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Plants, as sessile organisms, are continuously exposed to temperature changes in the environment. Low and high temperature stresses have a great impact on agricultural productivity, since they significantly alter plant metabolism and physiology. Plant response to temperature stress is a quantitative character, being influenced by the degree of stress, time of exposure, as well as plant adaptation ability; it involves profound cellular changes at the proteomic level. We describe here the quantitative variations of the protein repertoire of Arabidopsis thaliana rosette leaves after exposing seedlings to either short-term cold or heat temperature stress. A proteomic approach, based on two-dimensional electrophoresis and MALDI-TOF peptide mass fingerprinting and/or nanoLC-ESI-LIT-MS/MS experiments, was used for this purpose. The comparison of the resulting proteomic maps highlighted proteins showing quantitative variations induced by temperature treatments. Thirty-eight protein spots exhibited significant quantitative changes under at least one stress condition. Identified, differentially-represented proteins belong to two main broad functional groups, namely energy production/carbon metabolism and response to abiotic and oxidative stresses. The role of the identified proteins is discussed here in relation to plant adaptation to cold or heat stresses. Our results suggest a significant overlapping of the responses to opposite temperature extremes.

Radiation-induced modifications of human serum albumin mainly occurring at S-containing residues were investigated by Raman spectroscopy and mass spectrometry techniques. When HO˙ radicals were scavenged by t-BuOH, the H˙ atom and hydrated electron (e(aq)(-)) attack led to the chemical transformation of Cys into Ala residues and the conversion of Met residues into α-aminobutyric acid residues. Mapping experiments demonstrated that desulfurization selectively affects Cys34, Met123, Met298, Cys514, Met548 and Cys567 since the first stages of reaction. Generation of thiol functionality was also detected at specific residues involved in disulfide bonds, namely Cys200, Cys392 and Cys514, together with partial oxidation at Met87, Met123, Met298, Met329 and Met548, forming sulfoxides. When HO˙ radicals were not scavenged, lesser amounts of the previous modifications were observed, whereas some residues (Cys34, Cys461, Pro486, Phe488 and Phe502) resulted to be oxidatively modified. Based on the known cystine pairing in native albumin, no relationships were observed between desulfurization and disulfide reduction processes at Cys residues involved in disulfide bonds, thus suggesting either independent reactivities or, more probably, reactions at the same amino acids that then underwent quick disulfide scrambling events toward more stable disulfide/thiol populations. When these reactions were performed on protein species added to large unilamellar vesicles, desulfurization yielded sulfur radicals able to induce a cis-trans isomerization of lipids at the onset of irradiation. This study provides a description of the human albumin modifications resulting from reductive radical stress, thus suggesting the need for specific assays and future investigations to detect these events in proteins and lipids within challenged cells.