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Six commercial gum arabic samples and authenticated samples of gum from Acacia Senegal and Acacia seyal have been characterized using a range of chemical and physicochemical techniques including determination of specific rotation, sugar composition, nitrogen and amino acid content, and molecular mass distribution. Although some of the gums have slightly different chemical and physicochemical characteristics, gel permeation chromatography shows that each consists of essentially three molecular mass fractions classified as an arabinogalactan, an arabinogalactan-protein complex, and a glycoprotein.The proportions of each varied for the individual samples. The gums were tested using a specifically developed enzyme-linked immunosorbent assay which can identify gum from A. Senegal and chemically related species. Their interaction with the antibody could be correlated with differences observed in their molecular compositions. Such evidence will assist in their chemotaxonomic classification.

The unicellular green alga Monoraphidium minutum and the diatom Nitzschia perminuta were cultured under different concentrations of Co 2+ . Growth and pigment content were slightly increased at low concentrations and inhibited by high Co 2+ concentrations. The results concerning the effect of different concentrations of Co 2+ on photosynthetic O 2 evolution showed a reduction in the amount of O 2 evolved by each alga in response to increasing Co 2+ concentrations. However, an increase in O 2 evolution for both M. minutum and N. perminuta was observed at relatively low Co 2+ concentrations. Photosynthetic electron transport in M. minutum was more sensitive to Co 2+ toxicity than in N. perminuta. On the other hand, the effect of the heavy metal on respiration showed that higher Co 2+ concentrations were inhibitory to O 2 uptake by the two algal species. Low Co 2+ concentrations stimulated O 2 uptake by M. minutum throughout the experimental period. However, in N. perminuta, different concentrations of Co 2+ led to a reduction of O 2 uptake. To localize the action site of Co 2+ in the photosynthetic electron transport chain, the fluorescence induction technique was carried out. According to the results obtained, the inhibitory action of Co 2+ is located on the acceptor side of PSII for both M. minutum and N. perminuta.

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