Plant Physiology Preview
Published on May 18, 2007; 10.1104/pp.107.098103
OPEN ACCESS ARTICLE
Received February 15, 2007
Accepted April 30, 2007
Thioredoxin-linked Proteins Are Reduced during Germination of Medicago truncatula Seeds
Fatima Alkhalfioui , Michelle Renard , William H. Vensel , Joshua Wong , Charlene K. Tanaka , William J. Hurkman , Bob B. Buchanan , and Françoise Montrichard *
Physiologie Moléculaire des Semences, UMR 1191 Université d'Angers - Institut National d'Horticulture - INRA, ARES, 16 boulevard Lavoisier, 49045 Angers cedex 01, France; Department of Plant and Microbial Biology, University of California, 411 Koshland Hall, Berkeley, CA 94720-3102; Western Regional Research Center, U.S. Department of Agriculture, Agricultural Research Service, 800 Buchanan Street, Albany, CA, 94710
* Corresponding author; email: francoise.montrichard{at}univ-angers.fr.
Germination of cereals is accompanied by extensive change in the redox state of seed proteins. Proteins present in oxidized (S-S) form in dry seeds are converted to the reduced (SH) state following imbibition. Thioredoxin (Trx) appears to play a role in this transition in cereals. It is not known, however, whether Trx-linked redox changes are restricted to cereals or whether they take place more broadly in germinating seeds. To gain information on this point, we have investigated a model legume, Medicago truncatula. Two complementary gel-based proteomic approaches were followed to identify Trx targets in seeds: proteins were (i) labeled with a thiol-specific probe, monobromobimane (mBBr), following in vitro reduction by an NADP/Trx system (NTS), or (ii) isolated on a mutant Trx affinity column. Altogether, 111 Trx-linked proteins were identified with few differences between axes and cotyledons. Fifty-nine were new, 34 found previously in cereal or peanut seeds and 18 in other plants or photosynthetic organisms. In parallel, the redox state of proteins assessed in germinating seeds using mBBr revealed that a substantial number of proteins that are oxidized or partly reduced in dry seeds became more reduced upon germination. The patterns were similar for proteins reduced in vivo during germination or in vitro by Trx. In contrast, glutathione and glutaredoxin were less effective as reductants in vitro. Overall, more than half of the potential targets identified with the mBBr labeling procedure were reduced during germination. The results provide evidence that Trx functions in the germination of seeds of dicotyledons as well as monocotyledons.
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