Editing Plant physiology (section)

==Biochemistry of plants==
[[Image:Latex dripping.JPG|thumb|[[Rubber|Latex]] being collected from a [[rubber tapping|tapped]] [[rubber tree]].]]
{{main|Phytochemistry}}
{{citations needed|section|date=January 2024}}
The [[chemical element]]s of which plants are constructed—principally [[carbon]], [[oxygen]], [[hydrogen]], [[nitrogen]], [[phosphorus]], [[sulfur]], etc.—are the same as for all other life forms: animals, fungi, [[bacteria]] and even [[virus]]es.  Only the details of their individual molecular structures vary.

Despite this underlying similarity, plants produce a vast array of chemical compounds with unique properties which they use to cope with their environment.  [[Pigment]]s are used by plants to absorb or detect light, and are extracted by humans for use in [[dye]]s. Other plant products may be used for the manufacture of commercially important [[rubber]] or [[biofuel]].  Perhaps the most celebrated compounds from plants are those with [[pharmacological]] activity, such as [[salicylic acid]] from which [[aspirin]] is made, [[morphine]], and [[digoxin]].  [[Drug company|Drug companies]] spend billions of dollars each year researching plant compounds for potential medicinal benefits.

===Constituent elements===
{{further|Plant nutrition}}

Plants require some [[nutrient]]s, such as [[carbon]] and [[nitrogen]], in large quantities to survive.  Some nutrients are termed [[Macronutrient (ecology)|macronutrients]], where the prefix ''macro-'' (large) refers to the quantity needed, not the size of the nutrient particles themselves.  Other nutrients, called [[micronutrient]]s, are required only in trace amounts for plants to remain healthy.  Such micronutrients are usually absorbed as [[ion]]s dissolved in water taken from the soil, though [[carnivorous plant]]s acquire some of their micronutrients from captured prey.

The following tables list [[chemical element|element]] nutrients essential to plants.  Uses within plants are generalized.

{| class="wikitable"
|-
|+ '''Macronutrients''' – necessary in large quantities
|-
| Element || Form of uptake || Notes
|-
| style="height:50px;"| [[Nitrogen]] || NO<sub>3</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup>|| Nucleic acids, proteins, hormones, etc.
|-
| [[Oxygen]]  || O<sub>2,</sub> H<sub>2</sub>O ||[[Cellulose]], [[starch]], other organic compounds
|-
| [[Carbon]] || CO<sub>2</sub>|| Cellulose, starch, other organic compounds
|-
| [[Hydrogen]] ||H<sub>2</sub>O || Cellulose, starch, other organic compounds
|-
| [[Potassium]] ||K<sup>+</sup>|| Cofactor in protein synthesis, water balance, etc.        
|-
| [[Calcium]] ||Ca<sup>2+</sup> || Membrane synthesis and stabilization
|-
| [[Magnesium]] || Mg<sup>2+</sup>|| Element essential for chlorophyll
|-
| style="height:50px;"| [[Phosphorus]] || H<sub>2</sub>PO<sub>4</sub><sup>−</sup>|| Nucleic acids, phospholipids, ATP
|-
| style="height:50px;"| [[Sulfur|Sulphur]] ||SO<sub>4</sub><sup>2−</sup>|| Constituent of proteins
|}

{| class="wikitable"
|-
|+ '''Micronutrients''' – necessary in small quantities
|-
|Element || Form of uptake || Notes
|-
| [[Chlorine]] || Cl<sup>−</sup> ||Photosystem II and stomata function
|-
| [[Iron]] || Fe<sup>2+</sup>, Fe<sup>3+</sup>||Chlorophyll formation and nitrogen fixation
|-
| [[Boron]]  || HBO<sub>3</sub> ||Crosslinking pectin
|-
| [[Manganese]] || Mn<sup>2+</sup>|| Activity of some enzymes and photosystem II
|-
| [[Zinc]] || Zn<sup>2+</sup>|| Involved in the synthesis of enzymes and chlorophyll
|-
| [[Copper]] || Cu<sup>+</sup>|| Enzymes for lignin synthesis
|-
| style="height:50px;"| [[Molybdenum]] || MoO<sub>4</sub><sup>2−</sup> || Nitrogen fixation, reduction of nitrates
|-
| [[Nickel]] || Ni<sup>2+</sup>|| Enzymatic cofactor in the metabolism of nitrogen compounds
|}

