Far-red light blocks greening of Arabidopsis seedlings via a phytochrome A-mediated change in plastid development.

We have characterized a far-red-light response that induces a novel pathway for plastid development in Arabidopsis seedlings. This response results in the inability of cotyledons to green upon subsequent white light illumination, and the response is suppressed by exogenous sucrose. Studies with mutants showed that this far-red block of greening is phytochrome A dependent and requires an intact downstream signaling pathway in which FHY1 and FHY3 may be components but in which HY5 is not. This highlights a previously undefined branchpoint in the phytochrome signaling pathway. Ultrastructural analysis showed that the far-red block correlates with both the failure of plastids to accumulate prolamellar bodies and the formation of vesicles in the stroma. We present evidence that the far-red block of greening is the result of severe repression of protochlorophyllide reductase (POR) genes by far-red light coupled with irreversible plastid damage. This results in the temporal separation of phytochrome-mediated POR; repression from light-dependent protochlorophyllide reduction, two processes that normally occur in coordination in white light.

Influence of dietary sucrose on biological aging.

The segment of the population aged > 65 y is the fastest growing age segment in most developed countries. The increasing numbers of individuals living into their eighth and ninth decades of life have shifted the focus of biomedical research from seeking mechanisms for extending life to finding ways to improve health and to reduce age-related morbidity. One area of research that has shown considerable promise for improving the health of elderly people is nutrition. I review recent literature pertinent to the influences of nutrition on biological aging by discussing the effects of dietary sucrose and other carbohydrates on glucose homeostasis, age-related disorders and pathology, and life span. Although critical gaps remain in our understanding of how dietary sucrose can affect biological aging, evidence exits that the type and amount of dietary carbohydrate can significantly affect the health and life span of elderly people.

Replacing starch with sucrose in a high glycaemic index breakfast cereal lowers glycaemic and insulin responses.

OBJECTIVE: To test the hypothesis that replacing starch with sugar in a processed breakfast cereal that has a high glycaemic index could significantly decrease glycaemic and insulin responses. DESIGN: Subjects consumed in random order three equi-carbohydrate meals based on a popular puffed rice cereal containing three levels of sucrose (0, 21 and 43 g). Postprandial glucose and insulin responses were compared using the incremental area under the curve (AUC). SUBJECTS: Twelve healthy volunteers (5 males and 7 females) with normal glucose tolerance drawn from the university community, mean age 23 years (range: 20 to 27 year), mean body mass index 22.6 kg/m2 (range: 18.6 to 31.2 kg/m2). RESULTS: Glycaemia was significantly lower after the meal containing the highest amount of sugar (glucose AUC 101.7 +/- 14.0 mmol/l.120 min) compared with the non-sweetened cereal (155.5 +/- 18.0 mmol/l.120 min, P < 0.01). There was a significant inverse correlation between the amount of sucrose incorporated and the degree of glycaemia (analysis of covariance coefficient = -1.25, P = 0.00). Similarly, the plasma insulin response was significantly lower after the highest sugar meal (insulin AUC 2267 +/- 346 microU/ml.120 min) compared with the meal without sugar (3505 +/- 365 microU/ml.120 min, P < 0.01). CONCLUSIONS: We found a significant reduction in glycaemic and insulin responses when sugar replaced the rapidly digested starch in a processed breakfast cereal, i.e. the opposite of what is commonly believed. Thus sweetened breakfast cereals may not compromise glycaemic control more so than the unsweetened counterpart.

Separate cis sequences and trans factors direct metabolic and developmental regulation of a potato tuber storage protein gene.

The expression of genes encoding patatin, a major tuber protein, is highly tissue-specific but is also modulated by exogenous sucrose. The patterns of transcription observed in potato plants could be due to mechanisms conferring tuber-specificity or they could reflect the concentrations of sucrose found in different tissues. To distinguish between these possibilities, a detailed examination was made of the function of a region of the promoter previously implicated in conferring tissue-specific and sucrose-inducible expression. Internal deletions of this region revealed three separate functional domains regulating expression. The B repeat region acted as a positive activator of transcription in the tuber and was also responsible for a degree of sucrose-inducibility. The distal region of the A repeat repressed transcription in leaf and tuber tissue, while the proximal region of the A repeat was able to confer sucrose-responsiveness. Each of these regions specifically bound nuclear proteins which may be putative transcription factors involved in conferring these responses. The region found to confer sucrose-inducible expression was conserved among some other genes that are also regulated by exogenous sucrose.

