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Green Algae And The Origin Of Land Plants Pdf

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Doyle, James A. Last reviewed: August The process of biological and organic change within the plant kingdom by which the characteristics of plants differ from generation to generation. Understanding of the course of plant evolution Fig.

Green Algae and the Origins of Multicellularity in the Plant Kingdom

Green algae grow at the edges of a glacial lake in Wales. Hundreds of millions of years ago, similar algae adapted to survive temporarily outside of the water may have kicked off the evolution of green land plants. Around million years ago — when the Earth was already a ripe 4 billion years old — the first green plants appeared on dry land.

Precisely how this occurred is still one of the big mysteries of evolution. Before then, terrestrial land was home only to microbial life.

The first green plants to find their way out of the water were not the soaring trees or even the little shrubs of our present world. They were most likely soft and mossy, with shallow roots and few of the adaptations they would later evolve to survive and thrive on dry land.

And though scientists agree that these plants evolved from some kinds of seaweed, we know comparatively little about those green algal ancestors. But a few recent papers — two based on molecular biology, and one on rare, precious fossils from 1 billion years ago — are helping to fill in the gaps in our understanding of those ancient algae and what allowed them to eventually make the transition to land.

While fossils of land plants are abundant, ancient seaweed fossils are rare. To survive out of water, plants developed sturdy vascular systems and strong cell walls. Those same characteristics make for excellent preservation in fossils. The world is very, very different from what we know today. Ancient as the fossilized algae are, they seem to have many of the characteristics also seen in much later green seaweeds. Because that fossil is fragmented and poorly preserved, not all scientists agreed that it was a piece of green algae immortalized in rock; the uncertainty left the early history of seaweeds in doubt.

The new fossils from Dalian have weathered their billion-year existence more successfully. This recently unearthed billion-year-old microfossil, smaller than a grain of rice and surprisingly intact, seems to show the earliest known green algae. It suggests that multicellularity and some other advanced features were present in these algae very early in their history. But there is still room for doubt.

Andrew Knoll , a professor of natural history at Harvard University, expressed similar reservations. But the transition to land life would probably have begun hundreds of millions of years earlier, with green algae adapting to survive in damp soil or sand that was subject to temporary drying.

But evolution is not always a steady march forward. In a recent paper in Cell , Wong, Michael Melkonian of the University of Duisberg-Essen in Germany, and their colleagues showed through genetic analysis that the closest living relatives to land plants are a mossy freshwater species known as Zygnematophyceae. Although these green algae are most often unicellular, they must have shared an ancestor with land plants: They have many genes in common that are crucial for survival on land, including some that confer resistance to drying out and some for synthesizing a cell wall.

These commonalities suggest not only that many of the adaptations to dry land were gained before plants moved ashore, but also that some complex ancestral features were lost by the pond species over time when they ceased to be useful.

In fact, some of those genetic histories may reach beyond algae: The Cell paper showed that the genes for surviving the stresses of desiccation may have originally come from soil bacteria and been donated to Zygnematophyceae or their ancestors through horizontal transfer.

The foreground of the image shows how filaments of the algae might have become embedded in the seafloor and preserved.

In a separate study published in Current Biology last month, Paps, together with Alexander Bowles and Ulrike Bechtold of the University of Essex, compared the genomes of more than living plants and used them to construct an evolutionary tree of their deep ancestry.

In mapping the tree, they pinpointed when various genes emerged, and in the process they identified two bursts of extraordinary genomic novelty. The second one, which seems to have occurred when algae were beginning to make the transition to terrestrial life, produced genes for adaptive features such as ultraviolet-light protection and the ability to form a root system and interact with terrestrial microbes.

A much earlier burst occurred while the algae were still fully underwater and making the transition from unicellularity to multicellularity. In fact, most experts agree that many of the features in early green algae could have evolved independently more than once in a phenomenon known as convergent evolution. The discrepancy may therefore highlight the real lesson to take away from these discoveries: Any confident statement about exactly when and how the ancestors of land plants evolved may always involve an oversimplification of the zigzagging path that evolution often takes.

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Green algae and the origin of land plants.

Until recently, all photosynthetic eukaryotes were considered members of the kingdom Plantae. The brown, red, and gold algae, however, have been reassigned to the Protista kingdom. This is because apart from their ability to capture light energy and fix CO 2 , they lack many structural and biochemical traits that distinguish plants from protists. The position of green algae is more ambiguous. Green algae contain the same carotenoids and chlorophyll a and b as land plants, whereas other algae have different accessory pigments and types of chlorophyll molecules in addition to chlorophyll a. Both green algae and land plants also store carbohydrates as starch.


Embryophytes (land plants; bryophytes and vascular plants) are clearly descended from green algal-like ancestors, but the sister of the embryophytes includes.


Origin of land plants: Do conjugating green algae hold the key?

Green algae grow at the edges of a glacial lake in Wales. Hundreds of millions of years ago, similar algae adapted to survive temporarily outside of the water may have kicked off the evolution of green land plants. Around million years ago — when the Earth was already a ripe 4 billion years old — the first green plants appeared on dry land.

In this review, I focus on two of the best-studied multicellular groups of green algae: charophytes and volvocines. Charophyte algae are the closest relatives of land plants and encompass the transition from unicellularity to simple multicellularity. Many of the innovations present in land plants have their roots in the cell and developmental biology of charophyte algae. Volvocine algae evolved an independent route to multicellularity that is captured by a graded series of increasing cell-type specialization and developmental complexity.

Studies focused upon the evolutionary transition from ancestral green algae to the earliest land plants are important from a range of ecological, molecular and evolutionary perspectives. A substantial suite of ultrastructural, biochemical and molecular data supports the concept that land plants embryophytes are monophyletically derived from an ancestral charophycean alga. However, the details of phylogenetic branching patterns linking extant charophytes and seedless embryophytes are currently unclear.

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3 Comments

Zambnomviefo 10.06.2021 at 21:50

PDF | Over the past two decades, molecular phylogenetic data have allowed evaluations of hypotheses on the evolution of green algae based.

Anton B. 12.06.2021 at 12:46

PDF | The terrestrial habitat was colonized by the ancestors of modern land plants about to million years ago. Today it is widely.

Jeanette C. 17.06.2021 at 08:47

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