Transcript Lecture 9

BIOLOGY 3404F
EVOLUTION OF PLANTS
Fall 2008
Lecture 9
Thursday October 16
Chapter 16, The Bryophytes
The Move Onto Land – Barely
Today and next Thursday we will be discussing the
bryophytes – Anthocerophyta (Hornworts),
Hepatophyta (= Marchantiophyta; Liverworts), and
Bryophyta (Mosses). These plants have some
adaptations for life on land, but without true vascular
tissues (no phloem or xylem, tracheids or vessels)
and with aquatic fertilization, they can not grow too
far from free water.
What is a Bryophyte?
• Bryophytes are non-vascular, spore-bearing
members of the Kingdom Plantae
• Previously, we listed the 5 characters of
plants, including bryophytes, that are not
found in Chlorophyta*:
What makes a Plant?
1.
2.
3.
4.
5.
Protective layer of cells surrounding the male and female
gametangia,
Retention of zygote and developing sporophyte within female
gametophyte (i.e., within archegonium),
Multicellular diploid sporophyte (multiple meioses per mating
event),
Multicellular sporangia (capsules) with protective layer of
sterile cells,
Drying-resistant spores with walls containing sporopollenin (a
cyclic alcohol), which is also highly decay resistant. (*5
sporopollenin is found in zygote walls of Charophyceae)
Riccia, with sporophyte (right) embedded in gametophyte (left)
Hornwort gametophyte with sporophytes; note tetrad of spores
What makes a bryophyte?
6.
Like Chlorophyta and Tracheophyta, have chlorophyll a
dominant, chlorophyll b and carotenoids as accessory
pigments
7. Like vascular plants and some green algae, have cellulose cell
walls
8. Few bryophytes have a cuticle (vascular plants do).
9. No lignified tissues in gametophyte or sporophyte (present in
many vascular plants, esp. perennials)
10. Sporic meiosis with heteromorphic alternation of generations
11. Dominant gametophyte phase
Cross section of Marchantia gametophyte; multistratose with pores
surrounded by specialized cells, the lowermost of which can close
off the opening in a manner similar to guard cells of stomata
Protonema of a moss, with bud that forms developing gametophyte
Bryophyte characters II
12. Sporophyte (short-lived to annual), though photosynthetic
before spore dispersal, is attached to and at least partly
dependent on gametophyte (foot cells penetrate and derive
nutrients from gametophyte)
13. Gametophyte generally perennial (a few are ephemeral –
short-lived), with a juvenile filamentous phase (protonema)
followed by leafy or thalloid structure that produces the
gametangia
14. Sporophyte unbranched and determinate, with a single
terminal sporangium (gametophyte may be branched or
unbranched, determinate or indeterminate)
Bryophyte characters III
15. Spores (see #5 in first list) generally air-dispersed
16. Male gametes (sperm) produced in antheridium, a stalked,
club-shaped sac with a sterile jacket layer one cell thick
(unistratose) enclosing innumerable cells, each of which
produces a sperm (remember, no meiosis involved in gamete
formation)
17. Sperm have two whiplash flagella and must swim to egg in
archegonium in a water film (another reason bryophytes live
in at least seasonally wet places)
18. Female gamete (egg) produced singly in archegonium, a
flask-shaped structure with a unistratose neck and
multistratose basal bulb (venter)
Antheridium
Archegonium; calyptra develops from venter (bulb) of haploid tissue
Marchantia sporophytes develop from zygote within archegonium
Bryophyte characters IV
19. Growth of gametophyte is by a single apical cell. Sporophyte
has a meristematic zone at the base of seta (compare
meristematic zones in vascs)
20. Generally small – sporophyte usually less than 3 cm tall
(often much less), gametophyte generally less than 10 cm, but
may be less than 1 mm, or in some aquatic forms as long as 1
meter
21. Lack roots – have filaments one-celled thick called rhizoids
(single celled in hornworts and liverworts, multicelled in
mosses) for anchoring and some water and nutrient
absorption
Bryophyte characters V
22. Non-vascular – i.e., lack specialized phloem and xylem, and
therefore lack true stems and leaves – what we see as stems
and leaves are called caulids and phyllids. However,
sporophyte stalks (and some gametophyte stems) have waterconducting cells called hydroids (tubular cells lacking
protoplasts at maturity, with thin longitudinal and inclined end
walls, highly permeable, thus preferred path for water flow).
These lack spiral thickenings found in tracheids and vessels.
In some mosses, leptoids surround a strand of hydroids – these
are food-conducting (as are phloem tissues in vascs), and have
degenerate nuclei, but living protoplasm at maturity (common
ancestor to phloem and xylem).
Hydroids (center) and leptoids in conducting strand in seta of moss
sporophyte
Sexual features and ploidy
23. Antheridia and archegonia in same inflorescence (similar to
what we call a perfect flower) = synoicous. If not, =
autoicous, which may be:
a) monoicous (antheridia and archegonia in same plant) or
b) dioicous (different male and female plants)
24. Sporophyte (= seta and capsule) is diploid outgrowth of zygote
from within archegonium; calyptra (if present) is haploid,
developed from the venter
WHEN?
