On the evolution of the bacterial major sigma factors

Summary The existence of internal sequence homologies between the N-terminal halves of the gram-negative bacterial major sigma factors and their C-terminal halves, which correspond to minor factors, is reported. In the case of Escherichia-Salmonella sigma-70, an apparent homology was even found between the C-terminal helix-turn-helix DNA-binding motif and the corresponding region of the peptide N half, which, however, is not directly engaged in promoter recognition. It is proposed that major sigma factors may have originated by duplication and fusion of a DNA unit related to the ancestral gene for the whole sigma family. Coevolution of major sigma structures and complex promoters is suggested.     

Biphasic 24-Hour Variations in Cyclic GMP Accumulation in the Rat Pineal Gland Are Due to Corresponding Changes in the Activity of Cytosolic and Particulate Guanylate Cyclase

Various parameters of the rat pineal gland display a 24-h rhythm. However, nothing is known about possible 24-h variations in cyclic GMP (cGMP) metabolism. In the present study, 24-h variations in pineal gland cGMP accumulation were investigated by determining the increase in cGMP level with and without inhibitors of phosphodiesterase at different time points over a light/dark cycle (12/12 h). Furthermore, the activity of guanylate cyclase (GC) was determined under substrate-saturated conditions regarding the cytosolic and particulate forms of the enzyme. It has been found that cGMP accumulation and GC activity display biphasic 24-h variations with two peaks--one approximately 7 h after lights "on" and the other approximately 7 h after lights "off." The activity of cytosolic GC remains unchanged in the presence of the nitric oxide (NO) synthesis inhibitor N-monomethyl-L-arginine, indicating that 24-h variations in the activity do not reflect changes in the synthesis of the GC stimulator NO.     

The acquisition of inorganic carbon by four red macroalgae

Photosynthesis was studied in four species of red marine macroalgae: Palmaria palmata, Laurencia pinnatifida, Lomentaria articulata and Delesseria sanguinea. The rate of O₂ evolution for submersed photosynthesis was measured as a function of incident photon flux density at normal pH and inorganic carbon concentration (pH 8.0, 2 mol m^–3), and as a function of inorganic carbon concentration at pH 8.0 at saturating and at limiting photon flux density. The rate of CO₂ uptake was measured for emersed photosynthesis as a function of CO₂ partial pressure at saturating photon flux density. Previous pH-drift results suggest that Palmaria and Laurencia are able to use HCO _inf3 ^sup– as well as CO₂ whereas Lomentaria and Delesseria are restricted to CO₂. None of the algae are saturated by 2 mol m^–3 inorganic carbon at high light (400 mol m^–2 s^–1) but are saturated at low light (35 mol m^–2 s^–1). The inorganic C concentration at which half the light-saturated rate of O₂ evolution is achieved is higher for Palmaria and Laurencia (1.51 and 1.85 mol m^–3) than for Lomentaria and Delesseria (0.772 and 0.841 mol m^–3). The lower values for the latter two species could reflect their putative restriction to CO₂. If expressed in terms of CO₂, the half-saturation values yield 7.2 and 7.8 mmol m^–3 respectively, which are very similar to values obtained previously during pH-drift experiments but at lower concentrations of HCO _inf3 ^sup– , consistent with restriction to CO₂. The photosynthetic conductance (m s^–1), calculated from the initial slope for photosynthesis at low concentrations of inorganic carbon, correlates with the suggested ability to extract inorganic carbon based on pH-drift results. Calculations made assuming that CO₂ is the only species diffusing across the boundary layer are consistent with boundary layer thicknesses of 20 and 19 m for Lomentaria and Delesseria respectively, which is feasible given the rapid water movement in the experiments. For Laurencia however, an unreasonably small boundary layer thickness of 6 m is necessary to explain the flux, which indicates co-diffusion by HCO _inf3 ^sup– . In the apparent absence of external carbonic anhydrase, direct uptake of HCO _inf3 ^sup– , rather than external conversion to CO₂ is indicated in this species. In air, the CO₂ concentration at which photosynthesis is half-maximal increases in the same order as the ability to raise pH in drift experiments. At 21 kPa the CO₂ compensation partial pressures for Palmaria and Laurencia at 0.56 and 1.3 Pa are low enough to suggest a carbon-concentrating mechanism is operating, while those of Lomentaria at 1.8 Pa and particularly that of Delesseria at 4.5 Pa could be explained without a carbon-concentrating mechanism. The algae tested (all except Delesseria) showed more O₂ evolution than could be accounted for with a photosynthetic quotient of 1.0 and uncatalysed conversion of HCO _inf3 ^sup– to CO₂ outside the cell in high light at pH 8.0 when high algal fresh weight per unit medium was used. These results are concordant with other data suggesting use of HCO _inf3 ^sup– by Palmaria and Laurencia, but discordant with the rest of the available information in indicating use of HCO _inf3 ^sup– by Lomentaria. The reason for this is unclear. The lightsaturated rate of O₂ evolution on an algal area basis and the photon flux density needed to saturate photosynthesis were related partly to the habitat from which the seaweeds were collected, but more strongly to the ability to use HCO _inf3 ^sup– . Values for the two users of HCO _inf3 ^sup– , Palmaria (population used was intertidal; also occurs subtidally) and Laurencia (intertidal/shaded intertidal), were greater than for Lomentaria (shaded intertidal), which was greater than Delesseria (subtidal), both of which are believed to be restricted to CO₂. In accordance with earlier ¹³C data and, for Delesseria, estimates of the achieved growth rates in situ, carbon is likely to be saturating and use of HCO _inf3 ^sup– is unlikely to occur in the normal low-light habitats of Lomentaria and Delesseria. Analysis of N-use efficiencies show that they are closer to the low-CO₂-affinity Laminariales than the high-CO₂-affinity Fucaceae.     

