A cDNA clone encoding for pea (Pisum sativum L.) cytosolic fructose-1,6-bis
phosphatase (E.C. 3.1.3.11) has been isolated by reverse transcription-poly
merase chain reaction of the total mRNA. The sequence analysis displayed a
341-amino acid protein of about 37 300 Da molecular mass, corresponding to
the subunit of this homotetrameric enzyme; it showed about 80% homology wit
h the other ten higher plant cytosolic FBPases sequenced so far. The enzyme
displayed a strong transcriptional expression in green organs (sessile and
petioled leaves, stem, pod and grain), and poor expression in root and sen
escent basal leaves. It is noteworthy the high FBPase transcriptional expre
ssion in pod, which displays up to 4-fold higher content of FBPase-specific
mRNA than that of root. The mRNA related to cytosolic FBPase was detected
after 24 h continuous illumination of 24-h-dark-grown seedlings; this light
-induced transcriptional expression is slower than that of chloroplast FBPa
se, which appears soon after 2 h light. In both cases the corresponding mRN
As disappeared when the light was turned off. The translational expression
was also manifested, both as FBPase protein and activity, after 24 h illumi
nation. This delay in the expression of cytosolic FBPase with respect to th
at of the plastidic enzyme can be interpreted as an indirect effect induced
by a metabolite of the photosynthetic carbon pathway, rather than a direct
effect of light on the DNA-expression mechanism. Pea cytosolic FBPase was
not activated by dithiothreitol, with or without coupling to thioredoxins f
or m. The enzyme showed a half-life of 6 h.