The Transcript Levels of two Plant Mitochondrial Uncoupling Protein (pUCP)-Related Genes are not Affected by Hyperosmotic Stress in Durum Wheat Seedlings Showing an Increased Level of pUCP Activity

Etiolated early seedlings of durum wheat submitted to moderate and severe salt (NaCl) and osmotic (mannitol) stress showed no relevant increase of both transcript levels of two plant uncoupling protein (pUCP)-related genes and maximal pUCP activity in purified mitochondria (which estimates protein level); contrarily, pUCP functioning due to endogenous free fatty acids strongly increased. These results show that pUCP activation under hyperosmotic stress may be due to modulation of pUCP reaction rather than to an increased protein synthesis. Finally, a properly developed method, based on a single membrane potential measurement, to evaluate both pUCP maximal activity and functioning, is reported.

Mitochondrial protein expression in tomato fruit during on-vine ripening and cold storage

We have investigated the activity and abundance of a number of respiratory chain components in ripening and cold-treated tomato fruits (Lycopersicon esculentum L. Mill cvv. Moneymaker and Sweetie). Expression of the alternative oxidase (AOX) protein increased dramatically in both situations. Levels of the plant uncoupling protein (UCP) initially fell, but increased substantially in the later stages of ripening. In contrast, ATP synthase subunits and the COXII subunit of cytochrome oxidase decreased during ripening and increased slightly in response to cold stress. Other proteins involved in electron transport, tricarboxylic acid cycle function, chaperonin function, and membrane transport were also studied. These showed varying degrees of enhanced and depressed expression patterns. There were modest changes in whole fruit respiratory activities, and electron transport capacity of isolated mitochondria in response to these stimuli. However, respiratory control by ADP in the isolated mitochondria decreased as AOX capacity and abundance increased, indicating that although total respiration rates changed little, flux between the coupled and uncoupled pathways altered. The changes observed in AOX and UCP accumulation in tomato fruit that were vine-ripened were significantly different from post-harvest ripening patterns previously reported. The altered protein profiles are discussed in the context of on- and off-vine ripening and the potentially different roles of uncoupled respiration in each situation.

The uncoupling protein homologues: UCP1, UCP2, UCP3, StUCP and AtUCP

Animal and plant uncoupling protein (UCP) homologues form a subfamily of mitochondrial carriers that are evolutionarily related and possibly derived from a proton/anion transporter ancestor. The brown adipose tissue (BAT) UCP1 has a marked and strongly regulated uncoupling activity, essential to the maintenance of body temperature in small mammals. UCP homologues identified in plants are induced in a cold environment and may be involved in resistance to chilling. The biochemical activities and biological functions of the recently identified mammalian UCP2 and UCP3 are not well known. However, recent data support a role for these UCPs in State 4 respiration, respiration uncoupling and proton leaks in mitochondria. Moreover, genetic studies suggest that UCP2 and UCP3 play a part in energy expenditure in humans. The UCPs may also be involved in adaptation of cellular metabolism to an excessive supply of substrates in order to regulate the ATP level, the NAD+/NADH ratio and various metabolic pathways, and to contain superoxide production. A major goal will be the analysis of mice that either lack the UCP2 or UCP3 gene or overexpress these genes. Other aims will be to investigate the possible roles of UCP2 and UCP3 in response to oxidative stress, lipid peroxidation, inflammatory processes, fever and regulation of temperature in certain specific parts of the body.