Light-dark Regime Research Articles

Ovigerous Female Amphipods (Gammarus pseudolimnaeus) Face Increased Risks from Vertebrate and Invertebrate Predators

ABSTRACT We investigated the mortality rates of male and female amphipods resulting from stickleback fish Culaea inconstans) and dragonfly nymphs (Basiaeschna janata) predation. Both predators consumed significantly more ovigerous female amphipods than non-ovigerous females or males in 24-h trials. Stickleback fish consumed more non-ovigerous females than males, whereas dragonflies consumed more males than non-ovigerous females. These results were consistent across trials conducted under ambient light-dark regimes and those conducted in the absence of light, although overall mortality rates were highest in light trials. There were no significant differences in the recorded behaviors of the two predators. However, the behavior of ovigerous females differed significantly from that of males and non-ovigerous females, which may help to explain the overall differences in mortality. These results suggest that female amphipods incur a significant cost of increased predation risk associated with maternal care.

Nuclear targeted AtS40 modulates senescence associated gene expression in Arabidopsis thaliana during natural development and in darkness

The Arabidopsis thaliana AtS40-3 gene belongs to a group of genes sharing the conserved DUF548 sequence motif with up to now unknown function. One member of this group, the barley HvS40, was shown before to play a role in regulation of leaf senescence. Similar as the barley gene, AtS40-3 is induced during senescence and is also regulated in response to dark treatment, ABA, salicylic acid and pathogen attack. By localization of the GUS fusion protein, the AtS40-3 gene was shown to encode a nucleus targeted protein. The s40-3a mutant with a T-DNA insertion in the promoter region of the gene was observed to have a staygreen phenotype. By quantitative real-time PCR analyses expression of the AtS40-3 gene in this mutant was observed to be constitutive and not induced during senescence. This coincided with WRKY53 gene expression in nonsenescent leaves and lowered expression levels of WRKY53 and SAG12 at later stages of development. While in the wildtype expression of AtS40-3 was activated by darkness, in the s40-3a mutant the expression of AtS40-3 stayed at a low level. This coincided with lower expression of the SEN1 and SAG12 genes. In another promoter mutant with a T-DNA insertion further upstream of the coding sequence the levels of AtS40-3 and SAG12 transcripts increased in parallel both in a natural light-dark regime and in darkness. The data on gene expression in promoter T-DNA insertion mutants of the s40-3 gene indicate that AtS40 regulates senescence either by modulation of WRKY53 or by activation of SAG12 independent of WRKY53.

Effects of photoregime on the diel rhythmicity of male responses to sex pheromones in Glyphodes perspectalis (Lepidoptera: Crambidae)

We examined the effect of the photoregime on the timing of male responsiveness to sex pheromones in the box tree pyralid, Glyphodes perspectalis. Circadian oscillation was observed in the male responsiveness of G. perspectalis, evidenced by the rhythmic expression of male responsiveness in the duration corresponding to the expected scotophase of the continuous light or continuous dark conditions, when males reared under 16L8D were transferred to continuous light or continuous dark conditions. When male responsiveness to the sex pheromone was measured throughout the scotophase under three different photoregimes, it was shown that the time to reach the maximal response after lights-off was rather constant (approximately 2 h), regardless of the duration of the scotophase in three cases of 6, 8 and 10 h. The maximal response in the three cases appeared to be maintained until the end of the scotophase. Furthermore, in an experiment involving ±2-h shifts of lights-on or -off from the usual 16L8D, male responsiveness peaked within 2 hafter lights-off, and persisted throughout the remaining dark period. These results suggest that, at least under the present experimental conditions, the diel rhythmicity of male responsiveness based on the endogenous circadian rhythm is coordinated by the light-dark regime, and lights-off cues are critical for the timing and expression of the response rhythm leading to increased responsiveness.

Enabling mycelial application of Hirsutella thompsonii for managing the coconut mite

Laboratory and field studies were conducted to examine the prospect of mycelial application of Hirsutella thompsonii as an alternative to the use of mycelial-conidial formulations of the fungus in the suppression of the coconut mite, Aceria guerreronis. In a series of laboratory experiments, glycerol, yeast extract powder and dehydrated malt extract broth were found to be the best among nine substances investigated as possible adjuvants for use on coconut palms in the field along with H. thompsonii mycelia. H. thompsonii biomass in the presence of adjuvants not only produced more colonies but also yielded more conidia per pellet. In terms of the density of conidia generated on a mycelial mat the treatments varied highly significantly in two methods, with glycerol showing an average of 106% increase over control. Though irradiance with simulated sunlight resulted in reduced conidiogenesis, in general, adjuvant-treated pellets, both exposed and unexposed to simulated sunlight, produced substantial conidiation compared with control, irrespective of the two incubation conditions. Better conidiation was observed under alternating light-dark regime than under total darkness in all the treatments. Glycerol boosted the pathogenicity of H. thompsonii by 16.5% over control. In the field, a newly developed mycelial formulation of H. thompsonii applied after tank-mixing separately with the three selected adjuvants brought down the post-treatment population of the coconut mite by 85.6-97.1%. Application of the fungus in combination with glycerol resulted in a tolerable mean nut damage grade of 2.0 during the pre-harvest stage, compared with an acute score of 4.0 in control palms.

