Effects of elevated CO2 and increased nitrogen deposition on photosynthesis and growth of understory plants in spruce model ecosystems

We studied the effects of atmospheric CO₂ enrichment (280, 420 and 560 l CO₂ l^–1) and increased N deposition (0,30 and 90 kg ha^–1 year^–1) on the spruce-forest understory species Oxalis acetosella, Homogyne alpina and Rubus hirtus. Clones of these species formed the ground cover in nine 0.7 m² model ecosystems with 5-year-old Picea abies trees (leaf area index of approx 2.2). Communities grew on natural forest soil in a simulated montane climate. Independently of N deposition, the rate of light-saturated net photosynthesis of leaves grown and measured at 420 l CO₂ l^–1 was higher in Oxalis and in Homogyne, but was not significantly different in Rubus compared to leaves grown and measured at the pre-industrial CO₂ concentration of 280 l l^–1. Remarkably, further CO₂ enrichment to 560 l l^–1 caused no additional increase of CO₂ uptake. With increasing CO₂ supply concentrations of non-structural carbohydrates in leaves increased and N concentrations decreased in all species, whereas N deposition had no significant effect on these traits. Above-ground biomass and leaf area production were not significantly affected by elevated CO₂ in the more vigorously growing species O. acetosella and R. hirtus, but the slow growing H. alpina produced almost twice as much biomass and 50% more leaf area per plant under 420 l CO₂ l^–1 compared to 280 l l^–1 (again no further stimulation at 560 l l^–1). In contrast, increased N addition stimulated growth in Oxalis and Rubus but had no effect on Homogyne. In Oxalis (only) biomass per plant was positively correlated with microhabitat quantum flux density at low CO₂, but not at high CO₂ indicating carbon saturation. On the other hand, the less shade-tolerant Homogyne profited from CO₂ enrichment at all understory light levels facilitating its spread into more shady micro-habitats under elevated CO₂. These species-specific responses to CO₂ and N deposition will affect community structure. The non-linear responses to elevated CO₂ of several of the traits studied here suggest that the largest responses to rising atmospheric CO₂ are under way now or have already occurred and possible future responses to further increases in CO₂ concentration are likely to be much smaller in these understory species.     

Characterization of a calcium/calmodulin-dependent protein kinase homolog from maize roots showing light-regulated gravitropism

Roots of many species respond to gravity (gravitropism) and grow downward only if illuminated. This light-regulated root gravitropism is phytochrome-dependent, mediated by calcium, and inhibited by KN-93, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaMK II). A cDNA encoding MCK1, a maize homolog of mammalian CaMK, has been isolated from roots of maize (Zea mays L.). The MCK1 gene is expressed in root tips, the site of perception for both light and gravity. Using the [³⁵S]CaM gel-overlay assay we showed that calmodulin-binding activity of the MCK1 is abolished by 50 M KN-93, but binding is not affected by 5 M KN-93, paralleling physiological findings that light-regulated root gravitropism is inhibited by 50 M KN-93, but not by 5 M KN-93. KN-93 inhibits light-regulated gravitropism by interrupting transduction of the light signal, not light perception, suggesting that MCK1 may play a role in transducing light. This is the first report suggesting a physiological function for a CaMK homolog in light signal transduction.Abbreviations CaM calmodulin - CaMK (II) Ca²⁺/calmodulin-dependent protein kinase (II) - CBP CaM-binding protein - CDPK Ca²⁺-dependent protein kinase - MCK1 maize homolog of mamalian CaMK This work is supported by the National Aeronautics and Space Administration grant No: NAGW 238.     

