This chapter provides a detailed investigation of where, when, and how photosynthesis originated and then evolved in non-eukaryotic organisms. It looks at some of the best accepted geological evidence for the earliest photosynthesis that comes from marine sedimentary deposits in rocks from the Buck Reef Chert in South Africa dated to 3.4 Ga. It also talks about rocks found in the Isua Greenstone Belt in Greenland, dating back from about 3.8 Ga, which harbour geochemical signatures consistent with photosynthesis. The chapter highlights the possibility that anoxygenic photosynthesis had already evolved well before 3 Ga, at a time when the Earth was still a highly anaerobic planet. It covers the two key evolutionary innovations required for the evolution of photosynthesis: first is the evolution of the reaction centre (RC) proteins, and second is a requirement for the evolution of biosynthetic pathways of chlorophylls and related pigments.
The bacterial origins of photosynthesis
Classification and System in Flowering Plants: Historical Background
This chapter discusses the principal ways in which botanists have classified plants and some of the reasoning behind those classifications. It discusses the early collections on which plant systematics is based. These collections are intimately connected with European colonial expansion, what price owners of private herbaria were prepared to pay for specimens, and what kind of specimen they preferred. The chapter also describes the history of botanical classification and highlights the longstanding and continuing tension between the makers and the users of classifications. It clarifies how relationships are understood, how nature is visualized, and how higher taxa are delimited.
Endosymbiosis: How eukaryotes acquired photosynthesis
This chapter looks at how an oxygenic cyanobacterial cell is taken up by a scavenging heterotrophic eukaryotic cell. It reviews evidence that a very rare and unique event led to the combination of a cyanobacterial cell with a much larger heterotrophic eukaryotic cell to form the first eukaryotes capable of oxygenic photosynthesis. It also discusses how primary endosymbiosis started the beginning of the evolution of photosynthetic algae and plants, both terrestrial and aquatic. The chapter investigates the reduction of cyanobacterial endosymbiont from a free-living organism to an organelle. It details how plastids evolved in algae and plants, sometimes acquiring new non-photosynthetic functions related to storage, reproduction, or defence.
This chapter argues that oxygenic photosynthesis is the most important form of photosynthesis on Earth, which accounts for an estimated 3000-fold greater amount of carbon fixation. It discusses the emerging evidence that oxygenic photosynthesis might have its origins close to the beginnings of cellular life at around or before 4 Ga. It also recognizes oxygenic photosynthesis as the only form that was acquired by eukaryotes following a unique endosymbiotic event between a eukaryotic heterotroph and a cyanobacterium. The chapter focuses on the mechanisms of oxygenic photosynthesis in eukaryotes, and cites algae and plants. It also presents a comparative analysis of the extant cyanobacterial mechanisms which had a momentous effect on biological evolution.
The Evolution of Plant Diversity
This chapter describes natural variation among individuals as an essential ingredient of evolution, elaborating how this variation arises and is distributed geographically. The chapter examines processes that create discrete units of variation that are of central interest to systematists, especially those that result in the formation of species. It also analyses mating between individuals of different plant species, blurring the boundary between species. This has little effect on morphological variation within a species. The chapter furthermore discusses interspecific gene flow. This plays a dual role in speciation, which includes reducing diversity by merging species. It highlights speciation when coupled with polyploidy, an important source of genetic variation within plant species.
Evolution of the algae
This chapter investigates how the original primary endosymbiotic event between a eukaryotic heterotroph and a cyanobacterium led to multiple lineages of photosynthetic organisms. This included all of the main eukaryotic groups. It highlights original primary endosymbiosis which led directly to a single daughter lineage, the Archaeplastida, wherein all extant primary red and green algae and land plants emerged. It also explains that early red and green algae were highly efficient photosynthetic eukaryotes and these exploited a wide range of marine habitats. The chapter looks at how oxygenic photosynthesis increased atmospheric oxygen levels at around 0.6 Ga, which enabled the evolution of complex multicellular plants and animals. This set the stage for the colonization of land. The chapter describes certain algal groups which later evolved into non-photosynthetic heterotrophs, including important parasitic species of plants and animals.
