Simultaneous telemetric monitoring of the circadian changes in core and BAT temperature in rats: Endogenous vasopressin may contribute to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle

The purpose of the present study was to analyze simultaneously the temporal relationship between the changes of circadian rhythms of brown adipose tissue (BAT) thermogenesis and core temperature (T_c) by dual probe telemetric monitoring transmitters and to determine the role of endogenous arginine vasopressin (AVP) in the circadian rhythms of BAT temperature (T_BAT) and T_c in male rats. The key observations in this study are: (1) Increase in T_BAT commenced approximately 8 min before T_c increases at the start of transition from the light to dark phase. Whereas at the start of transition from the dark to light phase, decrease in T_BAT commenced approximately 3 min before T_c decreases. The data show that circadian changes of BAT thermogenesis do indeed play a significant role in the overall maintenance of the circadian rhythm of core temperature. (2) The plasma AVP level was significantly elevated when core temperature decreases during the light phase, suggesting that endogenous AVP is involved in thermoregulatory processes during the light phase. V1a receptor antagonist could elevate core and BAT temperature during the light period, suggesting that endogenous AVP, acting through V1a receptor, could be involved in tonic thermoregulatory processes.V1a receptor antagonist can increase the blood lipid metabolism, suggesting that the mechanism of endogenous AVP in tonic thermoregulatory processes during light period could involve the suppression of lipolysis in BAT and other peripheral tissues. In summary, this study demonstrated that endogenous vasopressin contributes to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle.     

Metabolism of Oat Leaves during Senescence : VII. The Interaction of Carbon Dioxide and Other Atmospheric Gases with Light in Controlling Chlorophyll Loss and Senescence

In air largely freed from CO₂, senescence of isolated oat (Avena sativa cv Victory) seedling leaves is no longer prevented by white light; instead, the leaves lose both chlorophyll and protein as rapidly as in the dark. Senescence in light is also accelerated in pure O₂, but it is greatly delayed in N₂; 100% N₂ preserves both protein and chlorophyll in light and in darkness. In light in air, most of the compounds tested that had previously been found to delay or inhibit senescence in darkness actually promote the loss of chlorophyll, but they do not promote proteolysis. Under these conditions, proteolysis can therefore be separated from chlorophyll loss. But in light minus CO₂, where chlorophyll loss is rapid in controls, two of these same reagents prevent the chlorophyll loss. Unlike the many reagents whose action in light is thus the opposite of that in darkness, abscisic acid, which promotes chlorophyll loss in the dark, also promotes it in light with or without CO₂. Kinetin, which prevents chlorophyll loss in the dark, also prevents it in light minus CO₂. In general, therefore, the responses to light minus CO₂ are similar to the responses to darkness, and (with the exception of abscisic acid and kinetin) opposite to the response to light in air.     

Negative feedback regulation is responsible for the non-linear modulation of photosynthetic activity in plants and cyanobacteria exposed to a dynamic light environment

Photosynthetic organisms exposed to a dynamic light environment exhibit complex transients of photosynthetic activities that are strongly dependent on the temporal pattern of the incident irradiance. In a harmonically modulated light of intensity I≈const.+sin(ωt), chlorophyll fluorescence response consists of a steady-state component, a component modulated with the angular frequency of the irradiance ω and several upper harmonic components (2ω, 3ω and higher). Our earlier reverse engineering analysis suggests that the non-linear response can be caused by a negative feedback regulation of photosynthesis. Here, we present experimental evidence that the negative feedback regulation of the energetic coupling between phycobilisome and Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC6803 indeed results in the appearance of upper harmonic modes in the chlorophyll fluorescence emission. Dynamic changes in the coupling of the phycobilisome to PSII are not accompanied by corresponding antiparallel changes in the Photosystem I (PSI) excitation, suggesting a regulation limited to PSII. Strong upper harmonic modes were also found in the kinetics of the non-photochemical quenching (NPQ) of chlorophyll fluorescence, of the P700 redox state and of the CO₂ assimilation in tobacco (Nicotiana tabaccum) exposed to harmonically modulated light. They are ascribed to negative feedback regulation of the reactions of the Calvin-Benson cycle limiting the photosynthetic electron transport. We propose that the observed non-linear response of photosynthesis may also be relevant in a natural light environment that is modulated, e.g., by ocean waves, moving canopy or by varying cloud cover. Under controlled laboratory conditions, the non-linear photosynthetic response provides a new insight into dynamics of the regulatory processes.     