Light-grown plants of transgenic tobacco expressing an introduced oat phytochrome A gene under the control of a constitutive viral promoter exhibit persistent growth inhibition by far-red light

A comparison of the photoregulation of development has been made for etiolated and light-grown plants of wild-type (WT) tobacco (Nicotiana tabacun L.) and an isogenic transgenic line which expresses an introduced oat phytochrome gene (phyA) under the control of a constitutive viral promoter. Etiolated seedlings of both the WT and transgenic line showed irradiance-dependent inhibition of hypocotyl growth under continuous far-red (FR) light; transgenic seedlings showed a greater level of inhibition under a given fluence rate and this is considered to be the result of the heterologous phytochrome protein (PhyA) functioning in a compatible manner with the native etiolated phytochrome. Deetiolation of WT seedlings resulted in a loss of responsiveness to prolonged FR. Light-grown transgenic seedlings, however, continued to respond in an irradiance-dependent manner to prolonged FR and it is proposed that this is a specific function of the constitutive PhyA. Mature green plants of the WT and transgenic lines showed a qualitatively similar growth promotion to a brief end-of-day FR-treatment but this response was abolished in the transgenic plants under prolonged irradiation by this same FR source. Growth inhibition (McCormac et al. 1991, Planta 185, 162–170) and enhanced levels of nitrate-reductase activity under irradiance of low red:far-red ratio, as achieved by the FR-supplementation of white light, emphasised that the introduced PhyA was eliciting an aberrant mode of photoresponse compared with the normal phytochrome population of light-grown plants. Total levels of the oat-encoded phytochrome in the etiolated transgenic tobacco were shown to be influenced by the wavelength of continuous irradiation in a manner which was qualitatively similar to that seen for the native, etiolated tobacco phytochrome, and distinct from that seen in etiolated oat tissues. These results are discussed in terms of the proposal that the constitutive oat-PhyA pool in the transgenic plants leads to a persistence of a mode of response normally restricted to the situation in etiolated plants.Abbreviations FR far-red light - R red light - WL white light - WL + FR white light supplemented with FR - HIR high-irradiance response - PAR photosynthetically active radiation - Pr, Pfr R- and FR-absorbing forms of phytochrome - Ptot total phytochrome - phyA (PhyA) gene (encoded protein) for phytochrome - WT wild type This work was supported by an Agricultural and Food Research Council research grant to H.S. and A.M.; J.R. Cherry and R.D. Vierstra, (Department of Horticulture, University of Wisconsin-Madison, USA) are thanked for the provision of the transgenic tobacco line.     

