Transcript seed coat
Vegetative Plant Development Chapter 37 Embryo Development Begins once the egg cell is fertilized -The growing pollen tube enters angiosperm embryo sac and releases two sperm cells -One sperm fertilizes central cell and initiates endosperm development -Other sperm fertilizes the egg to produce a zygote -Cell division soon follows, creating the embryo 2 3 Embryo Development 4 Embryo Development (Cont.) 5 Embryo Development 6 Development of Body Plan -Apical meristems establish the root-shoot axis in the globular stage The 3 basic tissue systems arise at this stage -Dermal, ground and vascular 7 Formation of Tissue Systems Primary meristems differentiate while the plant embryo is still at the globular stage -No cell movements are involved The outer protoderm develops into dermal tissue that protects the plant The ground meristem develops into ground tissue that stores food and water The inner procambium develops into vascular tissue that transports water & nutrients 8 9 The heart-shaped globular stage gives rise to bulges called cotyledons -2 in dicots and 1 in monocots These bulges are produced by embryonic cells, and not by the shoot apical meristem -This process is called morphogenesis 10 During embryogenesis, angiosperms undergo three other critical events: -Storage of food in the cotyledons or endosperm -Differentiation of ovule tissue to form a seed coat -Development of carpel wall into a fruit 11 12 Seeds In many angiosperms, development of the embryo is arrested soon after meristems and cotyledons differentiate -The integuments and ovule wall develop into a relatively impermeable seed coat -Encloses the seed with its dormant embryo and stored food 13 14 Seeds Seeds are an important adaptation because: 1. They maintain dormancy under unfavorable conditions 2. They protect the young plant when it is most vulnerable 3. They provide food for the embryo until it can produce its own food 4. They facilitate dispersal of the embryo 15 Seeds Once a seed coat forms, most of the embryo’s metabolic activities cease Germination cannot take place until the seed absorbs enough water and oxygen for metabolism. -Seeds of some plants have been known to remain viable for thousands of years -Germination requires an additional environmental signal such as specific wavelength of light, or appropriate temperature 16 Seeds Germination may also require: - That the seeds pass through the intestines of birds or mammals - The seeds lie within tough cones that do not open until exposed to fire 17 Fruits Fruits are most simply defined as mature ovaries (carpels) -During seed formation, the flower ovary begins to develop into fruit 18 19 20 21 22 Dispersal and Pollination Occurs through a wide array of methods -Ingestion and transportation by birds or other vertebrates -Hitching a ride with hooked spines on birds and mammals -Burial in caches by herbivores -Blowing in the wind -Floating and drifting on water 23 24 25 Germination Germination is defined as the emergence of the radicle (first root) from the seed coat - It begins with imbibition, the absorption of water - Various enzymes are activated which in turn activate biochemical process like respiration and growth. - Gibberellic acid, hormones, are activated 26 27 28 29 Germination Parts of the embryo - Epicotyl: top of embryo which becomes shoot tip - Plumule: first true leaves attached to epicotyl - Hypocotyl: below epicotyl, it becomes the shoot - Radicle: below hypocotyl, it becomes root - Coleoptile: surrounds and protects epicotyl 30 31 32