HOME

TheInfoList




Important structures in plant development are
buds In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the A ...

buds
,
shoot In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Anci ...

shoot
s,
root In vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large grou ...

root
s,
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaves
, and
flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other plan ...

flower
s;
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s produce these tissues and structures throughout their life from
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
will very early produce all of the body parts that it will ever have in its life. When the animal is born (or hatches from its egg), it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a
phylotypic stage In Embryology a phylotypic stage or phylotypic period is a particular developmental stage or developmental period during mid-embryogenesis where embryos of related species within a phylum express the highest degree of morphological and molecular re ...
that evolved independently and that causes a developmental constraint limiting morphological diversification. According to
plant physiologist Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology (structure of plants), plant ecology (interactions with the environment), phytochemistry (bioc ...

plant physiologist
A. Carl Leopold, the properties of organization seen in a plant are
emergent properties In philosophy Philosophy (from , ) is the study of general and fundamental questions, such as those about reason, Metaphysics, existence, Epistemology, knowledge, Ethics, values, Philosophy of mind, mind, and Philosophy of language, ...

emergent properties
which are more than the sum of the individual parts. "The assembly of these tissues and functions into an integrated multicellular organism yields not only the characteristics of the separate parts and processes but also quite a new set of characteristics which would not have been predictable on the basis of examination of the separate parts."


Growth

A
vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large group of plants ( 300,000 ...
begins from a single celled
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
, formed by
fertilisation Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes ...

fertilisation
of an egg cell by a sperm cell. From that point, it begins to divide to form a plant
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
through the process of embryogenesis. As this happens, the resulting cells will organize so that one end becomes the first root while the other end forms the tip of the shoot. In
seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was released to generally positi ...

seed
plants, the embryo will develop one or more "seed leaves" (
cotyledon A cotyledon (; ; ; , gen. (), ) is a significant part of the embryo within the seed of a plant, and is defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germination, germinating see ...
s). By the end of embryogenesis, the young plant will have all the parts necessary to begin in its life. Once the embryo
germinates
germinates
from its seed or parent plant, it begins to produce additional organs (leaves, stems, and roots) through the process of organogenesis. New roots grow from root
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s located at the tip of the root, and new stems and leaves grow from shoot
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s located at the tip of the shoot. Branching occurs when small clumps of cells left behind by the meristem, and which have not yet undergone
cellular differentiation Cellular differentiation is the process in which a cell changes from one cell type A cell type is a classification used to distinguish between morphologically or phenotypically distinct cell forms within a species In biology, a sp ...
to form a specialized tissue, begin to grow as the tip of a new root or shoot. Growth from any such meristem at the tip of a root or shoot is termed primary growth and results in the lengthening of that root or shoot.
Secondary growth In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Anc ...
results in widening of a root or shoot from divisions of cells in a
cambium A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic ...
. In addition to growth by cell division, a plant may grow through cell elongation. This occurs when individual cells or groups of cells grow longer. Not all plant cells grow to the same length. When cells on one side of a stem grow longer and faster than cells on the other side, the stem bends to the side of the slower growing cells as a result. This directional growth can occur via a plant's response to a particular stimulus, such as light (
phototropism File:Phototropism Diagram.svg, thumbnail, Auxin distribution controls phototropism. 1. Sunlight strikes the plant from directly above. Auxin (pink dots) encourages growth straight up. 2, 3, 4. Sunlight strikes the plant at an angle. Auxin is conc ...

phototropism
), gravity (
gravitropism Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all ...
), water, ( hydrotropism), and physical contact (
thigmotropism Thigmotropism is a directional growth movement which occurs as a mechanosensory response to a touch stimulus. Thigmotropism is typically found in twining plants and tendrils, however plant biologists have also found thigmotropic responses in flowe ...
). Plant growth and development are mediated by specific
plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (biology), cells and coordinates multiple-cell actions. A si ...
s and plant growth regulators (PGRs) (Ross et al. 1983).Ross, S.D.; Pharis, R.P.; Binder, W.D. 1983. Growth regulators and conifers: their physiology and potential uses in forestry. p. 35–78 ''in'' Nickell, L.G. (Ed.), Plant growth regulating chemicals. Vol. 2, CRC Press, Boca Raton FL. Endogenous hormone levels are influenced by plant age, cold hardiness, dormancy, and other metabolic conditions; photoperiod, drought, temperature, and other external environmental conditions; and exogenous sources of PGRs, e.g., externally applied and of rhizospheric origin.


