Evolutionary history of plants - Wikipedia
Actualité: The tree of life on Earth (archeas,bacterias,eucaryotes) are trying to remove the maximum amount of information stored in their DNA to keep only Fungi, animals, plants are grouped on the same branch of the tree of life, the branch Bacteria form the second part of the tree, cells with no nucleus or Eubacteria. Mar 30, Providing science and society with an integrated, up‐to‐date, high quality, However, synthesizing the growing body of DNA sequence data in the public The major branches of the land plant tree of life are now generally well .. The Open Tree of Life uses a git‐based system for tree storage, called. Dec 20, Dating branches on the Tree of Life using DNA .. be shortsighted to ignore the enormous, and still largely untapped, store of information that.
It is now possible to sequence and analyze ribosomal RNAs without culturing the microbes that make them, providing a much more comprehensive window into the diversity of organisms present in the environment.
Tree of life (Earth) — Astronoo
However, the molecules that make up the ribosome, including the ribosomal RNAs, differ subtly between species in their composition, due to differences caused by mutation in the sequences of the genes that encode them. For more detail on ribosomal RNA see here. However, the exact sequences of DNA that encode these components are not identical between organisms.
DNA sequences can have more variety than the proteins they encode because the triplet codes for amino acids see our DNA basics article contain redundancies, and because the functions of proteins and RNAs in cells are related largely to how the molecules fold into three dimensional shapes.
Slight differences in the DNA sequence encoding these molecules can arise without altering their shapes significantly, and thus without affecting their function. Two microbes with different rRNA sequences but same functional shape The end result is that, over evolutionary time, organisms very slowly accumulate changes in the sequences of the genes that encode parts of the ribosome.
Any large, rapid change is unlikely to survive because the ribosome is so critical to all aspects of life and reproduction in an organism. The components of the ribosome are an excellent resource for studying the evolution of all organisms because all cellular organisms have ribosomes.
The genes that encode the components of the ribosome originated in a common ancestor, and may be directly compared. We reason that the more closely related organisms are, the more similar to each other they will be in the DNA sequence of the genes that encode the ribosome, and use the gene variation both to identify organisms, and systematically derive their relationships to each other.
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This is analogous to comparing skeletons in vertebrates — the more closely related organisms are, the more similar their skeletons will be.
For most of the last years, biologists divided organisms into two main groups. This transition from poikilohydry to homoiohydry opened up new potential for colonisation. As CO2 was withdrawn from the atmosphere by plants, more water was lost in its capture, and more elegant water acquisition and transport mechanisms evolved.
By the end of the Carboniferous, when CO2 concentrations had been reduced to something approaching today's, around 17 times more water was lost per unit of CO2 uptake. Even today, water transport takes advantage of the cohesion-tension property of water. Water can be wicked along a fabric with small spaces, and in narrow columns of water, such as those within the plant cell walls or in tracheids, when molecules evaporate from one end, they pull the molecules behind them along the channels.
Therefore, transpiration alone provides the driving force for water transport in plants. The bands are difficult to see on this specimen, as an opaque carbonaceous coating conceals much of the tube.
Bands are just visible in places on the left half of the image. During the early Silurian, they developed specialized xylem cells, with walls that were strengthened by bands of lignification or similar chemical compounds. The early Devonian pretracheophytes Aglaophyton and Horneophyton have unreinforced water transport tubes with wall structures very similar to the hydroids of modern moss sporophytes, but they grew alongside several species of tracheophytes, such as Rhynia gwynne-vaughanii that had well-reinforced xylem tracheids.
The earliest macrofossils known to have xylem tracheids are small, mid-Silurian plants of the genus Cooksonia.
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Thickened bands on the walls of tubes, apparent from the early Silurian onwards,  are adaptations to increase the resistance to collapse under tension   and, when they form single celled conduits, are referred to as tracheids. These, the "next generation" of transport cell design, have a more rigid structure than hydroids, preventing their collapse at higher levels of water tension.
This is an important role where water supply is not constant, and indeed stomata appear to have evolved before tracheids, since they are present in the sporophytes of mosses and the non-vascular hornworts.
The endodermis can also provide an upwards pressure, forcing water out of the roots when transpiration is not enough of a driver. Once plants had evolved this level of controlled water transport, they were truly homoiohydricable to extract water from their environment through root-like organs rather than relying on a film of surface moisture, enabling them to grow to much greater size.
The tree of life on Earth
Pits in tracheid walls have very small diameters, preventing air bubbles from passing through to adjacent tracheids. By the Carboniferous, Gymnosperms had developed bordered pits  valve-like structures that seal the pits when one side of a tracheid is depressurized. Defunct tracheids were retained to form a strong, woody stem, produced in most instances by a secondary xylem. However, in early plants, tracheids were too mechanically vulnerable, and retained a central position, with a layer of tough sclerenchyma on the outer rim of the stems.
Tracheids end with walls, which impose a great deal of resistance on flow;  vessel members have perforated end walls, and are arranged in series to operate as if they were one continuous vessel.
