Ubiquitin Pool Modulation and Protein Degradation in Wheat Roots during High Temperature Stress

Abstract

Ubiquitin, a key component in an ATP-dependent proteolytic pathway, participates in the response of various eucaryotic organisms to high temperature stress. Our objective was to determine if ubiquitin serves a similar capacity for metabolizing altered proteins in higher plants during stress. Degradation of total proteins was measured, and ubiquitin pools (free versus conjugated) were extracted with an improved protocol from wheat (Triticum aestivum L. cv Len) roots treated at 22, 27, 32, 37, and 42 degrees C for 1 hour and assayed by western blots and radioimmunoassays. Heat-shock protein synthesis was detected by in vivo labeling and autoradiography. Mean half-life of total root proteins decreased from 51 hours at 22 degrees C to 23 hours at 40 degrees C. Ubiquitin pools were extracted better and proteolysis was slowed more by the improved protocol than by a conventional procedure for plant proteins. Amounts of high molecular mass conjugates were elevated and levels of low molecular mass conjugates and free ubiquitin were depressed when roots were treated at 37 or 42 degrees C than at lower temperatures; the same high temperatures also induced synthesis of heat-shock proteins. We concluded that high temperatures increase breakdown of root proteins, which are degraded via the ubiquitin proteolytic pathway. A conjugate with an apparent molecular mass of 23 kilodaltons was tentatively identified as an ubiquitinated histone.

Dry Pea Seed Proteasome

“…Proteasome may play a generalized, constitutive role in 'mopping up' target proteins made redundant in the normal course of metabolism. A significant body of direct and indirect evidence has accumulated suggesting that environmental stress and resulting damage and metabolic shifts result in increased protein ubiquitination and ultimate removal of such conjugates by the proteasome and related proteolytic particles (7,8,19,21,23,25). Seeds represent some of the most environmental stress-tolerant structures in nature and provide an ideal system for the study of the function of proteasome and related reactions and proteins.…”

“…The precise regulation of the targeting of cytoplasmic proteins for the ubiquitination pathway is not understood. Ubiquitin was shown to be one of the heat-shock proteins (2,7,17,19) and ubiquitination tends to increase following environmental stress (7,23,25). Damage to, or redundancy of, target proteins are generally considered to be signals for ubiquitin conjugation (18).…”

Tolerância cruzada induzida por choque térmico na germinação de semente de feijão

“…Ferguson et al(1990) citam que temperaturas elevadas podem direta ou indiretamente injuriar proteínas vegetais, pela inativação de enzimas, por alterações na conformação de peptídeos ou por desestruturação de complexos em membrana. Uma das funções das proteínas de choque térmico está relacionada à prevenção da desnaturação de proteínas durante a desidratação celular (Nepomuceno et al, 2002).…”

Ubiquitin Conjugation to Protein Increases following Chilling of Clerodendrum Leaves

“…The free ubiquitin moved close to the dye front and was removed prior to the blotting. As with other plant :n curve prepared for the FIA using free ubiquisystems studied (3,8,11), proteins conjugated to ubiquitin re obtained following subtraction of blanks and are evident in the extracts from both control and chilled of three replicates. leaves.…”

“…4). Ubiquitin is a highly conserved, 76-amino acid polypeptide that is involved in ATP-dependent protein degradation in eukaryotic cells, including plant cells (3,4,11). Ubiquination might also be involved in the response of many eukaryotic cells to various environmental stresses, including those related to extreme temperatures (4 Microsomal membranes were isolated from the leaves in the presence of 2 mm DTT and 2 mm PMSF using differential centrifugation as described previously (7).…”