Photosynthetic independence of initial light-caused increase in extractable nitrate reductase activity from maize seedlings

Comparisons of the effects of light on extractable nitrate reductase(EC 1.6.6.1 [EC] ) activity in Zea mays L. seedlings with and withoutnormally developing photosynthetic systems were made. Generally,plants lacking chlorophyll, due to either chemical treatment(fluridone) or genetic lesion (a chlorophyll and a carotenoidmutant), had as high or higher nitrate reductase (NR) activitiesas normally greening plants during the first 12 to 24 hr ofcontinuous white light (W) induction. This trend was especiallypronounced in mesocotyl tissues. In apical tissues (includingleaf, coleoptile and apical meristem) NR activity continuedto increase in normally greening plants between 24 and 48 hrwhile activities of achlorophyllous plants decreased markedly.These decreases could not be explained by a toxic accumulationof nitrite. Continuous far-red light (FR), which causes pronouncedphotomorphogenic development without significant greening, inducedabout one-half as much NR in the mesocotyls as did continuouswhite light. In apical tissues the effects of W and FR weresimilar throughout a 72 hr time course. Although trends weresimilar, the effects of light (W and FR) on nitrate concentrationwere kinetically different from effects on NR activity. Theseresults indicate that photosynthetic pigments are only secondarilyinvolved in NR induction. (Received June 12, 1979; )     

Increase in Nitrate Reductase Activity in Bean Leaves by Light Involves a Regulator Protein

Nitrate reductase activity, assayed either in vivo or in vitro was considerably higher in bean (Phaseolus vulgaris L.) leaves from 7-day-old light grown seedlings than those from dark grown, both in the absence as well as presence of nitrate. Cytochrome c reductase activity was however similar in both regimes, while peroxidase was lower in light than in dark. The light stimulated increase in nitrate reductase activity in leaf segments from dark grown seedlings was inhibited by cycloheximide, DNP, chloramphenicol, and sodium tungstate and was unaffected by lincomycin and DCMU. Under similar conditions, the increase in total chlorophyll was inhibited completely by cycloheximide and DNP, partially by chloramphenicol and lincomycin, and was unaffected by tungstate and DCMU. A supply of 1~5 mm reduced glutathione increased enzyme activity in the dark and also to some extent in light. The substrate induction of enzyme activity started after a lag of one hr in light or dark and continued for either 5 hr in the dark or 8 hr in light. Two proteinaceous inhibitors (Factors I and II) of nitrate reductase were isolated by ammonium sulfate precipitation and Sephadex gel filtration. The amount of Factor I was higher in the dark than in light. The amount and activity of Factor II was however, almost equal in light and dark. The inhibition of enzyme activity by these inhibitors increased with their concentration. It is proposed that light increases nitrate reductase activity by decreasing the amount of a nitrate reductase inhibitor.     

Phytochrome Regulation of Nitrite Reductase--a Chloroplast Enzyme--in Etiolated Maize Leaves

Nitrite reductase in the excised etiolated leaves of maize showedthe photoreversibility by red and far-red light. Five minutesof red light illumination lead to a 130% increase in the enzymeactivity which was reversed by far-red light. The kinetics ofnitrite reductase activity under continuous far-red light showeda lag phase of 1 hr. (Received January 17, 1981; Accepted February 20, 1981)     

Carnitine requirement of vascular endothelial and smooth muscle cells in imminent ischemia

Rats were subjected to bilateral carotid artery occlusion for 30 min, followed by reperfusion for varying time periods. The concentration of reduced and oxidized glutathione, glutathione peroxidase and glutathione reductase were determined in whole brain after varying periods of reperfusion. Lipid peroxidation was also assessed by determining the levels of malondialdehyde (MDA) in the brain. Reperfusion for 1 hr following bilateral carotid artery occlusion resulted in significant decrease in total glutathione (GSH) concentration along with small but significant increase in oxidized glutathione (GSSG) levels. After 4 hr of reperfusion, GSH levels recovered, although GSSG levels remained elevated up to 12 hr of reperfusion. Increase in malondialdehyde levels was also detected in the brain up to 12 hr of reperfusion. Glutathione reductase activity remained significantly low up to 144 hr of reperfusion, while glutathione peroxidase activity remained unaffected. These results demonstrate that oxidative stress is generated in the brain during reperfusion following partial ischemia due to bilateral carotid artery occlusion.     