Is sodium necessary for stimulus-secretion coupling in toad (Caudiverbera caudiverbera) adrenal chromaffin cells?

1. Chromaffin cells of the toad were used to investigate the effects of total replacement of extracellular Na+ by monovalent cations or sucrose on secretion of catecholamine (CA). 2. K+, Rb+ or Cs+ in place of Na+ produced an immediate secretory response, which are dependent on extracellular Ca2+ and it was blocked by Co2+. Li+ or choline+ did not affect basal secretion. 3. Isosmotic replacement of Na+ by sucrose caused CA secretion even in the absence of external Ca2+ or in the presence of Ca-channel blockers. 4. Tetraethylammonium decreased the extent of CA release produced by either K+ or Rb+. 5. The secretagogue effect of Na+/K+, Na+/Rb+ or Na+/Cs+ replacement could be explained by a depolarization of the cell membrane, which ultimately will cause Ca2+ influx through voltage-dependent Ca-channels. However, the present results indicate that Na+ may be sufficient but not necessary for CA secretion.

Adenylate cyclase responses to sucrose stimulation in membranes of pig circumvallate taste papillae.

1. Typical adenylate cyclase (AC) responses to guanine nucleotides were found in membranes of pig circumvallate (CV) taste papillae. 2. Sucrose stimulated AC activity in the CV membranes and this stimulation was GTP dependent and tissue specific. 3. The stimulatory effect of sucrose in the CV membranes was dependent on the concentration of membranes used in the AC assay. 4. This study provides the first biochemical data on cellular transduction of taste in the pig, compares positively to preliminary results in cattle and supports recent suggestions for a role of cAMP in sweet taste transduction.

Differential effects of (-)-baclofen on Ia and descending monosynaptic EPSPs.

1. In cats anesthetized with alpha-chloralose, population synaptic responses of motoneurons produced by stimulation of group I afferents were recorded from ventral roots with a sucrose gap or extracellularly from the motor pool. These responses were depressed, and often abolished, following the intravenous injection of 1-3 mg/kg of (-)-baclofen, a presumed GABAb agonist. 2. The monosynaptic population responses of motoneurons produced by stimulation of the ipsilateral ventromedial funiculus (VMF), the bulbar reticular formation or the vestibular nucleus, were also depressed following the administration of (-)-baclofen, but to a lesser degree than responses produced by stimulation of group I fibers. 3. Depression of the synaptic actions of Ia and of descending fibers following the administration of (-)-baclofen occurred without significant changes in the presynaptic volley recorded from the cord dorsum. However, in 3/4 experiments the intraspinally recorded Ia terminal potential was reduced following the injection of (-)-baclofen. The VMF terminal potentials were also depressed, but to a lesser degree. 4. Intracellular recordings from spinal motoneurons indicate that the (-)-baclofen-induced depression of the monosynaptic Ia- and VMF-EPSPs occurred without important changes in the time course of EPSP decay. This suggests that with the amounts used, postsynaptic changes were not contributing significantly to the EPSP depression. 5. It is suggested that (-)-baclofen depresses synaptic transmission probably by activation of GABAb receptors located at the intraspinal terminations of Ia and descending fibers. The lower sensitivity of VMF actions to (-)-baclofen would be accounted for by a relatively low density of baclofen receptors in descending fiber terminals.

Discontinuation of sustained sucrose-feeding aggravates morphine withdrawal.

