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# BIOL 108 Introduction to Biological Diversity
## Topic 13: Evolution of Land Plants
> Lecture A2
> Yan-yin Wang
Geological Setting
Terrestrial surface of the Earth remained lifeless for over 3 billion years.
Estimated timing of key events:
Cyanobacteria began utilising land resources at around 1.2 billion years ago.
Evidence of small plants, fungi, and animals appeared on land at around 500 million years ago.
Overall, approximately 250,000 extant species of land plants have been identified.
Most plants live in terrestrial environments, such as deserts, grasslands, and forests.
# Major events in Lifes history (top) and one of the earlest fossil land plants Cooksonia (bottom) .
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
> https://www.digitalatlasofancientlife.org/learn/embryophytes/land-plant-origins/
Characteristics Shared between Land Plants Protists
Most shared characteristics are from protists, primarily in algae.
1. Land plants are multicellular, photoautotrophic eukaryotes as in many photoautotrophic algae.
2. Land plants have cells with cell walls composed of cellulose, as in red, green, and brown algae plus some dinoflagellates.
3. Land plants have chloroplasts with chlorophyll a
and b, as in green algae, euglenids, and some dinoflagellates.
4. The presence of chloroplast is almost certainly a symplesiomorphy of land plants.
5. Land plants store photosynthetic sugars as starch in plastids, as in green algae.
6. Land plants have life cycle with alternation of generation, which is present in some algae.
Alternation of generation is considered convergence (i.e., occurred independently in these algae and plant lineages).
# SEM of cellulose at different temperature (top) Chlorophyll f (bottom).
> Huang, Y., Meng, F., Liu, R., Yu, Y., & Yu, W. (2019). Morphology and supramolecular structure characterization of cellulose isolated from heat-treated moso bamboo. Cellulose ,26 , 7067-7078.
> Behrendt, L., Brejnrod, A., Schliep, M., Srensen, S. J., Larkum, A. W., & Khl, M. (2015). Chlorophyll f-driven photosynthesis in a cavernous cyanobacterium. The ISME Journal ,9(9), 2108-2111.
Evolution of Green Algae Leading to Land Plants
The closest extant relatives of land plants are the freshwater green algae charophytes, which is based on nuclear and chloroplast DNA.
Examples: The charophyte Zygnema and closely related taxa are phylogenetically closest to land plants.
Species of the genera Chara and Zygnema are common charophytes in lakes of Alberta.
The clade Streptophyta includes both charophytes and land plants.
# Zygnema (top) and Chara (bottom).
> Arc, E., Pichrtov, M., Kranner, I., & Holzinger, A. (2020). Pre-akinete formation in Zygnema sp. from polar habitats is associated with metabolite re-arrangement. Journal of Experimental Botany ,71 (11), 3314-3322.
> Barbosa, M., Lefler, F., Berthold, D. E., & Laughinghouse, H. D. (2021). The Ecology of Charophyte Algae (Charales): SS-AGR-448/AG448, 01/2021. EDIS ,2021 (1).
Evolution of Green Algae Leading to Land Plants
Shared derived features of Streptophyta:
1. Plasma membrane has rings of proteins responsible for cellulose synthesis.
Cellulose is composed of polysaccharide (i.e., sugar polymer), which aggregates into bundles called microfibrils.
Cellulose microfibrils in charophytes and land plants are organised as hexagonal pattern called rosette complex, which provide rigidity to the cell wall.
In non-charophyte algae, cellulose microfibrils are organised linearly.
Cellulose deposition in the cell wall is similar in charophytes and land plants, the amount of which are higher than non-charophyte algae.
# The cellulose synthesising complex.
Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
Nixon, B. T., Mansouri, K., Singh, A., Du, J., Davis, J. K., Lee, J. G., ... & Haigler, C. H. (2016). Comparative structural and computational analysis supports eighteen cellulose synthases in the plant cellulose synthesis complex. Scientific reports , 6(1), 28696.
Quang, T. H. (2010). Applications of molecular characters to breeding of Eucalyptus urophylla in Vietnam . Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences. Evolution of Green Algae Leading to Land Plants
Shared derived features of Streptophyta:
2. Homologous structure of flagellated sperm
Sperms of both basal land plants and charophytes have flagella.
