Analyses of avocado (Persea americana) nectar properties and their perception by honey bees (Apis mellifera).

Honey bees are important avocado pollinators. However, due to the low attractiveness of flowers, pollination is often inadequate. Previous work has revealed that avocado honey is relatively unattractive to honey bees when compared with honey from competing flowers. We characterized avocado honey and nectar with respect to their odor, color, and composition of sugars, phenolic compounds, and minerals. Furthermore, we tested how honey bees perceive these parameters, using the proboscis extension response bioassay and preference experiments with free-flying bees. Naïve bees were indifferent to odors of avocado and citrus flowers and honey. Experienced bees, which were collected in the field during the blooming season, responded preferentially to odor of citrus flowers. The unique sugar composition of avocado nectar, which contains almost exclusively sucrose and a low concentration of the rare carbohydrate perseitol, and the dark brown color of avocado honey, had no negative effects on its attractiveness to the bees. Phenolic compounds extracted from avocado honey were attractive to bees and adding them to a solution of sucrose increased its attractiveness. Compared with citrus nectar and nonavocado honey, avocado nectar and honey were rich in a wide range of minerals, including potassium, phosphorus, magnesium, sulfur, iron, and copper. Potassium and phosphorus, the two major minerals, both had a repellent effect on the bees. Possible explanations for the presence of repellent components in avocado nectar are discussed.

Determination by near-infrared spectroscopy of perseitol used as a marker for the botanical origin of avocado (Persea americana Mill.) honey.

This paper reports the application of near-infrared (NIR) reflectance spectroscopy to determine the concentration in honey of perseitol, a sugar that is specific to avocado honey. Reference values for perseitol were obtained by high-performance liquid chromatography analysis in 109 honey samples. Although the average concentration of perseitol in honey samples was only 0.48%, accurate prediction equations were successfully developed. The regression model of modified partial least squares was superior to that of principal component regressions. Calibrations based on the first or second derivative of Log(1/R) were equally good (R(2) > 0.95). Using half of the samples for calibration and the second half for validation, the correlation between actual and predicted values of the second half was satisfactory (R(2) = 0.87), the slope did not differ from 1, bias was low (0.005%), and the standard error of prediction was relatively low (0.13%). It was concluded that NIRS analysis may be used to detect to what extent honeybees have harvested avocado nectar but not to authenticate avocado honey as unifloral.

The effect of heating on the expression and function of CD-2 molecules on human T-lymphocytes.

CD-2 molecules on the surface of human T-lymphocytes endow these cells with the capacity of binding sheep (SRBC) and human red blood cells (HRBC). It has recently become clear that they play an important role in the regulation of T-cell functions. The aim of the present study was to analyze the effect of heating at 45 degrees C for 1 hour on the capacity of human T-lymphocytes to bind SRBC and HRBC and to stain with CD-2 monoclonal antibody. Heating of human peripheral blood lymphocytes (PBL), thymus cells, or cells of the HD-MAR T-cell line drastically reduced their capacity of forming rosettes with SRBC. Heating of human thymus and HD-MAR cells also abrogated the formation of rosettes with HRBC. In contrast, the proportion of cells stained by high concentrations of CD-2 MoAb was reduced by only about 10-15%. Using radioiodine-labeled CD-2 MoAb, heating was found to reduce the number of cell surface E-receptors by 42% on PBL and by 27% on HD-MAR cells. The molecular weight of CD-2 molecules present on heated T-cells was identical with that of E-receptors on unheated cells. Heating was found to abolish antibody-induced capping of CD-2 molecules. Thus, heat treatment of human T-cells resulted in a moderate reduction in the number of cell-surface CD-2 molecules and in impaired mobility of CD-2 molecules in the membrane. It remains possible that in addition heating may affect the functional integrity of E-receptors or induce metabolic alterations detrimental for rosette formation.

Changes in the level of soluble CD-2 molecules in the serum of HIV-infected individuals.

It has been shown previously that the level of soluble CD-2 determinants (E-receptors) is elevated in the serum of patients with various immunodeficiency states. The aim of the present preliminary study was to determine the level of soluble CD-2 in the sera of individuals infected with human immunodeficiency virus (HIV), in order to assess the contribution of soluble CD-2 molecules to the immunological deterioration of these patients. The serum CD-2 concentration was determined by an enzyme-linked immunosorbent assay, using a monoclonal CD-2 antibody. Considerable levels of CD-2 were detected in the sera of 15.9% of 63 normal controls tested, with a mean absorbance at 492 nm of 0.154 +/- 0.033. In contrast, in none of the 13 asymptomatic HIV-infected individuals tested could soluble CD-2 be detected (mean absorbance of 0.00093 +/- 0.0048). Elevated concentrations of CD-2 were found in the sera of 3 of 12 patients tested who were suffering from acquired immunodeficiency syndrome (AIDS). Thus, following HIV infection there is an initial phase of reduction of soluble CD-2, probably reflecting diminished T-cell activation. Thereafter, in some AIDS patients episodes of T-cell destruction seem to be correlated with the release of CD-2 molecules into the serum.