An embolism is where an air bubble is created in a tracheid. This may happen as a result of freezing, or by gases dissolving out of solution. Once an embolism is formed, it usually cannot be removed but see later ; the affected cell cannot pull water up, and is rendered useless. End walls excluded, the tracheids of prevascular plants were able to operate under the same hydraulic conductivity as those of the first vascular plant, Cooksonia.
The branching pattern of megaphyll veins may indicate their origin as webbed, dichotomising branches. The megaphyllous leaf architecture arose multiple times in different plant lineages Leaves are the primary photosynthetic organs of a modern plant.
The origin of leaves was almost certainly triggered by falling concentrations of atmospheric CO2 during the Devonian period, increasing the efficiency with which carbon dioxide could be captured for photosynthesis. Based on their structure, they are classified into two types: It has been proposed that these structures arose independently. All three steps happened multiple times in the evolution of today's leaves.
However, Wolfgang Hagemann questioned it for morphological and ecological reasons and proposed an alternative theory. Axes such as stems and roots evolved later as new organs. Rolf Sattler proposed an overarching process-oriented view that leaves some limited room for both the telome theory and Hagemann's alternative and in addition takes into consideration the whole continuum between dorsiventral flat and radial cylindrical structures that can be found in fossil and living land plants.
Thus, James  concluded that "it is now widely accepted that In fact, it is simply the timing of the KNOX gene expression! Today's megaphyll leaves probably became commonplace some mya, about 40my after the simple leafless plants had colonized the land in the Early Devonian.
This spread has been linked to the fall in the atmospheric carbon dioxide concentrations in the Late Paleozoic era associated with a rise in density of stomata on leaf surface.
Increasing the stomatal density allowed for a better-cooled leaf, thus making its spread feasible, but increased CO2 uptake at the expense of decreased water use efficiency.
The early to middle Devonian trimerophytes may be considered leafy. This group of vascular plants are recognisable by their masses of terminal sporangia, which adorn the ends of axes which may bifurcate or trifurcate.
These are small, spiny outgrowths of the stem, lacking their own vascular supply. Around the same time, the zosterophyllophytes were becoming important. This group is recognisable by their kidney-shaped sporangia, which grew on short lateral branches close to the main axes. They sometimes branched in a distinctive H-shape. However, none of these had a vascular trace, and the first evidence of vascularised enations occurs in the Rhynie genus Asteroxylon.
A fossil clubmoss known as Baragwanathia had already appeared in the fossil record about 20 million years earlier, in the Late Silurian. Lycopods bear distinctive microphyllsdefined as leaves with a single vascular trace. Microphylls could grow to some size, those of Lepidodendrales reaching over a meter in length, but almost all just bear the one vascular bundle. An exception is the rare branching in some Selaginella species.
The more familiar leaves, megaphyllsare thought to have originated four times independently, in the ferns, horsetails, progymnosperms and seed plants. When stomata open to allow water to evaporate from leaves it has a cooling effect, resulting from the loss of latent heat of evaporation.
It appears that the low stomatal density in the early Devonian meant that evaporation and evaporative cooling were limited, and that leaves would have overheated if they grew to any size.Is DNA the future of data storage? - Leo Bear-McGuinness
The stomatal density could not increase, as the primitive steles and limited root systems would not be able to supply water quickly enough to match the rate of transpiration. Secondary evolution can also disguise the true evolutionary origin of some leaves. Some genera of ferns display complex leaves which are attached to the pseudostele by an outgrowth of the vascular bundle, leaving no leaf gap.
The popular belief that plants shed their leaves when the days get too short is misguided; evergreens prospered in the Arctic circle during the most recent greenhouse earth. Seasonal leaf loss has evolved independently several times and is exhibited in the ginkgoalessome pinophyta and certain angiosperms.
High trees rarely have large leaves, because they are damaged by high winds. Similarly, trees that grow in temperate or taiga regions have pointed leaves,[ citation needed ] presumably to prevent nucleation of ice onto the leaf surface and reduce water loss due to transpiration.
Herbivoryby mammals and insectshas been a driving force in leaf evolution. An example is that plants of the New Zealand genus Aciphylla have spines on their laminas, which probably functioned to discourage the extinct Moas from feeding on them. Other members of Aciphylla, which did not co-exist with the moas, do not have these spines.
This is brought about by ARP genes, which encode transcription factors. The ARP function appears to have arisen early in vascular plant evolution, because members of the primitive group Lycophytes also have a functionally similar gene.
The diversity of leaves The arrangement of leaves or phyllotaxy on the plant body can maximally harvest light and might be expected to be genetically robust.
However, in maizea mutation in only one gene called ABPHYL ABnormal PHYLlotaxy is enough to change the phyllotaxy of the leaves, implying that mutational adjustment of a single locus on the genome is enough to generate diversity. The genes involved in defining this, and the other axes seem to be more or less conserved among higher plants.
These proteins deviate some cells in the leaf primordium from the default abaxial state, and make them adaxial.