Continuous Low-intensity Light Research Articles

Effect of visible light treatments on postharvest senescence of broccoli (Brassica oleraceaL.)

Broccoli (Brassica oleracea L.) is a rapidly perishable vegetable crop. Several postharvest treatments have been applied in order to delay de-greening. Since light has been shown to have an effect on pigment accumulation during development and darkness is known to induce senescence, the effect of continuous and periodic exposure to low-intensity white light at 22 °C on postharvest senescence of broccoli heads was assayed. Exposure to a constant dose of 12 micromol m(-2) s(-1) was selected as the most suitable treatment and was employed for subsequent experiments. During the course of the treatments, hue and L* values as well as chlorophyll content and visual observation of florets indicated an evident delay in yellowing in treated samples compared with controls. No statistically significant differences in total protein content were found, but soluble protein content was higher in treated samples. Total and reducing sugar as well as starch levels decreased during postharvest senescence, with lower values in control samples. The results of this study indicate that storage under continuous low-intensity light is an efficient and low-cost treatment that delays postharvest senescence while maintaining the quality of harvested broccoli florets.

Quantitative trait loci (QTL) for circadian rhythms of locomotor activity in mice

The locomotor activity of male mice (Mus musculus) was monitored by infrared photo-electric beams under three lighting regimens: LD (12 h of light and 12 h of dark), DD (constant dark), and LL (constant broad-spectrum light, 10 lux). Circadian period of locomotor activity (tau) was compared among 3 inbred strains of mice, C57BL/6J (B6), BALB/c (C), and DBA/2J (D2), and 26 recombinant inbred strains B x D (B6 x D2). The tau under both continuous low-intensity light and continuous darkness varied significantly among strains. Under DD the mean tau was 23.8 h for B6, 23.7 h for D2, and 23.6 h for C. Under LL the mean tau was 25.1 h for B6, 23.9 h for D2, and 25.5 h for C. Frequency histograms of the mean tau of 26 B x D RI mouse strains (three to seven animals per strain) in either DD or LL and the difference between them, delta tau, had distributions which appeared unimodal, suggesting polygenic inheritances. The narrow-sense heritability determined using 26 strains of B x D RI mice was about 55% for tau and about 38% for both tau in LL and delta tau. An estimated four loci contribute to the variance of tau in constant darkness and five to the variance of tau in constant low-intensity light among the strains studied. Quantitative trait locus (QTL) analysis identified several potential genetic loci associated with tau in constant darkness, tau in constant low-intensity light, and delta tau. The associations of highest probability for each of these traits were the D1Nds4 locus (p < .001) on mouse chromosome 1, the D5Ncvs52 locus (p < .05) on mouse chromosome 5, and the Pmv12 locus (p < .01) at 70 cM on mouse chromosome 5, respectively. A QTL identified for tau was associated (p < .05) with the D2NDS1 marker at 45 cM on chromosome 2 near the Ea 6 marker at 46 cM associated (p < .05) with that reported for the period of wheel running activity in seven C x B RI strains (Schwartz, W.J., and Zimmerman, P., J. Neurosci. 10:3685 1990).

The development of carotenoid-deficient membranes in plastids of barley seedlings treated with norflurazon

