Thermogenic plant

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Thermogenic plants have the ability to raise their temperature above that of the surrounding air. Heat is generated in the mitochondria, as a secondary process of cellular respiration called thermogenesis. Alternative oxidase and uncoupling proteins similar to those found in mammals enable the process, which is still poorly understood.

Contents

The role of thermogenesis

Botanists are not completely sure why thermogenic plants generate large amounts of excess heat, but most agree that it has something to do with increasing pollination rates. The most widely accepted theory states that the endogenous heat helps in spreading chemicals that attract pollinators to the plant. [1] For example, the Voodoo lily uses heat to help spread its smell of rotting meat. [2] This smell draws in flies which begin to search for the source of the smell. As they search the entire plant for the dead carcass, they pollinate the plant. [3]

Other theories state that the heat may provide a heat reward for the pollinator: pollinators are drawn to the flower for its warmth. This theory has less support because most thermogenic plants are found in tropical climates.

Yet another theory is that the heat helps protect against frost damage, allowing the plant to germinate and sprout earlier than otherwise. For example, the skunk cabbage generates heat, which allows it to melt its way through a layer of snow in early spring. [4] The heat, however, is mostly used to help spread its pungent odor and attract pollinators.

Characteristics of thermogenic plants

Most thermogenic plants tend to be rather large. This is because the smaller plants do not have enough volume to create a considerable amount of heat. Large plants, on the other hand, have a lot of mass to create and retain heat. [5]

Thermogenic plants are also protogynous, meaning that the female part of the plant matures before the male part of the same plant. This reduces inbreeding considerably, as such a plant can be fertilized only by pollen from a different plant. This is why thermogenic plants release pungent odors to attract pollinating insects.

Examples

Thermogenic plants are found in a variety of families, but Araceae in particular contains many such species. Examples from this family include the dead-horse arum (Helicodiceros muscivorus), the eastern skunk cabbage (Symplocarpus foetidus), the elephant foot yam (Amorphophallus paeoniifolius), elephant ear ( Philodendron selloum ), lords-and-ladies ( Arum maculatum ), and voodoo lily ( Typhonium venosum ). The titan arum (Amorphophallus titanum) uses thermogenically created water vapor to disperse its scent—that of rotting meat—above the cold air that settles over it at night in its natural habitat. Contrary to popular belief, the western skunk cabbage (Lysichiton americanus), a close relative from the family Araceae, is not thermogenic. [6] Outside Araceae, the sacred lotus ( Nelumbo nucifera ) is thermogenic and endothermic, able to regulate its flower temperature to a certain range, [7] an ability shared by at least one species in the non-photosynthetic parasitic genus Rhizanthes , Rhizanthes lowii . [8]

Heat production

Many endothermy plant species rely on alternative oxidase (AOX), which is an enzyme in the mitochondria organelle and is a part of the electron transport chain. [9] The reduction of mitochondrial redox potential by alternative oxidase increases unproductive respiration. This metabolic process creates an excess of heat which warms thermogenic tissue or organs. [10] Plants containing this alternative oxidase are unaffected by the effects of cyanide because AOX acts as electron acceptor collecting electrons from ubiquinol while bypassing the third electron complex. The AOX enzyme then reduces oxygen molecules to water without the presence of a proton gradient which in turn is very inefficient yielding a drop in free energy from Ubiquinol to oxygen which is released in heat. [11]

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<span class="mw-page-title-main">Oxidative phosphorylation</span> Metabolic pathway

Oxidative phosphorylation or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine triphosphate (ATP). In eukaryotes, this takes place inside mitochondria. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is so pervasive because it releases more energy than alternative fermentation processes such as anaerobic glycolysis.

<span class="mw-page-title-main">Araceae</span> Family of flowering plants

The Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe. Also known as the arum family, members are often colloquially known as aroids. This family of 140 genera and about 4,075 known species is most diverse in the New World tropics, although also distributed in the Old World tropics and northern temperate regions.

<i>Amorphophallus</i> Genus of flowering plants

Amorphophallus is a large genus of some 200 tropical and subtropical tuberous herbaceous plants from the Arum family (Araceae), native to Asia, Africa, Australia and various oceanic islands. A few species are edible as "famine foods" after careful preparation to remove irritating chemicals. The genus includes the Titan arum of Indonesia, which has the largest inflorescence of any plant in the genus, and is also known as the 'corpse flower' for the pungent odour it produces during its flowering period, which can take up through seven years of growth before it occurs.

<span class="mw-page-title-main">Electron transport chain</span> Cellular electron transfer

An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. The electrons that transferred from NADH and FADH2 to the ETC involves 4 multi-subunit large enzymes complexes and 2 mobile electron carriers. Many of the enzymes in the electron transport chain are membrane-bound.

