STRUCTURAL STUDIES OF AN ARABINOGALACTAN——A WATER SOLUBLE POLYSACCHARIDE FROM THE POLLEN OF PAPAVER SOMNIFERUM

A polysaccharide,PS(1),has been isolated from the pollen of papaver somniferum.PS(1)is a highly branched arabinogalactan,which,mainly contains α—L—arabinofuranosyl(1→)and(3,6→1)— β—D—galactopyranosyl residues.We also studied the circular dichroism and immunoactivity of PS(1).

CARBOXYMETHYLPACHYMAN(Ⅰ),A NEW WATER SOLUBLE POLYSACCHARIDE WITH MARKED ANTITUMOUR ACTIVITY

Carboxymethylpachyman(Ⅰ)was formed by carboxymethylation of β-pachyman.The antitumour activity of carboxymethylpachyman(Ⅰ)against S_(180)、EAC、 MA、U_(14)was measured.The structure of carboxymethylpachyman(Ⅰ)was proved by IR ^(13)CNMR spectroscopy.

Effects of short light/dark cycles on photosynthetic pathway switching and growth of medicinal Dendrobium officinale in aeroponic cultivation

Dendrobium officinale has high medicinal value but grows slowly in natural environment due to its special CAM photosynthetic pathway.In this study,D.officinale were grown aeroponically with light/dark cycles of 12 h/12 h,4 h/4 h,and 2 h/2 h for 150 d.The photosynthetic electron transfer characteristics,photosynthetic CO_(2) fixation pathways,and accumulations of biomass and soluble polysaccharides in D.officinale leaves were studied.The results showed that the photosynthetic apparatus states of D.officinale in aeroponic cultivation under short light/dark cycles of 4 h/4 h and 2 h/2 h were better than that under 12 h/12 h.The dark net CO_(2) exchange percentages of D.officinale were negative in short light/dark cycles of 4 h/4 h and 2 h/2 h,and the daily net CO_(2) exchange amount and dry/fresh weight increases were doubled compared with those in 12 h/12 h light/dark cycle.High soluble polysaccharides content and the soluble polysaccharides yield of D.officinale were obtained in the shorter light/dark cycle of 2 h/2 h.Therefore,the photosynthetic pathway of D.officinale could be switched from CAM to C3 by short light/dark cycles of 4 h/4 h and 2 h/2 h,and its higher biomass accumulation and soluble polysaccharides yield could be obtained by the shorter light/dark cycle of 2 h/2 h in aeroponic cultivation.

Feruloylated Arabinoxylans Are Oxidatively Cross- Linked by Extracellular Maize Peroxidase but Not by Horseradish Peroxidase

Covalent cross-linking of soluble extracellular arabinoxylans in living maize cultures, which models the cross- linking of wall-bound arabinoxylans, is due to oxidation of feruloyl esters to oligoferuloyl esters and ethers. The oxidizing system responsible could be H2O2/peroxidase, O2/laccase, or reactive oxygen species acting non-enzymically, To distinguish these possibilities, we studied arabinoxylan cross-linking in vivo and in vitro. In living cultures, exogenous, soluble, extracellular, feruloylated [pentosyl-3H]arabinoxylans underwent cross-linking, beginning abruptly 8 d after sub-culture. Crosslinking was suppressed by iodide, an H2O2 scavenger, indicating dependence on endogenous H2O2. However, exogenous H2O2 did not cause precocious cross-linking, despite the constant presence of endogenous peroxidases, suggesting that younger cultures contained natural cross-linking inhibitors. Dialysed culture-filtrates cross-linked [^3H]arabinoxylans in vitro only if H2O2 was also added, indicating a peroxidase requirement. This cross-linking was highly ionic-strength-dependent. The peroxidases responsible were heat-labile, although relatively heat-stable peroxidases （assayed on o-dianisidine） were also present. Surprisingly, added horseradish peroxidase, even after heat-denaturation, blocked the arabinoxylancross-linking action of maize peroxidases, suggesting that the horseradish protein was a competing substrate for [^3H]arabinoxylan coupling. In conclusion, we show for the first time that cross-linking of extracellular arabinoxylan in living maize cultures is an action of apoplastic peroxidases, some of whose unusual properties we report.