The effect of carotenoid (Car) deficiency on the formation of thylakoid membranes in barley seedlings grown with norflurazon (NF) was investigated. To exclude photodestruction during the growth of Car-deficient seedlings, the etiolated seedlings were illuminated for 24 h with 2.5 ms flashes every 12 min. The morphometric analysis of seven main ultrastructural parameters of plastids control and NF-treated seedlings was carried out. The length of one partition and the number of partitions per plastids section, which characterize the initial stages of stacking, showed no difference in etiolated NF-treated and control seedlings. Compared with the control, the number of partitions was considerably lower in those plastids of Car-deficient seedlings which, after flash illumination, were kept for 1.5 h in continuous light of low intensity. The photobleaching of chlorophyll (Chl) in post-illuminated seedlings provides an indication of the photodestructive processes in Car-deficient seedlings exposed to low-intensity light. Chl bleaching did not appear in Car-deficient seedlings illuminated only with flashes; however, the stacking of the membranes was disturbed: the partition lengths and number of partitions per plastid section were higher in flashed, non-treated seedlings than in Car-deficient seedlings. Although the flashed control and NF-treated seedlings had an equal amount of Chl and the same polypeptide composition, no activity of photosystem II (PSII) and no PSII reaction centre complex were found in NF-treated seedlings. Car-deficient seedlings mainly contained photosystem I (PSI) with a ratio of Chl to P700 of 60 compared with 150 in the control. It is therefore suggested that Car deficiency in flashed leaves, which may accumulate only a small amount of light-harvesting Chl a b protein, prevents the assembly of the PSII complex and membrane stacking.

Tail Regeneration in Normal, Blinded and Pinealectomized Gekkonid Lizards, Hemidactylus flaviviridis, Exposed to Four Different Light Conditions During Three Seasons (Temperatures)

AbstractTail regeneration was followed for 60 days in 1470 normal (NL), blinded (BL) and pinealectomized (PX) gekkonid lizards, Hemidactylus flaviviridis, fed on cockroaches ad libitum and exposed to continuous light of high intensity (2500 lux), continuous light of low intensity (638 lux), 12 h of light (high intensity) and 12 h of darkness and continuous darkness in summer (March – May; cage temperature 30°C) monsoon (August – October; cage temperature 26°C) and winter (November – January; cage temperature 17°C) seasons. A comparative assessment of the new growth (regenerate) showed that the initiation of regeneration, the daily growth, the total length of tail replaced at the end of regeneration and the total percentage replacement of the lost (autotomized) tails were all enhanced by continuous light and depressed by continuous darkness. Furthermore, there was no significant difference between any of the parameters in NL and BL Hemidactylus; however, PX lizards generally showed retardation in the regeneration process. Seasonal differences in tail regeneration were noted—the best regenerative performance was obtained during the summer months and the worst during the winter months, with the regenerative performance during the monsoon season in between. Thermal and photoperiodic influences on tail regeneration in lizards are discussed.

Effect of Alternating Lights and Strain on Behavior and Leg Disorders of Roaster Chickens

The effects of light treatment and strain on movement, spacial distribution, activity, and incidence of leg disorders of 4 to 10-week-old male chickens were examined in two experiments. In both, an alternating light treatment, in which high-intensity light alternated from one side of the barn to the other against a background of low intensity light, was compared with a control light treatment of continuous low intensity light supplied to both sides of the barn. Two strains were tested in each experiment.In Experiment 1, chickens responded to the alternating light between 4 and 7 weeks of age, although not between 7 and 10 weeks of age, by moving into areas of relatively high intensity light. In Experiment 2, chickens responded during both periods by moving into areas of relatively low intensity light. Bird distribution was also affected by a geographical side preference.In both experiments, activity was higher in areas of high vs. low light intensity, higher under alternating than control light, and higher for younger than older birds (P<.05). Activity was also influenced by strain (P<.01). Incidence of leg disorders was influenced by strain (P<.01) but not light treatment.

Extended exposure to continuous low intensity light abolishes the photosensitivity of retinal dopamine neurons