Evolution of the land plants
This chapter examines the evolution of photosynthetic organisms on land, noting that the vast majority of photosynthetic life was confined to aquatic habitats for the first three billion years of their existance. It discusses genomic novelty, stating that this was common in streptophyte algae, which developed increasingly complex multicellular forms with a wider range of tissue and organ types. It also looks at bryophytes, noting how these dominated land flora from 450 to 360 Ma, which is a relatively warm, wet period favouring the rise of pteridophytes. The chapter reviews how high photosynthetic productivity led to atmospheric O2 levels rising to over 30% and the formation of the Carboniferous coal deposits from huge amount of plant remains. It explains that 1% of all flowering plants have partially or completely lost the ability to photosynthesize and have instead become parasites.
Future prospects for photosynthesis and plant evolution
This chapter reviews contemporary land flora and notes that it is increasingly dominated by human activities, such as agriculture. It points out that agriculture drastically reduced the global area occupied by natural vegetation and replaced it with a small number of domesticated plants used to feed either people or their livestock. It also looks at important photosynthetic processes that are amenable to improvement via biotechnology. The chapter talks about light-harvesting and electron-transfer mechanisms in crops that might be improved by incorporating features of cyanobacterial systems. It points out huge challenges facing photosynthetic life on Earth, emphasizing how many plant and animal groups are facing extinction. The chapter states that it is vital that strategies are developed to minimize human impacts.
Lycophytes, Ferns, and Gymnosperms
This chapter surveys the diversity of living tracheophytes, clarifying the term tracheo. This term refers to the presence of tracheids, and the Greek root part of the word phyte means plant. The chapter also explains how tracheophytes form a well-supported monophyletic group of generally large plants with branched sporophyte axes and well-developed tissues for the transport of water and carbohydrates within the plant. It also talks about a major clade within embryophytes. These are formed by tracheophytes, and are nested within the paraphyletic “bryophytes.” The chapter examines two major lineages within tracheophytes: lycophytes and euphyllophytes. It refers to the gymnosperm, in which seeds are not enclosed in a protective structure but may sometimes be enclosed at maturity by fused cone scales or bracts.
Methods and Principles of Biological Systematics
This chapter provides a background on biological systematics which focuses on the discovery of phylogeny and how phylogenies can be used to understand the processes underlying diversification. The chapter outlines how to determine the history of a group and discusses how this history can be used to uncover patterns of diversification and to construct a form of classification. Phylogeny can be understood as the history of DNA molecules: DNA replicates in a semi-conservative fashion to produce two daughter molecules that replicate again to produce their own two daughter molecules — a process that goes back to the beginning of life on Earth. This DNA replication process is diagrammed in phylogenetic trees to show ancestor-descendant relationships and trace the history of life. This chapter introduces these trees and analyzes the shape or topology of the trees that is determined by the connections between the branches that can be rotated around the nodes.
An Overview of Green Plant Phylogeny
This chapter traces the origin and evolution of several separately derived plant lineages, thereby putting the green plant lineage into a broad phylogenetic perspective. It focuses on the evolution of green plants and several critical transitions, including the origin of the land plants, vascular plants, seed plants, and flowering plants. It also chronicles the evolutionary events leading up to the mosses, the horsetails, or any other group leading to angiosperms. The chapter depicts phylogenetic relationships among the major branches of the entire tree of life based on recent analyses and explains the broad phylogenetic distribution of photosynthetic organisms. It refers to chloroplasts found in eukaryotes that are endosymbiotic organelles and derived ultimately from a cyanobacterial ancestor.