Contrasting correlation networks between leaf structure,nitrogen and chlorophyll in herbaceous and woody canopies

We studied acclimation patterns in leaf dry mass per area (M_A), nitrogen (N_A) and chlorophyll (ζ_A) content per area, and chlorophyll to nitrogen ratio (ζ/N) along vertical light gradients in natural temperate mixed herbaceous canopy and deciduous tree canopy. In the deciduous tree canopy, all leaves are formed at approximately the same time, and the light gradient during the rest of the growing season reflects the differences in light availability during leaf development, whereas in the herbaceous canopy, leaf production continues during most of the growing season and major changes in light conditions occur after leaf maturation. M_A and N_A increased strongly with increasing current light availability (I_D) in the tree canopy. In the herbaceous canopy, M_A and N_A were generally unrelated to I_D. Depending on species, the correlation between chlorophyll content per leaf area (ζ_A) and I_D was positive, negative, or non-significant. Path analyses revealed two opposite effects of I_D on the amount of leaf chlorophyll. In the tree canopy, increasing I_D enhanced ζ_A through changes in M_A and N_A, whereas the direct effect of light was negative in both canopies. The overall correlation network between foliage structural and chemical traits and the relationships with I_D were significantly stronger in the tree canopy, suggesting limited re-acclimation potential in the mixed herbaceous canopy. Within-species acclimation patterns reflected the patterns within the main functional types. These data demonstrate that the relationships of current light availability vs. leaf dry mass per area, leaf nitrogen and chlorophyll contents, and chlorophyll to nitrogen ratio differ among multi-species herbaceous canopies and deciduous tree canopies due to contrasting canopy development.     

Adaptation to quantum flux by the emerson photosynthetic unit

The size of the Emerson photosynthetic unit was measured in Chlorella pyrenoidosa strain no. 252 grown at light intensities between 50 and 1000 foot candles. The Emerson photosynthetic unit changed from a minimum size of 1970 molecules chlorophyll a + b/O₂ per flash in cells grown at 1000 foot candles to a maximum size of 3150 molecules chlorophyll a + b/O₂ per flash for cells grown at 50 foot candles. The size changes were interpreted as a partial adaptation where the trapping center antenna responded to changes in incident light intensity. Light-induced changes in chlorophyll content and size of the Emerson photosynthetic unit were directly related.     

A possible second role for calmodulin in biological clock-controlled processes of euglena

The response of the Euglena gracilis (Klebs strain Z) photosynthesis circadian rhythm to three calmodulin antagonists was examined. In the presence of an antagonist, the photosynthetic reactions were uncoupled from the biological clock. Instead of the highly predictable rhythmic pattern characteristic of a biological clock-controlled circadian rhythm, the photosynthetic rate appears to be influenced by the light/dark cycle. The rate of O₂ evolution increases throughout the light portion of the cycle and does not decrease until the cells are exposed to darkness. Shortterm exposure to a calmodulin antagonist (2 hour pulses) failed to cause phase shifts in the timing of the rhythm. This suggests that calmodulin is not part of the clock controlling photosynthesis and that it has a clock-related role different from that reported for the cell division rhythm in Euglena.     

Molecular characterization of the diurnal/circadian expression of the chlorophyll a/b-binding proteins in leaves of tomato and other dicotyledonous and monocotyledonous plant species

Diurnal oscillations of steady-state mRNA levels encoding the chlorophyll a/b-binding proteins were monitored inLycopersicon esculentum, Glycine max, Phaseolus vulgaris, P. aureus, P. coccineus, Pisum sativum, Sinapis alba, Hordeum vulgare, Triticum aestivum andZea mays. In these plant speciescab mRNA accumulation increases and decreases periodically indicating i) that the expression of the genes for chlorophyll a/b-binding proteins (cab genes) is controlled by a circadian rhythm, and ii) that the rhythm is widely distributed among monocotyledonous and dicotyledonous plant species. A detailed characterization of the pattern ofcab mRNA expression in tomato leaves shows that the amplitude of the oscillation is dependent on i) the developmental stage of the leaves, ii) the circadian phase and duration of light and iii) the circadian phase and duration of darkness. In addition to the chlorophyll a/b-binding proteins, genes coding for other cellular functions were examined for cyclic variations of their mRNA levels. The analysis includes genes involved in i) carbon metabolism (e.g. phosphoenolpyruvate carboxylase, pyruvate orthophosphate dikinase, alpha amylase, fructose-1,6-bisphosphate aldolase, triosephosphate isomerase), ii) photosynthesis (large and small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, Q_B-binding protein, reaction-center protein of photosystem I) and iii) other physiological or morphological reactions (e.g. ubiquitin, actin). However, no periodic fluctuation pattern was detected for the mRNA levels of these genes in tomato and maize leaves.     

Expression of cab Genes in Douglas-Fir Is Not Strongly Regulated by Light

Dark-grown Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings had approximately 30% of the major polypeptide of the light-harvesting chlorophyll a/b binding protein, 30% of cab mRNA, 54% of psbA mRNA, and 14% of total chlorophyll, in comparison with amounts in light-grown seedlings. Seedlings entrained under a 24-hour photoperiod of light and dark showed small diurnal fluctuations in cab and psbA mRNA levels and, when transferred to continuous conditions, no circadian rhythms in mRNA levels were apparent. These results suggest that regulation of cab gene expression in Douglas-fir differs from regulation in angiosperms, because in the latter, both light and circadian factors strongly influence the expression of cab genes.     

