Origin of Plants 1.) Quiz 1 2.) Abstract & graphs Due now 3.) Lecture on Plant diversity (have diversity terms handout ready) 4.) Cladistics exercise -- turn in worksheet 5.) Lab practical next week – study plant diversity slides on bioviewer & names of phyla, orders, etc.
Principal Biological Concepts
A. Charophytes as probable ancestors to terrestrial plants.
B. Terrestrial adaptations.
C. Alternation of generations.
D. Archegonia/ antheridia.
E. Vascular tissues.
G. Characters and synapomorphies of plant clades
Marine life was already diverse (~550 Ma) before the rise of the land plants (~450 Ma) why didn’t plants evolve earlier and colonize the land?
CO2 today is ~380 ppm Why?
CO2 today is ~380 ppm Cyanobacteria -- 2.7 billion 1 st land plants 425 million yrs ago
Gametophyte: gametophyte is the multicellular structure, or phase, that is haploid, containing a single set of chromosomes. The gametophyte produces male or female gametes (or both), by a process of cell division called mitosis
Sporophyte: the plant in which meiosis occurs and produces spores
Monoecious: male and female gametes produced on the same plant
Dioecious: male and female gametes produced on separate plants
Antheridia: the male sperm-bearing organ
Archegonia: the female egg-bearing organ
Gametangia: Archegonium of Marchantia (left) Antheridium of a hornwort (right)
Alternation of generations Diploid Haploid
Alternation of generations
1. Alternation between sporophyte (spore-producing) and gametophyte (gamete-producing), diploid and haploid .
2. Transitions of generations marked by meiosis and syngamy (fertilization) .
3. Evolutionarily important - haploid genes in plant gametophytes are transcribed (unlike those in animals). Gives the possibility of rapid selection.
Land plants: Apical meristems of shoots and roots shoots roots
" BRYOPHYTES " - non-vascular land plants
A. Gametophyte dominant – sporophyte reduced
B. Often with separate sexes ( dioecious ).
C. Antheridia - produce flagellated sperm.
D. Archegonia - produce egg and house developing embryo (sporophyte).
E. Antheridia and archegonia, or modifications thereof, are found in all early plant groups (through ferns).
F. Water required for sperm transfer. Sperm are flagellated (i.e., motile). This is true of all primitive plants.
2. Leaves are small and scalelike with traces of vascular tissue = microphylls .
3 . Strobilus = cluster of sporophylls (specialized leaves bearing sporangia ), at tips of branches ( Lycopodium ) or along branches ( Selaginella ).
4. Free-living gametophyte.
Lepidodendron - Ancient Lycopds (club mosses)
Phylum PTEROPHYTA ferns and fern allies
1. Whisk ferns ( Psilotum )
a. Well developed xylem and phloem in stem.
b. No true roots or leaves - secondarily lost .
c. Rhizome (underground stem - absorptive) with rhizoids and with myccorhizae.
d. Sporangia borne on shoots - unique character.
e. Gametophytes are free-living, nonphotosynthetic, saprophytes with associated mycorrhizae.
Horsetails ( Equisetum )
a. Ribbed, jointed (nodes) stems with silica crystals = "scouring rushes."
b. Leaves are non-photosynthetic microphylls .
c. Underground rhizomes - asexual reproduction.
d. True roots.
e. Terminal strobili on reproductive shoots.
f. Equisetum is only living genus.
This is how a forest of Calamites and Asteroxylon may have appeared just about anywhere on the Earth 390 million years ago. The Calamites are the slender "Christmas tree" shaped plants. They grew as tall as many of today's conifers, though they are the ancestors of the much smaller modern horsetails. The snake-like curlicue plants in the foreground are the now-extinct Asteroxylon, which emerged at the beginning of the Devonian period about 417 million years ago http://www.arcadiastreet.com/cgvistas/earth/earth_02_paleozoic_111.htm
a. Sporophyte dominant but dependent on gametophyte at first.
b. Independent (free-living, photosynthetic) gametophyte ( prothallus or prothallium ) - without vascular tissues. Has antheridia and archegonia.
c. True roots and stems (underground rhizomes) and leaves (megaphylls called fronds ).
d. Sporangia clustered in sori , often protected by indusium .
e. In lab:
i. Cyrtomium (no. 5)
ii. fern prothalium (no. 6)
iii. fern sporophyte (no. 7)
iv. live fern
The life cycle of a fern Haploid Diploid Homosporous (mostly)
Fern sporophyll, a leaf specialized for spore production Indusium
Life cycle of a fern: mature sporangium
Fern sporophytes growing out of fertilized gametophytes
Mature fern sporophyte – produces spores
Carboniferous forest – ferns abundant
SEED PLANTS " SPERMATOPHYTES "
A. Seed = plant embryo protected by integument (“seed coat”).
B. "GYMNOSPERMS" - "naked seeds"- seeds without protection of ovary.
C. Sporophyte dominant - gametophyte reduced to very small size.
1. Megagametophyte - multicellular archegonium.
2 . Microgametophyte - pollen grains - 3 or 4 cells. No antheridia.
3. “Mega” and “micro” are used in higher plants to denote the larger female structures and the smaller male ones.
Ginkgo has free swimming sperm! Ginkgo and the cycads are the only living seed-producing plants (spermatophytes) that have motile or free swimming sperm – discovered in 1896 in a botanical garden in Tokyo
Sequoia Sempervirens ( Cupressaceae ) Tallest redwoods over 300 feet
Over 4,000 years old
B. Strobili = cones - borne on spur shoots
1. Staminate cones - male - microsporangia on microsporophylls .
2. Ovulate cones - female - ovules on ovulate scales with woody bract.
a. Ovule = female gametophyte (haploid) surrounded by nucellus and integument (both diploid). Mature ovule = seed.
C. Wind-blown pollen enters the ovulate cones when they are very small. Pollen tubes (immotile sperm) grow very slowly. So - fertilization may not occur for many months, even years, until the seed cones and the megagametophytes have matured.
1. Two sperm nuclei in pollen tube but only one is functional; the other degenerates.
D. Reproduction does not depend on water .
E. Well over 1 year passes between pollination and fertilization. Seeds usually not mature until 2nd summer.
F. Fire very important to many of these species.
Pine female strobili
Staminate pine cones
The life cycle of a pine
Spores developing in male cones Turn to page 99 in your lab manual
Chlorophyta Charophyta Liverworts Hornworts Moss Lycophytes Monilophytes Gymnosperms Angiosperms chlorophyll a and b/ Starch as a storage product/Cell wall of cellulose phragmoplast Cuticle, multicellular gametangia, embryo, multicellular sporophyte BRYOPHYTES Gametophyte dominant Gametophyte vs. sporophyte dominance
STUDY for Practical A. Charophytes as probable ancestors to terrestrial plants. B. Terrestrial adaptations. C. Alternation of generations. D. Archegonia/ antheridia. E. Vascular tissues. F. Seeds. G. Characters and synapomorphies of plant clades. Slides - Chap 7 Lab model - Marchantia Recommended Bioviewer activities
Cladistic Analysis exercise
Data sheet (Relationships of Plant Taxa), pp. 103-104.
You must complete the taxon-character matrix. Complete everything except that for Magnolia and Gladiola this week.