This feature is lost in seed plants.
3. Phragmoplast formation takes place during the mitosis.
This process facilitate construction of cell wall plages and merge them with existing cell wall.
The formation of phragmoplast is designated to telophase of mitosis.
# Reconstructed sperm cells in liverwort and moss (top), and phragmoplast formation process (bottom).
Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
RENZAGLIA, K. S., AGUILAR, J. C. V., & GARBARY, D. J. (2018). Morphology supports the setaphyte hypothesis: mosses plus liverworts form a natural group. Bryophyte Diversity and Evolution , 40 (2), 11-17.
Livanos, P., Chugh, M., & Mller, S. (2017). Analysis of phragmoplast kinetics during plant cytokinesis. Plant protein secretion: methods and protocols , 137-150. Phylogeny of Basal Land Plants
Which taxon is closest to land plants, and how may we draw a line between land plants and algae?
Viridiplantae including embryophytes, charophytes, and chlorophytes
virid means green.
Supporting evidence: Chloroplast structure derived from primary endosymbiosis of cyanobacteria.
Streptophyta including embryophytes and charophytes
strepto means twisted.
Supporting evidence: Presence of phragmoplast during mitosis.
Embryophyta (the strictest, most exclusive definition)
Supporting evidence: Embryonic development takes place within the female gametophytes.
> Three possible plant kingdoms (required!).
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
Delineating the monophyletic group of land plants is an ongoing pursuit. Benefits of Moving to Terra Firma
1. Decreased competition: Spacious habitats with fewer competing species.
2. Increased photosynthesis: Sunlight on land is not filtered by water.
Water absorbs light
Organisms such as phytoplankton algae can block light.
3. Abundant carbon dioxide (CO 2 ): Concentration in the current atmosphere is about 0.04% (~ 400 ppm).
Carbon dioxide in the atmosphere is directly available for biological processes.
Carbon dioxide in water requires additional steps of conversion.
> Retallack, G. J. (2015). Late Ordovician glaciation initiated by early land plant evolution and punctuated by greenhouse mass extinctions. The Journal of Geology ,123 (6), 509-538.
Benefits of Moving to Terra Firma
4. Rich minerals in soil: Substrates on land are rich in essential minerals for plant growth (e.g., nitrogen).
5. Few herbivores or pathogens: Initially, there were few herbivorous organisms on land as selective agents.
> # Fossil Sphaeromorph, a group of eukaryotes from Ordovician.
> Wellman, C. H., Cascales-Miana, B., & Servais, T. (2023). Terrestrialization in the Ordovician.
Challenges of Moving to Terra Firma
1. Scarcity of water: Desiccation will lead to cessation of biological processes, and death of the organism.
2. Support against the heartless gravity: Without buoyancy of water, land plants would need structural support.
# Conceptual models that minimising effects of gravity and wind in plants.
> Niklas, K. J. (1998). The influence of gravity and wind on land plant evolution. Review of Palaeobotany and Palynology ,102 (1-2), 1-14.
Adaptations for Land Colonisation
1. The presence of sporopollenin.
Definition : Sporopollenin is an incredibly durable polymer in cell wall.
Evidence of sporopollenin has been found in rocks as old as 500 million years ago.
Sporopollenin is resistant to degradation by enzymes, inorganic chemicals, and environmental stresses (e.g. UV light).
Sporopollenin is found in charophyte zygotes, as well as spores and pollens in plants.
# SEM images of the sporopollenin capsules in the spores of dandelions.
> Fan, T., Park, J. H., Pham, Q. A., Tan, E. L., Mundargi, R. C., Potroz, M. G., ... & Cho, N. J. (2018). Extraction of cage-like sporopollenin exine capsules from dandelion pollen grains. Scientific reports ,8(1), 6565. https://organiclawnsbylunseth.com/how-to-kill-dandelions-naturally/
Adaptations for Land Colonisation
2. The presence of structures to conserve water.
Waxy cuticle: A waxy covering on the surface of stems and leaves that prevents desiccation in land plants.