Photosynthesis, oxygen, and the evolution of life
This chapter discusses photosynthesis, which involves the use of solar energy to convert simple inorganic substrates into complex carbon-based compounds. It surveys the basic processes involved in the various types of photosynthesis found in bacteria and eukaryotes and the pivotal role played by photosynthesis in the evolution of life on Earth. It also considers the broader significance of photosynthesis in terms of the many important roles that it plays in both the biosphere and the geosphere. The chapter shows how photosynthetic oxygen generated by cyanobacteria led to a global oxygen increase during the GOE1 about 2.4 Ga. It describes the evolution of photosynthetic eukaryotes, which gradually diversified and eventually overtook cyanobacteria as the major oxygen producers.
Denis Murphy and Tanai Cardona
Photosynthetic Life brings together the latest research to show how the process of photosynthesis has evolved over the last three to four billion years — from its beginnings in bacteria to the various refinements now present in modern land plants. Chapters explain how repeated endosymbiotic and gene gain/loss events have led to the evolution of the various algal groups and related non-photosynthetic groups, and how photosynthesis was modified as plants evolved and diversified into different ecological niches around the world. The role of photosynthesis in the alteration of the geology and biology of the earth, which enabled the colonisation of the land by plants and animals, is also explored. Finally, this title examines the limitations of photosynthesis and the emerging biotechnological improvements that could make this vital process even more attractive as a source of clean energy, food and other industrial products.
Phylogenetic Relationships of Angiosperms
This chapter concentrates on angiosperms or flowering plants, which are considered the dominant land plants and sister to a group that includes all other extant seed plants. Angiosperms have a long fossil record going back to the earliest Cretaceous period, and they possibly originated during the Jurassic period more than 140 million years ago. The chapter covers the two great groups of angiosperm species: monocots and eudicots. Monocots are plants with a single cotyledon and pollen grains that monosulcate, while eudicots are plants with two cotyledons and pollen grains that predominantly tricolpate. The chapter reviews data from DNA sequences and morphology that show that the monocot and eudicot clades are derived from members of a morphologically disparate, paraphyletic group of families.
Walter S. Judd, Christopher S. Campbell, Elizabeth A. Kellogg, Peter F. Stevens, and Michael J. Donoghue
Plant Systematics begins by looking at the field of plant systematics as a whole. It then introduces methods and principles of biological systematics before turning to the historical background of classification and system in flowering plants. Next, it examines taxonomic evidence, including an outline of structural and biochemical characters. The text also discusses the evolution of plant diversity and provides an overview of green plant phylogeny. Finally, the book ends with an analysis of lycophytes, ferns, and gymnosperm, and phylogenetic relationships of angiosperms.
The Science of Plant Systematics
This chapter considers the lineage of green plants, which is a major lineage that includes the so-called green algae and land plants. It explains that green plants share a number of features, including the presence of the photosynthetic pigments chlorophyll a and b and storage of carbohydrates in the form of starch. The chapter also examines the presence of two anterior whiplash flagella at some stage of the life cycle of green plants. The chapter also covers land plants or embryophytes, whose closest extant relatives are members of the “charophytes,” a green algal group. It traces the life histories of land plants, which involve the alternation of two morphologically distinct bodies, thick-walled spores, an embryonic stage in the life cycle, specialized structures that protect the gametes, and a cuticle.
Taxonomic Evidence: Structural and Biochemical Characters
The chapter focuses on taxonomic evidence consisting of the characters used in phylogenetic analyses. Plant classifications are based on this evidence, including characters used in describing patterns of variation at or below the species level. The chapter shows how taxonomic evidence can be gathered from a wide variety of sources, from all parts of a plant, and during all stages of a plant's development. It also summarizes the use of characters from morphology, anatomy, embryology, chromosomes, palynology, secondary metabolites, and proteins. The chapter also considers nucleic acids, namely DNA and RNA, as these are an increasingly important source of taxonomic characterization in plant taxonomy and the rapidly developing field of molecular systematics. The chapter also discusses morphological characters, which are used for practical plant identification and hypothesizing phylogenetic relationships.