GENETIC CONTROL OF CHLOROPHYLL BIOSYNTHESIS IN CHLAMYDOMONAS : Analysis of Mutants at Two Loci Mediating the Conversion of Protoporphyrin-IX to Magnesium Protoporphyrin

In this report we describe two nonallelic Mendelian protoporphyrin accumulating mutants br_s-1 and br_c-1. Results of experiments with these mutants lead us to postulate that porphyrin biosynthesis branches into light and dark steps between protoporphyrin-IX and magnesium protoporphyrin. We hypothesize that the br_c locus controls a dark step while the br_s locus either controls a step in the main pathway before the branch or mediates the preparation of the magnesium ion for its insertion into protoporphyrin-IX. The br_s-1 mutant is thought to be light sensitive because a block prior to the branch point in the porphyrin pathway prevents chlorophyll formation in either the light or the dark. The br_c-1 mutant, which also accumulates protoporphyrin in the dark, forms chlorophyll and chloroplast lamellae when transferred to the light, showing that function of the porphyrin pathway is normal in the light.     

Chlorophyll-Protein Complexes from the Red-Tide Dinoflagellate, Gonyaulax polyedra Stein : Isolation, Characterization, and the Effect of Growth Irradiance on Chlorophyll Distribution

A comparision of high (330 microeinsteins per meter squared per second) and low (80 microeinsteins per meter squared per second) light grown Gonyaulax polyedra indicated a change in the distribution of chlorophyll a, chlorophyll c₂, and peridinin among detergent-soluble chlorophyll-protein complexes. Thylakoid fractions were prepared by sonication and centrifugation. Chlorophyll-protein complexes were solubilized from the membranes with sodium dodecyl sulfate and resolved by Deriphat electrophoresis. Low light cells yielded five distinct chlorophyll-protein complexes (I to V), while only four (I′ to IV′) were evident in preparations of high light cells. Both high molecular weight complexes I and I′ were dominated by chlorophyll a absorption and associated with minor amounts of chlorophyll c. Both complexes II and II′ were chlorophyll a-chlorophyll c₂-protein complexes devoid of peridinin and unique to dinoflagellates. The chlorophyll a:c₂ molar ratio of both complexes was 1:3, indicating significant chlorophyll c enrichment over thylakoid membrane chlorophyll a:c ratios of 1.8 to 2:1. Low light complex III differed from all other high or low light complexes in that it possessed peridinin and had a chlorophyll a:c₂ ratio of 1:1. Low light complexes IV and V and high light complexes III′ and IV′ were spectrally similar, had high chlorophyll a:c₂ ratios (4:1), and were associated with peridinin. The effects of growth irradiance on the composition of chlorophyll-protein complexes in Gonyaulax polyedra differed from those described for other chlorophyll c-containing plant species.     

Effect of light quality on the organization of photosynthetic electron transport chain of pea seedlings

The activity of NADP and O₂ photoreduction by water is essentially higher in chloroplasts isolated from pea seedlings (Pisum sativum L.) grown under blue light as compared with that from plants grown under red light. In contrast, the photoreduction of NADP and O₂ with photosystem I only is practically the same or even lower in chloroplasts isolated from plants grown under blue light. The addition of plastocyanin does not affect the rate or the extent of NADP photoreduction by water in the chloroplasts isolated from plants grown under blue light, whereas it sharply activates NADP reduction in the chloroplasts isolated from plants grown under red light. The extent of the light-induced oxidation of cytochrome f is appreciably higher in chloroplasts isolated from plants grown under blue light. Cytochrome b₅₅₉ plays the predominant role in the oxidoreductive reactions of these chloroplasts. Furthermore, the fluorescence measurements indicate more effective transfer of excitation energy from chlorophyll to the photosystem II reaction center in chloroplasts isolated from plants grown under blue light.     

