Electrical Polarization of Tobacco Cells by Ca2+ Ion Channels

It has been suggested that neighbouring cells in higher plantsco-ordinate their direction of growth by sensing the electricalpolarities of their neighbours. The present work sets out toexamine the role played by calcium in the response of theirindividual cells to externally-applied fields. The transcellular currents of cultured tobacco cells were investigatedwith a vibrating probe before and after the application of anartificial electric current with a density of 250 µA cm^–2,giving a potential difference of approximately 3 mV across thecell. When calcium was omitted from the experimental medium,the externally-applied current had little effect on either thedirection or magnitude of the cells' own transcellular currents.When 01 mM calcium was present, the external current repolarizedthe cells so that their own currents tended to flow in the samedirection as the current applied. This was due to a large localizedincrease in inward current in the region nearest the positiveelectrode, with the outward current being more evenly spread. Adding cobalt ions (a Ca²⁺ -channel blocker) in the presenceof external calcium had little immediate effect on the transcellularcurrents themselves, but they lost their ability to change inresponse to the artificially applied current. This suggeststhat the cells may have detected the applied current by enhancedcalcium ingress through calcium channels in the most hyperpolarizedregion of the membrane. An hypothesis is presented which proposesthat asymmetric calcium entry results in the electrical polarizationof cells by a mechanism involving both the opening of calcium-gatedion channels and the lateral movement of electrophoreticallymobile channels. Key words: Cell-culture, cobalt, plant electrophysiology, polarity, vibrating-probe     

FORMULATING A NEW PASSION FRUIT JUICE BEVERAGE WITH DIFFERENT SWEETENER SYSTEMS

The aim of this work was to optimize the acceptability of a natural passion fruit beverage using different levels of passion fruit pulp and sucrose, and to determine the equi-sweet concentrations of aspartame, sucralose, and a blend of 80% aspartame  +  20% acesulfame-K for the optimized formula. A 2² central composite design was used to optimize the acceptability of the sucrose-sweetened beverage, which was accessed using a 9-point structured hedonic scale. Acceptability data were fitted to a second-order model equation provided in the design. The selected pulp content and sucrose concentration were, respectively, 2.5 ° Brix and 10%. Measurements of sweetness equivalence were accomplished using two types of sensory methods: magnitude estimation and difference-from-control tests. The concentrations of aspartame, sucralose and a blend of 80% aspartame  +  20% acesulfame-K found as equi-sweet to 10% sucrose in the studied passion fruit beverage were, respectively, 0.043, 0.016 and 0.026%.

PRACTICAL APPLICATIONS

This article deals with formulating a new passion fruit juice beverage with different sweetener systems. The research makes a very important contribution to the literature on sensory science used on product development by demonstrating the necessity to study the substitution of sucrose by high-intensity sweeteners every time a formulation is changed or a new product is developed.     

THE POWER FUNCTION OF CARBONATION

The relationship between the physical carbonation level of carbonated spring water and the magnitude of carbonation perception was determined by a trained panel using two assessing conditions, swallowing and expectoration. Spring water was carbonated to 5 carbonation levels. Panelists were asked to rate their perception of carbonation intensity by using magnitude estimation. The power function equations were established with high correlation coefficients for both assessing conditions. The exponents, 2.79 (swallowing) and 2.65 (expectoration), suggested a sharp increase of perceived CO₂ magnitude with increasing concentration. There was no significant difference between exponents resulting from the two assessing conditions. Therefore, the response should not be affected if samples are expectorated in studies of carbonation perception.     

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild‐type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.     

Induction of Growth Factor Receptors on Cultured Human Melanocytes

Using a sensitive and selective culture system for human epidermal melanocytes, we have demonstrated that the morphologic changes induced by addition of phorbol 12-tetradecanoate 13-acetate (TPA) to proliferating newborn melanocytes are associated with induction of nerve growth factor (NGF) receptors, as measured by messenger RNA (mRNA) levels and protein accumulation and by cell surface immunofluorescent staining. Growth factor deprivation or addition of NGF similarly results in NGF receptor induction. NGF is believed to function in vivo and in vitro as a survival factor for many neural crest-derived cells and has been demonstrated to promote specific neural cell functions ranging from neurite outgrowth to enzyme induction, but to date no role for NGF has been identified with regard to normal human melanocytes. Our data demonstrate that, given appropriate stimulation, cultured human melanocytes may express the NGF receptor gene and therefore suggest that NGF may modulate human melanocyte behavior in vivo. This first demonstration of a growth factor receptor on human melanocytes provides an important opportunity to explore signal transduction relevant to their growth, differentiation, and malignant transformation.     

Effects of photoperiod and temperature on the rhythm and free‐running of adult eclosion in the Indian meal moth Plodia interpunctella

The rhythm of adult eclosion in the Indian meal moth Plodia interpunctella Hübner (Lepidoptera: Pyralidae) is investigated under various photoperiods and temperatures aiming to determine the nature of the temperature compensation and the free‐running period. Insects that are committed to a nondiapause larval development show diel rhythms of adult eclosion at 30, 25 and 20 °C. At 30 °C, the eclosion peak (i.e. the mean time of eclosion) occurs approximately 20 h after lights off under an LD 4 : 20 h photocycle, and at approximately 15 h under an LD 20 : 4 h photocycle. At 25 °C, the peak of eclosion occurs approximately 19 h after lights off under an LD 2 : 20 h photocycle and at approximately 16 h under an LD 20 : 4 h photocycle. At 20 °C, the eclosion peak is significantly advanced under long days of >12 h (i.e. approximately 20 h after lights off under an LD 4 : 20 h photocycle and approximately 9 h under an LD 20 : 4 h photocycle), indicating an effect of both lights‐off and lights‐on signals on the timing of the adult eclosion. To determine the involvement of a self‐sustained oscillator, the rhythm of adult eclosion is examined under darkness at different temperatures (30 to 21 °C). The mean free‐running periods are 22.4, 22.8, 22.0 and 22.5 h at 30, 24, 23 and 22 °C, respectively, indicating that the eclosion rhythm is temperature‐compensated. However, this rhythm does not free‐run under constant darkness at 21 °C. Because a clear diel rhythm is observed under 24‐h photocycles at 20 °C, the oscillator might be damped out within 24 h at the lower temperature.