Plant pathology is the scientific study of diseases in plants caused by pathogens and environmental conditions. Organisms that cause infectious disease include fungi, bacteria, viroids, virus-like organisms, protozoa and parasitic plants. Not included are ectoparasites like insects, vertebrate, or other pests that affect plant health by eating of plant tissues. Plant pathology involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, management of plant diseases. Control of plant diseases is crucial to the reliable production of food, it provides significant problems in agricultural use of land, water and other inputs. Plants in both natural and cultivated populations carry inherent disease resistance, but there are numerous examples of devastating plant disease impacts such as Irish potato famine and chestnut blight, as well as recurrent severe plant diseases like rice blast, soybean cyst nematode, citrus canker.
However, disease control is reasonably successful for most crops. Disease control is achieved by use of plants that have been bred for good resistance to many diseases, by plant cultivation approaches such as crop rotation, use of pathogen-free seed, appropriate planting date and plant density, control of field moisture, pesticide use. Across large regions and many crop species, it is estimated that diseases reduce plant yields by 10% every year in more developed settings, but yield loss to diseases exceeds 20% in less developed settings. Continuing advances in the science of plant pathology are needed to improve disease control, to keep up with changes in disease pressure caused by the ongoing evolution and movement of plant pathogens and by changes in agricultural practices. Plant diseases cause major economic losses for farmers worldwide; the Food and Agriculture Organization estimates indeed that pests and diseases are responsible for about 25% of crop loss. To solve this issue, new methods are needed to detect diseases and pests early, such as novel sensors that detect plant odours and spectroscopy and biophotonics that are able to diagnose plant health and metabolism.
Most phytopathogenic fungi belong to the Ascomycetes and the Basidiomycetes. The fungi reproduce both sexually and asexually via the production of other structures. Spores may be spread long distances by air or water. Many soil inhabiting fungi are capable of living saprotrophically, carrying out the part of their life cycle in the soil; these are facultative saprotrophs. Fungal diseases may be controlled through the use of other agriculture practices. However, new races of fungi evolve that are resistant to various fungicides. Biotrophic fungal pathogens colonize living plant tissue and obtain nutrients from living host cells. Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells. Significant fungal plant pathogens include: Fusarium spp. Thielaviopsis spp. Verticillium spp. Magnaporthe grisea Sclerotinia sclerotiorum Ustilago spp. smut of barley Rhizoctonia spp. Phakospora pachyrhizi Puccinia spp. Armillaria spp; the oomycetes are fungus-like organisms.
They include some of the most destructive plant pathogens including the genus Phytophthora, which includes the causal agents of potato late blight and sudden oak death. Particular species of oomycetes are responsible for root rot. Despite not being related to the fungi, the oomycetes have developed similar infection strategies. Oomycetes are capable of using effector proteins to turn off a plant's defenses in its infection process. Plant pathologists group them with fungal pathogens. Significant oomycete plant pathogens include: Pythium spp. Phytophthora spp. including the potato blight of the Great Irish Famine Some slime molds in Phytomyxea cause important diseases, including club root in cabbage and its relatives and powdery scab in potatoes. These are caused by species of Spongospora, respectively. Most bacteria that are associated with plants are saprotrophic and do no harm to the plant itself. However, a small number, around 100 known species, are able to cause disease. Bacterial diseases are much more prevalent in tropical regions of the world.
Most plant pathogenic bacteria are rod-shaped. In order to be able to colonize the plant they have specific pathogenicity factors. Five main types of bacterial pathogenicity factors are known: uses of cell wall–degrading enzymes, effector proteins and exopolysaccharides. Pathogens such as Erwinia species use cell wall–degrading enzymes to cause soft rot. Agrobacterium species change the level of auxins to cause tumours with phytohormones. Exopolysaccharides are produced by bacteria and block xylem vessels leading to the death of the plant. Bacteria control the production of pathogenicity factors via quorum sensing. Significant bacterial plant pathogens: Burkholderia Proteobacteria Xanthomonas spp. Pseudomonas spp. Pseudomonas syringae pv. tomato causes tomato plants to produce less fruit, it "continues to adapt to the tomato by minimizing its recognition by the tomato immune system." Phytoplasma and Spiroplasma are genera of bacteria that lack cell walls and are related to the mycoplasmas, which are human pathogens.