Inhibition of Photosystem II Precedes Thylakoid Membrane Lipid Peroxidation in Bisulfite-Treated Leaves of Phaseolus vulgaris

Exposure of leaves to SO₂ or bisulfite is known to induce peroxidation of thylakoid lipids and to inhibit photosynthetic electron transport. In the present study, we have examined the temporal relationship between bisulfite-induced thylakoid lipid peroxidation and inhibition of electron transport in an attempt to clarify the primary mechanism of SO₂ phytotoxicity. Primary leaves of bean (Phaseolus vulgaris L. cv Kinghorn) were floated on a solution of NaHSO₃, and the effects of this treatment on photosynthetic electron transport were determined in vivo by measurements of chlorophyll a fluorescence induction and in vitro by biochemical measurements of the light reactions using isolated thylakoids. Lipid peroxidation in treated leaves was followed by monitoring ethane emission from leaf segments and by measuring changes in fatty acid composition and lipid fluidity in isolated thylakoids. A 1 hour treatment with bisulfite inhibited photosystem II (PSII) activity by 70% without modifying Photosystem I, and this inhibitory effect was not light-dependent. By contrast, lipid peroxidation was not detectable until after the inhibition of PSII and was strongly light dependent. This temporal separation of events together with the differential effect of light suggests that bisulfite-induced inhibition of PSII is not a secondary effect of lipid peroxidation and that bisulfite acts directly on one or more components of PSII.     

Nature of photooxidative events in leaves treated with chlorosis-inducing herbicides

Leaves of rye seedlings (Secale cereale L.) grown in the presence of four chlorosis-inducing herbicides under a low light intensity of 10 lux formed chlorophyll. When segments of such dim-light-grown leaves were exposed to 30,000 lux at either 0°C or 30°C, treatments with aminotriazole or haloxidine (group 1) showed no or only minor changes of their chlorophyll contents. In treatments with San 6706 or difunon (group 2), however, rapid photodestruction of chlorophyll occurred both at 0°C and at 30°C and was accompanied by an increase of malondialdehyde that was not seen in the presence of group 1 herbicides. Unlike the in vivo behavior, virtually equal rates of chlorophyll breakdown were observed for aminotriazole and San 6706 treatments in suspensions of isolated chloroplasts from 10 lux-grown leaves after exposure to strong light. The free radical scavengers p-benzoquinone and hydroquinone and the d-penicillamine copper complex exerting superoxide dismutating activity effectively prevented photooxidation of chlorophyll in 10 lux-grown herbicide-treated leaf segments or even restored an accumulation of chlorophyll at 30,000 lux. Ascorbate and several singlet oxygen or hydroxyl radical scavengers had no protective effects. Deuterium oxide and H₂O₂ did not enhance the degradation of chlorophyll. Superoxide dismutase activity was decreased in leaves bleached in the presence of group 2 herbicides.     

Effects of growth irradiance levels on the ratio of reaction centers in two species of marine phytoplankton

Cells of two species of single-celled marine algae, the diatom Skeletonema costatum (Greve), Cleve, and the chlorophyte Dunaliella tertiolecta Butcher, were cultured in white light of high (500-600 microeinsteins per square meter per second) and low (30 microeinsteins per square meter per second) intensity. For both algal species, cells grown at low light levels contained more chlorophyll a and had a lower ratio of chlorophyll a to chlorophylls b or c than did cells grown at high light levels. When photosynthetic unit sizes were measured on the basis of either oxygen flash yields or P₇₀₀ photooxidation, different results were obtained with the different species. In the chlorophyte, the cellular content of photosystem I (PSI) and photosystem II (PSII) reaction centers increased in tandem as chlorophyll a content increased so that photosynthetic unit sizes changed only slightly and the ratio PSI:PSII reaction centers remained constant at about 1.1. In the diatom, as the chlorophyll content of the cells increased, the number of PSI reaction centers decreased and the number of PSII reaction centers increased so that the ratio of PSI:PSII reaction centers decreased from about unity to 0.44. In neither organism did photosynthetic capacity correlate with changes in cellular content of PSI or PSII reaction centers. The results are discussed in relationship to the physical and biological significance of the photosynthetic unit concept.     

Photochemical activities and organization of photosynthetic apparatus of C3 and C4 plants grown under different light intensities

Changes in the photochemical activities, influenced by variation in the growth light intensity, were followed in typical C₃ (Phaseolus, Ipomoea) and C₄ (Amaranthus, Sorghum) plants. Progressive decrease in the growth light intensity accelerated the O-P fluorescence induction in whole leaves. Such acceleration of the fluorescence kinetics was found to be not due to enhanced photosystem II activity but possibly a result of reduced rate of electron flow between the two photosystems. This is supported by 4 lines of evidence: (1) by the Hill activity determined in the presence of electron acceptors functioning before and after plastoquinone; (2) the photosynthetic unit size determined after flash excitation showing variations that were apparently too small to account for the changes observed fluorescence induction; (3) modification of the kinetics of secondrange light-induced absorbance changes at 520 nm; and (4) absence of significant changes in the ratio of P₇₀₀/total chlorophyll ratio. The P₇₀₀/cytochrome f ratio, however, increased from the usual 1–1.5 to 3–4 in plants grown under 9% sunlight. Increase in the P₇₀₀/cytochrome f ratio was found to be due to a decrease in the cytochrome f/chlorophyll ratio, and this was due to perhaps to a simultaneous increase in chlorophyll and decrease in cytochrome content.