Fig. 1. Respiration of floating and submerged leaves of S. minima after 6 days of
exposure to different Cr concentrations. (A) Total respiration, (B) AOX capacity,
(C) Residual respiration. Values are mean ± SD of three independent experiments
(n = 10). Lines on top of the bars represent standard deviation (SD). Bars with different
letters are significantly different at p < 0.05 (Tukey’s Multiple Range Test).
164.3% and 349.5% over control values (1.54 and 9.90 × 10−2 nmol
O2 mg−1 FW min−1, respectively). AOX was less affected by 2
and 10 mg L−1 Cr concentrations, while total respiration was not
significantly (p < 0.05) affected. By contrast, in submerged leaves
maxima values of both parameters were observed at 2 mg L−1 metal
concentration (0.805 and 3.98 × 10−2 nmol O2 mg−1 FW min−1,
respectively), being increased by 161.0% and 251.9% over control
values (0.50 and 1.58 × 10−2 nmol O2 mg−1 FW min−1, respectively).
Thereafter they remained relatively stable; however, the
highest values of total respiration and AOX capacity were observed
in floating leaves (Fig. 1A and B). It is necessary to point out that AOX
measurements do not reflect actual AOX activity during respiration
in uninhibited conditions, because the addition of inhibitors may
modify the partitioning of electron flux over the cytochrome respiratory
pathway and alternative respiratory pathway [46]. Thus,