Sprague-Dawley rats were allowed ad lib access to a 20% sucrose solution in addition to their normal diet to investigate the relationship between the prolonged consumption of a high carbohydrate diet and opioid function as evidenced by opioid dependence and withdrawal. Morphine dependence, assayed by tailflick, was induced, followed by naloxone-precipitated withdrawal, gauged by weight loss. Sucrose-fed animals developed lowered pain thresholds prior to dependence induction relative to those of control animals, but failed to exhibit any differences from controls in the development of dependence. Weight loss during withdrawal was increased by the discontinuation of sustained sucrose-feeding. In addition, the induction of dependence first decreased, then increased the animals' preference for sucrose. It is concluded that changes in opioid function caused by sustained sucrose-feeding are insufficient to affect the development of tolerance to morphine analgesia, but do aggravate the symptoms of precipitated withdrawal when access to sucrose is denied prior to the injection of naloxone.

Why do sugars taste good?

The preference humans and animals show for sweet solutions has been the subject of hundreds of publications. Nevertheless, the evolutionary origin of sweet preference remains enigmatic because of the relatively low nutritional value of sugars and the absence of specific tastes for other, more essential, nutrients. Moderate concentrations of sugars are found in most plant foods because sugars play an important role in plant physiology. Widespread occurrence of sugars in plants is paralleled by widespread preference for sugar solutions in mammals. These observations suggest that preference for sugars evolved because they are common in plants and easy to detect rather than because of any special nutritional merits they offer. Perception of sweetness cannot be used to accurately meter the metabolizable energy or nutritive value of a food.

Acute effects of exercise intensity on appetite in young men.

This study investigated the acute effects of two exercise intensities on three measures of appetite. Fifteen, 12-h-fasted, college-age males completed three experimental sessions in counterbalanced orders: no-exercise control; cycle exercise performed at 35% VO2max; and cycle exercise performed at 68% VO2max. Both exercise conditions involved a total energy expenditure of 4.1 kcal.kg-1 body weight. Dependent measures were intermittent hunger and sucrose palatability ratings, and food intake at a test meal given approximately 1 h post-exercise. Hunger was briefly suppressed in the high-intensity exercise condition compared to low-intensity exercise and control, while intake of liquid-source kilocalories and carbohydrates was higher after the exercise sessions. Total caloric intake remained stable. Sucrose palatability did not vary across sessions. Intensity is inferred to be an important variable mediating exercise effects on appetite. Relations between appetite measures are discussed, and validity of sucrose palatability ratings and common methods of measuring food intake questioned. Exercise, while not decreasing food intake, does not appear to increase it, and the benefits of exercise for body fat reduction are not immediately offset by compensatory caloric intake.

Do starch statoliths act as the gravisensors in cereal grass pulvini?

To determine if starch statoliths do, in fact, act as gravisensors in cereal grass shoots, starch was removed from the starch statoliths by placing 45-day-old intact barley plants (Hordeum vulgare cv 'Larker') in the dark at 25 degrees C for 5 days. Evidence from staining with I2-KI, scanning electron microscopy, and transmission electron microscopy indicated that starch grains were no longer present in plastids in the pulvini of plants placed in the dark for 5 days. Furthermore, gravitropic curvature response in these pulvini was reduced to zero, even though pulvini from vertically oriented plants were still capable of elongating in response to applied auxin plus gibberellic acid. However, when 0.1 molar sucrose was fed to the dark pretreated, starch statolith-free pulvini during gravistimulation in the dark, they not only reformed starch grains in the starch-depleted plastids in the pulvini, but they also showed an upward bending response. Starch grain reformation appeared to precede reappearance of the graviresponse in these sucrose-fed pulvini. These results strongly support the view that starch statoliths do indeed serve as the gravisensors in cereal grass shoots.

Behavioral and metabolic effects of sucrose-supplemented feeding in hyperactive rats.

