Gene expression during germination and post-germination of dried and non-dried developing seeds of tomato
In a number of species, the period of desiccation that terminates seed development is considered essential in effecting the metabolic switch to a germinative program. However, in orthodox seeds developing within fleshy fruits, such as those of tomato, this developmental shift is not only promoted by desiccation, but also by the isolation of undesiccated seeds from the fruit tissues and their continued hydration. In this study, germinative, transcriptional (by northern blotting), and translational (by western blotting) responses to isolation and/or desiccation were examined using Micro-Tom tomato seeds isolated at different stages of development. Desiccation increased the speed of germination of seeds removed from the plant shortly after mass maturity (i.e. 38 days after pollination [DAP]). Similarly, in 38-DAP seeds, the loss of transcripts associated with seed development, as well as the on- or up-regulation of those related to (post)germination, occurred earlier in the dried seeds, underlying the changes occurring at the morphophysiological level. Although the accumulation pattern of few proteins resembled those of the transcripts, overall, the proteins were relatively stable to drying, and no substantial differences were observed between non-dried and dried germinating seeds. Additionally, the transcription profile of germination of non-dried and dried immature seeds of the tomato cultivar CC337 was determined by microarray analysis. Transcriptional changes reflected the progress of germination, which was influenced by desiccation of the seeds. The role of ABA and osmoticum in maintaining seed development and/or preventing germination, and of seed isolation and/or desiccation in terminating development, was also investigated in germinable immature tomato seeds at the transcriptional level. While both ABA and osmoticum prevented the seeds from germinating, the osmoticum was unique in causing the resumption and maintenance of developmental events, and preventing the continuation of the germinative ones. Moreover, desiccation did not terminate irreversibly the developmental program, with both non-dried and dried seeds being equally efficient in inducing developmental events, in response to osmoticum.