Phosphoenolpyruvate carboxylase isolated from Panicům maximum Jacq. leaf presented a hysteretic behaviour that resulted in a kinetical lag in the reaction progress curve. This lag depended on the concentration of etuiyme, total phosphoenolpyruvate (PEP) and total Mg2+. Through an analysis of these dependences it is suggested that the hysteresis is due to an association-dissociation process influenced by union, to one form of the enzyme, of more than one of the three possible ligands; free Mg2+, free PEP or PEP-Mg2+ complex. The partially purified enzyme showed, during steady statě, a Michaelis-Menten kinetics for PEP and Mg2+ (total concentrations) and pH optima between 7.8 and 8.2.
Peanut plants were adapted to drought. Due to parahelionastic leaf movements under water stress they decreased heat load and transpiring area, Folding of leaflets minimised damage to photosynthetic apparatus by high temperatoe. A positive correlation between transpiration rate (E) and leaf water potential indicated the dependence of the latter on E. Phosphoenolpyruvate carboxylase (PEPC) activity progressively increased with increased period of stress, whereas activities of ribulose-l,5-bisphosphate carboxylase (RuBPC) and NADP-glyceraldehyde-3- phosphate dehydrogenase (NADP-G-3-PDH) decreased gradually.
In the temperate haptophyceaen Pavlova luíheri (Droop) Green and Pavlova sp. (not yet estimated) the dominant pigments were chlorophyll (Chl) a (57 %), fucoxanthin (17 %) and diadinoxanthin (13 %); other estimated pigments were p-carotene, Chl c, cA-fucoxanthin and diatoxanthin. UV-A of 1.7 W m-2 had no effect on pigmentation of P. luíheri, but led to a reduction of the pigment contents of Pavlova sp. The damaging effect of a high UV-A dose (11.0 W m'^) was more pronounced than that of UV-B irradiance. The strongest reduction of pigment concentrations of both Pavlova species was observed after an exposure to UV-A (11.0 W m'^) plus UV-B (1.2 W m-2). Under this combined irradiation an increase of the diatoxanthin content and a decrease of the diadinoxanthin content was found.
Carbonic anhydrase (CA) activity and net photosynthetic rate (/’N) in the leaves, and plant dry mass (DM) in twelve cultivars of mustard (Brassica juncea L.) were measured 50, 70 and 90 d after sowing. At different sampling stages CA was strongly associated with PN and DM.