Together they are referred to
Botany called plant science, plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist; the term "botany" comes from the Ancient Greek word βοτάνη meaning "pasture", "grass", or "fodder". Traditionally, botany has included the study of fungi and algae by mycologists and phycologists with the study of these three groups of organisms remaining within the sphere of interest of the International Botanical Congress. Nowadays, botanists study 410,000 species of land plants of which some 391,000 species are vascular plants, 20,000 are bryophytes. Botany originated in prehistory as herbalism with the efforts of early humans to identify – and cultivate – edible and poisonous plants, making it one of the oldest branches of science. Medieval physic gardens attached to monasteries, contained plants of medical importance, they were forerunners of the first botanical gardens attached to universities, founded from the 1540s onwards.
One of the earliest was the Padua botanical garden. These gardens facilitated the academic study of plants. Efforts to catalogue and describe their collections were the beginnings of plant taxonomy, led in 1753 to the binomial system of Carl Linnaeus that remains in use to this day. In the 19th and 20th centuries, new techniques were developed for the study of plants, including methods of optical microscopy and live cell imaging, electron microscopy, analysis of chromosome number, plant chemistry and the structure and function of enzymes and other proteins. In the last two decades of the 20th century, botanists exploited the techniques of molecular genetic analysis, including genomics and proteomics and DNA sequences to classify plants more accurately. Modern botany is a broad, multidisciplinary subject with inputs from most other areas of science and technology. Research topics include the study of plant structure and differentiation, reproduction and primary metabolism, chemical products, diseases, evolutionary relationships and plant taxonomy.
Dominant themes in 21st century plant science are molecular genetics and epigenetics, which are the mechanisms and control of gene expression during differentiation of plant cells and tissues. Botanical research has diverse applications in providing staple foods, materials such as timber, rubber and drugs, in modern horticulture and forestry, plant propagation and genetic modification, in the synthesis of chemicals and raw materials for construction and energy production, in environmental management, the maintenance of biodiversity. Botany originated as the study and use of plants for their medicinal properties. Many records of the Holocene period date early botanical knowledge as far back as 10,000 years ago; this early unrecorded knowledge of plants was discovered in ancient sites of human occupation within Tennessee, which make up much of the Cherokee land today. The early recorded history of botany includes many ancient writings and plant classifications. Examples of early botanical works have been found in ancient texts from India dating back to before 1100 BC, in archaic Avestan writings, in works from China before it was unified in 221 BC.
Modern botany traces its roots back to Ancient Greece to Theophrastus, a student of Aristotle who invented and described many of its principles and is regarded in the scientific community as the "Father of Botany". His major works, Enquiry into Plants and On the Causes of Plants, constitute the most important contributions to botanical science until the Middle Ages seventeen centuries later. Another work from Ancient Greece that made an early impact on botany is De Materia Medica, a five-volume encyclopedia about herbal medicine written in the middle of the first century by Greek physician and pharmacologist Pedanius Dioscorides. De Materia Medica was read for more than 1,500 years. Important contributions from the medieval Muslim world include Ibn Wahshiyya's Nabatean Agriculture, Abū Ḥanīfa Dīnawarī's the Book of Plants, Ibn Bassal's The Classification of Soils. In the early 13th century, Abu al-Abbas al-Nabati, Ibn al-Baitar wrote on botany in a systematic and scientific manner. In the mid-16th century, "botanical gardens" were founded in a number of Italian universities – the Padua botanical garden in 1545 is considered to be the first, still in its original location.