Morphological variation during growth

Plants exhibit natural variation in their form and structure. While all organisms vary from individual to individual, plants exhibit an additional type of variation. Within a single individual, parts are repeated which may differ in form and structure from other similar parts. This variation is most easily seen in the leaves of a plant, though other organs such as stems and flowers may show similar variation. There are three primary causes of this variation: positional effects, environmental effects, and juvenility. There is variation among the parts of a mature plant resulting from the relative position where the organ is produced. For example, along a new branch the leaves may vary in a consistent pattern along the branch. The form of leaves produced near the base of the branch differs from leaves produced at the tip of the plant, and this difference is consistent from branch to branch on a given plant and in a given species. The way in which new structures mature as they are produced may be affected by the point in the plants life when they begin to develop, as well as by the environment to which the structures are exposed. Temperature has a multiplicity of effects on plants depending on a variety of factors, including the size and condition of the plant and the temperature and duration of exposure. The smaller and more succulent the plant, the greater the susceptibility to damage or death from temperatures that are too high or too low. Temperature affects the rate of biochemical and physiological processes, rates generally (within limits) increasing with temperature. Juvenility or heteroblasty is when the organs and tissues produced by a young plant, such as a
seedling A seedling is a young sporophyte 350px, Sporophytes of moss during spring A sporophyte () is the diploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic ...

seedling
, are often different from those that are produced by the same plant when it is older. For example, young trees will produce longer, leaner branches that grow upwards more than the branches they will produce as a fully grown tree. In addition, leaves produced during early growth tend to be larger, thinner, and more irregular than leaves on the adult plant. Specimens of juvenile plants may look so completely different from adult plants of the same species that egg-laying insects do not recognize the plant as food for their young. The transition from early to late growth forms is referred to as '
vegetative phase changeVegetative phase change is the juvenile (organism), juvenile-to-adult transition in plants. This transition is distinct from the Flower#Flowering transition, reproductive transition and is most prolonged and pronounced in Woody plant, woody species. ...
', but there is some disagreement about terminology.


Adventitious structures

Plant structures, including, roots, buds, and shoots, that develop in unusual locations are called ''adventitious''. Such structures are common in vascular plants. Adventitious roots and buds usually develop near the existing vascular tissues so that they can connect to the
xylem Xylem is one of the two types of transport tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North Ame ...

xylem
and
phloem Phloem (, ) is the living tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa ...

phloem
. However, the exact location varies greatly. In young stems, adventitious roots often form from
parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the Ancient G ...

parenchyma
between the
vascular bundle A vascular bundle is a part of the transport system in vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'wind ...
s. In stems with secondary growth, adventitious roots often originate in phloem parenchyma near the
vascular cambium The vascular cambium is the main growth tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ...
. In stem cuttings, adventitious roots sometimes also originate in the
callus A callus is an area of thickened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may occur anywhere on the ski ...
cells that form at the cut surface. Leaf cuttings of the ''
Crassula ''Crassula'' is a genus of succulent plants containing about 200 accepted species, including the popular jade plant (''Crassula ovata''). They are members of the stonecrop family (Crassulaceae) and are native to many parts of the globe, but cultiv ...

Crassula
'' form adventitious roots in the epidermis.


Buds and shoots

Adventitious
bud In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the An ...

bud
s develop from places other than a shoot
apical meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dub ...
, which occurs at the tip of a stem, or on a shoot node, at the leaf axil, the bud being left there during the primary growth. They may develop on roots or leaves, or on shoots as a new growth. Shoot apical meristems produce one or more axillary or lateral buds at each node. When stems produce considerable
secondary growth In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Anc ...
, the axillary buds may be destroyed. Adventitious buds may then develop on stems with secondary growth. Adventitious buds are often formed after the stem is wounded or
pruned Pruning is a horticultural Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfort and ornamental purposes. Horticulturists grow flowers, fruits and nuts, vegetables and herbs, as wel ...

pruned
. The adventitious buds help to replace lost branches. Adventitious buds and shoots also may develop on mature tree trunks when a shaded trunk is exposed to bright sunlight because surrounding trees are cut down.
Redwood Sequoioideae, popularly known as redwoods, is a subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family (biology), family but more inclusive than genus. Standa ...

