Botany

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mace) enclosing the dark brown nutmeg
.

Botany, also called plant science (or plant sciences), plant biology or phytology, is the

phycologists respectively, with the study of these three groups of organisms remaining within the sphere of interest of the International Botanical Congress. Nowadays, botanists (in the strict sense) study approximately 410,000 species of land plants of which some 391,000 species are vascular plants (including approximately 369,000 species of flowering plants),[4] and approximately 20,000 are bryophytes.[5]

Botany originated in prehistory as

herbalism with the efforts of early humans to identify – and later cultivate – plants that were edible, poisonous, and possibly medicinal, making it one of the first endeavours of human investigation. Medieval physic gardens, often attached to monasteries, contained plants possibly having medicinal benefit. 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, and led in 1753 to the binomial system of nomenclature of Carl Linnaeus
that remains in use to this day for the naming of all biological species.

In the 19th and 20th centuries, new techniques were developed for the study of plants, including methods of

DNA sequences
to classify plants more accurately.

Modern botany is a broad, multidisciplinary subject with contributions and insights from most other areas of science and technology. Research topics include the study of plant

environmental management, and the maintenance of biodiversity
.

History

Early botany

, 1665

Botany originated as

Ancient Iranic Avestan writings, and in works from China purportedly from before 221 BCE.[7][10]

Modern botany traces its roots back to

Enquiry into Plants and On the Causes of Plants, constitute the most important contributions to botanical science until the Middle Ages, almost seventeen centuries later.[11][12]

Another work from Ancient Greece that made an early impact on botany is

Ibn al-Baitar (d. 1248) wrote on botany in a systematic and scientific manner.[14][15][16]

In the mid-16th century, botanical gardens were founded in a number of Italian universities. The Padua botanical garden in 1545 is usually considered to be the first which is still in its original location. These gardens continued the practical value of earlier "physic gardens", often associated with monasteries, in which plants were cultivated for suspected medicinal uses. They supported the growth of botany as an academic subject. Lectures were given about the plants grown in the gardens. Botanical gardens came much later to northern Europe; the first in England was the University of Oxford Botanic Garden in 1621.[17]

German physician Leonhart Fuchs (1501–1566) was one of "the three German fathers of botany", along with theologian Otto Brunfels (1489–1534) and physician Hieronymus Bock (1498–1554) (also called Hieronymus Tragus).[18][19] 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

Conrad von Gesner (1516–1565) and herbalist John Gerard (1545–c. 1611) published herbals covering the supposed medicinal uses of plants. Naturalist Ulisse Aldrovandi (1522–1605) was considered the father of natural history, which included the study of plants. In 1665, using an early microscope, Polymath Robert Hooke discovered cells, a term he coined, in cork, and a short time later in living plant tissue.[21]

Early modern botany

Photograph of a garden
The Linnaean Garden of Linnaeus' residence in Uppsala, Sweden, was planted according to his Systema sexuale.

During the 18th century, systems of

phyletic order of the taxa in synoptic keys.[22] By the 18th century, new plants for study were arriving in Europe in increasing numbers from newly discovered countries and the European colonies worldwide. In 1753, Carl Linnaeus published his Species Plantarum, a hierarchical classification of plant species that remains the reference point for modern botanical nomenclature. This established a standardised binomial or two-part naming scheme where the first name represented the genus and the second identified the species within the genus.[23] For the purposes of identification, Linnaeus's Systema Sexuale classified plants into 24 groups according to the number of their male sexual organs. The 24th group, Cryptogamia, included all plants with concealed reproductive parts, mosses, liverworts, ferns, algae and fungi.[24]