Regulation of nitrate reductase and phosphoenolpyruvate carboxylase activities in barley leaf protoplasts

Barley leaf protoplasts were incubated in light or darkness in the presence of various inhibitors, metabolites or weak acids/bases. Nitrate reductase (NR) and phosphoenolpyruvate carboxylase (PEPCase) were rapidly extracted from the protoplasts and assayed under sub-optimal conditions, i.e. in the presence of Mg²⁺ and malate, respectively. Under these conditions changes in activities are thought to reflect changes in the phosphorylation states of the enzymes. The NR was activated by illumination to 90% of its maximal activity within 10 min. Photosynthetic electron transport appeared necessary for light activation of NR since activation was inhibited by the photosynthetic electron-transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and, additionally, an electron acceptor (HCO ₃ ^- ) was required. The PEPCase was also activated by light. However, this activation was not prevented by DCMU or lack of HCO ₃ ^- . Loading of protoplasts in the dark with a weak acid resulted in activation of both NR and PEPCase. For NR, full activation was completed within 5 min, whereas for PEPCase a slower, modest activation continued for at least 40 min. Incubation of protoplasts with a weak base also gave activation of PEPCase, but not of NR. On the contrary, base loading counteracted light activation of NR. Since several treatments tested resulted in the modulation of either NR or PEPCase activity, but not both, signal transduction cascades leading to changes in activities appear to be very different for the two enzymes.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) - DMO 5,5-dimethyl-2,4 oxazolidinedione - NR nitrate reductase - PEPCase Phosphoenolpyruvate carboxylase This work was supported by the Norwegian Research Council by a Grant to C.L: L.H.S. was supported by the Biotechnology and Biological Sciences Research Council.     

Sedimentology of the Upper Triassic reef complex at the Hochkönig Massif (Northern Calcareous Alps,Austria)

Summary The Upper Triassic Dachsteinkalk of the Hochk?nig Massif, situated 50 km south of Salzburg in the Northern Calcareous Alps, corresponds to a platform margin reef complex of exceptional thickness. The platform interior limestones form equally thick sequences of the well known cyclic Lofer facies. Sedimentation in the reef complex was not so strongly controlled by low-amplitude sea-level oscillations as was the Lofer facies. The westernmost of the 8 facies of the reef complex is an oncolite-dominated lagoon, in which wave-resistant stromatolite mounds with a relief of a few metres were periodically developed. The transition to the central reef area is accomplished across the back-reef facies. In the back-reef facies patch reefs and calcisponges appear. The proportion of coarse bioclastic sediment increases rapidly over a few hundred metres before the central reef area is encountered. The central reef area consists of relatively widely spaced small patch reefs that did not develop wave-resistant reef framework structures. The bulk of the sediment in the central reef area is coarse bioclastic material, provided by the dense growth of reef organisms and the wave-induced disintegration of patch reefs. Collapse of the reef margin is recorded by the supply of large blocks of patch reef material to the upper reef slope. Additionally, coarse, loose bioclastic debris was supplied to the upper reef slope and this was incorporated into debris flows on the reef slope and turbidites found at the base of the slope and in the off-reef facies. Partially lithified packstones and wackestones of the lower to middle reef slope were modified by mass movement to form breccia and rudstone sheets. The latter reach out hundreds of metres into the off-reef facies environment. A reef profile is presented which was derived by the restoration of strike and dip information. In conjunction with constraints imposed by sedimentary facies related to slope processes, the angle of slope in the reef margin area ranged from 11° to 5°, forming a concave (dished downwards) slope. Water depth estimations require that the central reef area did not develop in water of less than 10 metres depth. At the reef margin water depths were about 30 metres, at the base of the reef slope 200 metres and deepening in the off-reef facies to 250 metres. While previous work on reef complexes from this type of setting suggests growth in a heavily storm-dominated environment, the present author finds little evidence for the storm generation of the fore reef breccias, although there is good evidence for storm-influenced sedimentation and reworking in the central reef area. Post-depositional processes were characterised by continued slope processes causing brecciation and hydraulic injection of red internal sediments downwards into the reef slope and off-reef limestones. Hydrothermal circulation caused a number of phases of post-depositional (diagenetic) brecciation. There appears not to have been an important period of emergence at the Triassic/Jurassic boundary.     