Redwood
(''Sequoia sempervirens'') trees often develop many adventitious buds on their lower trunks. If the main trunk dies, a new one often sprouts from one of the adventitious buds. Small pieces of redwood trunk are sold as souvenirs termed redwood burls. They are placed in a pan of water, and the adventitious buds sprout to form shoots. Some plants normally develop adventitious buds on their roots, which can extend quite a distance from the plant. Shoots that develop from adventitious buds on roots are termed suckers. They are a type of natural
vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction Asexual reproduction is a type of that does not involve the fusion of s or change in the number of ...
in many
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
, e.g. many grasses,
quaking aspen ''Populus tremuloides'' is a deciduous In the fields of horticulture and botany, the term ''deciduous'' (; ) means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in ...
and
Canada thistle ''Cirsium arvense'' is a perennial species of flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may ref ...
. The Pando quaking aspen grew from one trunk to 47,000 trunks via adventitious bud formation on a single root system. Some leaves develop adventitious buds, which then form adventitious roots, as part of
vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction Asexual reproduction is a type of that does not involve the fusion of s or change in the number of ...
; e.g. piggyback plant (''
Tolmiea menziesii The plant ''Tolmiea menziesii'' () is a member of the genus ''Tolmiea''. It is known by the common names youth on age, pick-a-back-plant, piggyback plant, and thousand mothers. It is a perennial plant native to the West Coast of North America, occu ...

Tolmiea menziesii
'') and mother-of-thousands (''
Kalanchoe daigremontiana ''Kalanchoe daigremontiana'', formerly known as ''Bryophyllum daigremontianum'' and commonly called mother of thousands, alligator plant, or Mexican hat plant is a succulent plant native to Madagascar. Like other members of ''Bryophyllum'' (now ...

Kalanchoe daigremontiana
''). The adventitious plantlets then drop off the parent plant and develop as separate
clone Clone or Clones or Cloning or The Clone may refer to: Places * Clones, County Fermanagh * Clones, County Monaghan, a town in Ireland Biology * Clone (B-cell), a lymphocyte clone, the massive presence of which may indicate a pathological conditio ...

clone
s of the parent.
Coppicing Coppicing is a traditional method of woodland management which exploits the capacity of many species of trees to put out new shoots from their tree stump, stump or roots if cut down. In a coppiced wood, which is called a copse, young tree stems ...
is the practice of cutting
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...

tree
stems to the ground to promote rapid growth of adventitious shoots. It is traditionally used to produce poles, fence material or firewood. It is also practiced for
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...

biomass
crops grown for fuel, such as
poplar
poplar
or willow.


Roots

Adventitious rooting may be a stress-avoidance acclimation for some species, driven by such inputs as hypoxia or nutrient deficiency. Another ecologically important function of adventitious rooting is the vegetative reproduction of tree species such as ''Salix'' and ''Sequoia'' in
riparian A riparian zone or riparian area is the interface between land and a river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the grou ...
settings. The ability of plant stems to form adventitious roots is utilised in commercial propagation by
cutting Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force. Implements commonly used for wikt:cut, cutting are the knife and saw, or in medicine and science the scal ...
s. Understanding of the physiological mechanisms behind adventitious rooting has allowed some progress to be made in improving the rooting of cuttings by the application of synthetic auxins as rooting powders and by the use of selective basal wounding. Further progress can be made in future years by applying research into other regulatory mechanisms to commercial propagation and by the comparative analysis of molecular and ecophysiological control of adventitious rooting in 'hard to root' vs. 'easy to root' species. Adventitious roots and buds are very important when people propagate plants via cuttings,
layering Layering has evolved as a common means of vegetative propagation of numerous species in natural environments. Layering is also utilized by horticulturists to propagate desirable plants. Natural layering typically occurs when a branch touches th ...