These gardens continued the practical value of earlier "physic gardens" associated with monasteries, in which plants were cultivated for medical use. They supported the growth of botany as an academic subject. Lectures were given about the plants grown in the gardens and their medical uses demonstrated. Botanical gardens came much to northern Europe. Throughout this period, botany remained subordinate to medicine. German physician Leonhart Fuchs was one of "the three German fathers of botany", along with theologian Otto Brunfels and physician Hieronymus Bock. Fuchs and Brunfels broke away from the tradition of copying earlier works to make original observations of their own. Bock created his own system of plant classification. Physician Valerius Cordus authored a botanically and pharmacologically important herbal Historia Plantarum in 1544 and a pharmacopoeia of lasting importance, the Dispensatorium
The gymnosperms known as Acrogymnospermae, are a group of seed-producing plants that includes conifers, cycads and gnetophytes. The term "gymnosperm" comes from the Greek composite word γυμνόσπερμος, meaning "naked seeds"; the name is based on the unenclosed condition of their seeds. The non-encased condition of their seeds stands in contrast to the seeds and ovules of flowering plants, which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, which are modified to form cones, or solitary as in Yew, Ginkgo; the gymnosperms and angiosperms together compose the spermatophytes or seed plants. The gymnosperms are divided into six phyla. Organisms that belong to the Cycadophyta, Ginkgophyta and Pinophyta phyla are still in existence while those in the Pteridospermales and Cordaitales phyla are now extinct. By far the largest group of living gymnosperms are the conifers, followed by cycads and Ginkgo biloba. Roots in some genera have fungal association with roots in the form of mycorrhiza, while in some others small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.
The current formal classification of the living gymnosperms is the "Acrogymnospermae", which form a monophyletic group within the spermatophytes. The wider "Gymnospermae" group is thought to be paraphyletic; the fossil record of gymnosperms includes many distinctive taxa that do not belong to the four modern groups, including seed-bearing trees that have a somewhat fern-like vegetative morphology. When fossil gymnosperms such as these and the Bennettitales and Caytonia are considered, it is clear that angiosperms are nested within a larger gymnospermae clade, although which group of gymnosperms is their closest relative remains unclear; the extant gymnosperms include 12 main families and 83 genera which contain more than 1000 known species. Subclass Cycadidae Order Cycadales Family Cycadaceae: Cycas Family Zamiaceae: Dioon, Macrozamia, Encephalartos, Ceratozamia, Zamia. Subclass Ginkgoidae Order Ginkgoales Family Ginkgoaceae: GinkgoSubclass Gnetidae Order Welwitschiales Family Welwitschiaceae: Welwitschia Order Gnetales Family Gnetaceae: Gnetum Order Ephedrales Family Ephedraceae: EphedraSubclass Pinidae Order Pinales Family Pinaceae: Cedrus, Cathaya, Pseudotsuga, Pseudolarix, Nothotsuga, Abies Order Araucariales Family Araucariaceae: Araucaria, Agathis Family Podocarpaceae: Phyllocladus, Prumnopitys, Halocarpus, Lagarostrobos, Saxegothaea, Pherosphaera, Dacrycarpus, Falcatifolium, Nageia, Podocarpus Order Cupressales Family Sciadopityaceae: Sciadopitys Family Cupressaceae: Cunninghamia, Athrotaxis, Sequoia, Cryptomeria, Taxodium, Austrocedrus, Pilgerodendron, Diselma, Callitris, Thuja, Chamaecyparis, Cupressus, Xanthocyparis, Tetraclinis, Microbiota Family Taxaceae: Austrotaxus, Taxus, Amentotaxus, Torreya There are over 1000 living species of gymnosperm.