Redox-state of intactNitella cells: dependency on intracellular pH and photosynthesis

Summary The present paper describes the construction and properties of a Pt/Ir-semi-microelectrode and its application as a redoxsensitive electrode in intact cells of the giant algaNitella. For compartmental analysis of the stationary redox-state voltage (E_RED), a value reflecting the interaction of the dominant redox couples with a Pt/Ir-electrode, the redox-sensitive electrode was inserted into the vacuole of leaf cells or cytoplasm enriched fragments (CEF) fromNitella internodal cells. After correction for the membrane voltage, measured with a second, conventional voltage electrode, E_RED values of+237±93mVand+419±51 mV with respect to a normal H⁺-electrode were obtained for cytoplasm and vacuole, respectively. The redox-state of the cell culture medium was+604 mV. The steady state E_RED in the cytoplasm can be perturbed by experimental treatments: indirect acidification of the cytoplasm by an external pH jump from 7.5 to 5.8 and direct acidification, by acid loading with 5 mM butyrate, both resulted in a positive shift of E_RED, i.e., to an increase in cytoplasmic oxidation. At the same time the membrane depolarized electrically following the external pH jump, but hyperpolarized in response to acid loading. The data demonstrate the direct dependence of cytoplasmic redox state on intracellular pH, probably due to enhanced oxidation of protonated redox couples favoured by mass action. The electrical membrane voltage changes were not correlated with the shift in cytoplasmic E_RED. This demonstrated that redox energy does not determine the electrical membrane voltage. Cytoplasmic E_RED was also affected by photosynthesis. When CEFs were transferred from light to dark, or exposed to 10M 3-(3,4-dichlorophenyl)-1,l-dimethylurea (DCMU), E_RED shifted negatively (more reduced) by 6.4±4.5mV or 4.2±2mV, respectively. These data compare favourably with biochemical estimates of cytoplasmic pyridin nucleotides which also show an increase in cytoplasmic reduction in the dark. Therefore, it is unlikely that diffusable reducing equivalents are supplied to the cytoplasm from photosynthetically-active chloroplasts to act as secondary messengers.Abbreviations E_M transmembrane voltage - E_RED redox-state voltage - E₀ midpoint-redox-voltage - APW artificial pond water - CEF cytoplasm enriched fragment     

The Casparian strip in pea epicotyls: Effects of light on its development

The Casparian strip, which is specific to roots, was studied in the epicotyls of dark-grown seedlings of pea (Pisum sativum L.) where it was found to have the same morphology and properties as the strip in roots. In dark-grown seedlings, the distance between the upper-most position of the Casparian strip and the bending point of the hook (about 37 mm) did not change during growth of the seedlings. In the uppermost 0.5-mm region of the region in which the Casparian strip could be detected by fluorescence microscopy, the plasma membrane was not firmly attached to the cell wall. The development of the Casparian strip continued for about 42 h after dark-grown seedlings were transferred to the light, indicating that (i) the cells that have been determined to form the Casparian strip in darkness form the strip in the light, and that (ii) it takes about 42 h for the cells to complete formation of the strip. Cells in the hook of dark-grown seedlings did not form a Casparian strip when such seedlings were transferred to the light. The Casparian strip was formed in rapidly elongating internodes of light-grown seedlings when the seedlings were transferred to darkness. Light did not control the formation of the Casparian strip in roots.Abbreviation PBS phosphate-buffered saline     

Binding of malate dehydrogenase and NADH channelling to complex I

As previously reported, mitochondrial malate dehydrogenase (MDH) binds to purified complex I of the electron transport system. With conditions used in previous reports, MDH binds even more extensively, but probably predominantly non-specifically, to the matrix side of the inner mitochondrial membrane of submitochodrial particles (SMP). Herein we report experimental conditions for highly specific binding of malate dehydrogenase to complex I within SMP. These conditions permit us to demonstrate NADH channelling from malate dehydrogenase to complex I using the completing reaction test. This test, though not ideal for all situations, has several advantages over the enzyme buffering test previously used. These advantages should facilitate further studies elucidating NADH channeling to complex I from MDH and other dehydrogenases. Independent evidence of NADH channelling to the electron transport chain and the potential advantages of substrate channelling in general are also discussed. Substrate channelling from MDH in particular may be especially beneficial because of the unfavourable equilibrium and kinetics of this enzyme reaction.     