Effect of different light-dark schedules on survival from heart failure

Our earlier work showed that life in constant light prolonged life for hamsters with an inherited cardiomyopathy when compared to littermates spending their lives in 24 hour days (lights on 12 hr each day). This study was designed to begin evaluating the mechanism for this effect. 4-5.5 month old cardiomyopathic hamsters (CMHs) were placed on one of 5 different light-dark (LD) schedules for the remainder of their lives: (1) LD 12:12 (moderate total light exposure, short photoperiodic effect, 24 hr daylength); (2) LD 12:13 (same total light as LD 12:12, long photoperiodic effect, non-24 hr daylength); (3) LD 6:30 (less total light than LD 12:12, long photoperiodic effect, non-24 hr daylength); (4) LD 18:6 (more total light than LD 12:12, long photoperiodic effect, 24 hr daylength); (5) constant light (high total light exposure, long photoperiodic effect, non-24 hr daylength). CMHs living on the first two non-24 hr schedules lived longer than LD 12:12 controls. This study therefore suggests that manipulating the biological clock can have positive therapeutic consequences. However, in contrast to our earlier studies, hamsters living in constant light were not protected--perhaps because the hamsters began the treatment later in their lives or because their inherited disease was less severe than had been the case in hamsters used in previous studies. Defining the conditions that diminish or enhance the photobiological effect is an important challenge for future research.     

Studies on the vegetative life cycle of Chlamydomonas reinhardi Dangeard in synchronous culture I. Some characteristics of the cell cycle

Cells of Chlamydomonas reinhardi Dangeard were grown synchronouslyunder a 12 hr light-12 hr dark regime. Time courses of nucleardivision, chloroplast division, "apparent cytokinesis" and zoosporeliberation were followed during the vegetative cell cycle inthe synchronous culture. Liberation of zoospores occurred atabout 23–24 hr after the beginning of the light periodat 25°C. Four zoospores were produced per mother cell underthe conditions used. At lower temperatures, the process of zoosporeliberation as well as length of the cell cycle was markedlyprolonged, but the number of zoospores produced per mother cellwas approximately the same. At different light intensities,lengths of the cell cycle were virtually the same, while thenumber of zoospores liberated was larger at higher rather thanat lower light intensities. During the dark period, nuclear division, chloroplast divisionand apparent cytokinesis took place, in diis order, and proceededless synchronously than did the process of zoospore liberation.When the 12 hr dark period was replaced with a 12 hr light periodduring one cycle, the time of initiation as well as the durationof zoospore liberation was litde affected in most cases, whereasnuclear division, chloroplast division and apparent cytokinesiswere considerably accelerated by extended illumination. Whenalgal cells which had been exposed to light for 24 hr were furtherincubated in the light, zoospore liberation started much earlierand proceeded far less synchronously, compared with that under12 hr light-12 hr dark alternation. (Received October 12, 1970; )     

Comparative stability of ammonium- and nitrate-induced nitrate reductase activity in maize leaves

Ammonium sulfate (5 mM) had no effect on nitrate reductase activity during a 3 hr dark incubation, but the enzyme was increased 2.5-fold during a subsequent 24 hr incubation of the maize leaves in light. The enzyme activity induced by ammonium ion declined at a slower rate under non-inducing conditions than that induced by nitrate. The decline in ammonium stimulated enzyme activity in the dark was also slower than that with nitrate. Further. cycloheximide accelerated the dark inactivation of the ammonium-enzyme while it had no effect on the nitrate-enzyme. The experiments demonstrate that increase in nitrate reductase activity by ammonium ion is different from the action of nitrate action.     

