BIOL 2P93 Lecture Notes - Lecture 4: Rhizoid, Common Cold, Polysaccharide
8 May 2018
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Spring BIOL 2P93 Lecture 2 Part 2 07/05/2018
Chapter 16: Bryophytes
• Common Morphology
o Bryophytes are Embryophytes
▪ do’t hae asular tissue
▪ multicellular sporangia & gametangia
▪ reproductive cells surrounded by 1 or more layers of sterile cells
▪ odies are’t oposed of filaets as i algae, they are composed of parenchyma which is
derived from apical growth
o they look like small versions of flowering plants
o Lierorts & Hororts are thalloid
▪ Their gametophytes are flat, wrinkled &/or lobed
▪ Thalli are thin bodies undifferentiated into roots, stems or leaves, facilitating uptake of
water & CO2
▪ Upper surfaces of Bryophyte gametophytes are adapted to allow increased CO2
permeability, while reducing water loss at the same time
▪
• Thalloid liverwort, distinguished from Mosses & Leafy Liverworts by the leaf
arrageet. They do’t hae stes or leaes; istead their ai ody is flat, like a
green pancake. This flat sheet is the thallus which constitutes the dominant
gametophyte generation
o Bryophytes anchor to substrate by rhizoids
▪ Simple hair-like extensions protruding from lower epidermal cells
o Absorption of water & inorganic ions directly via the gametophyte
o In mosses -> special hairs on leaves/stems help in water transport
o All bryophytes engage in symbiotic relationships w/ fungi or
cyanobacteria
▪ Aids in mineral & nutrient uptake
o Bryophytes lack true roots.
▪ They have filaments of cells (rhizoids) which serve as a point of
attachment to soil/substrate, not to absorb water or inorganic ions
o Tissue cells interconnected by cellular junctions known as
plasmodesmata
▪ Similar to VLP, Bryophytic plasmodesmata possess an internal component known as the
desmotube
• Narrow tube of endoplasmic reticulum
• Transports material b/n 2 adjacent tissue cells
• Liverwort plasmodesmata. Desmotube in plasmodesma on right
(arrows) is continuous w/ ER in cytosol. Longitudinal view ------->
find more resources at oneclass.com
find more resources at oneclass.com
Spring BIOL 2P93 Lecture 2 Part 2 07/05/2018
• Asexual Reproduction
o Production of gemmae is a widespread means of asexual reproduction in Liverworts/Mosses
o Liverworts -> Marchantia spp. the flattened plant body or thallus is a haploid gametophyte w/
gemma cups scattered about its upper surface
o Gemma cups
▪ Cup-like structures containing gemmae, small discs of haploid tissue, that directly give rise
to new gametophytes
▪ They are dispersed from gemma cups by rainfall
o Gemmae
▪ Bilaterally symmetrical & not differentiated into dorsal & ventral surfaces
▪ Mature gemmae fall on the ground, once conditions are suitable, they germinate
▪ Gemma surface that comes in contact w/ soil produces rhizoids
• This surface eventually becomes the lower (ventral) surface of the thallus
▪ Apical cells present in the 2 lateral notches become active & form 2 thalli in opposite
directions
▪
• Gametophyte of Marchantia spp. (liverwort) w/ gemma cups containing gemmae.
o Gemmae splashed out by rain & grow into gametophytes
▪ Each genetically identical to the parent plant derived through mitotic division
•
o Longitudinal section of Marchantia spp. gemma cup. The gemmae are the dark
structures which appear lens shaped in sectional view
▪ Video on gemmae dispersal -> http://www.youtube.com/watch?v=20OtCqfW3rM
• Common Reproductive Traits
o Sexual reproduction involves the production of male & female gametangia (antheridia &
archegonia), often on separate male & female gametophytes
o Stalked antheridium
▪ consists of a one cell thick sterile jacket layer surrounding
spermatogenous cells
▪ Each spermatogenous cell develops a single biflagellated
sperm which swims through water to reach an egg located in
the archegonium
▪ Male gametangium of Marchantia spp. has a stalk & sterile
jacket layer enclosing spermatogenous tissue which develops
into spermatogenous cells each w/ a biflagellate sperm. Sperm
find more resources at oneclass.com
find more resources at oneclass.com
Spring BIOL 2P93 Lecture 2 Part 2 07/05/2018
requires water to reach archegonium (& the egg). Sterile jacket layer is incapable of sperm
production
o Archegonia
▪ Flask-shaped w/ long necks, basal portion known as venter
which encloses a single egg
▪ Central neck cells known as neck canal cells disintegrate upon
egg maturity resulting in a fluid-filled tube through which
sperm swim to the egg
▪ Chemical attractants released to attract sperm
▪ Post fertilization -> Zygote remains in the archegonium and is
nourished by the maternal gametophyte (matrotrophy)
• Zygote undergoes mitosis generating a multicellular
embryo
o Develops into a mature sporophyte
▪ Photo of female gametangia (archegonia) of Marchantia spp. at
differing developmental stages. Egg contained in venter.
o Marchantia spp. embryo
• After fertilization of the egg, a zygote is created.
Through mitotic divisions of the zygote, a multicellular
embryo (young sporophyte) is generated. Here, the
embryo is in the early developmental stages & is still
w/n the enlarged venter (now called calyptra).
o Eventually, mature sporophyte is produced from
undifferentiated cell mass
o Spores encased in a wall containing the biopolymer
sporopollenin
▪ Allows spores to survive air dispersal from 1 moist site to another & resists decay &
chemicals
▪ Charophytic algal zygotes are also lined w/ sporopollenin, tolerating exposure & microbes &
remaining viable for an extended period of time
• Sporopollenin-walled plant spores though to have originated from these Charophycean
zygotes
o After germination, some Bryophyte spores form juvenile developmental stages, which in Mosses
are called protonemata (singular protonema)
▪ From protonemata, gametophytes & gametangia develop
• Characteristics of all mosses, some liverworts, but NOT hornworts
• Liverworts: Phylum Marchantiophyta
o ~5200 species, small & inconspicuous
o Grows in moist soils in greenhouses
o On early every continent, inhabiting a diverse array of ecosystems
o Can be found in harsh environments that many organisms find difficult to live & reproduce in
o Some species rely on photosynthate produced form VLP and mosses
▪ May form symbiotic relationships w/ fungi (typically located on rhizoids)
▪
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
This flat sheet is the thallus which constitutes the dominant gametophyte generation: bryophytes anchor to substrate by rhizoids, simple hair-like extensions protruding from lower epidermal cells, absorption of water & inorganic ions directly via the gametophyte. Desmotube in plasmodesma on right (arrows) is continuous w/ er in cytosol. 07/05/2018 requires water to reach archegonium (& the egg). Egg contained in venter: marchantia spp. embryo, after fertilization of the egg, a zygote is created. Through mitotic divisions of the zygote, a multicellular embryo (young sporophyte) is generated. Liverwort is about 30 cells thick at the midrib & approx. Rhizoids anchor the plant and pores allow exchange of gases in the air-filled chambers which dot the upper photosynthetic layer. Specialized cells surround pores perforating function similar to stomata in vlp that is to retard water loss. Liverworts produce mucilage, a highly hydrated polysaccharide, also aiding in water retention: pores are not stomata, they cannot close & contain no guard cells.