This clinical categorization of plants was soon followed by the creation of the categories of race and sexuality; the classification of plants necessitated classification of all other living things, including humans.[25] As a result, taxonomy and botany played an influential role in the development of scientific racism.[25] One example of this progression is in the works of Carl Linnaeus, the previously mentioned 18th century botanist.[25] As Linnaeus moved on from classifying plants to classifying all organisms, he published Systema Naturae, a major classificatory piece that he would continue to edit and grow over time.[26] In his 10th edition he expands from four "varieties" of man - Europeans Albus, Americanus Rubescens, Asiaticus Fuscus, and Africanus Niger, based on the four known continents - he also attributes certain skin color, medical temperament, body posture, physical traits, behavior, manner of clothing, and form of government to each variety of people.[26] In these descriptions he labels Asian people as stern, taught, and greedy; black people as sly, sluggish, and neglectful; white people as light, wise, and inventors.[26] Linnaeus is only one of many botanists who influenced scientific racism through the categorization of organisms.[25]

Increasing knowledge of

Candollean system reflected his ideas of the progression of morphological complexity and the later Bentham & Hooker system, which was influential until the mid-19th century, was influenced by Candolle's approach. Darwin's publication of the Origin of Species in 1859 and his concept of common descent required modifications to the Candollean system to reflect evolutionary relationships as distinct from mere morphological similarity.[27]

Botany was greatly stimulated by the appearance of the first "modern" textbook,

Adolf Fick formulated Fick's laws that enabled the calculation of the rates of molecular diffusion in biological systems.[30]

The system in which early modern botany was practiced was very extensive. Modern botany emerged following the surge in exploration of other continents by European colonizers. Plant collectors would travel to different countries in search of new specimens for botanists to classify. Plants usable for cultivataion would then be hybridized.

St. Vincent Island, plantation slavery was vital for the economic success of the sugar colonies and for the maintenance of the breadfruit cultivation project in the St. Vincent botanical gardens.[31]

Echeveria glauca in a Connecticut greenhouse. Botany uses Latin names for identification; here, the specific name glauca means blue.

Late modern botany

Building upon the gene-chromosome theory of heredity that originated with Gregor Mendel (1822–1884), August Weismann (1834–1914) proved that inheritance only takes place through gametes. No other cells can pass on inherited characters.[32] The work of Katherine Esau (1898–1997) on plant anatomy is still a major foundation of modern botany. Her books Plant Anatomy and Anatomy of Seed Plants have been key plant structural biology texts for more than half a century.[33][34]

Class of alpine botany in Switzerland, 1936

The discipline of

centres of origin, and evolutionary history of economic plants.[38]

Particularly since the mid-1960s there have been advances in understanding of the physics of

stomatal apertures. These developments, coupled with new methods for measuring the size of stomatal apertures, and the rate of photosynthesis have enabled precise description of the rates of gas exchange between plants and the atmosphere.[39][40] Innovations in statistical analysis by Ronald Fisher,[41] Frank Yates and others at Rothamsted Experimental Station facilitated rational experimental design and data analysis in botanical research.[42] The discovery and identification of the auxin plant hormones by Kenneth V. Thimann in 1948 enabled regulation of plant growth by externally applied chemicals. Frederick Campion Steward pioneered techniques of micropropagation and plant tissue culture controlled by plant hormones.[43] The synthetic auxin 2,4-dichlorophenoxyacetic acid or 2,4-D was one of the first commercial synthetic herbicides.[44]

Micropropagation of transgenic plants
Micropropagation of transgenic plants

20th century developments in plant biochemistry have been driven by modern techniques of

antibiotics or other pharmaceuticals, as well as the practical application of genetically modified crops designed for traits such as improved yield.[47]

Modern morphology recognises a continuum between the major morphological categories of root, stem (caulome), leaf (phyllome) and

angiosperm families and species.[54] The theoretical possibility of a practical method for identification of plant species and commercial varieties by DNA barcoding is the subject of active current research.[55][56]

Scope and importance

A herbarium specimen of the lady fern, Athyrium filix-femina
Botany involves the recording and description of plants, such as this herbarium specimen of the lady fern Athyrium filix-femina.

