FLOW‐CYTOMETRIC CHARACTERIZATION OF THE CELL‐SURFACE GLYCANS OF SYMBIOTIC DINOFLAGELLATES (SYMBIODINIUM SPP.)1

Symbiodinium spp. dinoflagellates are common symbionts of marine invertebrates. The cell‐surface glycan profile may determine whether a particular Symbiodinium is able to establish and maintain a stable symbiotic relationship. To characterize this profile, eight Symbiodinium cultures were examined using eight glycan‐specific fluorescent lectin probes. Confocal imaging and flow‐cytometric analysis were used to determine significant levels of binding of each probe to the cell surface. No significant variation in glycan profile was seen within each Symbiodinium culture, either over time or over growth phase. No cladal trends in glycan profile were found, but of note, two different Symbiodinium cultures (from clades A and B) isolated from one host species had very similar profiles, and two other cultures (from clades B and F) from different host species had identical profiles. Two lectin probes were particularly interesting: concanavalin A (ConA) and Griffonia simplicifolia‐II (GS‐II). The ConA probe showed significant binding to all Symbiodinium cultures, suggesting the widespread presence of cell‐surface mannose residues, while the GS‐II probe, which is specific for glycans possessing N‐acetyl groups, showed significant binding to six of eight Symbiodinium cultures. Other probes showed significant binding to the following percentage of Symbiodinium cultures examined: wheat germ agglutinin (WGA), 37.5%; peanut agglutinin (PNA), 50%; Helix pomatia agglutinin (HPA), 50%; phytohemagglutinin‐L (PHA‐L), 62.5%; soybean agglutinin (SBA), 50%; and Griffonia simplicifolia‐IB₄ (GS‐IB₄), 12.5%. This study highlights the complexity of cell‐surface glycan assemblages and their potential role in the discrimination of different dinoflagellate symbionts by cnidarian hosts.     

Anisotropic yield behavior of bone under combined axial force and torque

In this study the yield behavior of cortical bone was determined under combined loading conditions involving tension, compression and torsion. The axis of each test sample coincided with the long bone axis. To minimize viscoelastic behavior, tests were conducted using an effective strain rate in the range of 0.01-0.06 s-1. Experimental yield loci for bovine and human cortical bone were determined using a strain offset technique to determine the 'common yield point' for combined loading. Several failure criteria which have been used for composite materials were examined for applicability to the experimental results. Data were obtained for bovine and human tibial and femoral bone. The Tsai-Wu criterion was in best agreement to the test data, although Hill's criterion could describe the individual compression-torsion or tension-torsion regimes with good accuracy.     

Use of a Fluorimetric Method to Assay the Binding and Transfer of Phospholipids by Lipid Transfer Proteins from Maize Seedlings and Arabidopsis Leaves

A fluorimetric method has been used to study the binding andtransfer of phospholipids mediated by a lipid transfer protein(LTP) from maize seedlings and by proteins extracted from Arabidopsisleaves. This method is based on the use of donor vesicles preparedby sonication or injection and consisting of either self quenchingvesicles of (1-palmitoyl 2-{12-{(7-nitrobenzoxadiazol-4-yl)amino}dodecanoyl}-Sn-glycero-3-phosphocholine(NBD-PC) or trinitrophenylphosphate phosphatidyl ethanolamine(TNP-PE) quenched vesicles of l-palmitoyl-2(l-pyredecanoyl)-Snglycero-3-phosphocholine(Pyr-PC). Acceptor vesicles consisted in a mixture (90/10; v/v)of dioleoylphosphatidylcholine and phosphatidyl inositol (DOPC-PI).The use of injected vesicles of Pyr-PC allowed to achieve sensitiveand qualitative tests of binding and transfer since 0.05 µMLTP were detected. By contrast, when sonicated vesicles of NBD-PCwere used, quantitative determinations of phospholipid-LTP complexas well as measurement of the initial rate of phospholipid transferon a large range of protein concentration (0.5 to 20 µM)were performed. This fluorimetric method has been successfullyused to study the activity of maize LTP during its purificationor the activity of LTPs present in Arabidopsis extracts. (Received December 5, 1993; Accepted December 7, 1993)