origin of seeds late Devonian 360 mya seed

origin of seeds • • • late Devonian, 360 mya seed = embryo + food + protective coat advantage: protection from desiccation wait for good conditions own food to get started

reproductive adaptations of seed plants • gametophytes smaller • female gametophyte retained on parent sporophyte • male gametophyte transports sperm • water not required for fertilization • seeds are means of dispersal

2 types of seed plants • 1. Gymnosperms “naked seeds” – seeds exposed (on cones) • 2. Angiosperms “vessel seeds” – seeds inside fruits

gymnosperm life cycle • • heterospory w/2 types of cones: 1) small cones w/microsporangia microspores develop into pollen = immature male gametophyte reduced in size—no antheridia whole gametophyte travels (pollination) fertilization without water

gymnosperm life cycle • 2) large cones have megasporangia • megasporangium protected by integuments • ovule = megasporangium + integuments • seed = mature ovule • integuments become seed coat • megaspore stays in megasporangium

gymnosperm seed example: Pine • seed coat (2 n) female gametophyte (n) embryo (2 n) embryo is new sporophyte female gametophyte is stored food

pine life cycle • 3 years to make seed • pollination & seed dispersal by wind

gymnosperms--cycads • • prominent w/dinosaurs today 11 genera 130 sp tough leaves look like ferns but have cones w/seeds roots assoc. w/cyanobacteria plants defended by toxic compounds

gymnosperms--Ginkgo • • • only genus in group Ginkgophyta thought extinct good urban tree stinky seeds veins dichotomously branched

gymnosperms--Gnetophyta 3 very different genera, 70 sp • • 1) Ephedra desert “mormon tea” ephedrine

gymnosperms--Gnetophyta • 2) Gnetum • tropical vine • flat leaves

gymnosperms--Gnetophyta • 3) Welwitschia mirabilis • Namib desert, 2 leaves, ~1500 yrs old

gymnosperms--conifers • very successful. 50 genera, 550 sp • most evergreen • needle leaves adapted for drought – small surface area, thick cuticle – stomata sunken in valleys

Taxodium distichum bald cypress Heron Pond, Cache River State Natural Area , S IL deciduous relative of redwoods & sequoias

• oldest plants • Bristlecone Pines 4600 years old

gymnosperms--conifers • most massive plants • Giant Sequoia 26 m circumference, (8. 3 m diameter!) 3000 years old • tallest living plants • Coast Redwoods 367 ft tall, 600 -800 yrs old • Watterson Towers only 281 ft

types of growth • primary growth (up or down): shoot & root apical meristems • secondary growth (out): cambium— meristem makes shoot & root thick

secondary growth • vascular cambium: – xylem to inside, phloem to outside • wood is secondary xylem • cork cambium makes cork to outside • bark = cork + phloem – everything outside of vascular cambium

tree rings: seasonal changes in xylem cell size

dendrochronology • • • tree rings date historical events similar patterns in neighboring trees overlap rings: to get complete record need consistent rings regular wet & dry cycles

Plant tissue culture Fig 38. 14 • plant cells are totipotent: – any cell can grow into whole new plant • • • new plant is clone (same genes) examples: leaf cutting, Wollemi Pine callus = undifferentiated tissue (wound) develops roots and shoots balance of hormones required biotech: insert gene into callus