Complex sound analysis in the lesser bulldog bat: evidence for a mechanism for processing frequency elements of frequency modulated signals over restricted time intervals

A stereotypical approach phase vocalization response of the lesser bulldog bat, Noctilio albiventris, to artificial echoes simulating a virtual approaching object was used to assess the ability of the bat to analyze and extract distance information from the artificial echoes. The performance of the bat was not significantly different when presented with naturally structured CF/FM echoes containing FM elements that sweep continuously from about 75-55 kHz in 4 ms or with CF/FM echoes containing FM components constructed from a series of 98 pure tone frequency steps, each with a duration of 0.04 ms. The performance of the bat remained unchanged when the duration of the tone steps was increased up to 0.08 ms but declined sharply to a level that was significantly below that seen with a naturally structured echo when the steps were 0.09 ms or longer. The performance of the bat depended on the duration of the individual tone steps, which could not exceed a specific upper limit of about 0.08 ms. The study suggests that the bats have adaptations for processing individual narrow band segments of FM signals over specific time intervals.Abbreviations CF constant frequency - FM frequency modulation     

Resynchronization of the Circadian Corticosterone Rhythm After a Light/Dark Shift in Juvenile and Adult Mice

Most of the extensive literature concerning the resynchronization of circadian rhythms after a Zeitgeber shift is devoted to the dependence of resynchronization on the mode of the shift and the strength of the Zeitgeber, as well as on the circadian function investigated. Ontogenetic influences have rarely been investigated. Therefore, we studied the resynchronization of several circadian rhythms in juvenile and adult female laboratory mice. We present here the results concerning the corticosterone rhythm. The daily rhythms were determined as transverse profiles (2-h intervals) before as well as 3, 7, and 14 days after an 8-h phase delay of the light/dark cycle produced by a single prolongation of dark time. The corticosterone concentration in serum was determined radioimmunologically. In the control animals the daily patterns were bimodal, with main maxima at the end of the light time and secondary ones just after lights on. Ontogenetic differences were small. In adult mice the amplitude was slightly increased due to an increase in the maximum values, and the time of highest hormone concentrations was slightly phase advanced. In juvenile mice, a distinct daily pattern with a phase position in relation to the light/dark cycle corresponding to that of control animals was present on the 3rd day after the Zeitgeber shift. The daily mean as well as the minimum and maximum values increased initially and reached the values of control animals during the second week. In adult animals, a pronounced daily rhythm with the normal phase position was present only at the 7th postshift day. The amplitude, daily mean, and maximum values were decreased, and the minimum values were increased. The initial values were not reached even after 2 weeks. The results show that resynchronization was faster in juvenile mice compared with adult mice. As a possible cause for the observed age-related differences, a not yet stabilized phase-coupling between various circadian rhythms is supposed.     

光照对蕨类植物配子体假根向重力性的影响

对８种蕨类植物配子体假根向重力性反应的研究结果表明,除卷柏Ｓｅｌａｇｉｎｅｌｌａ ｔａｍａｒｉｓｃｉｎａ Ｓｐｒｉｎｇ配子体假根无向重力性反应并且其生长方向与光照方向无关外,其它７种的配子体假根均有向重力性反应,并且假根的向重力性反应在配子体发育初期,因光照的方向不同而异,表现为负向光性。随着配子体发育至片状体阶段,光对其向重力性反应的影响逐渐减弱,而重力的影响增强。在蕨类植物配子体发育初期,光对