It is accepted that the gymnosperms originated in the late Carboniferous period, replacing the lycopsid rainforests of the tropical region. This appears to have been the result of a whole genome duplication event around 319 million years ago. Early characteristics of seed plants were evident in fossil progymnosperms of the late Devonian period around 383 million years ago, it has been suggested that during the mid-Mesozoic era, pollination of some extinct groups of gymnosperms was by extinct species of scorpionflies that had specialized proboscis for feeding on pollination drops. The scorpionflies engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms. Evidence has been found that mid-Mesozoic gymnosperms were pollinated by Kalligrammatid lacewings, a now-extinct genus with members which resembled the modern butterflies that arose far later. Conifers are by far the most abundant extant group of gymnosperms with six to eight families, with a total of 65-70 genera and 600-630 species.
Conifers most are evergreens. The leaves of many conifers are long and needle-like, other species, including most Cupressaceae and some Podocarpaceae, have flat, triangular scale-like leaves. Agathis in Araucariaceae and Nageia in Podocarpaceae have flat strap-shaped leaves. Cycads are the next most abundant group of gymnosperms, with two or three families, 11 genera, 338 species. A majority of cycads are native to tropical climates and are most abundantly found in regions near the equator; the other extant groups are one species of Ginkgo. Gymnosperms have major economic uses. Pine, fir and cedar are all examples of conifers that are used for lumber, paper production, resin; some other common uses for gymnosperms are soap, nail polish, food and perfumes. Gymnosperms, like all vascular plants, have a sporophyte-dominant life cycle, which means they spend most of their life cycle with diploid cells, while
Miles Joseph Berkeley
Miles Joseph Berkeley was an English cryptogamist and clergyman, one of the founders of the science of plant pathology. The standard author abbreviation Berk. is used to indicate this person as the author when citing a botanical name. Berkeley was born at Biggin Hall, Benefield and educated at Rugby School and Christ's College, Cambridge. Taking holy orders, he became incumbent of Apethorpe in 1837, vicar of Sibbertoft, near Market Harborough, in 1868, he acquired an enthusiastic love of cryptogamic botany in his early years, soon was recognized as the leading British authority on fungi and plant pathology. Christ's College made him an honorary fellow in 1883, he was well known as a systematist in mycology with some 6000 species of fungi being credited to him, but his Introduction to Cryptogamic Botany, published in 1857, his papers on Vegetable Pathology in the Gardener's Chronicle in 1854 and onwards, show that he had a broad grasp of the whole domain of physiology and morphology as understood in those days.
Berkeley began his work as a field naturalist and collector, his earliest objects of study having been the mollusca and other branches of zoology, as testified by his papers in the Zoological Journal and the Magazine of Natural History, between 1828 and 1836. As a microscopist he was an assiduous and accurate worker, as shown by his numerous drawings of the smaller algae and fungi, his admirable dissections of mosses and Hepaticae, his investigations on the potato murrain, caused by Phytophthora infestans, on the grape mildew, to which he gave the name Oidium Tuckeri, on the pathogenic fungi of wheat rust, hop mildew, various diseases of cabbage, coffee, onions and other plants, were important in results bearing on the life-history of these pests, at a time when little was known of such matters, must always be considered in any historical account of the remarkable advances in the biology of these organisms made between 1850 and 1880. When it is remembered that this work was done without any of the modern appliances or training of a properly equipped laboratory, the real significance of Berkeley's pioneering work becomes apparent.
It has been said that "... when the history of Plant Pathology is elaborated, Berkeley's name will undoubtedly stand out more prominently than that of any other individual. In fact, it is not saying too much to pronounce Berkeley as the originator and founder of Plant Pathology." As the founder of British mycology, his significant work is contained in the account of native British fungi in Sir William Jackson Hooker's British Flora, in his Introduction to Cryptogamic Botany, in his Outlines of British Fungology. His herbarium at the Royal Botanic Gardens, Kew, is one of the world's most extensive, containing over 9000 specimens as well as numerous notes and sketches. Berkeley corresponded with Anna Maria Hussey assisting her with identifying specimens while she supplied specimens she had collected to add to his herbarium. In 1857, Miles Joseph Berkeley was elected as member of the German Academy of Sciences Leopoldina. In June, 1879 he was elected a Fellow of the Royal Society and was awarded their Royal Medal in 1863.