The study of plants is vital because they underpin almost all animal life on Earth by generating a large proportion of the oxygen and food that provide humans and other organisms with aerobic respiration with the chemical energy they need to exist. Plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide[57] into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells.[58] As a by-product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. In addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion.[59] Plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil.[60]

Historically, all living things were classified as either animals or plants

phylogeny and evolution, structure (anatomy and morphology), or function (physiology) of plant life.[63]

The strictest definition of "plant" includes only the "land plants" or

haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life,[64] even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte.[65] Other groups of organisms that were previously studied by botanists include bacteria (now studied in bacteriology), fungi (mycology) – including lichen-forming fungi (lichenology), non-chlorophyte algae (phycology), and viruses (virology). However, attention is still given to these groups by botanists, and fungi (including lichens) and photosynthetic protists are usually covered in introductory botany courses.[66][67]

changing the ancient oxygen-free, reducing, atmosphere to one in which free oxygen has been abundant for more than 2 billion years.[68][69]

Among the important botanical questions of the 21st century are the role of plants as primary producers in the global cycling of life's basic ingredients: energy, carbon, oxygen, nitrogen and water, and ways that our plant stewardship can help address the global environmental issues of

Human nutrition

grains of brown rice, a staple food
The food we eat comes directly or indirectly from plants such as rice.

Virtually all staple foods come either directly from

wild ancestral plants with the most desirable characteristics.[74]

Botanists study how plants produce food and how to increase yields, for example through

ecosystems.[76] Ethnobotany is the study of the relationships between plants and people. When applied to the investigation of historical plant–people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany.[77] Some of the earliest plant-people relationships arose between the indigenous people of Canada in identifying edible plants from inedible plants. This relationship the indigenous people had with plants was recorded by ethnobotanists.[78]

Plant biochemistry

Plant biochemistry is the study of the chemical processes used by plants. Some of these processes are used in their

aroma compounds
.

Paper chromatography of some spinach leaf extract shows the various pigments present in their chloroplasts.
Plants make various
photosynthetic pigments, some of which can be seen here through paper chromatography
Xanthophylls

Plants and various other groups of photosynthetic eukaryotes collectively known as "

molecular oxygen
(O2) as a by-product.

The Calvin cycle (Interactive diagram) The Calvin cycle incorporates carbon dioxide into sugar molecules.
The Calvin cycle (Interactive diagram) The Calvin cycle incorporates carbon dioxide into sugar molecules.
RuBisCo
Carbon fixation
Reduction
3-phosphoglycerate
3-phosphoglycerate
1,3-biphosphoglycerate
Glyceraldehyde-3-phosphate
(G3P)
Inorganic phosphate
Ribulose-1,5-bisphosphate

The light energy captured by

rubisco to produce molecules of the 3-carbon sugar glyceraldehyde 3-phosphate (G3P). Glyceraldehyde 3-phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. Some of the glucose is converted to starch which is stored in the chloroplast.[84] Starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family Asteraceae. Some of the glucose is converted to sucrose
(common table sugar) for export to the rest of the plant.

Unlike in animals (which lack chloroplasts), plants and their eukaryote relatives have delegated many biochemical roles to their

amino acids.[87] The fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. [88]

Plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, pectin and xyloglucan[89] from which the land plant cell wall is constructed.[90] Vascular land plants make

vessels to keep them from collapsing when a plant sucks water through them under water stress. Lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. Sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. It is widely regarded as a marker for the start of land plant evolution during the Ordovician period.[91]
The concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the
dicots like the Asteraceae have since independently evolved[92] pathways like Crassulacean acid metabolism and the C4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common C3 carbon fixation
pathway. These biochemical strategies are unique to land plants.

Medicine and materials

fermentation of carbohydrate-rich plant products such as barley (beer), rice (sake) and grapes (wine).[96] Native Americans have used various plants as ways of treating illness or disease for thousands of years.[97] This knowledge Native Americans have on plants has been recorded by enthnobotanists and then in turn has been used by pharmaceutical companies as a way of drug discovery.[98]

Plants can synthesise coloured dyes and pigments such as the anthocyanins responsible for the red colour of red wine, yellow weld and blue woad used together to produce Lincoln green, indoxyl, source of the blue dye indigo traditionally used to dye denim and the artist's pigments gamboge and rose madder.

