plant respiration


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Plant respiration

A biochemical process whereby specific substrates are oxidized with a subsequent release of carbon dioxide, CO2. There is usually conservation of energy accompanying the oxidation which is coupled to the synthesis of energy-rich compounds, such as adenosine triphosphate (ATP), whose free energy is then used to drive otherwise unfavorable reactions that are essential for physiological processes such as growth. Respiration is carried out by specific proteins, called enzymes, and it is necessary for the synthesis of essential metabolites, including carbohydrates, amino acids, and fatty acids, and for the transport of minerals and other solutes between cells. Thus respiration is an essential characteristic of life itself in plants as well as in other organisms.

Reaction sequence for anaerobic glycolysisenlarge picture
Reaction sequence for anaerobic glycolysis

Overall aerobic respiration is the end result of a sequence of many biochemical reactions that ultimately lead to O2 uptake and CO2 evolution. In the absence of O2, as may occur in bulky plant tissues such as the potato tuber and carrot root and in submerged plants such as germinating rice seedlings, the breakdown of hexose does not go to completion. The end products are either lactic acid or ethanol, which are produced by anaerobic glycolysis or fermentation.

The sequence of reactions of anaerobic glycolysis or fermentation is shown in the illustration. The enzymes associated with anerobic glycolysis have been isolated from many plant tissues, but more often ethanol and not lactic acid is the final product.

In aerobic tissues, pyruvic acid produced during glycolysis is completely oxidized with the accompanying synthesis of much more ATP than in anaerobic glycolysis. Pyruvic acid oxidation takes place in the mitochondria by means of a cyclic sequence of reactions, the Krebs cycle (also known as the citric acid cycle) which begins when the first product of pyruvate oxidation, acetyl coenzyme A, reacts with oxaloacetic acid to produce citric acid. Oxaloacetic acid is eventually regenerated. Thus the cycle can be repeated. In terms of conservation of chemical energy, the Krebs cycle is about 12 times more efficient than anaerobic glycolysis per mole of glucose oxidized. See Citric acid cycle

In addition to anaerobic glycolysis and the Krebs cycle, there are two other sequences of biochemical reactions related to respiration that are important in plant tissues: (1) The pentose phosphate pathway permits an alternate mechanism for converting hexose phosphate to pyruvate, and (2) in germinating fatty seeds the reactions of the Krebs cycle are modified so that acetyl coenzyme A is converted to succinic acid and then to hexose by a pathway called the glyoxylate cycle. See Photorespiration, Photosynthesis, Plant growth, Plant metabolism

plant respiration

[′plant ‚res·pə‚rā·shən]
(botany)
A biochemical process in plants whereby specific substrates are oxidized with a subsequent release of carbon dioxide, CO2.
References in periodicals archive ?
Normally, plant respiration process involves in using of atmospheric oxygen, carbohydrates, organic acids and the consequent production of metabolic energy, heat, carbon dioxide and moisture vapour.
About half of that is released again through plant respiration, while the other half is released through respiration by animals, microbes, and other organisms.
Low night-time dissolved oxygen levels and associated chemical stressors associated with aquatic plant respiration could explain the recent fish kills.
When temperatures remain high during the night hours, increased plant respiration diminishes kernel growth as photosynthetic sugars are allocated to plant maintenance instead of kernel formation.
p], [phi] are net primary production, the average rate of photosynthesis, and the proportion of assimilated C lost through plant respiration as well as other processes such as exudation of readily available C substrate from plants to soil, respectively (Lloyd and Farquhar 2008); that study reported that the parameter (p was relatively constant.
The levels of this gas in uncontaminated atmospheres depend on emissions from the ground, as well as plant respiration and photosynthesis, but also on developments in the atmosphere as a whole, which may facilitate or inhibit the dispersal of this substance," Isidro PE[umlaut]rez, one of the authors and a researcher from the UVA's Applied Physics Department said.
is the rate at which energy is stored in the organic matter of plants per unit area of the earth's surface," while net primary productivity (NPP) is the amount left over after plant respiration.
Terrestrial biomass is a huge short-term carbon reservoir (~2000 Gt C) that uses photosynthesis and plant respiration to exchange carbon with the atmosphere.
2] increased plant growth, they lowered plant respiration.
Beyond improving scientists' understanding of its role as a hormone, studies of salicylic acid in plants may help solve some nagging mysteries about plant respiration.