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Quantitative detection of changes in the leaf‐mesophyll tonoplast proteome in dependency of a cadmium exposure of barley ( Hordeum vulgare L.) plants
Author(s) -
Schneider Thomas,
Schellenberg Maja,
Meyer Stefan,
Keller Felix,
Gehrig Peter,
Riedel Kathrin,
Lee Youngsook,
Eberl Leo,
Martinoia Enrico
Publication year - 2009
Publication title -
proteomics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.26
H-Index - 167
eISSN - 1615-9861
pISSN - 1615-9853
DOI - 10.1002/pmic.200800806
Subject(s) - vacuole , hordeum vulgare , cadmium , cytosol , transporter , biochemistry , apoplast , transport protein , proteome , chemistry , isobaric labeling , biology , quantitative proteomics , proteomics , cell wall , botany , enzyme , gene , cytoplasm , poaceae , organic chemistry
Although the vacuole is the most important final store for toxic heavy metals like cadmium (Cd 2+ ), our knowledge on how they are transported into the vacuole is still insufficient. It has been suggested that Cd 2+ can be transported as phytochelatin‐Cd 2+ by an unknown ABC transporter or in exchange with protons by cation/proton exchanger (CAX) transporters. To unravel the contribution of vacuolar transporters to Cd 2+ detoxification, a quantitative proteomics approach was performed. Highly purified vacuoles were isolated from barley plants grown under minus, low (20 μM), and high (200 μM) Cd 2+ conditions and protein levels of the obtained tonoplast samples were analyzed using isobaric tag for relative and absolute quantitation (iTRAQ™). Although 56 vacuolar transporter proteins were identified, only a few were differentially expressed. Under low‐Cd 2+ conditions, an inorganic pyrophosphatase and a γ‐tonoplast intrinsic protein (γ‐TIP) were up‐regulated, indicating changes in energization and water fluxes. In addition, the protein ratio of a CAX1a and a natural resistance‐associated macrophage protein (NRAMP), responsible for vacuolar Fe 2+ export was increased. CAX1a might play a role in vacuolar Cd 2+ transport. An increase in NRAMP activity leads to a higher cytosolic Fe 2+ concentration, which may prevent the exchange of Fe 2+ by toxic Cd 2+ . Additionally, an ABC transporter homolog to AtMRP3 showed up‐regulation. Under high Cd 2+ conditions, the plant response was more specific. Only a protein homologous to AtMRP3 that showed already a response under low Cd 2+ conditions, was up‐regulated. Interestingly, AtMRP3 is able to partially rescue a Cd 2+ ‐sensitive yeast mutant. The identified transporters are good candidates for further investigation of their roles in Cd 2+ detoxification.