The waxy cuticle is composed of polymers called polyesters and waxes.
Stomata: A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.
Stomata can close to minimise water loss, which is regulated by guard cells.
Waxy cuticles and stomata likely evolved early in the evolutionary history of land plants.
The origin, evolution, and plausible initial function of these two structures are unclear.
# Effects of waxy cuticle (top left), the waxy layer (top right), and stomata in plants (bottom).
> https://sonomamountainecologynotes.com/waxy-cuticle/
> https://beyondthehumaneye.blogspot.com/2011/11/plant-cuticles.html
> Guan, Z. J., Zhang, S. B., Guan, K. Y., Li, S. Y., & Hu, H. (2011). Leaf anatomical structures of Paphiopedilum and Cypripedium and their adaptive significance. Journal of Plant Research ,124 , 289-298.
Adaptations for Land Colonisation
3. The presence of lignified vascular tissues for internal transportation.
Lignification : the process by which plant cell walls become waterproofed and rigid through the deposition of a polymer called lignin.
Main functions:
Provide rigidity for vertical growth
Transport and distribute water and nutrients
Two types based on functions:
Xylem transports water and minerals from root to the rest of the body via microscopic conduits formed by dead, lignified cells.
Phloem transport and distribute soluble organic molecules produced during photosynthesis via living cells.
Section of the root in a typical eudicot plant (left) and close-up on the xylem and phloem (right). The special relationship between xylem and phloem is required.
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
# SEM of the sieve structures in phloem.
> Mullendore, D. L., Windt, C. W., Van As, H., & Knoblauch, M. (2010). Sieve tube geometry in relation to phloem flow. The Plant Cell ,22 (3), 579-593.
Adaptations for Land Colonisation
4. Functional compartmentalisation of the plant body
Various parts of the plants are differentiated for specialised roles
Examples:
Roots exploring underground for water and minerals
Stems support the plant structure, transport water, nutrients, and sugars between roots and leaves.
Shoots seeking lights and gases above ground.
# Root and shoot systems in a typical canopy.
> Tracy, S. R., Nagel, K. A., Postma, J. A., Fassbender, H., Wasson, A., & Watt, M. (2020). Crop improvement from phenotyping roots: highlights reveal expanding opportunities. Trends in plant science ,25 (1), 105-118.
Shared, Derived Traits of Land Plants
Five distinctive characteristics group land plants together.
1. The alternation of two multicellular generations.
The sporophyte (2n) is specialised for dispersal.
The gametophyte is specialised for fertilisation.
Generalised process of life cycle:
Fusion of two gametes form a sporophyte (2n).
Sporophyte releases spores (1n).
Spores develop into multicellular gametophyte (1n) through mitosis.
Gametophytes (1n) generate gametes (1n) through mitosis.
Gametes are fertilised into sporophyte (2n).
Animals lack the multicellular haploid (1n) stage.
Charophytes lack the alternation of generations.
The spores do not develop into sporophytes (2n)
> Typical process of alternation of generations (required!). Fig. 29.5.
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
Shared, Derived Traits of Land Plants
Five distinctive characteristics group land plants together.
2. The fertilised embryo is retained in the female gametophyte (i.e., multicellular, dependent embryos).
The name embryophytes (i.e., land plants) comes from this feature.
Development of the embryo is nurtured by the parent via placental transfer cells.
A nutrient dependency is formed between parent and the embryo.
The placental transfer cells are analogous to the placenta in placental mammals (e.g., human).
# Micrographs (left) and ultrastructure (right) of land plant embryos, showing the placental transfer cells.
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
# Micrograph of sporophytic body of a liverwort.
> Graham, L. E., Cook, M. E., & Busse, J. S. (2000). The origin of plants: body plan changes contributing to a major evolutionary radiation. Proceedings of the National Academy of Sciences ,97 (9), 4535-4540.
Shared, Derived Traits of Land Plants
Five distinctive characteristics group land plants together.
3. Sporangia produce walled spores
Sporangia : Multicellular organs in plants where meiosis takes place and haploid spores (1n) develop.
