Pectic polysaccharides, labeling

Xylose-rich pectic polysaccharide was extracted from defatted and protein-free cell wall preparation (5) using HCl solution (pH 1.6) at 85° C for 4 h. The extract was adjusted to pH 5.0 with ammonia, concentrated on a rotary evaporator under reduced pressure at 40°C, and precipitated with 5 volumes of 96% ethanol. After washing twice with 80% ethanol and drying in an air circulated oven at 40°C for 2 h, the pellet was ledissolved with distilled water and then precipitated with 4 vols 96% ethanol. Before the pellet was gently ground, the precipitated pellet was washed twice with 70% ethanol and dried at 40 ° in an air circulated oven for 16 h. The resultant white powder was labelled "xylose-rich pectic polysaccharide" and stored in a refrigerator. 

Labelling of Pectic Polysaccharides. We have successfully achieved the labelling of pectic polysaccharides by using two methods described below ... 

The specific radioactivity of the labelled pectic polysaccharides thus obtained was about 8000 cpm/mg of polysaccharides, counting efficiency of 3H being 30%. Of the total radioactivity incorporated, almost 50% was localized in the galacturonic acid... 

In our study, formation of isoluble complexes between pectin, a heterogeneous mixture of a number of neutral and acidic polysaccharides, and lipoprotein was studied. The basic limitation with the formation of insoluble complexes is that it is difficult to quantitate the said interaction. Furthermore, the observed interaction between pectic polysaccharides and lipoprotein is at a pH which is not physiological. We, therefore, are attempting to study this interaction under physiological conditions and by use of buffer systems which are devoid of cations, in order to facilitate formation of soluble complexes. In addition, by using labelled pectic polysaccharides, studies resulting in the elucidation of kinetics, specificity and nature of the interaction between labelled pectic polysaccharides and lipoprotein will be performed. 

Oligogalacturonides have been suggested to act as mobile wound hormones, switching on the synthesis of protease inhibitors in several leaves of a tomato plant in response to a localised injury in one leaf [56]. In experiments carried out to test the mobility of pectic fragments within the plant, exogenous C-labelled pectic polysaccharides and H-labelled oligogalacturonides were applied to wound-sites on tomato leaves. The radioactivity moved towards the tip and margins of the leaf (a pattern characteristic of the xylem stream... 

Fig. 8. — Partial Model of Primary Cell-Wall in Lupin Hypocotyl, Proposed by Monro and Coworkers.49 [The half of the Figure labeled (A) represents the extensin-hemicellulose network, and the half labeled (B) represents the separate, pectic network, which is believed not to involve the wall glycoprotein (extensin). Thus, the cellulose microfibrils (M) are separately cross-linked by two networks of polymers, the first (A) being composed of the wall glycoprotein and polysaccharide (probably hemicelluloses), and the second (B) being composed of the pectic polymers. These two networks have been separated in the Figure for clarity. This model is tentative and incomplete, as the nature of the linkages between the polymers in these two networks has not yet been identified. The...

Imai, T., and Terashima, N., 1991, Determination of the distribution and reaction of polysaccharides in wood cell-walls by the isotope tracer techniques. II. Selective radio-labeling of pectic substances in mitsumata Edgeworthiapapyrifera). Mokuzai Gakkaishi 37 733-740 (in English). 

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