Orcadian Manifestations of Barbiturate Habituation, Addiction and Withdrawal in the Rat

The thermal acrophase for the circadian oscillation of core temperature in Charles River male rats fed ad libitum and entrained by light (12 hr dim light and 12 hr bright light) (DL12: 12 hr) occurred near the middle of the dim phase on a control diet of 30+ protein. Dietary phenobarbital (0.25+) caused an increase in amplitude of the oscillation (from 0.7° to 1.2°C) and a phase-angle difference (ψ-advance) between the zeitgeber and the biological oscillation of about 32°, equivalent to an advance in the thermal acrophase of 2.1 hr in the steady-state. Food consumption was monitored continually and was nearly the same in the two groups; however, animals on the control diet ate around the clock, albeit at a greater rate during dim light than during the bright light phase, whereas rats on phenobarbital started to eat earlier and confined their feeding almost exclusively to early dim phase. This pattern of increase in amplitude of the thermal oscillation and of feeding closely resembling programmed feeding, persisted in phenobarbital-treated animals even in the absence of a dim light-bright light (DL) zeitgeber for eight days. Similar behavior was seen in rats entrained by illumination cycles of 17 hr of dim light and 7 hr of bright light, but with this reduced phase ratio for the zeitgeber, few (ψ-shifts occurred, and these were smaller than those induced in the group receiving 12 hr of dim light and 12 hr of bright light. In each group, introduction of the drug into the diet and, even more noticeably, removal of the drug from the diet, induced transients of circadian dyschronism that persisted for 4-5 days.     

Lack of correlation between 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and lovastatin resistance in nerve growth factor treated PC-12 cells

Summary 1. The relationships among the mevalonic acid (MVA) forming enzyme, 3-hydroxy-3-methylglutaryl coenzyme A (CoA) reductase, cell growth and differentiation, and the cytotoxic effects of the reductase inhibitor lovastatin were studied in PC-12 cells, exposed to growth factors.2. When added individually, nerve growth factor (NGF), basic fibroblast growth factor, and epidermal growth factor induce an increase in HMG-CoA reductase activity in cells grown in serum-containing medium. In the presence of serum, the effect of NGF on HMG-CoA reductase is persistent.3. Short-term serum starvation and long-term NGF treatment, in combination, have an additive effect, resulting in a high reductase activity.4. Unlike serum and MVA, which downregulate levels of HMG-CoA reductase by accelerating its degradation, NGF upregulates reductase by slowing the rate of its degradation. This mechanism, however, appears to operate only in the presence of serum, as after prolonged growth with NGF in serum-free medium, cells have a low reductase activity.5. PC-12 cells grown in the absence of NGF are highly sensitive to lovastatin (25 µM) and more than 70% of the cells die after 48 hr. NGF confers lovastatin resistance on cells grown in the presence or in the absence of serum (only 30–40% cell death after 48 hr with lovastatin).6. NGF-induced resistance on lovastatin develops with time and is apparent only in the well-differentiated PC-12 cells whether or not the cells express a high reductase activity.7. Thus, levels of HMG-CoA reductase activity and lovastatin resistance in PC-12 cells are not directly correlated, though clearly inversed lovastatin cytotoxicity and elevated reductase activities are expressed during the period of cell proliferation.8. These data suggest that fully differentiated neuronal cells may not be affected by prolonged high doses of lovastatin.     

Synchronization of motor activity in young pigs to a non-circadian rhythm without affecting food intake and growth

The influence of length of light:dark cycle on motor activity, food intake and growth has been investigated in young pigs subject to either 12 hr light:12 hr dark, or 9 hr light:9 hr dark. Motor activity was positively correlated with the light phase in both groups. No differences were found in growth rate or in the average amount of food eaten in a 72 hr period between the two treatments. Body conformation and composition were also similar. Thus, unlike many other mammals the young pig can synchronize its activity to a non-circadian rhythm. Moreover, this does not affect growth.     

