Editing Germination (section)

== Germination rate and germination capacity ==
[[File:Seedling of Eucalyptus.jpg|thumb|Germination of [[seedlings]] raised from [[seeds]] of [[eucalyptus]] after three days of [[sowing]]]]

In [[agriculture]] and [[gardening]], the '''germination rate''' describes how many seeds of a particular [[plant]] [[species]], variety or seedlot are likely to germinate over a given period. It is a measure of germination time course and is usually expressed as a percentage, e.g., an 85% germination rate indicates that about 85 out of 100 seeds will probably germinate under proper conditions over the germination period given. Seed germination rate is determined by the seed genetic composition, morphological features and environmental factors.{{citation needed|date=September 2019}} The germination rate is useful for calculating the number of seeds needed for a given area or desired number of plants. For seed physiologists and seed scientists "germination rate" is the reciprocal of time taken for the process of germination to complete starting from time of [[sowing]]. On the other hand, the number of seed able to complete germination in a population (i.e. seed lot) is referred to as '''germination capacity'''.

Soil salinity is one of the stress factors that can limit the germination rate. Environmental stress activates some stress-related activities [CuZn-[[superoxide dismutase]] (SOD), Mn-SOD, [[L-ascorbate oxidase]] (AO), [[DNA polymerase]] Delta 1 (POLD)-1, Chaperon (CHAPE) and heat shock protein (HSP)-21], genetic template stability and photosynthetic pigment activation.<ref name="FH">{{cite journal |first1= Kamile |last1= Ulukapi | first2= Ayse Gul |last2= Nasircilar | title = The role of exogenous glutamine on germination, plant development and transcriptional expression of some stress-related genes in onion under salt stres | journal = [[Folia Horticulturae]] | volume = 36 | issue = 1 | pages = 19–34 | date = February 2024 | pmid = | doi = 10.2478/fhort-2024-0002 | publisher = Polish Society of Horticultural Science | s2cid = 19887643 | doi-access = free }}</ref>  Application of exogenic [[glutamine]] limiting this process. Research carried out on [[onion]] seeds shows a reduction in the mean germination time, an increase in the coefficient of germination velocity, the germination index and germination percentage after administration of exogenous glutamine to plants.<ref name="FH"/>

===Repair of DNA damage===

Seed quality deteriorates with age, and this is associated with accumulation of genome damage.<ref name="pmid25750428">{{cite journal | vauthors = Waterworth WM, Bray CM, West CE | title = The importance of safeguarding genome integrity in germination and seed longevity | journal = Journal of Experimental Botany | volume = 66 | issue = 12 | pages = 3549–58 | date = June 2015 | pmid = 25750428 | doi = 10.1093/jxb/erv080 | doi-access = free }}</ref> During germination, [[DNA repair|repair]] processes are activated to deal with accumulated [[DNA damage (naturally occurring)|DNA damage]].<ref name="pmid11321247">{{cite journal | vauthors = Koppen G, Verschaeve L | title = The alkaline single-cell gel electrophoresis/comet assay: a way to study DNA repair in radicle cells of germinating Vicia faba | journal = Folia Biologica | volume = 47 | issue = 2 | pages = 50–4 | year = 2001 | pmid = 11321247 }}</ref> In particular, single- and double-strand breaks in DNA can be repaired.<ref name="pmid20584150">{{cite journal | vauthors = Waterworth WM, Masnavi G, Bhardwaj RM, Jiang Q, Bray CM, West CE | title = A plant DNA ligase is an important determinant of seed longevity | journal = The Plant Journal | volume = 63 | issue = 5 | pages = 848–60 | date = September 2010 | pmid = 20584150 | doi = 10.1111/j.1365-313X.2010.04285.x | doi-access = free }}</ref> The DNA damage checkpoint kinase [[ATM serine/threonine kinase|ATM]] has a major role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.<ref name="pmid27503884">{{cite journal | vauthors = Waterworth WM, Footitt S, Bray CM, Finch-Savage WE, West CE | title = DNA damage checkpoint kinase ATM regulates germination and maintains genome stability in seeds | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 113 | issue = 34 | pages = 9647–52 | date = August 2016 | pmid = 27503884 | pmc = 5003248 | doi = 10.1073/pnas.1608829113 | bibcode = 2016PNAS..113.9647W | doi-access = free }}</ref>

=== Dicot germination ===
[[File:Stages of germination in pea plants.svg|thumb|The stages of germination of a pea plant: A.&nbsp;seed coat, B.&nbsp;radicle, C.&nbsp;primary root, D.&nbsp;secondary root, E.&nbsp;cotyledon, F.&nbsp;plumule, G.&nbsp;leaf, H.&nbsp;tap root]]

The part of the plant that first emerges from the seed is the embryonic root, termed the [[radicle]] or primary root. It allows the seedling to become anchored in the ground and start absorbing water. After the root absorbs water, an embryonic [[Shoot (botany)|shoot]], termed the plumule emerges from the seed. This shoot comprises three main parts: the [[cotyledon]]s (seed leaves), the section of shoot below the cotyledons ([[hypocotyl]]), and the section of shoot above the cotyledons ([[epicotyl]]). The way the shoot emerges differs among plant groups.<ref name="Raven">{{cite book | first1 = Peter H | last1 = Raven | first2 = Ray Franklin | last2 = Evert | first3 = Susan E | last3 = Eichhorn | name-list-style = vanc | title = Biology of Plants | url = https://archive.org/details/biologyofplants00rave_0 | url-access = registration | edition = 7th | publisher = W.H. Freeman and Company Publishers | year = 2005 | location = New York | pages = [https://archive.org/details/biologyofplants00rave_0/page/504 504–508] | isbn = 978-0-7167-1007-3}}</ref>

==== Epigeal ====
[[Epigeal germination]] (or epigeous germination) is a botanical term indicating that the germination takes place above the ground. In epigeal germination, the ''hypocotyl'' elongates and forms a hook, pulling rather than pushing the [[cotyledon]]s and [[apical meristem]] through the soil. Once it reaches the surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlings into the air. [[Bean]]s, tamarind, and papaya are examples of plants that germinate this way.<ref name="Raven"/>

==== Hypogeal ====
Germination can also be done by hypogeal germination (or hypogeous germination), where the epicotyl elongates and forms the hook. In this type of germination, the cotyledons stay underground where they eventually decompose. For example: peas, [[chickpea]]s and mango germinate this way.<ref>{{cite book| vauthors = Sadhu MK |title=Plant propagation|url=https://books.google.com/books?id=K-gQh6OI7GcC&q=mango+hypogeous+germination&pg=PA61|year=1989|publisher=New Age International|page=61|isbn=978-81-224-0065-6}}</ref>

=== Monocot germination ===
In [[monocot]] seeds, the embryo's radicle and cotyledon are covered by a [[coleorhiza]] and [[coleoptile]], respectively. The coleorhiza is the first part to grow out of the seed, followed by the radicle. The coleoptile is then pushed up through the ground until it reaches the surface. There, it stops elongating and the first leaves emerge.<ref name="Raven"/>

=== Precocious germination ===
When a seed germinates without undergoing all four stages of seed development, i.e., globular, heart shape, torpedo shape, and cotyledonary stage, it is known as precocious germination.{{cn|date=June 2024}}