination: transfer pollen from anther to stigma
If a pollen grain germinates, a pollen tube grows down the style toward the ovary.
The pollen tube discharges two sperm into the female gametophyte (embryo sac) within an ovule.
One sperm fertilizes the egg, forming the zygote. The other sperm combines with the two polar nuclei of the embryo sac’s large central cell, forming a triploid cell that develops into the nutritive tissue called the endosperm.
Endosperm- a food storing tissue of the seed.
Pollination: transfer pollen from anther to stigma
Pollen tube grows down into ovary for 2 sperm to travel to egg

8. “Pin” and “thrum” flower types reduce self-fertilization
Some plants are self-pollinated
Cross-pollinated plants:
Self-incompatibility: plant rejects own pollen or closely related plant
Maximize genetic variation
Stigma
Pin flower
Anther
with
pollen
Thrum flower
“Pin” and “thrum” flower types reduce self-fertilization
An insect foraging for nectar would collect pollen on different parts of its body; pin pollen would be deposited on thrum stigma and vise versa.

9. The development of a plant embryo
By the time the ovule becomes a mature seed and integuments harden and thicken to form the seed coat, the zygote has given rise to an embryonic plant with rudimentary organs.
The development of a plant embryo

10. Fruit Egg cell  plant embryo Ovules inside ovary  seeds
Ripe ovary  fruit
Fruit protects enclosed seed(s)
Aids in dispersal by water, wind, or animals
Fertilization: triggers hormonal changes that cause the ovary to begin its transformation into a fruit.
If the flower is not pollinated, fruit usually does not develop, and the entire flower withers and falls away.

11. Types of Fruit
As the ovary grows, the other parts of the flower wither and are shed: pea pod tip is the remains of the pea flower.
Simple fruit – derived from one single carpel (fleshy: peach or dry: pea pod/ nut)
Aggregate fruit – results from a single flower that has one separate carpel, each forming a small fruit. (Fruitlets: are clustered together on a single receptacle – raspberries)
Multiple fruit – develops from a group of flowers tightly clustered together (When walls of many ovaries start to thicken, they fuse together and become incorporated – pineapple)

12. Seeds Mature seed  dormancy (resting) Low metabolic rate
Growth & development suspended
Resumes growth when environmental conditions suitable for germination

15. Germination
Seed take up water (imbibition)  trigger metabolic changes to begin growth
Root develops
Shoot tip emerges above ground
Stimulated by light
Foliage leaves expand & turn green  photosynthesis
Very hazardous for plants due to vulnerability
Predators, parasites, wind
Imbibition: the uptake of water due to low water potential of the dry seed. Imbibing water causes the seed to expand and rupture its coat and also triggers metabolic changes in the embryo that enable it to resume growth.
The 1st organ to emerge from the germinating seed is the radicle, the embryonic root.
Next the shoot tip must break through the soil surface.
Foliage leaves expand, become green, and begin making food by photosynthesis.

16. Seed Germination
Bean Plant: Straightening of a hook in the hypocotyl pulls the cotyledons from the soil.
Maize: the shoot grows straight up through the tube of the coleoptile.

17. (Vegetative Reproduction)
Plant Reproduction
Sexual
Asexual
(Vegetative Reproduction)
Flower  Seeds
Runners, bulbs, grafts, cuttings
vegetative (grass), fragmentation, test-tube cloning
Genetic diversity
Clones
More complex & hazardous for seedlings
Simpler (no pollinator needed)
Advantage in unstable environments
Suited for stable environments

18. Asexual reproduction in aspen trees
Each grove of trees derives from the root system of one parent. Notice that genetic differences between groves descended from different parents result in different timing for development of fall color and the loss of leaves.

19. Test-tube cloning of carrots
Just a few parenchyma cells from a carrot gave rise to this callus, a mass of undifferentiated cells.
The callus differentiates into an entire plant, with leaves, stems, and roots.

20. Humans Modify Crops Artificial selection of plants for breeding
Plant Biotechnology:
Genetically modified organisms
“Golden Rice”: engineered to produce beta-carotene (Vit. A)
Bt corn: transgenic – expresses Bt (bacteria) gene  produces protein toxic to insects
Biofuels – reduce CO2 emissions
Biodiesel: vegetable oils
Bioethanol: convert cellulose into ethanol
One concern is the genetic engineering may transfer allergens, molecules to which some humans are allergic, from a gene source to a plant used for food.
Golden rice produces vitamin A by receiving those genes fro daffodils. Golden Rice is a transgenic organism.
Bt Maize, contains 90% less cancer-causing mycotoxin called fumonisin that is highly resistant to degradation and has been found alarmingly high concentrations on some batches of processed maize products. Fumonisin is produced by fungus that infects insect-damaged maize. Since Bt maize generally suffers less insect damage than non-GM maize, it contains much less fumonisin.