Figure 3.

The maximal extractable activities of NR (I), PEPCase (II), or SPS (III) of leaves of maize plants continuously irrigated (shaded bars) or exposed to 1 week of water deprivation (black bars). Total extractable NR activity (μmol mg⁻¹ chlorophyll [Chl] h⁻¹) was assayed in the presence of 5 mm EDTA (A) or in the presence of 10 mm Mg²⁺, allowing calculation of the activation state (D). Total extractable PEPCase activities (mmol mg⁻¹ Chl h⁻¹) were measured in the absence of malate (B). In E, each given value represents the ratio of total extractable PEPCase activity and the respective PEPCase activity assayed in the presence of 3 mm malate. Maximal extractable SPS activities (μmol mg⁻¹ Chl h⁻¹) are given in C, and F shows the ratio of maximal catalytic SPS activity to that measured under conditions of limiting substrates in the presence of Pi. Each value represents the mean of three replicate experiments. se is indicated for each value.