Circadian rhythm resetting in sparrows: early response to doublet light pulses

Circadian responses were studied using the perching activity of house sparrows (Passer domesticus). The sparrows were subjected to single or double 4-hr light pulses (the single pulses or the second pulses of the doublets scanned 24 hr) in the first cycle after previous entrainment to a light-dark cycle (LD 12:12). The differences in times at which the birds commenced perch-hopping in LD 12:12 before the pulses and in the five cycles immediately following the pulses were determined (phase shifts). A 24-hr time profile for phase shifts in response to single light pulses replicated our previous study: Early-night pulses delayed the rhythm (-1.7 hr), while late-night pulses advanced the rhythm (+3.8 hr). After pretreatment with a light pulse that advanced the birds +2.7 hr, the resetting curve was advanced. There were no delays; the range of average shifts was +0.1 hr to +6.2 hr. After pretreatment with a light pulse that delayed the birds -1.7 hr, the resetting curve was delayed. Average delays as much as -1.1 hr and advances up to +2.1 hr were measured. The data for double pulses were interpreted from predictions made from single-pulse data.     

Temporal variation in the effects of warfarin on the vitamin K cycle

In this in vivo study, the time-dependent effect of oral sodium warfarin was studied in male rats synchronized under a 12-hr light-dark cycle (light 0600-1800). Groups of 5 animals received an oral dose of 500 micrograms/kg of warfarin or saline at 0600 or 1800 and 1 mg/kg of vitamin K 8 hr later and the rats were sacrificed 240 min after vitamin K administration. The activities of the vitamin K reductase and vitamin K epoxide reductase were measured indirectly by determining the content of vitamin K1 and vitamin K epoxide reductase in the plasma and liver. The data obtained in control rats indicated that vitamin K and vitamin K 2,3 epoxide concentrations in plasma and liver were higher (P less than 0.05) at 1800 than at 0600. Warfarin had a greater (P less than 0.05) inhibitory effect on the vitamin K and vitamin K-epoxide reductases at 0600 compared to 1800; plasma levels of S- and R-warfarin did not vary with time of administration. The findings suggest that the activity of both reductases under control conditions, and the warfarin-induced inhibition of these enzymes varied depending on the time of drug administration.     

Effect of a light pulse during the dark on photoperiodic regulation of the rate of thyroxine-induced, spontaneous, and prolactin-inhibited metamorphosis in Rana pipiens tadpoles

Since Rana pipiens tadpoles injected with thyroxine (T4) early in the dark develop more slowly than those injected in the light, we studied the effect of giving a light pulse of 1 hr early in the dark. Tadpoles injected under a 7.5-W red light bulb in a darkened room with 0.2 microgram T4 daily at 2200 hr went through metamorphosis faster on a 12L:3D:1L:8D cycle with a light pulse after injection than on a 12L:12D cycle without a light pulse, and even faster on a 12L:1.5D:1L:9.5D cycle with a light pulse before the injection. Thus a 1-hr light pulse counteracted the metamorphic delay resulting from administration of T4 in the dark, and set in motion the conditions that resulted in a more rapid response to an injection of T4. However, a 1-hr light pulse in the early dark had no effect on growth and development of older or younger untreated tadpoles or those constantly immersed in 30 micrograms/liter T4. Larvae on 21L:3D with T4 injection in the dark and on 12L:3D:1L:8D with T4 injection at 0700 hr just before the start of the main light phase progressed faster than 12L:3D:1L:8D with injection at 2200 hr in the dark before only a 1-hr light pulse. Thus the length of the light phase immediately after T4 injection was significant. There was no difference on 12L:12D and 12L:3D:1L:8D cycles in the effectiveness of daily injections of 10 micrograms prolactin (PRL) in the early dark at 2200 hr in promoting tail growth or antagonizing tail resorption induced by T4 immersion. Under these conditions, PRL utilization did not appear to be inhibited by the light pulse.     