• First fossils found in Devonian (probable origin in
Silurian or even Ordovician)
• The oldest unequivocal bryophyte fossil is a liverwort –
Pallavicinites (very similar to Pallavicinia, which we
saw in lab), from upper Devonian (370 MYA) in New
York state – probably have it here in Southern Ontario
too.
• Great liverwort flora in Jurassic/Triassic of Sweden
(200+ MYA).
Fossil and extant pallavicinalean liverworts. 1. Pallavicinites devonicus,
portion of thallus (from Oostendorp, 1987).
2. Pallavicinia xiphoides thallus (from Karssilov et al., 1984). Arrows
indicate position of marginal teeth.
vis-pc.plantbio.ohiou.edu/ moss/dunn1.html
Fossilized spores preserved in 440-470 million-year-old sediments afford
the earliest evidence for plant life on land. Were the plants that produced
them Bryophytes?
Wellman, C., Osterloff, P.L. and Mohiuddin, U., 2003. Fragments of the
earliest land plants. Nature, 425: 282-284.
WHEN II
• Oldest moss is Carboniferous (Pennsylvanian; 300
MYA) – Muscites, close to modern Polytrichum
(which is considered an advanced moss).
• The best fossil mosses are “Protosphagnales” from
Permian (280 MYA) in Russia, with radiallyarranged, unistratose leaves, cell arrangement like
modern Sphagnum, but no sex organs preserved (or
found).
WHERE?
• From Arctic to Antarctic and everywhere in between,
abundant in moist tropics, and a few occur in deserts.
• Like lichens, they wet rapidly but dry out much more
rapidly.
• Some can survive desiccated for months or years and
can survive extreme temperatures when dry, but rapid
drying or extreme temperatures when wet can be
damaging.
WHERE II
• Epiliths (= saxicolous), epiphytes (= corticolous if on
bark, epiphyllous on leaves), on soil (= terrestrial), or
aquatic, but not marine
• Like lichens, are largely independent of substrate for
nutrients, but may have some substrate specificity
because of pH or other chemistry, or microclimate.
• Tend to be found in moist environments, bathed in
surface water, because of aquatic fertilization
Bryophyte ecology and nutrition
• Bryophytes, like lichens, may take in nutrients
through “leafy” tissues of thallus, in addition
to uptake through rhizoids and (in a few) via
symbiosis with Glomeromycota
• Because of this, they are sensitive to the
environments where they live: some prefer
acidic sites, others basic or calcium-rich sites;
some are pollution intolerant, others tolerant
• Saxicolous, corticolous, epiphyllous, …
Economic Importance of Bryophytes
I. Liverworts and hornworts: not much! (but many
contain N-fixing cyanobacteria, important in
ecosystem nutrient availability; some are mycorrhizal
with Glomeromycota)
II. SPHAGNIDAE: "economic" importance
• 1. Important in hydrodynamics of large areas of
especially northern hemisphere - bogs and
“muskeg”.
• 2. Sphagnum dressings, in medicine, shoes and
diapers
• III. Other mosses, various other uses
BOG FORMATION
• a) open pond, slow-moving stream: margins
with floating aquatics, especially Carex spp.
with roots anchored in Sphagnum
• b) Sphagnum builds above (growth) and below
(death and deposition) water-line; enables
margin to grow inwards
• c) increased Sphagnum growth allows
colonization of mat by bog shrubs, and
eventually conifers such as black spruce &
tamarack
Bog Formation II
• d) continued encroachment of water surface by
floating bog mat may eventually cover surface if
disturbance is slight. Waves or stream-flow erode
edges
• e) amelioration of water table by increased
Sphagnum mat away from water-line allows
development of forest; hummocks may have white
pine or white birch
• f) in permafrost areas, forest lowers summer
temperature of forest floor, permafrost moves upward,
water is trapped, and trees are drowned, so open
Sphagnum bog cycles with forest
SPHAGNUM ION-EXCHANGE
MECHANISM
• Metal2+ + 2HA ---> MA+ + A- + 2H+
• Gives off H+, lowering pH and eliminating
competing mosses (and many vascular
plants)
• Metal ions can be displaced by shaking in
H+ (e.g., dilute HCl) to assay metal content
BOG SIDE-BENEFITS
a)
b)
Bog fossils
PEAT (1.5m = 6,000y): for fuel and
horticulture
c) Conservation aspects: exploitations and
emissions
d) Carbon sink – unless climate warms!
Sphagnum dressings, in medicine, shoes
and diapers
• Absorbs 16-20 X dry weight in water (cotton 4-6); comfortable;
mildly antiseptic (vs diaper rash, gangrene)
• Sphagnum dressing used greatly in wars: Russo-Japanese (19045); WW I (both sides). Millions of dressings made by thousands of
volunteers
a) crude sphagnum collected, partially air-dried, cleaned of debris, and
sorted.
b) wrapped in sewn gauze
c) sterilized before use by autoclaving or with antiseptics
d) preferred species was S. papillosum; also used were S. palustre, S.
imbricatum & S. magellanicum
From Prince Rupert Public Library
III. Other Mosses, Other Uses:
1. Housing
2. Boat-building
3. Fibre for baskets
4. Bedding and pillows
5. Cultivation
6. Mosses as living mulch in nurseries and
orchards
7. Problem mosses in lawns and roofs