Sugar,

mosquitoes.[101] These bug repelling properties of sweetgrass were later found by the American Chemical Society in the molecules phytol and coumarin.[101]

Plant ecology

Sinorhizobium meliloti. The plant provides the bacteria with nutrients and an anaerobic environment, and the bacteria fix nitrogen for the plant.[102]

Plant ecology is the science of the functional relationships between plants and their habitats – the environments where they complete their life cycles. Plant ecologists study the composition of local and regional floras, their biodiversity, genetic diversity and fitness, the adaptation of plants to their environment, and their competitive or mutualistic interactions with other species.[103] Some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists.[104] This information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time.[104] The goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change.[105]

Plants depend on certain

.

Plants, climate and environmental change

Plant responses to climate and other environmental changes can inform our understanding of how these changes affect ecosystem function and productivity. For example, plant

land plants.[114] Ozone depletion can expose plants to higher levels of ultraviolet radiation-B (UV-B), resulting in lower growth rates.[115] Moreover, information from studies of community ecology, plant systematics, and taxonomy is essential to understanding vegetation change, habitat destruction and species extinction.[116]

Genetics

heterozygous
for purple (B) and white (b) blossoms

Inheritance in plants follows the same fundamental principles of genetics as in other multicellular organisms.

jumping genes" were discovered by Barbara McClintock while she was studying maize.[117]
Nevertheless, there are some distinctive genetic differences between plants and other organisms.

Species boundaries in plants may be weaker than in animals, and cross species

Unlike in higher animals, where

bulbs, may develop instead of flowers, replacing sexual reproduction with asexual reproduction and giving rise to clonal populations genetically identical to the parent. This is one of several types of apomixis that occur in plants. Apomixis can also happen in a seed, producing a seed that contains an embryo genetically identical to the parent.[123]

Most sexually reproducing organisms are diploid, with paired chromosomes, but doubling of their

is a triploid that produces viable seeds by apomictic seed.

As in other eukaryotes, the inheritance of

Mendelian. Chloroplasts are inherited through the male parent in gymnosperms but often through the female parent in flowering plants.[125]

Molecular genetics

Flowers of Arabidopsis thaliana, the most important model plant and the first to have its genome sequenced
Thale cress, Arabidopsis thaliana, the first plant to have its genome sequenced, remains the most important model organism.

A considerable amount of new knowledge about plant function comes from studies of the molecular genetics of

monocots
generally.

soybeans and a moss Physcomitrella patens are commonly used to study plant cell biology.[134]

Agrobacterium tumefaciens, a soil rhizosphere bacterium, can attach to plant cells and infect them with a callus-inducing Ti plasmid by horizontal gene transfer, causing a callus infection called crown gall disease. Schell and Van Montagu (1977) hypothesised that the Ti plasmid could be a natural vector for introducing the Nif gene responsible for nitrogen fixation in the root nodules of legumes and other plant species.[135] Today, genetic modification of the Ti plasmid is one of the main techniques for introduction of transgenes to plants and the creation of genetically modified crops.

Epigenetics

silencer regions of the DNA and prevent that region of the DNA code from being expressed. Epigenetic marks may be added or removed from the DNA during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. Epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell's life. Some epigenetic changes have been shown to be heritable,[138]
while others are reset in the germ cells.

