Plastid thioredoxins f and m are related to the developing and salinity response of post-germinating seeds of Pisum sativum.

Plastid thioredoxins (TRXs) f and m have long been considered to regulate almost exclusively photosynthesis-related processes. Nonetheless, some years ago, we found that type-f and m TRXs were also present in non-photosynthetic organs such as roots and flowers of adult pea plants. In the present work, using pea seedlings 2-5 days old, we have determined the mRNA expression profile of the plastid PsTRX f, m1, and m2, together with the ferredoxin NADP reductase (FNR). Our results show that these TRX isoforms are expressed in cotyledons, underlying similar expression levels in roots for PsTRX m2. We have also noted plastid TRX expression in cotyledons of etiolated seedlings of Arabidopsis thaliana lines carrying constructs corresponding to PsTRX f and m1 promoters fused to the reporter gene GUS, pointing to a role in reserve mobilization. Furthermore, the response of plastid TRXs to NaCl and their capacity in restoring the growth of a TRX-deficient yeast under saline conditions suggest a role in the tolerance to salinity. We propose that these redox enzymes take part of the reserve mobilization in seedling cotyledons and we suggest additional physiological functions of PsTRX m2 in roots and PsTRX m1 in the salinity-stress response during germination.