Editing Halophyte (section)

== Salt tolerance ==
True halophytes do not just tolerate saline water, but show optimal growth in saline water.<ref>{{cite journal |last1=Yuan |first1=Fang |last2=Xu |first2=Yanyu |last3=Leng |first3=Bingying |last4=Wang |first4=Baoshan |title=Beneficial Effects of Salt on Halophyte Growth:  Morphology, Cells, and Genes |journal=Open Life Sciences |date=2019 |page=191 |doi=10.1515/biol-2019-0021|pmc=7874760 }}</ref>

One quantitative measure of salt tolerance ([[halotolerance]]) is the total dissolved solids in irrigation water that a plant can tolerate. [[Seawater]] typically contains 40&nbsp;grams per litre (g/L) of dissolved salts (mostly [[sodium chloride]]). [[Beans]] and [[rice]] can tolerate about 1–3 g/L, and are considered glycophytes (as are most [[crop plant]]s). At the other extreme, ''[[Salicornia bigelovii]]'' (dwarf glasswort) grows well at 70 g/L of dissolved solids, and is a promising halophyte for use as a crop.<ref name=":4">
Glenn, E. P.; Brown, J. J.; O'Leary, J. W. (1998). [http://www.miracosta.edu/home/kmeldahl/writing/..%5Carticles/crops.pdf "Irrigating Crops with Seawater"], ''[http://www.sciam.com Scientific American]'', Vol. 279, no. 8, Aug. 1998, pp. 56–61.</ref> Plants such as barley (''[[Hordeum vulgare]]'') and the date palm (''[[Phoenix dactylifera]]'') can tolerate about 5 g/L, and can be considered as marginal halophytes.<ref name="Glenn99" />

Adaptation to saline environments by halophytes may take the form of salt tolerance or salt avoidance. Plants that avoid the effects of high salt even though they live in a saline environment may be referred to as facultative halophytes rather than 'true', or obligatory, halophytes.[[File:Pneumatophore overkill - grey mangrove.JPG|thumb|320px|right|[[Pneumatophores]] of [[Avicennia marina|Grey mangrove]]]]

For example, a short-lived plant species that completes its reproductive life cycle during periods (such as a [[rainy season]]) when the salt concentration is low would be avoiding salt rather than tolerating it. Or a plant species may maintain a 'normal' internal salt concentration by excreting excess salts through its leaves, by way of [[Salt gland|salt glands]], or by concentrating salts in salt bladders in leaves that later die and drop off.<ref name=":3" />

In an effort to improve agricultural production in regions where crops are exposed to salinity, research is focused on improving understanding of the various mechanisms whereby plants respond to salinity stress, so that more robust crop halophytes may be developed.  Adaptive responses to salinity stress have been identified at molecular, cellular, metabolic, and physiological levels.<ref name=Gupta-2014>{{cite journal| title=Mechanism of Salinity Tolerance in Plants: Physiological, Biochemical, and Molecular Characterization| first1=Bhaskar| last1=Gupta| first2=Bingru| last2=Huang| journal=[[International Journal of Genomics]]| volume=2014| pages=701596| doi=10.1155/2014/701596| pmid=24804192| date=3 April 2014| pmc=3996477| doi-access=free}}</ref>