Angiosperm Reproduction and Biotechnology Dillin Snape Overview • Sexual VS asexual reproduction. • Growth of a seed and fruit • Since agriculture started, breeders have genetically manipulated traits of some wild crops by artificial selection. • Now the speed and extent of plant modification have increased in recent decades with Genetic Engineering. Flower Structure • Four modified leaves called floral organs: – Sepals • Enclose and protect the floral bud before it opens. – Stamens • Reproductive organ. • Stalk and anther. – Carpel • May have one or more carpels. • Ovary at the base – One or more ovules inside. • Long slender neck called the style. – At the top there is a sticky structure called stigma. » Landing platform for pollen. Pollination Enables Gametes to Come Together Within a Flower • Angiosperm sporophytes have a flower, a reproductive structure. • Pollination brings a male gametophyte to the stigma of a flower. • Germination brings a sperm from the gametophyte to a female gametophyte. – Located in the ovule, embedded in the ovary of the flower. • Fertilization happens within each ovule. Gametophyte Development and Pollination • • • • • Male gametophytes form in the pollen sac. Female gametophytes forms in each ovule. Pollination is transferring pollen from an anther to a stigma. A pollen grain makes it way down to the ovary. – Discharges sperm to a embryo sac. – An embryo develops. • The ovule develops into a seed. – The ovary develops into a fruit which contains one or more seeds.. When the conditions are ready they develop into seedlings. Preventing Self-Fertilization • Sexual reproduction has many advantages. – Genetic Diversity. – Better chance of some offspring surviving a challenge. • Self-Incompatibility – A plant rejects it’s own pollen by not growing the pollen tube. – Gametophytic selfincompatibility. – Sporophytic selfincompatibility. After Fertilization • • • • Double Fertilization – One sperm makes a zygote. – The other sperm make a triploid nucleus called an endosperm. • Food storing tissue of the seed. Ovules turn into seeds. Ovaries turn into fruit. – Protect seeds. – Aids in dispersal. Types of fruit – Simple – From a single carpel or fused carpel's. – Aggregate – A single flower with more than one separate carpel forming fruits. • All clustered together. – Multiple- A group of flowers clustered together. When the ovary’s grows they all fuse together to form one fruit. Seed germination • • Dormancy – As it matures it enters a phase of low metabolic rate. – Waiting for the right condition to germinate The right conditions – Many species differ, some example: • A lot of rain (Desert) • Forest fire (Competing plants are gone) • The right season (Ensuring a long growth season) • Light (Lettuce) • Weakened by chemicals (Animals digestive tract) – Some seeds can remain dormant for days to decades, some even longer. Seed to Seedling • • • Begin by a process called Imbibition – Uptake of water from the low water potential of the dry seed. The first organ to emerge form the seed is the radicle – Embryonic root. Then there are two ways for the shoot tip to break through the soil surface. – First Way • A hook shape forms from the hypocotyl. • Growth pushes the hook above the surface. • Light stimulates it to straighten. • Leaves emerge and start making food from photosynthesis – Second Way • The coleoptile, pushes upwards through the soil and into the air. • The shoot tip grows through the tubular coleoptile. Breaking though the tip. Asexual Reproduction • Exact clone of the parent • Advantages – If it is in a stable environment then all of it’s offspring will be suited for that environment. – Offspring aren’t as frail. • Usually mature vegetative fragment from the parent plants. • Disadvantages – An unstable enviroment • New pathogens • Varied offspring means some can survive. – If a catastrophic event happened like a new disease, then all of them would die. Mechanisms • • • • Plants are able to renew or sustain growth indefinitely. Parenchyma cells can divide and differentiate into more specialized types of cells. – A stem can get cut off and it will grow roots and become a whole plant. Fragmentation – Separation of a parent plants into parts the develop whole new plants. Apomixis – Producing seeds without pollination. – No joining of sperm and egg. • A diploid cell in the ovule gives rise to an embryo. Vegetative Propagation and Agriculture • • • • Propagation is a form of asexual reproduction which plants grow new roots. Cutting – Cutting of parts of a plant that will grow adventitious roots and form a whole new plant. – A callus forms first and then the roots grow from that. • If a node is included in the fragment then the callus stage is skipped. Grafting – A twig or bud from one plant can be grafted onto a plant of a closely related species. • Combines the best qualities of each – The plant that provides the root system is the Stock. – The grafted part of the other plant is called the Scion. Test Tube Cloning – Able to grow whole plants by culturing smalls pieces of tissue or even single parenchyma cells. – Callus's form and hormones are used to shoot out roots. – Then transferred to soil. – Can make transgenic plants by inserting foreign genes. Plant Biotechnology Transforming Agriculture • Two meanings: – Innovations in the use of plants, or the substances made by plants, to make products for humans. – Genetically modifying plants in agriculture and industry Artificial Selection