layering
,
tissue culture Tissue culture is the growth of tissues or cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious rec ...
.
Plant hormones Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (biology), cells and coordinates multiple-cell actions. A sig ...
, termed
auxin Auxins (plural of auxin ) are a class of plant hormone Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (bio ...

auxin
s, are often applied to stem,
shoot In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Anci ...

shoot
or
leaf A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are ...

leaf
cuttings to promote adventitious root formation, e.g.,
African violet
African violet
and
sedum ''Sedum'' is a large genus of flowering plants in the family Crassulaceae, members of which are commonly known as stonecrops. The genus has been described as containing up to 600 species, subsequently reduced to 400–500. They are leaf succulen ...

sedum
leaves and shoots of
poinsettia The poinsettia ( or ) (''Euphorbia pulcherrima'') is a commercially important plant species of the diverse spurge family ( Euphorbiaceae). Indigenous to Mexico and Central America, the poinsettia was first described by Europeans in 1834. It is ...

poinsettia
and
coleus ''Coleus'' is a genus of annual or perennial herbs or shrubs, sometimes succulent, sometimes with a fleshy or tuberous rootstock, found in the Old World tropics and subtropics. The relationship among the genera ''Coleus'', ''Solenostemon'' and ' ...

coleus
. Propagation via root cuttings requires adventitious bud formation, e.g., in
horseradish Horseradish (''Armoracia rusticana'', syn. ''Cochlearia armoracia'') is a perennial plant of the family Brassicaceae (which also includes Mustard plant, mustard, wasabi, broccoli, cabbage, and radish). It is a root vegetable, cultivated and us ...

horseradish
and
apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...

apple
. In layering, adventitious roots are formed on aerial stems before the stem section is removed to make a new plant. Large houseplants are often propagated by air layering. Adventitious roots and buds must develop in tissue culture propagation of plants.


=Modified forms

= *Tuberous roots lack a definite shape; example:
sweet potato The sweet potato or sweetpotato (''Ipomoea batatas'') is a dicotyledon The dicotyledons, also known as dicots (or more rarely dicotyls), are one of the two groups into which all the flowering plant The flowering plants, also known as Angi ...

sweet potato
. *Fasciculated root (tuberous root) occur in clusters at the base of the stem; examples:
asparagus Asparagus, or garden asparagus, folk name sparrow grass, scientific name ''Asparagus officinalis'', is a perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom ...

asparagus
,
dahlia Dahlia ( or ) is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including the ...

dahlia
. *Nodulose roots become swollen near the tips; example:
turmeric Turmeric (pronounced , also ) is a flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: ...
. *Stilt roots arise from the first few nodes of the stem. These penetrate obliquely down into the soil and give support to the plant; examples:
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It can also be ...

maize
,
sugarcane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, ...

sugarcane
. *Prop roots give mechanical support to aerial branches. The lateral branches grow vertically downward into the soil and act as pillars; example:
banyan A banyan, also spelled "banian", is a fig that begins its life as an epiphyte 200px, '' Tillandsia bourgaei'' growing on an oak tree in Mexico An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrie ...

banyan
. *Climbing roots arising from nodes attach themselves to some support and climb over it; example:
money plant
money plant
. *Moniliform or beaded roots the fleshy roots give a beaded appearance, e.g.:
bitter gourd ''Momordica charantia'' (colloquially: bitter melon; bitter apple; bitter gourd; bitter squash; balsam-pear; with many more #Alternative names, names listed below) is a tropical and subtropical vine of the family Cucurbitaceae, widely grown in A ...

bitter gourd
,
Portulaca
Portulaca
, some grasses


Leaf development

The genetics behind leaf shape development in ''Arabidopsis thaliana'' has been broken down into three stages: The initiation of the leaf primordium, the establishment of dorsiventrality, and the development of a marginal
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
. Leaf primordium is initiated by the suppression of the genes and proteins of the class I '' KNOX'' family (such as ''SHOOT APICAL MERISTEMLESS''). These class I KNOX proteins directly suppress
gibberellin Gibberellins (GAs) are plant hormone Plant hormones (also known as phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, from ...
biosynthesis in the leaf primodium. Many genetic factors were found to be involved in the suppression of these genes in leaf primordia (such as ''ASYMMETRIC LEAVES1,'' ''BLADE-ON-PETIOLE1'', ''SAWTOOTH1'', etc.). Thus, with this suppression, the levels of gibberellin increase and leaf primorium initiates growth.


