Nitrate accumulation in Xenopus oocytes. Mixed mRNA of either synthetic genes (synthetic OsNAR2.1 and OsNRT2.3a) or the original genes (original OsNAR2.1 and OsNRT2.3a) were injected into oocytes. Oocytes were incubated in MBS with 0.5 mM NaNO3 for 16 h and washed four times with NO3- free MBS solution. Four oocytes were pooled for each sample. The values are means SE of four replicates with a and b indicating the statistical significance at p ≤ 0.05. The example shown is representative of the results from two frogs.