Structural analysis and anticoagulant activities of the novel sulfated fucan possessing a regular well-defined repeating unit from sea cucumber.

Sulfated fucans, the complex polysaccharides, exhibit various biological activities. Herein, we purified two fucans from the sea cucumbers Holothuria edulis and Ludwigothurea grisea. Their structures were verified by means of HPGPC, FT-IR, GC-MS and NMR. As a result, a novel structural motif for this type of polymers is reported. The fucans have a unique structure composed of a central core of regular (1→2) and (1→3)-linked tetrasaccharide repeating units. Approximately 50% of the units from L. grisea (100% for H. edulis fucan) contain sides of oligosaccharides formed by nonsulfated fucose units linked to the O-4 position of the central core. Anticoagulant activity assays indicate that the sea cucumber fucans strongly inhibit human blood clotting through the intrinsic pathways of the coagulation cascade. Moreover, the mechanism of anticoagulant action of the fucans is selective inhibition of thrombin activity by heparin cofactor II. The distinctive tetrasaccharide repeating units contribute to the anticoagulant action. Additionally, unlike the fucans from marine alga, although the sea cucumber fucans have great molecular weights and affluent sulfates, they do not induce platelet aggregation. Overall, our results may be helpful in understanding the structure-function relationships of the well-defined polysaccharides from invertebrate as new types of safer anticoagulants.

Efficient Regeneration of Eucalyptus urophylla x Eucalyptus grandis from Stem Segment

The aim of the present study was to establish an efficient regeneration system for the hybrid E. urophylla x E. grandis by means of organogenesis. Stem segments from seedlings were used as explants and cultured in a modified Murashige and Skoog medium (MS), supplemented with 13.2 µM N-phenyl-N'-[6-(2-chlorobenzothiazol)-yl] urea (PBU) and 0.285 µM indole-3-acetic acid (IAA). PBU was a useful growth regulator. After cultivating for 5 d, 96% explants formed callus. After 30 d, the calli obtained were transferred to MS medium containing different combinations of 6-benzyladenine (BA) and naphthalene acetic acid (NAA). Compared with other growth regulator combinations, PBU stimulated more vigorous calli and restrained browning. In addition, a large percentage (91.3%) of the calli induced by PBU showed adventitious buds formation. Shoot elongation was then stimulated on half-strength MS mineral salts medium supplemented with 6.6 µM PBU and 0.285 µM IAA for 20 d. For rooting, the elongated shoots were cultivated on root induction medium containing 2.46 µM indole-3-butyric acid (IBA). Plantlets were then successfully transplanted to a greenhouse. This procedure represented an efficient way of E. urophylla x E. grandis plant regeneration.