=== Pigments ===
[[Image:Chlorophyll-a-3D-vdW.png|thumb|Space-filling model of the [[chlorophyll]] molecule.]]
[[Image:orange violet pansies.jpg|thumb|[[Anthocyanin]] gives these [[pansies]] their dark purple pigmentation.]]
{{main|Biological pigment}}

Among the most important molecules for plant function are the [[pigment]]s.  Plant pigments include a variety of different kinds of molecules, including [[porphyrin]]s, [[carotenoid]]s, and [[anthocyanin]]s.  All [[biological pigment]]s selectively absorb certain [[wavelength]]s of [[light]] while [[Reflection (physics)|reflecting]] others.  The light that is absorbed may be used by the plant to power [[chemical reaction]]s, while the reflected wavelengths of light determine the [[color]] the pigment appears to the eye.

[[Chlorophyll]] is the primary pigment in plants; it is a [[porphyrin]] that absorbs red and blue wavelengths of light while reflecting [[green]].  It is the presence and relative abundance of chlorophyll that gives plants their green color.  All land plants and [[green alga]]e possess two forms of this pigment: chlorophyll ''a'' and chlorophyll ''b''.  [[Kelp]]s, [[diatom]]s, and other photosynthetic [[heterokont]]s contain chlorophyll ''c'' instead of ''b'',  [[red algae]] possess  chlorophyll ''a''.  All chlorophylls serve as the primary means plants use to intercept light to fuel [[photosynthesis]].

[[Carotenoid]]s are red, orange, or yellow [[tetraterpenoid]]s.  They function as accessory pigments in plants, helping to fuel [[photosynthesis]] by gathering wavelengths of light not readily absorbed by chlorophyll.  The most familiar carotenoids are [[carotene]] (an orange pigment found in [[carrot]]s), [[lutein]] (a yellow pigment found in fruits and vegetables), and [[lycopene]] (the red pigment responsible for the color of [[tomato]]es).  Carotenoids have been shown to act as [[antioxidant]]s and to promote healthy [[eyesight]] in humans.

[[Anthocyanin]]s  (literally "flower blue") are [[solubility|water-soluble]] [[flavonoid]] [[pigments]] that appear red to blue, according to [[pH]]. They occur in all [[Tissue (biology)|tissues]] of higher plants, providing color in [[leaf|leaves]], [[plant stem|stems]], [[root]]s, [[flower]]s, and [[fruit]]s, though not always in sufficient quantities to be noticeable. Anthocyanins are most visible in the [[petal]]s of flowers, where they may make up as much as 30% of the dry weight of the tissue.<ref>{{cite book| author = Trevor Robinson| title = The organic constituents of higher plants: their chemistry and interrelationships| year = 1963| publisher = Cordus Press| page = 183  }}</ref>  They are also responsible for the purple color seen on the underside of tropical shade plants such as ''[[Tradescantia zebrina]]''. In these plants, the anthocyanin catches light that has passed through the leaf and reflects it back towards regions bearing chlorophyll, in order to maximize the use of available light

[[Betalain]]s are red or yellow pigments.  Like anthocyanins they are water-soluble, but unlike anthocyanins they are [[indole]]-derived compounds synthesized from [[tyrosine]].  This class of pigments is found only in the [[Caryophyllales]] (including [[cactus]] and [[amaranth]]), and never co-occur in plants with anthocyanins. Betalains are responsible for the deep red color of [[beet]]s, and are used commercially as food-coloring agents.  Plant physiologists are uncertain of the function that betalains have in plants which possess them, but there is some preliminary evidence that they may have fungicidal properties.<ref>{{cite journal
| last= Kimler
| first= L. M.
| year=1975
| title=Betanin, the red beet pigment, as an antifungal agent
| journal= Botanical Society of America, Abstracts of Papers
| volume= 36 }}</ref>