He died at his vicarage, near Market Harborough, on 30 July 1889. Berkeley was the father of the scientific illustrator Ruth Ellen Berkeley and named Agaricus ruthae for her. List of mycologists This article incorporates text from a publication now in the public domain: Boulger, George Simonds. "Berkeley, Miles Joseph". Dictionary of National Biography. London: Smith, Elder & Co; this article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Berkeley, Miles Joseph". Encyclopædia Britannica. 3. Cambridge University Press. Taylor, George. "Berkeley, Miles Joseph". Dictionary of Scientific Biography. 2. New York: Charles Scribner's Sons. Pp. 18–19. ISBN 0-684-10114-9. Griffith, John William; the Micrographic Dictionary. Volume II -- Plates. London: John Van Voorst. Retrieved 2009-04-07. Works by Miles Joseph Berkeley at Project Gutenberg Works by or about Miles Joseph Berkeley at Internet Archive
Vascular plants known as tracheophytes, form a large group of plants that are defined as those land plants that have lignified tissues for conducting water and minerals throughout the plant. They have a specialized non-lignified tissue to conduct products of photosynthesis. Vascular plants include the clubmosses, ferns and angiosperms. Scientific names for the group include Tracheophyta and Equisetopsida sensu lato; the term higher plants should be avoided as a synonym for vascular plants as it is a remnant of the abandoned concept of the great chain of being. Vascular plants are defined by three primary characteristics: Vascular plants have vascular tissues which distribute resources through the plant; this feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to small sizes. In vascular plants, the principal generation phase is the sporophyte, which produce spores and is diploid. By contrast, the principal generation phase in non-vascular plants is the gametophyte, which produces gametes and is haploid.
They have true roots and stems if one or more of these traits are secondarily lost in some groups. The formal definition of the division Tracheophyta encompasses both these characteristics in the Latin phrase "facies diploida xylem et phloem instructa". One possible mechanism for the presumed switch from emphasis on the haploid generation to emphasis on the diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. In other words, elaboration of the spore stalk enabled the production of more spores, enabled the development of the ability to release them higher and to broadcast them farther; such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane is as follows, with modification to the gymnosperms from Christenhusz et al. Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al.
This phylogeny is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns are not monophyletic. Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements; the xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall contains the polymer lignin; the phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
The most abundant compound in all plants, as in all cellular organisms, is water which serves an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is transpired from the plant through its stomata to the atmosphere and replaced by soil water taken up by the roots; the movement of water out of the leaf stomata creates a transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules; the draw of water upwards may be passive and can be assisted by the movement of water into the roots via osmosis. Transpiration requires little energy to be used by the plant. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts. Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure.
It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is due to high temperatures, high humidity, darkness or drought. Xylem and phloem tissues are involved in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves by photosynthesis and transported to the growing shoots and roots for use in growth, cellular respiration or storage. Minerals are transported to the shoots to allow cell division and growth. Fern allies Non-vascular plant “Higher plants” or “vascular plants”
A pteridophyte is a vascular plant that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are referred to as "cryptogams", meaning that their means of reproduction is hidden; the pteridophytes include the ferns and the lycophytes. These are not a monophyletic group because ferns and horsetails are more related to seed plants than to the lycophytes. Therefore, "Pteridophyta" is no longer a accepted taxon, although the term pteridophyte remains in common parlance, as do pteridology and pteridologist as a science and its practitioner, to indicate lycophytes and ferns as an informal grouping, such as the International Association of Pteridologists and the Pteridophyte Phylogeny Group. Ferns and lycophytes are free-sporing vascular plants that have a life cycle with free-living, independent gametophyte and sporophyte phases, their other common characteristics include vascular plant apomorphies and land plant plesiomorphies. Of the pteridophytes, ferns account for nearly 90% of the extant diversity.