Male Sprague-Dawley rats were divided into 2 groups. One group (experimental) was housed for 6 months in continuous low intensity light while the other (control) was exposed to standard 14 hr light: 10 hr dark cyclic lighting conditions for the entire time. For both the control and experimental groups the light intensity was 350–700 Lux. After 6 months, the experimental rats were returned to cyclic lighting. At one week and again at 2 months the light aversion behavior of all rats was tested in a light/dark test box. The experimental rats chose the dark side of the box only 58% of the time while control animals preferred the dark 79% of the time. Since rats normally are nocturnal and avoid light, these results suggest that the experimental rats may have permanently lost a functionally significant portion of the ability to detect light. After the second behavioral test all rats were dark adapted and 15 hr later the effect of short term (30 or 60 min) exposure to light on DA turnover in one retina from each rat was assessed. The other retina from each rat was fixed and examined histologically. Light significantly enhanced the α methyl-p-tyrosine induced decline of DA in the retinas of the control rats but exerted no similar effect in the experimental animals. The retinal DA contents of the experimental rats were substantially depleted. Histological examination suggested that the outer nuclear layers of the experimental retinas were more severly damaged than those from rats exposed to continuous light for 4 months but still contained a few pycnotic photoreceptor nuclei and nearly normal looking inner neural layers. These results indicate that extended exposure to light eventually abolishes light aversion behavior and at this time there is also a loss of the photosensitivity of the dopaminergic amacrine neurons.

Dopaminergic amacrine neurons of rat retinas with photoreceptor degeneration continue to respond to light

Exposure of albino rats to continuous light of low intensity (350–700 lux) for 4 months produces massive degeneration of the photoreceptor segments and cell bodies of the outer nuclear layer of the retina. Only a few heterochromatic, receptor cell nuclei remain, and no photoreceptor segments are present. On the other hand, the inner layers of these retinas remain morphologically intact. The inner nuclear layer of the normal rat retina contains a group of amacrine cells which contain the putative neurotransmitter, dopamine (DA). Short term exposure to light (30 or 60 min) markedly stimulates the rate of DA turnover in these cells in normal, previously dark-adapted rats. Such enhancement of the rate of neurotransmitter turnover in the brain has been correlated with an increase in nerve impulse activity. The present study was undertaken to determine if the dopaminergic amacrine cells of the inner nuclear layer were still responsive to light in the retinas of rats whose photoreceptors were previously destroyed by long term exposure to continuous illumination. One week before sacrifice, the animals which had been housed in continuous light for 4 months were returned to normal 14 hr light: 10 hr dark lighting conditions. At the end of this time they and a group of control rats which had been housed in cyclic lighting conditions for the entire 4 months were dark adapted for approximately 15 hr. Then the rate of retinal DA turnover was estimated from the depletion of DA following inhibition of DA synthesis by α methyl para-tyrosine. The turnover of DA in the dark-adapted retinas of the control rats and of experimental rats with photoreceptor degeneration was dramatically enhanced 2–4 fold by short term exposure (up to 1 hr) to light. Since rats are nocturnal and avoid light, we tested the light aversion of another group of rats which had been exposed to light for 4 months and then returned to cyclic lighting conditions for one week. These rats and control animals which had been maintained in cyclic lighting conditions for 4 months both chose the dark side of a light-dark box over 80% of the time. This behavior of the rats with retinal degeneration was taken as a crude indication of their continued ability to detect light. The light-induced increase in DA activity in retinas with photoreceptor degeneration may play a role in the continued ability of these rats to perceive light.

Studies of the pathogenic mechanisms of light on rat retina.

The effects of low-intensity light on the rat retina was investigated by light, transmission and scanning electron microscopy. The earliest signs of light damage were observed in the retinal pigment epithelium (RPE) of albino rats after 24 h of exposure to 35 footcandles of fluorescent light at room temparature (24 °C). These changes included an increase in the electron density of the cytoplasmic matrix, modifications of the endoplasmic reticulum, changes in the number and distribution of lysosomes and changes in the number and size of apical processes and their population of inclusions. Newly phagocytized outer segments were not seen in the RPE whereas large numbers of condensed lamellated inclusions had accumulated. This suggested that damaged RPE is unable to phagocytize outer segments and to digest previously phagocytized outer segments as a result of changes in the endoplasmic reticulum and the phagolysosomal system. Pigmented rats were more resistant to light damage than albino rats; when exposed to the same continuous low-intensity light of 35 footcandles for 4 weeks, pigmented rats developed remarkable alterations in the RPE without any morphological changes in the photoreceptor cells or their outer segments. The initial site of light damage was apparently in the RPE. The early extensive changes in RPE indicated the disruption of normal metabolic activities in the RPE; the subsequent alterations of the RPE-photoreceptor metabolic equilibrium is probably the initial step of photic retinal damage induced by low-intensity light.