Insect photoperiodism: diversity of results in night-break experiments, including nonresponsiveness to light

Three night-break experiment protocols were utilized in an attempt to help clarify the role of the circadian system in photoperiodic time measurement in the European corn borer, Ostrinia nubilalis. Larvae raised in a light-dark (LD) cycle consisting of 12 hr of light alternating with 12 hr of darkness (LD 12:12), at a constant temperature of 30 degrees C, enter a state of arrested growth and development known as diapause (Takeda and Skopik, 1985). In the present research (Experiment 1), the induction of diapause was prevented by 1-hr light pulses that systematically scanned the dark phase of LD 12:12. Thus, the importance of 12 hr of uninterrupted darkness for maximal induction of diapause is stressed. The same experimental protocol applied to larvae already in diapause (Experiment 2), however, resulted in a bimodal curve of diapause termination. Although this result is consistent with the proposition that a nonperiodic hourglass timer underlies this event (Skopik and Takeda, 1986), it does not rule out the circadian system. Like LD 12:12, a thermoperiod in constant darkness (12 hr at 4 degrees C alternating with 12 hr at 25 degrees C) also induces diapause. Scanning such a thermoperiod with 1-hr light pulses, however, resulted in only a small effect (reduction of diapause) when light fell in the early to middle part of the warm phase (Experiment 3). Thus, the time-measuring system, under these experimental conditions, showed only a weak response to light. This unexpected result is discussed with respect to Experiment 1 and two general models that have been proposed to account for photoperiodic time measurement in insects.     

Influence of cytokinins and phytochrome on nitrate reductase activity in etiolated leaves of maize

Of the different hormones tested, cytokinins stimulated nitrate-induced nitrate reductase (NR) activity in the dark. The optimal stimulation was obtained at 16 hr and this was sensitive to tungstate, 6-methylpurine and cycloheximide. The cytokinin stimulation of NR activity was further enhanced by brief irradiation with red light, but this effect was not noticed when leaves were exposed to far-red light. Both kinetin and red light, when given together, or given with a darkness interruption, stimulated the NR activity more than with either of them alone.     

Continuous Darkness Stimulates Body Growth of the Juvenile Giant Freshwater Prawn, Macrobrachiumrosenbergiide Man

-The effect of photoperiod on growth of juvenile giant freshwater prawns, Macrobrachium rosenbergii de Man, was tested. The prawns were divided into four groups and each group was reared under one of the following light-dark conditions: continuous darkness (L0:D24), 12 hr light: 12 hr dark (L12:D12), 16 hr light: 8 hr dark (L16:D8), and 20 hr light: 4 hr dark (L20:D4). Body size was determined at the age of 45, 75, and 110 days by measuring total length, orbital length, and carapace length; body weight was determined at the age of 110 days. At 110 days of age, the prawns reared under L0:D24 photoperiod were significantly longer and heavier than those reared under other light-dark conditions. The survival rate of the prawns reared under L0:D24 photoperiod was also higher than that of other groups. This study indicates a positive effect of continuous darkness on growth and survival rate of juvenile giant freshwater prawns, M. rosenbergii.     

