FIGURE 7.

¹³C and¹⁵N uptake rates as ATP/CTP equivalents of excised poplar roots achieved from ¹³C/¹⁵N labeled ATP or CTP. Excised poplar roots were taken from poplar plants grown with 0.25 mM P_i (July). ¹³C and ¹⁵N uptake rates calculated as ATP and CTP equivalents were analyzed by the application of 0.169 mM labeled ATP-¹³C₁₀¹⁵N₅ (10 atom%) or CTP-¹³C₉¹⁵N₃ (10 atom%). The competition with P_i was tested by the addition of 0.25 mM P_i. The effect of acid phosphatases was investigated by the simultaneous application of nucleotides plus 0.5 mM MoO₄^2-. Data presented are box plots for ¹³C uptake rates as ATP equivalents (A) and ¹³C uptake rates as CTP equivalents (B). Left to the box plots individual values achieved from single incubation cambers are presented (n = 4). ¹⁵N uptake rates as ATP and CTP equivalents were similar to the ¹³C uptake rates as ATP and CTP equivalents. Significant differences were analyzed by One Way ANOVA followed by the Post hoc tests Bonferroni and Tukey with p < 0.05 but, statistically significant differences were not found. Correlations over all treatments between ¹³C and ¹⁵N uptake rates are provided for ATP (C) and CTP (D). Slopes and Pearson correlation coefficients are given in Table 1.