Editing Developmental biology (section)

== Plant development ==
{{further|Plant development}}
Plant '''development''' is the process by which structures originate and mature as a plant grows. It is studied in [[plant anatomy]] and [[plant physiology]] as well as plant morphology.

Plants constantly produce new tissues and structures throughout their life from [[meristem]]s<ref>{{cite journal | vauthors = Bäurle I, Laux T | title = Apical meristems: the plant's fountain of youth | journal = BioEssays | volume = 25 | issue = 10 | pages = 961–70 | date = October 2003 | pmid = 14505363 | doi = 10.1002/bies.10341 | department = Review }}</ref> located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal [[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.

The properties of organization seen in a plant are [[emergence|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."<ref>{{cite book | vauthors = Leopold AC | title = Plant Growth and Development | url = https://archive.org/details/plantgrowthdevel00leoprich | url-access = registration | page = [https://archive.org/details/plantgrowthdevel00leoprich/page/183 183] | location = New York | publisher = McGraw-Hill | date = 1964 }}</ref>

=== Growth ===
A [[vascular plant]] begins from a single celled [[zygote]], formed by [[fertilisation]] of an egg cell by a sperm cell. From that point, it begins to divide to form a plant [[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]] plants, the embryo will develop one or more "seed leaves" ([[cotyledon]]s). By the end of embryogenesis, the young plant will have all the parts necessary to begin its life.

Once the embryo [[germination|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]]s located at the tip of the root, and new stems and leaves grow from shoot [[meristem]]s located at the tip of the shoot.<ref>{{cite journal | vauthors = Brand U, Hobe M, Simon R | title = Functional domains in plant shoot meristems | journal = BioEssays | volume = 23 | issue = 2 | pages = 134–41 | date = February 2001 | pmid = 11169586 | doi = 10.1002/1521-1878(200102)23:2<134::AID-BIES1020>3.0.CO;2-3 | s2cid = 5833219 | department = Review }}</ref> Branching occurs when small clumps of cells left behind by the meristem, and which have not yet undergone [[cellular differentiation]] 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]] results in widening of a root or shoot from divisions of cells in a [[Cambium (botany)|cambium]].<ref>{{cite journal | vauthors = Barlow P | title = Patterned cell determination in a plant tissue: the secondary phloem of trees | journal = BioEssays | volume = 27 | issue = 5 | pages = 533–41 | date = May 2005 | pmid = 15832381 | doi = 10.1002/bies.20214 }}</ref>

In addition to growth by [[cell (biology)|cell]] division, a plant may grow through '''cell elongation'''.<ref>{{cite journal | vauthors = Pacifici E, Di Mambro R, Dello Ioio R, Costantino P, Sabatini S | title = Arabidopsis root | journal = The EMBO Journal | volume = 37 | issue = 16 | date = August 2018 | pmid = 30012836 | pmc = 6092616 | doi = 10.15252/embj.201899134 }}</ref> This occurs when individual cells or groups of cells grow longer. Not all plant cells will 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 will bend 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]]), gravity ([[gravitropism]]), water, ([[hydrotropism]]), and physical contact ([[thigmotropism]]).

Plant growth and development are mediated by specific [[plant hormone]]s and plant growth regulators (PGRs) (Ross et al. 1983).<ref name="ross">{{cite book | vauthors = Ross SD, Pharis RP, Binder WD | date = 1983 | chapter = Growth regulators and conifers: their physiology and potential uses in forestry. | pages = 35–78 | veditors = Nickell LG | title = Plant growth regulating chemicals | volume = 2 | publisher = CRC Press | location = Boca Raton, FL }}</ref> 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 ===
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.

=== Evolution of plant morphology ===
Transcription factors and transcriptional regulatory networks play key roles in plant morphogenesis and their evolution. During plant landing, many novel transcription factor families emerged and are preferentially wired into the networks of multicellular development, reproduction, and organ development, contributing to more complex morphogenesis of land plants.<ref name="MBE_1767">{{cite journal | vauthors = Jin J, He K, Tang X, Li Z, Lv L, Zhao Y, Luo J, Gao G | display-authors = 6 | title = An Arabidopsis Transcriptional Regulatory Map Reveals Distinct Functional and Evolutionary Features of Novel Transcription Factors | journal = Molecular Biology and Evolution | volume = 32 | issue = 7 | pages = 1767–73 | date = July 2015 | pmid = 25750178 | pmc = 4476157 | doi = 10.1093/molbev/msv058 | url =http://mbe.oxfordjournals.org/content/32/7/1767.full| url-status = live | archive-url = https://web.archive.org/web/20160602063847/http://mbe.oxfordjournals.org/content/32/7/1767.full | archive-date = 2016-06-02 }}</ref>

Most land plants share a common ancestor, multicellular algae. An example of the evolution of plant morphology is seen in charophytes. Studies have shown that charophytes have traits that are homologous to land plants. There are two main theories of the evolution of plant morphology, these theories are the homologous theory and the antithetic theory. The commonly accepted theory for the evolution of plant morphology is the antithetic theory. The antithetic theory states that the multiple mitotic divisions that take place before meiosis, cause the development of the sporophyte. Then the sporophyte will development as an independent organism.<ref>{{cite journal | vauthors = Pires ND, Dolan L | title = Morphological evolution in land plants: new designs with old genes | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 367 | issue = 1588 | pages = 508–518 | date = February 2012 | pmid = 22232763 | pmc = 3248709 | doi = 10.1098/rstb.2011.0252 }}</ref>