Sexual dimorphism and gynoecium size variation in the andromonoecious shrub Caesalpinia gilliesii.

The degree of sexual dimorphism in flowers and inflorescences can be evaluated early in flower development through the study of floral organ size co-variation. In the present work, the gynoecium-androecium size relationship was studied to assess the degree of sexual expression in flowers and inflorescences of the andromonoecious shrub Caesalpinia gilliesii. The co-variation pattern of floral organ sizes was compared between small and large inflorescences, under the hypothesis that inflorescence size reflected differential resource availability. Also, staminate and perfect flowers were collected from three populations and compared on the basis of gynoecium, ovule length, filament length, pollen size and number. The obtained results indicated that staminate and perfect flowers differed only in the gynoecium and ovule length, whereas filament length, pollen size, and number varied across populations. The gynoecium size was smaller and its variability was much higher in staminate than in perfect flowers, as explained by a recent hypothesis about pollinator-mediated gynoecium size selection acting upon perfect flowers. The analysis of the gynoecium-androecium size relationship during flower development, revealed a dissociation of gynoecium growth relative to other floral structures in some buds. Lower gynoecium-androecium regression slopes and smaller gynoecia length characterized smaller inflorescences, thus reflecting the fact that sexual expression was more male-biased. This trend is in agreement with a differential resource-related response at the inflorescence level, however, post-mating resource allocation and the inclusion of other modular levels may also help us to understand the variation in sexual dimorphism in this species.

Regional tongue sensitivity for sweetness and pungency of ethanol-aspartame mixtures.

Binary mixtures of aspartame prepared at three levels of concentration and dissolved in four ethanolic dilutions were perceptually evaluated. Sweet-pungent combinations were presented in solution or in disks of filter paper (paper) soaked in the solutions. Variations in sweetness and pungency were examined at two oral loci including the tip and the back plus the front of the tongue in the liquid condition or the tip and the back of the tongue in the paper condition. A similar behavior was observed in liquid and paper conditions; as the concentration of aspartame and ethanol increased so did the intensity for sweet and pungent qualities. Whereas sweetness was not influenced by ethanol addition (2-8% V/V), a suppressive effect of aspartame (1-4 mM) on pungency was noted for liquid but not for the paper condition. Sweetness was enhanced when the back plus the front of the tongue was stimulated by solutions. Finally, there was a complex pattern of regional effects on the perceived pungency of alcoholic-sweet solutions that was not replicated in the paper condition.

Perception of sweetness and bitterness in different vehicles.

In the present study, we investigated taste-taste, taste-vehicle, and simultaneous taste-vehicle-taste mixtures. Subjects made estimates of the sweetness and bitterness of 27 stimuli. Sucrose (292, 585, and 1170 mM), caffeine (13, 26, and 52 mM), and binary mixtures of low (292-13 mM), middle (585-26 mM), and high (1170-52 mM) levels of both components were dispersed in water, carboxymethylcellulose (CMC) 1% w/v, and gelatin 6% w/v. The sweetness and bitterness of the sucrose-vehicle-caffeine combinations were significantly weaker than the respective sucrose-vehicle and caffeine-vehicle combinations. The emerged mutual suppressive effects were asymmetrical and persisted when both tastants were presented in CMC and gelatin. Moreover, the increase in vehicle consistency and the simultaneous addition of another taste reduced the perceived intensity of a taste either presented alone or dissolved in water. For both sweetness and bitterness, the total taste suppression observed was always significant.

Spatial and temporal suppressive behavior of bitter-sweet mixtures.

Bitter-sweet suppression in sucrose-caffeine mixtures was checked directly by measure of perceived intensity and total persistence time and indirectly by measure of the volume of water employed to remove each taste sensation.

Interactions between CO2 oral pungency and taste.

Two experiments are reported in which the perceptual interactions between oral pungency, evoked by CO2, and the taste of each of four tastants--sucrose (sweet), quinine sulfate (bitter), sodium chloride (salty), and tartaric acid (sour)--were explored. In experiment 1 the effect of three concentrations of each tastant on the stimulus-response function for perceived oral pungency, in terms of both rate of change (slope) and relative position along the perceived pungency axis, was determined. In experiment 2 the effect of three concentrations of CO2 on the stimulus-response function for the perceived taste intensity of each tastant was examined. Results show that the characteristics of the mutual effects of tastant and pungent stimulus depend on the particular tastant employed. Sucrose sweetness and CO2 oral pungency have no mutual effect; sodium chloride saltiness or tartaric acid sourness and CO2 oral pungency show mutual enhancement; and quinine sulfate bitterness abates CO2 oral pungency, whereas CO2 has a double and opposite effect on quinine sulfate bitterness--at low concentrations of bitter tastant CO2 enhances bitterness, and at high concentrations of bitter tastant CO2 abates bitterness. It is suggested that the perceptual attributes of saltiness and sourness are closer, from a qualitative point of view, to oral pungency than are the attributes of bitterness and sweetness.

Perception of sweetness: the effects of concentration and temperature.

The shape of the sweetness function remained unaltered when different concentration ranges of sucrose were evaluated at different temperatures by either one of two psychophysical methods: magnitude estimation or magnitude matching. Results of the sweetness-temperature interaction showed that cool solutions were judged less sweet than warmer solutions. Furthermore the rate of growth of sweetness increased with decreasing temperature, but this effect disappeared when the concentration reached between 0.4 and 0.5 M. That point coincides with the zone in which sweetness functions typically show an inflection point. When Beidler's taste equation was applied to psychophysical data obtained at constant or variable temperature, it was possible to show that sweetness is mediated by an adsorption process rather than an enzymatic reaction.

Effects of concentration and temperature on gustatory persistence.

The effects of concentration and temperature on the perceived persistence of citric acid, sodium chloride, sucrose, and urea were determined. The results obtained by a modified magnitude-estimation procedure suggest that power functions of the form P = K X Cn related the perceived persistence (P in seconds) to the concentration (C in % W/V) at each temperature and for each taste compound. Furthermore, the relative persistence (K) and the slope of the functions of persistence (n) showed changes when the temperature of taste stimuli varied.