Dehydroascorbate reductase (DHAR) plays a critical role in the ascorbate-glutathione recycling reaction for most higher plants. To date, studies on DHAR in higher plants have focused largely on Arabidopsis and agricultural plants, and there is virtually no information on the molecular characteristics of DHAR in gymnosperms. The present study reports the cloning and characteristics of a DHAR (PbDHAR) from a pine, Pinus bungeana Zucc. ex Endl. The PbDHAR gene encodes a protein of 215 amino acid residues with a calculated molecular mass of 24.26 kDa. The predicted 3-D structure of PbDHAR showed a typical glutathione S-transferase fold. Reverse transcription-polymerase chain reaction revealed that the PbDHAR was a constitutive expression gene in P. bungeana. The expression level of PbDHAR mRNA in P. bungeana seedlings did not show significant change under high temperature stress. The recombinant PbDHAR was overexpressed in Escherichia coli following purification with affinity chromatography. The recombinant PbDHAR exhibited enzymatic activity (19.84 micromol/min per mg) and high affinity (a K(m) of 0.08 mM) towards the substrates dehydroascorbate (DHA). Moreover, the recombinant PbDHAR was a thermostable enzyme, and retained 77% of its initial activity at 55 degrees C. The present study is the first to provide a detailed molecular characterization of the DHAR in P. bungeana.

The rheological properties of quinacridone pigment dispersion with ammonium salt of styrene-maleate (SMA) copolymer (SMA-NH 4 ) as a dispersant were measured at 258C. The effects of the SMA-NH 4 concentration, pH, and ionic strength of the system on the rheology of concentrated quinacridone pigment dispersion (in aqueous medium) were studied. All of the experimental results were correlated with the Herschel-Bulkley model. The estimated values of yield stress, t y , and model parameters such as the consistency coefficient, K, and the flow characteristic exponential, n, could reflect the variation of the surface charges of pigment particles, interactions between particles and the structure of dispersion. The flow curve of the quinacridone pigment dispersion without SMA-NH 4 showed a pseudoplastic character, while the flow curve of the quinacridone pigment dispersion with SMA-NH 4 copolymer showed a nearly Newtonian behavior. The rheological properties of aqueous quinacridone pigment dispersion with SMA-NH 4 were strongly affected by both pH and ionic strength.