Canopy structure,nitrogen distribution and whole canopy photosynthetic carbon gain in growing and flowering stands of tall herbs

Using a combination of mathematical modeling and field studies we showed that in dense stands of growing herbaceous plants the vertical pattern of leaf nitrogen distribution resembles the pattern of mean light attenuation in the stand and hence tends to maximize total daily photosynthetic carbon gain of the whole stand. Flowering represents a strong sink of nitrogen away from the photosynthetic apparatus and in herbs like Solidago altissima it induces leaf shedding. We studied both the effect of nitrogen reallocation and leaf shedding on the whole canopy photosynthesis and changes in leaf nitrogen distributions in stands moving from the growing to the flowering stage. Despite a decrease in leaf area index and total nitrogen available for photosynthesis in the flowering stand, the leaf nitrogen distribution here also leads to an almost maximum canopy photosynthesis. In both the growing and the flowering stands the leaf area index was higher than calculated optimum values. It is pointed out that this should not necessarily be interpreted as non-adaptive.     

Age-related flight and reproductive performance of the light brown apple moth, Epiphyas postvittana

The relationship between flight activity, reproduction and age of Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae) was studied using tethered flight assays. Flights began on the day of emergence, peaking on days four and five in females and on day five in males, and lasted for nine to ten days. The development of flight capacity was well synchronised with the build-up and decline of reproductive behaviours (calling, mating and oviposition). Flights of E. postvittana are thus inter-reproductive, and there is no obvious pre-oviposition period. Males were more active than females as 45–50% of male moths in comparison to 15–18% of female moths were capable of prolonged flights during the peak activity period. The results suggest that flights of E. postvittana are appetitive flights to a large extent, but it is suggested that some individuals may migrate, as there is no diapause in this species. The sexual dimorphism of flight capacity is discussed in relation to those of other tortricids and Lepidoptera in general.

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Zusammenfassung Die Beziehungen zwischen Flugaktivität, Fortpflanzung und Alter von Epiphyas postvittana (Walker) (Tortricidae) wurden untersucht mit Hilfe von angebudenen Flugapparaten. Flüge begannen am Tage des Schlüpfens, mit einen Maximum am vierten und fünften Tag bei Weibchen und am fünten Tag bei Männchen, und dauerten neun bis zehn Tage. Die Entwicklung des Flugvermögens war gut mit der Zu- und Abnahme des Fortpflanzungsverhaltens (Rufen, Kopulieren und Eiablage) korreliert. Flüge von E. postivittana finden also während der Fortpflanzungsperiode statt, und es gibt keine deutliche Periode vor der Eiablage. Männchen waren aktiver als Weibchen: 45–50% der Männchen verglichen mit 15–18% der Weibchen waren zu langen Flügen während der maximalen Aktivitätsperiode fähig. Das Ergebnis deutet an, das Flüge von E. postvittana im grossen Masse Appetenzflüge sind, doch es wird auf die Möglichkeit hingewiesen, dass einige Individuen wandern können, da die Art keine Diapause hat. Der Geschlechtsdimorphismus in der Flugaktivität wird diskutiert und verglichen mit dem anderer Tortriciden und der Lepidoptera allgemein.

     

The role of availability of food and water to the adult Epiphyas postvittana, the light brown apple moth, in its reproductive performance

Female Epiphyas postvittana (Lepidoptera, Tortricidae) moths were able to lay fertile eggs without feeding, but they require water to achieve their full reproductive potential. Fecundity of moths given water from emergence was not different from that of moths fed with 30% honey solution. Deprivation of feeding during the early stage (up to three days after emergence) showed no significant decrease in fecundity provided that honey solution was available from the age of four days after emergence. Starved moths laid less than 30% of the number of eggs laid by those fed with honey solution or water. Fecundity was correlated with moth weight at emergence when moths were fed with water or honey solution, but not when no food or water was provided. Moths of both sexes fed on honey solution copulated less frequently, lost body weight at a lower rate and had a greater longevity, compared with those fed with water or nothing. These results are discussed in relation to the reproductive strategy of this species.