<span class="mw-page-title-main">Spadix (botany)</span>

In botany, a spadix is a type of inflorescence having small flowers borne on a fleshy stem. Spadices are typical of the family Araceae, the arums or aroids. The spadix is typically surrounded by a leaf-like curved bract known as a spathe. For example, the "flower" of the well known Anthurium spp. is a typical spadix with a large colorful spathe.

Thermogenesis is the process of heat production in organisms. It occurs in all warm-blooded animals, and also in a few species of thermogenic plants such as the Eastern skunk cabbage, the Voodoo lily, and the giant water lilies of the genus Victoria. The lodgepole pine dwarf mistletoe, Arceuthobium americanum, disperses its seeds explosively through thermogenesis.

<i>Nelumbo</i> Genus of aquatic flowering plants known as "lotus."

Nelumbo is a genus of aquatic plants with large, showy flowers. Members are commonly called lotus, though the name is also applied to various other plants and plant groups, including the unrelated genus Lotus. Members outwardly resemble those in the family Nymphaeaceae, but Nelumbo is actually very distant to that family.

<i>Symplocarpus foetidus</i> Species of flowering plant

Symplocarpus foetidus, commonly known as skunk cabbage or eastern skunk cabbage, is a low growing plant that grows in wetlands and moist hill slopes of eastern North America. Bruised leaves present an odor reminiscent of skunk.

<span class="mw-page-title-main">Zoophily</span> Pollination by animals

Zoophily, or zoogamy, is a form of pollination whereby pollen is transferred by animals, usually by invertebrates but in some cases vertebrates, particularly birds and bats, but also by other animals. Zoophilous species frequently have evolved mechanisms to make themselves more appealing to the particular type of pollinator, e.g. brightly colored or scented flowers, nectar, and appealing shapes and patterns. These plant-animal relationships are often mutually beneficial because of the food source provided in exchange for pollination.

<span class="mw-page-title-main">Carrion flower</span> Flowers that smell like rotting flesh

Carrion flowers, also known as corpse flowers or stinking flowers, are mimetic flowers that emit an odor that smells like rotting flesh. Apart from the scent, carrion flowers often display additional characteristics that contribute to the mimesis of a decaying corpse. These include their specific coloration, the presence of setae and orifice-like flower architecture. Carrion flowers attract mostly scavenging flies and beetles as pollinators. Some species may trap the insects temporarily to ensure the gathering and transfer of pollen.

<i>Arum</i> Genus of flowering plants in the family Araceae

Arum is a genus of flowering plants in the family Araceae, native to Europe, northern Africa, and western and central Asia, with the highest species diversity in the Mediterranean region. Frequently called arum lilies, they are not closely related to the true lilies Lilium. Plants in closely related Zantedeschia are also called "arum lilies".

<i>Sauromatum venosum</i> Species of flowering plant

Sauromatum venosum is a species of plant in the arum family, Araceae. It is native to Asia and Africa, where it grows in forests and riparian meadows.

<i>Helicodiceros</i> Genus of flowering plants

Helicodiceros muscivorus, the dead horse arum lily, is an ornamental plant native to Corsica, Sardinia and the Balearic Islands. It is the only species in the genus Helicodiceros. Within the family Araceae the plant is part of the subfamily Aroideae.

<i>Amorphophallus paeoniifolius</i> Species of flowering plant

Amorphophallus paeoniifolius, the elephant foot yam or whitespot giant arum, is a tropical tuber crop grown primarily in Africa, South Asia, Southeast Asia and the tropical Pacific islands. Because of its production potential and popularity as a vegetable in various cuisines, it can be raised as a cash crop.

<span class="mw-page-title-main">Alternative oxidase</span>

The alternative oxidase (AOX) is an enzyme that forms part of the electron transport chain in mitochondria of different organisms. Proteins homologous to the mitochondrial oxidase and the related plastid terminal oxidase have also been identified in bacterial genomes.

<i>Dracunculus vulgaris</i> Species of flowering plant in the family Araceae

Dracunculus vulgaris is a species of aroid flowering plant in the genus Dracunculus and the arum family Araceae. Common names include the common dracunculus, dragon lily, dragon arum, black arum and vampire lily. In Greece, part of its native range, the plant is called drakondia, the long spadix being viewed as a small dragon hiding in the spathe.