Smith et al. the first higher-level pteridophyte classification published in the molecular phylogenetic era, considered the ferns as monilophytes, as follows: Division Tracheophyta - vascular plants Sub division Euphyllophytina Infradivision Moniliformopses Infradivision Spermatophyta - seed plants, ~260,000 species Subdivision Lycopodiophyta - less than 1% of extant vascular plantswhere the monilophytes comprise about 9,000 species, including horsetails, whisk ferns, all eusporangiate and all leptosporangiate ferns. Both lycophytes and monilophytes were grouped together as pteridophytes on the basis of being spore-bearing. In Smith's molecular phylogenetic study the ferns are characterised by lateral root origin in the endodermis mesarch protoxylem in shoots, a pseudoendospore, plasmodial tapetum, sperm cells with 30-1000 flagella; the term "moniliform" as in Moniliformopses and monilophytes means "bead-shaped" and was introduced by Kenrick and Crane as a scientific replacement for "fern" and became established by Pryer et al..
Christenhusz and Chase in their review of classification schemes provide a critique of this usage, which they discouraged as irrational. In fact the alternative name Filicopsida was in use. By comparison "lycopod" or lycophyte means wolf-plant; the term "fern ally" included under Pteridophyta refers to vascular spore-bearing plants that are not ferns, including lycopods, whisk ferns and water ferns, a much wider range of taxa. This is not a natural grouping but rather a convenient term for non-fern, is discouraged, as is eusporangiate for non-leptosporangiate ferns; however both Infradivision and Moniliformopses are invalid names under the International Code of Botanical Nomenclature. Ferns, despite forming a monophyletic clade, are formally only considered as four classes, 11 orders and 37 families, without assigning a higher taxonomic rank. Furthermore, within the Polypodiopsida, the largest grouping, a number of informal clades were recognised, including leptosporangiates, core leptosporangiates and eupolypods.
In 2014 Christenhusz and Chase, summarising the known knowledge at that time, treated this group as two separate unrelated taxa in a consensus classification. 1,300 species Polypodiophyta 4 sublasses, 11 orders, 21 families, approx. 212 genera, approx. 10,535 species Subclass Equisetidae Warm. Subclass Ophioglossidae Klinge Subclass Marattiidae Klinge Subclass Polypodiidae Cronquist, Takht. & Zimmerm. These subclasses correspond to Smith's four classes, with Ophioglossidae corresponding to Psilotopsida; the two major groups included in Pteridophyta are phylogenetically related as follows: Pteridophytes consist of two separate but related classes, whose nomenclature has varied. The terminology used by the Pteridophyte Phylogeny Group is used here: Classes and ordersLycopodiopsida Lycopodiidae Selaginellidae Polypodiopsida Equisetidae Ophioglossidae Psilotales Ophioglossales Marattiidae Polypodiidae In addition to these living groups, several groups of pteridophytes are now extinct and known only from fossils.
These groups include the Rhyniopsida, Zosterophyllopsida, Trimerophytopsida, the Lepidodendrales and the Progymnospermopsida. Modern studies of the land plants agree that all pteridophytes share a common ancestor with seed plants. Therefore, pteridophytes constitute a paraphyletic group. Just as with seed plants and mosses, the life cycle of pteridophytes involves alternation of generations; this means. Pteridophytes differ from mosses and seed plants in that both generations are independent and free-living, although the sporophyte is much larger and more conspicuous; the sexuality of pteridophyte gametophytes can be classifi
The plastid is a membrane-bound organelle found in the cells of plants and some other eukaryotic organisms. Plastids were discovered and named by Ernst Haeckel, but A. F. W. Schimper was the first to provide a clear definition. Plastids are the site of manufacture and storage of important chemical compounds used by the cells of autotrophic eukaryotes, they contain pigments used in photosynthesis, the types of pigments in a plastid determine the cell's color. They have a common evolutionary origin and possess a double-stranded DNA molecule, circular, like that of prokaryotic cells. Plastids that contain chlorophyll are called chloroplasts. Plastids can store products like starch and can synthesize fatty acids and terpenes, which can be used for producing energy and as raw material for the synthesis of other molecules. For example, the components of the plant cuticle and its epicuticular wax are synthesized by the epidermal cells from palmitic acid, synthesized in the chloroplasts of the mesophyll tissue.