Intestinal HMG-CoA reductase activity is low in hypercholesterolemic patients and is further decreased with lovastatin therapy

Significant cholesterol synthesis occurs in gut mucosa of animals and humans. However, the role of gut synthesis in hypercholesterolemia and the effect of drugs on this function have not been defined. We obtained jejunal biopsies and bile samples from 21 Type II hypercholesterolemic subjects (mean serum cholesterol = 331 mg/dl) on a low fat diet after an over-night fast. Whole gut mucosal homogenate was assayed for activity of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, the rate-determining enzyme of cholesterol synthesis. Mean reductase activity (pmol/mg per min) was 5.5 +/- 1.0 (n = 21) in hypercholesterolemic subjects versus 11.3 +/- 1.0 in 52 normal subjects (P less than 0.01). This is consistent with the hypothesis that the primary defect in these patients is not excessive cholesterol synthesis but decreased low density lipoprotein (LDL) clearance. It implies that high LDL levels down-regulate gut reductase activity. After treatment of 7 patients with lovastatin (40-80 mg/day for at least 6-13 weeks), gut reductase activity decreased from 7.7 +/- 2.6 to 3.6 +/- 0.5 (P less than 0.05), in biopsies obtained 12 hr after the last drug dose. Inhibition of reductase activity by this drug was detected 12 hr after a dose, and the enzyme was not measurably induced during 6-13 weeks of therapy. In keeping with the decrease in serum cholesterol (332----239 mg/dl) and mucosal reductase activity during lovastatin therapy, mean gallbladder bile cholesterol saturation index also decreased (1.045 +/- 0.112 vs. 0.883 +/- 0.109, n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influences of some internal and external conditions on the induction of nitrate reductase in rice seedlings

Induction of nitrate reductase (NR) in 7-day-old rice seedlingswas depressed when endosperms were removed. NR activity in theseedlings from which endosperms were removed (deendospermedseedlings), reached a maximum 6 hr after supplying NaNO₃ andthen gradually decreased. That in intact seedlings continuedto increase for 12 hr, and then decreased fairly rapidly. Sucrose(30 mM concentration) supplied exogenously to deendospermedseedlings raised NR activity to the level of the intact seedlings.Macronutrients added exogenously did not show such an effect. NR activity in deendospermed seedlings placed in the dark wasextremely low. However, in the presence of exogenous sucrose,the activity was raised to the same level as that in the lightin the absence of exogenous sucrose. This suggests that sucrosesubstitutes for light in the induction of NR in deendospermedseedlings. Protein inhibitors suppressed NR induction when theplants were fed continuously with nitrate solution containingthe inhibitor. In cases where the plant roots were immersedin inhibitor solutions for 2 hr before transfer to nitrate solution,only chloramphenicol promoted and the others inhibited NR induction.NR induction was also suppressed by respiratory inhibitors,of which sodium azide was very potent. (Received August 25, 1976; )     

Circadian locomotor activity rhythm under the influences of temperature cycle in the Djungarian hamster, Phodopus sungorus, entrained by 12 hour light-12 hour dark cycle

Effects of temperature cycle (25 degrees C during light and 10 degrees C during dark) on circadian locomotor activity rhythm entrained by 12 hr light-12 hr dark cycle were studied in the dark active Djungarian hamster. The amounts of activity per 24 hr were significantly greater under temperature cycle than under constant temperature of 25 degrees C. Phase angle difference between activity onset and light off was always more positive under temperature cycle than under constant temperature. These findings are discussed in terms of circadian physiology.     

Intact plastids are required for nitrate- and light-induced accumulation of nitrate reductase activity and mRNA in squash cotyledons

Induction of nitrate reductase activity and mRNA by nitrate and light is prevented if chloroplasts are destroyed by photooxidation in norflurazon-treated squash (Cucurbita maxima L.) cotyledons. The enzyme activity and mRNA can be induced if norflurazon-treated squash seedlings are kept in low-intensity red light, which minimizes photodamage to the plastids. It is concluded that induction of nitrate reductase activity and nitrate reductase mRNA requires intact plastids. If squash seedlings grown in low-intensity red light are transferred to photooxidative white light, nitrate reductase activity accumulates during the first 12 hours after the shift and declines thereafter. Thus photodamage to the plastids and the disappearance of nitrate reductase activity and mRNA are events separable in time, and disappearance of the enzyme activity is a consequence of the damage to the plastids.