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

Thioredoxin h (Trx h) proteins are ubiquitous in all wheat organs, but show the highest accumulation in mature seeds. This distribution suggests the expression of Trx h during seed development. In the present study, we have analyzed the pattern of Trx h 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 Trx h 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 Trx h proteins localized to maternal tissues (nucellus projection cells and pedicel), the route of transport of nutrients to the developing endosperm. In the endosperm, Trx h proteins accumulated at a high level in the aleurone layer. At later stages of development, during seed maturation, Trx h proteins localized predominantly to the nucleus of both aleurone and scutellum cells, a feature exclusive of these seed tissues. The nuclear localization of Trx h proteins was associated with oxidative stress in these tissues, as shown by in situ staining of superoxide radicals in developing and germinating seeds.