Spores are produced from diploid sporocytes (2n) via meiosis.
Walls of spores contains sporopollenin, which allow spores to survive harsh environmental factors (e.g., desiccation).
# Gross and microscopic morphology of sporangium (top) and sporocytes (bottom).
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
> Shimamura, M., Itouga, M., & Tsubota, H. (2012). Evolution of apolar sporocytes in marchantialean liverworts: implications from molecular phylogeny. Journal of plant research ,125 , 197-206.
Shared, Derived Traits of Land Plants
Five distinctive characteristics group land plants together.
4. The presence of multicellular gametangia.
Gametangia: multicellular organs that produce gametes by mitosis.
Flowering plants (i.e., angiosperms) lack gametangia but gametes are still produced by mitosis.
Two types of gametangia:
Archegonia : The female gametangia that house eggs and serve as sites of fertilisation.
Antheridia : The male gametangia that produce and release sperms.
# Diagram (right) and histological (bottom) comparison between archegonia and antheridia.
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
> Simpson, M. G. (2019). Plant systematics . Academic press.
Shared, Derived Traits of Land Plants
Five distinctive characteristics group land plants together.
5. The presence of apical meristems.
Apical meristems : Embryonic plant tissues in the tips of roots and buds of shoots. The dividing cells of an apical meristem enable the plant to grow in length.
Meristem-produced cells differentiate into various tissues (e.g., outer dermal tissues, vascular tissues).
Apical meristems are located at the tips of shoots and roots.
The movements in plants are achieved by growing.
Histological sections of apical meristems. The locations of apical meristem are required.
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
> Husakova, E., Hochholdinger, F., & Soukup, A. (2013). Lateral root development in the maize (Zea mays) lateral rootless1 mutant. Annals of Botany ,112 (2), 417-428.
Origin of Land Plants
Major events of land plant evolution:
Terrestrial photosynthetic cyanobacteria likely emerged approximately 1.2 billion years ago.
Fossilised spores and tissues suggest that plants live on terra firma as old as 470 million years ago.
Molecular clock method estimates the origin of land plants between 425 and 490 million years ago.
# Molecular clock: A method for estimating the time required for a given amount of evolutionary change, based on the observation that some regions of genomes evolve at constant rates.
# formula = 2
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
> #Major events in Lifes history (top), fossil spores (bottom left), and fossil Cooksonia (bottom right) .
Divergence of Land Plants
Basal land plants diversifies into multiple extant groups.
Land plants are informally classified into non-vascular and vascular plants.
Non-vascular plants are collectively called bryophytes, including liverworts, mosses, and hornworts.
The classification is informal, as the phylogenetic relationships are unresolved.
Bryophytes are most definitely not a monophyletic group.
Phylogeny of Embryophyta.
> Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2024). Campbell biology (4th Canadian ed.). Pearson.
# Phylogeny of Streptophytes.
> de Len, I. P. (2024). Evolution of immunity networks across embryophytes. Current Opinion in Plant Biology ,77 , 102450.
Basic Phylogenetic Framework of Land Plant
Non-vascular plants
Vascular plants
Paraphyletic seedless vascular plants
Lycophytes
Monilophytes
Seed plants
Gymnosperms
Angiosperms (i.e., flowering plants)
# Lycophytes (top left), monilophytes (top right), gymnosperms (bottom left), and angiosperms (bottom right).
https://www.nybg.org/blogs/plant-talk/tag/lycophytes/
https://thaifernflora.myspecies.info/taxonomy/term/218
https://plants.ces.ncsu.edu/plants/pinus-contorta-var-latifolia/
By Zachi Evenor - Flickr: https://www.flickr.com/photos/zachievenor/9438824400/in/set-72157633416612860/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=27565865 Some Reflective Questions (Not an Exhaustive List for Exam!)
Why do we think that land plants evolved from algae?
Did characteristics of land plants appear gradually, why?
How can we define land plants?
What adaptations likely facilitated transition to land in streptophytes?
How may the terrestrial adaptations solve challenges of living on land?
Can you draw simple diagrams depicting characteristics of land plants?