Two hyperactive rat strains [spontaneously hypertensive rats (SHR) and SHR-Wistar-Kyoto cross (WK-HA)] and their nonhyperactive genetic control strain (Wistar-Kyoto) were fed ad libitum sucrose-supplemented rat chow, or chow alone in controls, to determine the effects of dietary sugar on behavior. The diets were given either overnight (acute sugar) or for 14-18 days (chronic sugar), and testing was carried out on the morning after each of the dietary schedules. The metabolic studies revealed significant strain, sex, and age differences in appetite for sucrose, caloric intake, postprandial plasma levels of glucose and insulin, and weight gain after sucrose feeding. The findings indicate that sugar feeding led to increased plasma glucose and insulin levels; however, total caloric intake was decreased, and less weight gain was observed than in chow-fed controls, particularly among the hyperactive strains. In behavioral tests, sugar feeding did not alter spontaneous activity levels in any of the strains after either acute or chronic diets. There were also no significant effects of sucrose consumption on spatial learning and memory in a plus-shaped maze as determined by use of a shock-avoidance paradigm. The only significant behavioral effects of sucrose observed were an impairment in habituation and distractibility among the WK-HA females, the most hyperactive group among these strains.

Nutrients that modify the speed of internal clock and memory storage processes.

Two experiments assessed the effects of nutrients on timing behavior by rats. The nutrients were laced with saccharin and given to rats as a snack before training on a 20-s peak-interval procedure. The primary component of the snacks for four groups of 10 rats was lecithin (phosphatidylcholine), protein (casein), carbohydrate (sucrose), or a nonnutrient (saccharin). The primary measure of behavior was the time of the rat's highest response rate during a trial (peak time), which represented the interval during which the rat maximally expected food. With a lecithin snack, peak time was gradually shifted over sessions to a shorter time, remained shifted to the left of the normal function with additional testing, and then remained at the shorter time on two sessions after the snack was discontinued; with the protein snack, peak time was abruptly shifted to a shorter time, returned to normal with additional testing, and then rebounded to a longer time when the snack was discontinued; with a carbohydrate, snack peak time was abruptly shifted to a longer time, returned to normal with additional testing, and then rebounded to a shorter time when the snack was discontinued. The behavioral patterns produced by the nutrients were interpreted in terms of precursor effects on central neurotransmitter synthesis and release, psychological stages of an information-processing model, and mathematical parameters of a scalar timing theory.

Voltage clamp simulations for multifiber bundles in a double sucrose gap: cable complications.

A theoretical model is presented for voltage clamp of a bundle of cylindrical excitable cells in a double sucrose gap. The preparation in the test node is represented by a single one-dimensional cable (length/diameter ratio approximately) with standard Hodgkin-Huxley kinetics for transmembrane Na current. Imperfections of voltage control due to internal (longitudinal) resistivity and external (radial) resistance in series to the membrane are analysed. The electrical behavior of a fiber is described by the cable equation with appropriate boundary conditions and subsidiary equations reflecting the membrane characteristics. Membrane voltage and current distribution in response to a step command was obtained by numerical integration. The results are described in two papers. The present paper deals with the effect of internal resistivity with the external resistance being neglected. The closed loop response of a fiber displays a strong tendency to oscillate. To stabilize the system a phase lead was inserted and the gain of the control amplifier was reduced. Conditions for stability were examined by Nyquist analysis. When the Na system was activated by a command pulse below ENa, a voltage gradient developed between a depolarization (relative to the command signal) at the end where voltage was monitored and a hyperpolarization at the site of current injection. In spite of a poor voltage control the total measured current appeared to have a smooth transient. With large voltage gradients a small, second inward current was seen. At a low (high) Na conductance maximum peak inward current was larger (smaller) that the current expected from ideal space clamping.

A structure-activity study on the sucrose taste antagonist methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside.

In order to assess the effect of the antagonist methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside (MAD-diCl-Gal) upon the gerbil's chorda tympani sucrose taste response, we tested several concentrations of this compound, as well as single concentrations of closely related derivatives, and found that MAD-diCl-Gal was the most potent inhibitor tested. It appears that the inhibition mechanism is very specific. For example, we have found that 2 chlorine atoms at the C-4 and C-6 positions on the glucopyranoside ring are required for inhibition. In addition, with regard to the orientation of the chlorine atoms, the galacto derivative seems to be more potent than the gluco derivative. We have also found that the methyl glycoside is more potent than the free sugar. With regard to the orientation of the methyl group, MAD-diCl-Gal is more potent than its beta-anomer. (Because of this discovery of the methyl group enhancement and orientation effect, we shall discontinue using the acronym diCl-Gal and replace it with the more specific MAD-diCl-Gal.) Of particular significance is the fact that there appears to be a structure-activity relationship between the most active stimulants and inhibitors in that the requirement for an axial orientation at C-1 and the enhancement by the methyl group at that position are the same in both cases. These results suggest that both the stimulator and the antagonist are acting at the same receptor site.(ABSTRACT TRUNCATED AT 250 WORDS)

Antagonism of the gerbil's sucrose taste response by p-nitrophenyl alpha-D-glucopyranoside and chloramphenicol.

