*4.3. Enzyme Activity*

Frozen leaf tissue collected midday and during the middle of the night period was utilized for phosphoenolpyruvate carboxylase (PEPCase) and NADP-malic enzyme (ME) activity. Assays of crude extracts were done in triplicate under well-watered and water-stress conditions. The samples were assayed spectrophotometrically by following the oxidation of NADH (for PEPCase) or the reduction of NADP<sup>+</sup> at 340 nm as previously described by Guralnick and Ting [31]. Results were expressed as μmol mg chl−<sup>1</sup> h<sup>−</sup>1.