Effect of continuous low-intensity light on the lysosomal enzymes in the retina of albino rats

Lysosomal enzyme activities in the retina of albino rats following the exposure to continuous low-intensity light were studied biochemically. The total and free acid phosphatase and β-glucuronidase activities in the continuously exposed neuroretina were higher than those in the control neuroretina exposed to a diurnal rhythm of light. The highest activities were observed in the 9 day-exposed retina. Total and free cathepsin D activities in the retinal pigment epithelium and choroid in experimental eyes were also higher than those in the control tissues exposed to a diurnal rhythm of light. It is suggested that lysosomal enzymes are involved in the damaging process of the continuously exposed retina.

The Influence of Dietary Energy on the Performance of Broilers Reared Under Different Lighting Regimes

Body weights and feed conversions of male broilers reared under different light regimes and fed diets containing varying nutrient densities were compared. Broilers subjected to continuous light with alternate intervals of high and low-intensity had significantly lower 49-day body weights when compared with broilers subjected to continuous low-intensity or intermittent light regimes. Feed conversion comparisons followed a similar pattern. Intermittent light regimes improved neither body weight nor feed conversion when compared to continuous low-intensity illumination.Broilers fed diets containing 3080 kcal of metabolizable energy per kg of starter diet (24.0% protein) and 3135 kcal per kg of finisher diet (22.0% protein) had significantly poorer body weights and feed conversions than did broilers fed diets containing metabolizable energy levels of 3160 (24.8% protein), 3300 (25.6% protein), and 3410 (26.4% protein) kcal per kg of starter diet and 3245 (22.8% protein), 33 55 (23.6% protein), and 3465 (24.4% protein) kcal per of finisher diet. There was also a significant light regime-nutrient density interaction for body weight. Diets containing higher nutrient densities resulted in increased body weights when fed to broilers reared under continuous low-intensity light but did not increase the performance of broilers subjected to the other light regimes.

Rhodopsin content and electroretinographic sensitivity in light-damaged rat retina.

EXPOSURE of rats to continuous illumination leads to cellular deterioration within the retina and a concurrent reduction of electroretinogram (ERG) responses1,2. Grignolo et al.3 showed that at early stages, this ‘damage’ due to light is hypertrophic in that tubules and vesciculae appear in receptor cell outer segments. They surmised that losses in retinal functioning are initially due to disorganisation rather than degeneration. But, experiments on recovery from light damage2 indicate that ERG sensitivity returns as the rhodopsin-containing disks of the outer segments are regenerated even though their original lamellar structure is not restored. It is thereby implied that as long as visual pigment is present at functional sites, the normal structure of the outer segments may not be crucial to ERG responsivity. Here we describe an experiment which quantitatively examines the role of visual pigment remaining in the albino rat retina which has been exposed to continuous low-intensity light. The ERG sensitivity, rhodopsin content and morphological state of the retina were assessed for various exposure durations. Our findings indicate that reductions in visual pigment levels due to constant light persist indefinitely in the dark. Furthermore, the log ERG (b wave) sensitivity varied directly with the rhodopsin content of exposed retinas even as progressive deterioration was apparent. With respect to this log–lienar relationship, light damage resembles ‘normal’ light adaptation due to short term bleaching exposure.

