origin of seeds

1
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

2
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

3
2 types of seed plants

• 1. Gymnosperms naked seeds
• seeds exposed (on cones)
• 2. Angiosperms vessel seeds
• seeds inside fruits

4
gymnosperm life cycle

• heterospory w/2 types of cones
• 1) small cones w/microsporangia
• microspores develop into pollen
• pollen immature male gametophyte
• reduced in sizeno antheridia
• whole gametophyte travels (pollination)
• fertilization without water

5
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

6
gymnosperm seedexample Pine

seed coat (2n)
female gametophyte (n)
embryo (2n)
embryo is new sporophyte female gametophyte is
stored food
7
pine life cycle

• 3 years to make seed
• pollination seed dispersal by wind

8
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

9
gymnosperms--Ginkgo

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

10
gymnosperms--Gnetophyta3 very different genera,
70 sp

• 1) Ephedra
• desert
• mormon tea
• ephedrine

11
gymnosperms--Gnetophyta

• 2) Gnetum
• tropical vine
• flat leaves

12
gymnosperms--Gnetophyta

• 3) Welwitschia mirabilis
• Namib desert, 2 leaves, 1500 yrs old

13
gymnosperms--conifers

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

14
Taxodium distichum bald cypress Heron Pond,
Cache River State Natural Area , S IL
deciduous relative of redwoods sequoias
15

• oldest plants
• Bristlecone Pines 4600 years old

16
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

17
types of growth

• primary growth (up or down) shoot root apical
  meristems
• secondary growth (out) cambium meristem makes
  shoot root thick

18
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

19
tree rings seasonal changes in xylem cell size
20
dendrochronology

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

21
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
• balance of hormones required