ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Upon continuous illumination of dark-grown spinach (Spinacia oleracea L. cv. Winter Giant) seedlings, the thioredoxin f (Td f) content (ELISA) showed a steep rise, which can be evaluated after 3 and 36 h illumination as 3 times and 10 times the dark value, respectively. These figures correspond to 0.03% and 0.1% of total soluble protein, which means a higher biosynthetic rate for Td f compared to the average of total proteins in the earlier steps of plant development. After 40-50 h light the Td f level reached its highest value which remained stable for an additional 40 h and then decreased. Pulse-chase in vivo experiments with [35S]-methionine also showed this sharp increase of Td f in the dark-light transition. From the pattern of decay of [35S]-labelled Td f, a half-life of 7 h was determined for this chloroplast protein. In vitro translation experiments with poly(A)-mRNA isolated from illuminated young spinach seedlings, coupled to a wheat-germ synthesizing system, showed the appearance of a labelled fraction of ca 19 kDa molecular mass, recognizable by a specific Td f antiserum. When intact spinach chloroplasts were added to the translation assay medium, and then illuminated, the 19 kDa band disappeared, with a parallel increase of an internalized 13 kDa labelled polypeptide, also recognized by the Td f antiserum. These results are good evidence for a nuclear-coded synthesis of a Td f precursor, which travels through the chloroplast envelope, leaving the functional protein inside the organelle after the loss of a 6 kDa transit peptide.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1992.tb04659.x