Determination of [formula omitted] ratios in chloroplasts with flashing light

Using a rapid pH electrode, measurements were made of the flash-induced proton transport in isolated spinach chloroplasts. To calibrate the system, we assumed that in the presence of ferricyanide and in steady-state flashing light, each flash liberates from water one proton per reaction chain. We concluded that with both ferricyanide and methylviologen as acceptors two protons per electron are translocated by the electron transport chain connecting Photosystem II and I. With methyl viologen but not with ferricyanide as an acceptor, two additional protons per electron are taken up due to Photosystem I activity. One of these latter protons is translocated to the inside of the thylakoid while the other is taken up in H 2O 2 formation. Assuming that the proton released during water splitting remains inside the thylakoid, we compute H + e − ratios of 3 and 4 for ferricyanide and methyl viologen, respectively. In continuous light of low intensity, we obtained the same H + e − ratios. However, with higher intensities where electron transport becomes rate limited by the internal pH, the H + e − ratio approached 2 as a limit for both acceptors. A working model is presented which includes two sites of proton translocation, one between the photoacts, the other connected to Photosystem I, each of which translocates two protons per electron. Each site presents a ≈ 30 ms diffusion barrier to proton passage which can be lowered by uncouplers to 6–10 ms.

Influence of moisture supply, temperature, and light on frost-hardiness changes in Douglas-fir seedlings

Effects of moisture supply, temperature regime, and light on frost-hardiness changes in 2-year-old Douglas-fir seedlings were studied. Frost-hardiness was measured by an electrolytic method. Eight-hour light (3000 ft-c) periods caused increase in hardiness, compared with 16-hour light periods, when seedlings grew under a 12-hour day/night temperature regime of 13 °C/7.5 °C. Long days retarded development of hardiness, under otherwise natural conditions in autumn, but did not prevent plants becoming frost-hardy later. Moisture supply had no direct effect on hardiness, although low supply may have reduced response to photoperiod. Development of hardiness was dependent on night temperature when day and night temperatures were in the range 7.5°–24 °C, and lower night temperatures favored hardening. Loss of hardiness was not influenced by photoperiod.Seedlings did not harden in darkness at 2.5 °C over 9 weeks, but hardening occurred if low intensity light (40 or 100 ft-c) was provided. Continuous low-intensity light caused more hardening than 8-hour light periods, and 100 ft-c caused more hardening than 40 ft-c. An exception was that seedlings previously exposed to 16-hour high-intensity photoperiods showed some ability to harden in darkness.Factors important in development of frost-hardiness were day length, night temperature, and light. Only temperature affected loss of hardiness.

Die Tagesperiodik der Photosynthese bei Acetabularia und ihre Abhängigkeit von Kernaktivität, RNS- und Protein-Synthese

Normal and enucleate cells of the unicellular marine alga Acetabularia crenulata showed a diurnal rhythm of photosynthesis when cultivated in a 12 hour cycle of light and dark; it is characterized by a maximum and a minimum value of photosynthetic capacity in the middle of the light and the dark period respectively. In cells which had been raised from zygotes in continuous light, and from which the nucleus had been removed by severing the basal rhizoid before exposure to the 12 hour light-dark schedule the typical photosynthetic rhythm occurred. Obviously the nucleus is not essential for the induction and the maintenance of the latter. In aged enucleate cells the rhythm of photosynthesis persisted even 33 days after removal of the nucleus; as synthesis of cellular RNA and proteins had ceased long before it is evident that DNA-dependent RNA synthesis is probably not involved in rhythmicity and in a biological clock mechanism. The observed diurnal rhythm of photosynthesis did not persist in continuous light of low intensity and in darkness.

Effect of Light and Temperature on Floral Initiation in Cocklebur and Biloxi Soybean

1. In cocklebur, the conditions brought about during the photoperiod may be diminished to such a point that plants fail to initiate floral primordia when subsequently subjected to a 12-hour dark period. The methods employed are the insertion between the photoperiod and the dark period of the photoinductive cycle of a given number of short alternating periods of darkness and light or of a given number of hours of continuous light of low intensity. When Biloxi soybean was treated in the same manner there was no reduction in the number of plants flowering, although there was a decrease in the number of nodes with flowers. 2. In Biloxi soybean, short cycles of light and darkness, or continuous light of low intensity, when inserted following the dark period of each photoinductive cycle, reduced considerably the number of plants flowering as well as the average number of nodes per plant with flowers. This response appears rhythmical, and there are indications that utilization of cycles other than those under wh...