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Keywords:

  • Biosynthesis;
  • fructose-1;
  • 6-bisphosphatase;
  • photosynthesis;
  • Pisum sativum;
  • chloroplast

summary

Photosynthetic fructose- 1, 6-bisphosphatase (FBPase) determined immunologically by ELISA undergoes a sharp increase when etiolated pea (Pisum sativum L. cv. Lincoln) seedlings are illuminated for 24 h. The rise of enzyme activity appears slower than that of FBPase protein, which means an earlier synthesis of a precursor or some other immunologically related but inactive form of the enzyme. A second possibility is a delayed synthesis of a factor – i.e. a component of the ferredoxin-thioredoxin activation system – necessary for the expression of the enzyme activity. With more extended illumination times, the highest FBPase content, as well as maximum activity, was obtained after 4 d of light exposure, the former representing 0.66 % of the total soluble protein. After that time, a decrease of both FBPase protein and enzyme activity was observed, probably as a consequence of a premature senescence promoted by such an extended and continuous light exposure. A maximum FBPase labelling was obtained at 6.5 h after leaf application of a [35S]methionine pulse to etiolated pea seedlings, which were then continuously illuminated. From the pattern of the radioactive decay of FBPase labelling, a half-life of 14 h was calculated for this photosynthetic enzyme.