Flower development

Flower development is the process by which
angiosperms Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...
produce a pattern of
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...

gene expression
in
meristem The meristem is a type of tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa du ...
s that leads to the appearance of an organ oriented towards
sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Greek, ...
, the flower. There are three
physiological Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. ...
developments that must occur in order for this to take place: firstly, the plant must pass from sexual immaturity into a sexually mature state (i.e. a transition towards flowering); secondly, the transformation of the apical meristem’s function from a vegetative meristem into a floral meristem or
inflorescence An inflorescence is a group or cluster of flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some ...
; and finally the growth of the flower’s individual organs. The latter phase has been modelled using the ''ABC model'', which describes the biological basis of the process from the perspective of
molecular A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atom An atom is the smallest unit of ordinary matter In ...
and
developmental Development of the human body is the process of growth to maturity. The process begins with fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the ...
genetics. An external
stimulus A stimulus is something that causes a physiological response. It may refer to: *Stimulation Stimulation is the encouragement of development or the cause of activity generally. For example, "The press provides stimulation of political discourse." ...
is required in order to trigger the
differentiation Differentiation may refer to: Business * Differentiation (economics), the process of making a product different from other similar products * Product differentiation, in marketing * Differentiated service, a service that varies with the identity o ...
of the meristem into a flower meristem. This stimulus will activate
mitotic In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In gene ...

mitotic
cell division in the meristem, particularly on its sides where new
primordia Image:Root primordia.JPG, 250px, Root primordia (brown spots) as seen on the butt of a freshly cut pineapple crown intended for vegetative reproduction. A primordium (; plural: primordia; synonym: anlage) in embryology, is an Organ (anatomy), orga ...
are formed. This same stimulus will also cause the meristem to follow a
developmental Development of the human body is the process of growth to maturity. The process begins with fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the ...
pattern that will lead to the growth of floral meristems as opposed to vegetative meristems. The main difference between these two types of meristem, apart from the obvious disparity between the objective organ, is the verticillate (or whorled)
phyllotaxis In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancie ...
, that is, the absence of
stem Stem or STEM may refer to: Biology * Plant stem, the aboveground structures that have vascular tissue and that support leaves and flowers ** Stipe (botany), a stalk that supports some other structure ** Stipe (mycology), the stem supporting the c ...

stem
elongation among the successive
whorls A whorl is a type of spiral or circular pattern. Other meanings of whorl include: * Whorl (botany), the attachment of sepals, petals, leaves, or branches at a single point * Whorl (biology), the structure of some organs, used in the aid of ident ...
or verticils of the primordium. These verticils follow an acropetal development, giving rise to
sepal A sepal ( or ) is a part of the flower A flower, sometimes known as a bloom or blossom Cherry blossoms in Paris in full bloom. In botany, blossoms are the flowers of stone fruit fruit tree, trees (genus ''Prunus'') and of some other p ...
s,
petal Petals are modified leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together fo ...

petal
s,
stamen The stamen (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ve ...
s and
carpel Gynoecium (; ) is most commonly used as a collective term for the parts of a flower A flower, sometimes known as a bloom or blossom Image:Cerisier du Japon Prunus serrulata.jpg, Cherry blossoms in Paris in full bloom. In botany, blossoms ...
s. Another difference from vegetative axillary meristems is that the floral meristem is «determined», which means that, once differentiated, its cells will no longer
divide
divide
. The identity of the organs present in the four floral verticils is a consequence of the interaction of at least three types of
gene products A gene product is the biochemical material, either RNA or protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of fu ...
, each with distinct functions. According to the ABC model, functions A and C are required in order to determine the identity of the verticils of the
perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower, and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (botany), calyx (sepals) and the corolla (flower), ...
and the reproductive verticils, respectively. These functions are exclusive and the absence of one of them means that the other will determine the identity of all the floral verticils. The B function allows the differentiation of petals from sepals in the secondary verticil, as well as the differentiation of the stamen from the carpel on the tertiary verticil.


