Evolving concepts in plant glycolysis: two centuries of progress

Cv. Givan, Evolving concepts in plant glycolysis: two centuries of progress, BIOL REV, 74(3), 1999, pp. 277-309
Citations number
Categorie Soggetti
Biology,"Experimental Biology
Journal title
ISSN journal
1464-7931 → ACNP
Year of publication
277 - 309
SICI code
Glycolysis, the process responsible for the conversion of monosaccharides t o pyruvic acid, is a ubiquitous feature of cellular metabolism and was the first major biochemical pathway to be well characterized. Although the majo rity of glycolytic enzymes are common to all organisms, the past quarter of a century has revealed that glycolysis in higher plants possesses numerous distinctive features. Research in the nineteenth century established convi ncingly that plants carry out alcoholic fermentation under anaerobic condit ions. In 1878, Wilhelm Pfeffer asserted that a non-oxygen-requiring 'intram olecular respiration' was involved in the aerobic respiration of plants. Be tween 1900 and 1950 it was demonstrated that plants metabolize sugar and st arch by a glycolytic pathway broadly similar to that of yeasts and muscle t issue. In 1948, the first purification and characterization of a plant glyc olytic enzyme, aldolase, was published by Paul Stumpf. By 1960 the presence of each of the 10 enzymes of glycolysis, presumed at the time to be locate d in the cytosol, had been confirmed in higher plants. Shortly after 1960 i t was shown that the mechanism of glycolytic regulation in plants had featu res in common with that of animals and yeasts, especially as regards the im portant role played by the enzyme phosphofructokinase; but important regula tory properties peculiar to plants were soon demonstrated. In the last 30 y ears, higher-plant glycolysis has been found to exhibit a number of additio nal characteristics peculiar to plant systems. One conspicuous feature of p lant glycolysis, discovered in the 1970s, is the presence of a complete or nearly complete sequence of glycolytic enzymes in plastids, distinct and sp atially separated from the glycolytic enzymes located in the cytosol. Plast idic and cytosolic isoenzymes of glycolysis have been shown to differ in th eir kinetic and regulatory properties, suggesting that the two pathways are independently regulated. Since about 1980 it has become increasingly clear that the cytosolic glycolysis of plants may make use of several enzymes ot her than the conventional ones found in ye as ts, muscle tissue and plant p lastids: these enzymes include a pyrophosphate- dependent phosphofructokina se, a non-reversible and nonphosphorylating glyceraldehyde-3-phosphate dehy drogenase, a phosphoenolpyruvate phosphatase (vacuolar location) and a thre e-enzyme sequence able to produce pyruvate from phosphoenolpyruvate avoidin g the pyruvate-kinase step, These non-conventional enzymes may catalyze gly colysis in the plant cytosol especially under conditions of metabolic stres s. Experiments on transgenic plants possessing significantly elevated or re duced (reduced to virtually nil in some cases) levels of glycolytic enzymes are currently playing an important part in improving our understanding of the regulation of plant glycolysis; such experiments illustrate an impressi ve degree of flexibility in the pathway's operation. Plant cells are able t o make use of enzymes bypassing or substituting for several of the conventi onal enzymic steps in the glycolytic pathway; the extent and conditions und er which these bypasses operate are the subject of current research. The du plication of the glycolytic pathway in plants and the flexible nature of th e pathway have possibly evolved in relation to the crucial biosynthetic rol e played by plant glycolysis beyond its function in energy generation; both functions must proceed if a plant is to survive under varying and often st ressful environmental or nutritional conditions.