<span class="mw-page-title-main">Uncoupling protein</span> Mitochondrial protein

An uncoupling protein (UCP) is a mitochondrial inner membrane protein that is a regulated proton channel or transporter. An uncoupling protein is thus capable of dissipating the proton gradient generated by NADH-powered pumping of protons from the mitochondrial matrix to the mitochondrial intermembrane space. The energy lost in dissipating the proton gradient via UCPs is not used to do biochemical work. Instead, heat is generated. This is what links UCP to thermogenesis. However, not every type of UCPs are related to thermogenesis. Although UCP2 and UCP3 are closely related to UCP1, UCP2 and UCP3 do not affect thermoregulatory abilities of vertebrates. UCPs are positioned in the same membrane as the ATP synthase, which is also a proton channel. The two proteins thus work in parallel with one generating heat and the other generating ATP from ADP and inorganic phosphate, the last step in oxidative phosphorylation. Mitochondria respiration is coupled to ATP synthesis but is regulated by UCPs. UCPs belong to the mitochondrial carrier (SLC25) family.

<i>Amorphophallus titanum</i> Species of flowering plant in the arum family Araceae

Amorphophallus titanum, the titan arum, is a flowering plant in the family Araceae. It has the largest unbranched inflorescence in the world. The inflorescence of the talipot palm, Corypha umbraculifera, is larger, but it is branched rather than unbranched. A. titanum is endemic to rainforests on the Indonesian island of Sumatra.

Rhizanthes lowii is a species of parasitic flowering plant without leaves, stems, roots, or photosynthetic tissue. It grows on the roots of the Tetrastigma vine. It includes the specimens with the largest measured flowers in Rhizanthes, from 25 to 43 cm across. They are endothermic, not only producing their own heat, but they also have the rare ability to regulate their own temperature.

<span class="mw-page-title-main">Supercomplex</span>

Modern biological research has revealed strong evidence that the enzymes of the mitochondrial respiratory chain assemble into larger, supramolecular structures called supercomplexes, instead of the traditional fluid model of discrete enzymes dispersed in the inner mitochondrial membrane. These supercomplexes are functionally active and necessary for forming stable respiratory complexes.

References

  1. ↑ Plantguy (16 January 2010). "Plants That Heat Themselves". How Plants Work. Retrieved 4 December 2012.
  2. ↑ Turner M (August 2010). "Plant of the month: Voodoo Lily". Turner Photographics. Retrieved 4 December 2012.
  3. ↑ Schultz N (22 December 2008). "Giant Stinking Flower". NewScientist. Retrieved 4 December 2012.
  4. ↑ "Skunk Cabbage". National Wildlife Federation. Archived from the original on 25 November 2012. Retrieved 4 December 2012.
  5. ↑ Seymour R, Schultze-Motel P (1997). "Heat Producing Flowers" (PDF). Endeavor. 3. 21 (3): 125–129. doi:10.1016/s0160-9327(97)80222-0. Archived from the original (PDF) on 25 May 2014.
  6. ↑ Onda Y, Kato Y, Abe Y, Ito T, Morohashi M, Ito Y, et al. (February 2008). "Functional coexpression of the mitochondrial alternative oxidase and uncoupling protein underlies thermoregulation in the thermogenic florets of skunk cabbage". Plant Physiology. 146 (2): 636–45. doi: 10.1104/pp.107.113563 . PMC   2245847 . PMID   18162588.
  7. ↑ Yoon CK (1 October 1996). "Heat of Lotus Attracts Insects And Scientists". The New York Times. Retrieved 14 November 2012.
  8. ↑ Patiño S, Grace J, Bänziger H (August 2000). "Endothermy by flowers of Rhizanthes lowii (Rafflesiaceae)". Oecologia. 124 (2): 149–155. Bibcode:2000Oecol.124..149P. doi:10.1007/s004420050001. PMID   28308173. S2CID   22301706.
  9. ↑ Watling JR, Grant NM, Miller RE, Robinson SA (August 2008). "Mechanisms of thermoregulation in plants". Plant Signaling & Behavior. 3 (8): 595–7. doi:10.4161/psb.3.8.6341. PMC   2634508 . PMID   19704809.
  10. ↑ Ito K, Seymour RS (December 2005). "Expression of uncoupling protein and alternative oxidase depends on lipid or carbohydrate substrates in thermogenic plants". Biology Letters. 1 (4): 427–30. doi:10.1098/rsbl.2005.0338. PMC   1626365 . PMID   17148224.
  11. ↑ Ito K, Ogata T, Seito T, Umekawa Y, Kakizaki Y, Osada H, Moore AL (September 2020). "Degradation of mitochondrial alternative oxidase in the appendices of Arum maculatum". The Biochemical Journal. 477 (17): 3417–3431. doi: 10.1042/BCJ20200515 . PMC   7505559 . PMID   32856714.
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