Floral fragrance

Plants use floral form, flower, and scent to attract different insects for
pollination Pollination is the transfer of pollen Pollen is a powdery substance consisting of pollen grains which are Sporophyte, microsporophytes of spermatophyta, seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat ...

pollination
. Certain compounds within the emitted scent appeal to particular
pollinator A pollinator is an animal that moves pollen File:Pollen Tube.svg, Pollen Tube Diagram Pollen is a powdery substance consisting of pollen grains which are Sporophyte, microsporophytes of spermatophyta, seed plants, which produce male gametes ...

pollinator
s. In ''
Petunia ''Petunia'' is genus of 20 species of flowering plants of South American origin. The popular flower of the same name derived its epithet from the French, which took the word ''petun'', meaning "tobacco," from a Tupi–Guarani language. An Annual ...

Petunia
'' ''hybrid''a, volatile benzenoids are produced to give off the floral smell. While components of the benzenoid biosynthetic pathway are known, the enzymes within the pathway, and subsequent regulation of those enzymes, are yet to be discovered.Schuurink, R.C., Haring, M. A., Clark, D. G. (2006) "Regulation of volatile benzenoid biosynthesis in petunia flowers." ''Trends Plant Sci'', 11 (1). doi: 10.1016/j.tplants.2005.09.009 To determine pathway regulation, ''P. hybrida'' Mitchell flowers were used in a petal-specific
microarray A microarray is a multiplex Multiplex may refer to: * Multiplex (automobile), a former American car make * Multiplex (comics), a DC comic book supervillain * Multiplex communication or multiplexing, combining many signals into a single transmiss ...
to compare the flowers that were just about to produce the scent, to the ''P. hybrida'' cultivar W138 flowers that produce few volatile benzenoids. cDNAs of genes of both plants were sequenced. The results demonstrated that there is a transcription factor upregulated in the Mitchell flowers, but not in the W138 flowers lacking the floral aroma. This gene was named ODORANT1 (ODO1). To determine expression of ODO1 throughout the day, RNA gel blot analysis was done. The gel showed that ODO1 transcript levels began increasing between 1300 and 1600 h, peaked at 2200 h and were lowest at 1000 h. These ODO1 transcript levels directly correspond to the timeline of volatile benzenoid emission. Additionally, the gel supported the previous finding that W138 non-fragrant flowers have only one-tenth the ODO1 transcript levels of the Mitchell flowers. Thus, the amount of ODO1 made corresponds to the amount of volatile benzenoid emitted, indicating that ODO1 regulates benzenoid biosynthesis. Additional genes contributing to the biosynthesis of major scent compounds are OOMT1 and OOMT2. OOMT1 and OOMT2 help to synthesize orcinol O-methyltransferases (OOMT), which catalyze the last two steps of the DMT pathway, creating 3,5-dimethoxytoluene (DMT). DMT is a scent compound produced by many different roses yet, some rose varieties, like ''gallica'' and Damask rose ''damascene'', do not emit DMT. It has been suggested that these varieties do not make DMT because they do not have the OOMT genes. However, following an immunolocalization experiment, OOMT was found in the petal epidermis. To study this further, rose petals were subjected to ultracentrifugation. Supernatants and pellets were inspected by
western blot The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Western blot ...
. Detection of OOMT protein at 150,000g in the supernatant and the pellet allowed for researchers to conclude that OOMT protein is tightly associated with petal epidermis membranes. Such experiments determined that OOMT genes do exist within ''Rosa gallica'' and Damask rose ''Rosa damascene'' varieties, but the OOMT genes are not expressed in the flower tissues where DMT is made.Scalliet, G., Lionnet, C., Le Bechec, M., Dutron, L., Magnard, J. L., Baudino, S., Bergougnoux, V., Jullien, F., Chambrier, P., Vergne, P., Dumas, C., Cock, J. M., Hugueney, P. (2006). "Role of Petal-Specific Orcinol O-Methyltransferases in the Evolution of Rose Scent." ''Plant Physiol'', 140: 18-29. doi: https://doi.org/10.1104/pp.105.070961


References

{{Authority control
Development Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking#Development, Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material i ...