Epigenetic changes in

cell lines of the embryo, which in turn become fully differentiated cells. A single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. The process results from the epigenetic activation of some genes and inhibition of others.[139]

Unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. Exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. While plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate.[140]

Epigenetic changes can lead to paramutations, which do not follow the Mendelian heritage rules. These epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other.[141]

Plant evolution

colour image of a cross section of a fossil stem of Rhynia gwynne-vaughanii, a Devonian vascular plant
Transverse section of a fossil stem of the Devonian vascular plant Rhynia gwynne-vaughani

The

endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident.[142][143][144][145]

The

Nonvascular land plants are

sister clade to the gymnosperms.[153]

Plant physiology

A Venn diagram of the relationships between five key areas of plant physiology
Five of the key areas of study within plant physiology

Plant physiology encompasses all the internal chemical and physical activities of plants associated with life.[154] Chemicals obtained from the air, soil and water form the basis of all plant metabolism. The energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. Photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. Heterotrophs including all animals, all fungi, all completely parasitic plants, and non-photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues.[155] Respiration is the oxidation of carbon compounds by breaking them down into simpler structures to release the energy they contain, essentially the opposite of photosynthesis.[156]

Molecules are moved within plants by transport processes that operate at a variety of spatial scales. Subcellular transport of ions, electrons and molecules such as water and enzymes occurs across cell membranes. Minerals and water are transported from roots to other parts of the plant in the transpiration stream. Diffusion, osmosis, and active transport and mass flow are all different ways transport can occur.[157] Examples of elements that plants need to transport are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. In vascular plants, these elements are extracted from the soil as soluble ions by the roots and transported throughout the plant in the xylem. Most of the elements required for plant nutrition come from the chemical breakdown of soil minerals.[158] Sucrose produced by photosynthesis is transported from the leaves to other parts of the plant in the phloem and plant hormones are transported by a variety of processes.

Plant hormones

A diagram of the mechanism of phototropism in oat coleoptiles
1 An oat coleoptile with the sun overhead. Auxin (pink) is evenly distributed in its tip.
2 With the sun at an angle and only shining on one side of the shoot, auxin moves to the opposite side and stimulates cell elongation there.
3 and 4 Extra growth on that side causes the shoot to bend towards the sun.[159]

Plants are not passive, but respond to

bladderworts, and the pollinia of orchids.[160]

The hypothesis that plant growth and development is coordinated by

gravity, and concluded "It is hardly an exaggeration to say that the tip of the radicle . . acts like the brain of one of the lower animals . . directing the several movements".[162] About the same time, the role of auxins (from the Greek auxein, to grow) in control of plant growth was first outlined by the Dutch scientist Frits Went.[163] The first known auxin, indole-3-acetic acid (IAA), which promotes cell growth, was only isolated from plants about 50 years later.[164] This compound mediates the tropic responses of shoots and roots towards light and gravity.[165] The finding in 1939 that plant callus could be maintained in culture containing IAA, followed by the observation in 1947 that it could be induced to form roots and shoots by controlling the concentration of growth hormones were key steps in the development of plant biotechnology and genetic modification.[166]

Venus's fly trap, Dionaea muscipula, showing the touch-sensitive insect trap in action

gibberelic acid are diterpenes synthesised from acetyl CoA via the mevalonate pathway. They are involved in the promotion of germination and dormancy-breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering.[169] Abscisic acid (ABA) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. It inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. It was so named because it was originally thought to control abscission.[170] Ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. It is now known to be the hormone that stimulates or regulates fruit ripening and abscission,[171][172] and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric
crops.

Another class of

phytohormones is the jasmonates, first isolated from the oil of Jasminum grandiflorum[173] which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack.[174]

In addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. This can result in adaptive changes in a process known as photomorphogenesis. Phytochromes are the photoreceptors in a plant that are sensitive to light.[175]

Plant anatomy and morphology

Colour image of a 19th-century illustration of the morphology of a rice plant
A nineteenth-century illustration showing the morphology of the roots, stems, leaves and flowers of the rice plant Oryza sativa

Plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form.[176] All plants are multicellular eukaryotes, their DNA stored in nuclei.

streptophyte cells and those of the green algal order Trentepohliales[180] divide by construction of a phragmoplast as a template for building a cell plate late in cell division.[84]

eudicot, the most common type of plant (three-fifths of all plant species).[181]
However, no plant actually looks exactly like this.