All plastids are derived from proplastids, which are present in the meristematic regions of the plant. Proplastids and young chloroplasts divide by binary fission, but more mature chloroplasts have this capacity. In plants, plastids may differentiate into several forms, depending upon which function they play in the cell. Undifferentiated plastids may develop into any of the following variants: Chloroplasts: green plastids for photosynthesis; each plastid creates multiple copies of a circular 75–250 kilobase plastome. The number of genome copies per plastid is variable, ranging from more than 1000 in dividing cells, which, in general, contain few plastids, to 100 or fewer in mature cells, where plastid divisions have given rise to a large number of plastids; the plastome contains about 100 genes encoding ribosomal and transfer ribonucleic acids as well as proteins involved in photosynthesis and plastid gene transcription and translation. However, these proteins only represent a small fraction of the total protein set-up necessary to build and maintain the structure and function of a particular type of plastid.
Plant nuclear genes encode the vast majority of plastid proteins, the expression of plastid genes and nuclear genes is co-regulated to coordinate proper development of plastids in relation to cell differentiation. Plastid DNA exists as large protein-DNA complexes associated with the inner envelope membrane and called'plastid nucleoids'; each nucleoid particle may contain more than 10 copies of the plastid DNA. The proplastid contains a single nucleoid located in the centre of the plastid; the developing plastid has many nucleoids, localized at the periphery of the plastid, bound to the inner envelope membrane. During the development of proplastids to chloroplasts, when plastids convert from one type to another, nucleoids change in morphology and location within the organelle; the remodelling of nucleoids is believed to occur by modifications to the composition and abundance of nucleoid proteins. Many plastids those responsible for photosynthesis, possess numerous internal membrane layers. In plant cells, long thin protuberances called stromules sometimes form and extend from the main plastid body into the cytosol and interconnect several plastids.
Proteins, smaller molecules, can move within stromules. Most cultured cells that are large compared to other plant cells have long and abundant stromules that extend to the cell periphery. In 2014, evidence of possible plastid genome loss was found in Rafflesia lagascae, a non-photosynthetic parasitic flowering plant, in Polytomella, a genus of non-photosynthetic green algae. Extensive searches for plastid genes in both Rafflesia and Polytomella yielded no results, however the conclusion that their plastomes are missing is still controversial; some scientists argue that plastid genome loss is unlikely since non-photosynthetic plastids contain genes necessary to complete various biosynthetic pathways, such as heme biosynthesis. In algae, the term leucoplast is used for all unpigmented plastids, their function differs from the leucoplasts of plants. Etioplasts and chromoplasts are plant-specific and do not occur in algae. Plastids in algae and hornworts may differ from plant plastids in that they contain pyrenoids.
Glaucophyte algae contain muroplasts, which are similar to chloroplasts except that they have a peptidoglycan cell wall, similar to that of prokaryotes. Red algae contain rhodoplasts, which are red chloroplasts that allow them to photosynthesise to a depth of up to 268 m; the chloroplasts of plants differ from the rhodoplasts of red algae in their ability to synthesize starch, stored in the form of granules within the plastids. In red algae, floridean starch is stored outside the plastids in the cytosol. Most plants inherit the plastids from only one parent. In general, angiosperms inherit plastids from the female gamete, whereas