We have discovered that the gerbil's chorda tympani nerve response to sucrose is suppressed by p-nitrophenyl alpha-D-glucopyranoside (PNP-Glu) and chloramphenicol (CAP). Mixture experiments of PNP-Glu and CAP with sodium chloride, potassium chloride, hydrochloric acid, and sucrose gave rise to the following observations: Neither PNP-Glu nor CAP alone stimulates the gerbil's taste nerve; while the sucrose response is suppressed by these inhibitors, taste responses produced by sodium chloride, potassium chloride, and hydrochloric acid are unaffected by the presence of PNP-Glu or CAP; the antagonisms of PNP-Glu and CAP were surmounted by a high concentration of sucrose; CAP is a more potent antagonist (IC50 = 0.0013 M) than PNP-Glu (IC50 = 0.022 M), and both are more potent than methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside (IC50 = 0.048 M); and sucrose antagonism occurs only when PNP-Glu and CAP are mixed with sucrose. It is short-lived and ceases when the mixtures are rinsed from the gerbil's tongue. Structure-activity studies provided the following information: The alpha anomer of PNP-Glu is a more potent inhibitor than its beta anomer; among the PNP-Glu derivatives tested (p-aminophenyl, p-nitrophenyl, and phenyl) only p-nitrophenyl inhibited; among the nitrophenyl galactosides, the para derivative was more potent than the ortho or meta; and p-nitrophenyl alpha-D-mannopyranoside and p-nitrophenyl alpha-D-galactoside are slightly more potent than PNP-Glu. On the basis of concentration experiments, we believe that the inhibitory mechanisms of PNP-Glu and CAP are different, which suggests the existence of at least 2 sucrose receptor sites.

Myocardial adaptations to dietary sucrose in spontaneously hypertensive rats.

The effects of dietary sucrose upon specific myocardial and hemodynamic parameters were examined in spontaneously hypertensive rats (SHR). Following a 6 wk program, SHR consuming a supplement of 10% sucrose in the drinking water exhibited increased heart weight, heart mass, left ventricular free wall thickness and increased resting heart rate when compared to the hypertensive control group. Total caloric intake was similar between groups. Cardiac alpha 1-adrenoceptor density and affinity were also altered following sucrose feeding. These data suggest that modest intake of dietary sucrose is associated with cardiovascular adaptations that may further burden a heart already compromised by the presence of systemic hypertension.

Sucrose permeability of the blood-retinal and blood-brain barriers. Effects of diabetes, hypertonicity, and iodate.

The permeabilities of the blood-retinal (BRB) and blood-brain (BBB) barriers to sucrose were determined simultaneously using an intravenous injection technique in the rat. The method involved direct sampling of retinal tissue in order to avoid errors caused by sucrose penetration across other components of the blood-ocular barrier. The permeability X surface area (PS) product for the BRB was approximately four times greater than for the BBB. Intracarotid infusion of a hypertonic arabinose solution resulted in a dose-dependent increase in the permeability of both barrier systems. In contrast, 24 hr after treatment of animals with iodate, the PS product for the BRB but not the BBB was increased. The permeability of the blood-retinal barrier to sucrose was measured in normal and 2-, 6-, and 20-week streptozocin diabetic rats. The BRB was unaffected at 2 and 6 weeks of diabetes, and showed only a small increase in permeability at 20 weeks. Our results suggest that alterations in the blood-ocular barrier in early diabetes do not result from an increased passive permeability of the BRB. The method described should permit direct comparison of BRB and BBB permeabilities to a variety of compounds under various conditions.