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Zusammenfassung Weibliche Motten der Art Epiphyas postvittana (Lepidoptera, Tortricidae) legten fruchtbare Eier ohne Nahrung aufzunehmen, brauchten jedoch Wasser, um ihr volles Fortpflanzung — Potential zu erreichen. Fruchtbarkeit von Motten, denen Wasser von der Zeit des Schlüpfens an gegeben wurde, unterschied sich nicht von der Fruchtbarkeit der Motten, die mit einer 30 prozentigen Honiglösung gefüttert wurden. Nahrungsentzug während der frühen Entwicklung (bis zu drei Tagen nach Schlüpfen) führte nicht zu einer Reduktion der Fruchtbarkit, vorausgesetzt dass Honiglösung von einem Alter von vier Tagen nach Schlüpfen angeboten wurde. Hungernde Motten legten weniger als 30% der Eier als mit Honiglösung oder Wasser gefütterte Motten. Fruchtbarkeit war korreliert mit dem Gewicht der Motten zur Zeit des Schlüpfeus, wenn die Motten mit Wasser oder Honiglösung gefüttert wurden, jedoch nicht, wenn weder Nahrung noch Wasser angeboten wurde. Mit Honiglösung gefütterte Motten beiderlei Geschlechts kopulierten weniger häufig, verloren Gewicht langsamer und lebten langer als mit Wasser oder nicht gefütterte Motten. Die Ergebnisse werden diskutiert in Bezug auf die Fortpflanzungsstrategie der Art.

     

Phytochrome control of plastid mRNA in mustard (Sinapis alba L.)

The steady-state levels of plastid RNA sequences in dark-grown and light-grown mustard (Sinapis alba L.) seedlings have been compared. Total cellular RNAs were labeled in vitro with ³²P and hybridized to separated restriction fragments of plastid DNA. Cloned DNA fragments which encode the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxylase (dimerizing), EC 4.1.1.39] and a 35,000 plastid polypeptide were used as probes to assess the levels of these two plastid mRNAs. The 1.22-kilobase-pair mRNA for the 35,000 polypeptide is almost undetectable in dark-grown seedlings, but is a major plastid mRNA in light-grown seedlings. The hybridization analysis of RNA from seedlings which were irradiated with red and far-red light indicates that the level of this mRNA, but not of LS mRNA, is controlled by phytochrome.Abbreviations LS large subunit - RuBP ribulose-1,5-bisphosphate - ptDNA plastid DNA     

Synthesis and turnover of the light-harvesting chlorophylla/b-protein inLemna gibba grown with intermittent red light: possible translational control

Lemna gibba L. G-3 plants grown heterotrophically in the dark with intermittent red light (2 min every 8 h) contain a substantial amount of translatable mRNA encoding the light-harvesting chlorophyll (Chl)a/b-protein. However, very little [³⁵S]methionine is incorporated into the apoproteins during a 1-h labeling period in the dark in these plants compared to plants grown in continuous white light. The Chla/b-protein mRNA is found to be associated with functioning polysomes in plants grown in the dark with intermittent red illumination (R plants). The small amounts of the apoproteins which are synthesized by these plants are found in the membrane fraction; neither the mature apoproteins nor their precursor(s) can be detected immunologically in the soluble fraction. The protein does not accumulate in these plants. Pulse-chase experiments with the R plants demonstrate that the newly synthesized apoproteins have a half-life of about 10 h in the dark. This turnover is not sufficient to explain the observed 20-fold difference in [³⁵S]methionine incorporation into the apoprotein between white-light-grown and R plants. We therefore suggest that the synthesis of the Chla/b-apoproteins can be regulated by a light-dependent step at the level of translation, and that this regulation occurs after the initiation of translation.Abbreviations Chl chlorophyll - W Lemna plants grown in continuous white light - R plants grown heterotrophically in the dark with intermittent red light (2 min/8 h)     

Control of light-induced bean leaf expansion: Role of osmotic potential,wall yield stress,and hydraulic conductivity

The role of three-turgor-related cellular parameters, the osmotic potential ( _s), the wall yield stress (Y) and the apparent hydraulic conductivity (L'p), in the initiation of ligh-induced expansion of bean (Phaseolus vulgaris L.) leaves has been determined. Although light causes an increase in the total solute content of leaf cells, the water uptake accompanying growth results in a slight increase in _s. Y is about 4 bar; and is unaffected by light. L'p, as calculated from growth rates and isopiestic measurements of leaf water potential, is only slightly greater in rapidly-growing leaves. The turgor pressure of growing cells is lower than that of the controls by about 35%. We conclude that light does not induce cell enlargement in the leaf by altering any of the above parameters, but does so primarily by increasing wall extensibility.Abbreviations and symbols RL red light - WL white light - L'p apparent hydraulic conductivity - OC osmotic concentration - Y wall yield stress - _s osmotic potential