Type-h thioredoxins accumulate in the nucleus of developing wheat seed tissues suffering oxidative stress

Thioredoxin h (Trxh) proteins are ubiquitous in all wheat organs, but show the highest accumulation in mature seeds. This distribution suggests the expression of Trxh during seed development. In the present study, we have analyzed the pattern of Trxh expression in developing wheat (Triticum aestivum L.) seeds. Northern blot analysis detected a single band at any stage of development, which corresponded to the expression of at least two genes, TrxhA and TrxhB, as shown by competitive reverse transcription-polymerase chain reaction experiments. The analysis of the content of Trxh polypeptides showed the highest content in the embryo. The spatial pattern of accumulation of these proteins was established by immunocytological techniques. At early stages of development Trxh proteins localized to maternal tissues (nucellus projection cells and pedicel), the route of transport of nutrients to the developing endosperm. In the endosperm, Trxh proteins accumulated at a high level in the aleurone layer. At later stages of development, during seed maturation, Trxh proteins localized predominantly to the nucleus of both aleurone and scutellum cells, a feature exclusive of these seed tissues. The nuclear localization of Trxh proteins was associated with oxidative stress in these tissues, as shown by in situ staining of superoxide radicals in developing and germinating seeds.