Day-night activity rhythm of the cold seep shrimp Alvinocaris stactophila (Caridea: Alvinocarididae) from the Gulf of Mexico

The activity rhythm of the cold seep shrimp Alvinocaris stactophila from the Gulf of Mexico slope (650 m depth) was investigated in the laboratory in relation to an artificial 12 h light-dark regime. Animals were sampled with a submersible and transferred into individual aquaria where their activity was monitored for 5 d by taking digital video snapshots every 30 s. An observer analysed the footage by counting the number of times an animal crossed two perpendicular lines drawn on a PC screen per 30 min interval. Resulting time series were represented over consecutive days and the waveform analysis was used to precisely assess the phase (i.e. the peak timing) and its limits (i.e. onset and offset) in relation to light ON and OFF. The majority (73%) of animals showed a marked nocturnal pattern of activity with number of movements close to zero during the photophase. Waveform analysis showed that the behavioural transition from activity to inactivity after light ON occurred within approximately 1 h. Considering the general lack of knowledge on the regulation of activity rhythms of crustaceans from subtidal areas, the present data provide a new insight on the role played by light in the regulation of animal activity rhythm in deep-water environments such as those of the cold seeps in the Gulf of Mexico.

Seed Germination Strategies of Desmostachya Bipinnata: A Fodder Crop for Saline Soils

Desmostachya bipinnata (L.) Stapf. (Poaceae), or drub, a perennial grass of near-coastal and inland deserts, is a potential fodder crop for either saline soils or where only brackish water is available for irrigation. The responses of D. bipinnata seeds under various salinity (0, 100, 200, 300, 400, and 500 mM NaCl), temperature (10u–20u ,1 5u–25u, 20–30u, and 25u–35uC) and light (12:12-h dark:light and 24-h dark) regimes were investigated. All seeds germinated under nonsaline conditions, however, increase in salinity resulted in a progressive decrease in germination, and few seeds germinated at 500 mM NaCl. Change in temperature had little effect on seed germination under nonsaline conditions, however, seed germination was inhibited under cooler saline conditions. The germination under saline conditions improved at warmer temperature regimes. Seed germination under nonsaline control in dark was similar to those of seeds germinated in light. However, at high salinities, seed germination was substantially inhibited in dark in comparison to those germinated in light. When ungerminated seeds were transferred to distilled water they germinated immediately, and those from higher salinity and temperature regimes had higher recovery. The ability of seeds to germinate over a range of salinity and temperature regimes suggests possibilities for sustainable use of this species as a cash crop in saline soils. Resumen El Desmostachya bipinnata (L.) Stapf. (Poaceae), un zacate perenne que crece cerca de las costas y en el interior de los desiertos,

Effects of short light-dark regimes on in vitro shoot rooting of some fruit tree rootstocks

Experiments were carried out to evaluate the effects of 4/2 light-dark cycles (4 h of light followed by 2 h of dark) on the rooting responses of shoots cultivated in vitro of the fruit tree rootstocks GF 677 (peach × almond hybrid), Mr.S. 2/5 (Prunus cerasifera), MM 106 (apple Nothern Spy × Paradise M1) and BA 29 (Cydonia oblonga). Under this light regime rooting percentage of GF 677, Mr.S. 2/5 and MM 106 shoots reached 100 % as in the control treatment (16/8), while in BA 29 shoots, short light-dark cycles increased rooting response by about 65 %. Moreover, the shoots of all rootstocks submitted to the 4/2 cycle showed an appreciable increase in root number and length, and an earlier root emergence of about 4 - 5 d compared to the 16/8 cycle. Finally, rooting percentage of BA 29 shoots submitted to the 4/2 light regime and treated with 0.2 mg dm-3 indolebutyric acid (IBA), was equal to that reported with 0.4 mg dm-3 IBA under the 16/8 regime, indicating that the former light regime also amplified the rhizogenic effect of auxin.

Identification, subcellular localization and biochemical characterization of water‐soluble heteroglycans (SHG) in leaves of Arabidopsis thaliana L.: distinct SHG reside in the cytosol and in the apoplast

Water-soluble heteroglycans (SHG) were isolated from leaves of wild-type Arabidopsis thaliana L. and from two starch-deficient mutants. Major constituents of the SHG are arabinose, galactose, rhamnose, and glucose. SHG was separated into low (<10 kDa; SHG(S)) and high (>10 kDa; SHG(L)) molecular weight compounds. SHG(S) was resolved into approximately 25 distinct oligoglycans by ion exchange chromatography. SHG(L) was further separated into two subfractions, designated as subfraction I and II, by field flow fractionation. For the intracellular localization of the various SHG compounds several approaches were chosen: first, leaf material was subjected to non-aqueous fractionation. The apolar gradient fractions were characterized by monitoring markers and were used as starting material for the SHG isolation. Subfraction I and SHG(S) exhibited a distribution similar to that of cytosolic markers whereas subfraction II cofractionated with crystalline cellulose. Secondly, intact organelles were isolated and used for SHG isolation. Preparations of intact organelles (mitochondria plus peroxisomes) contained no significant amount of any heteroglycan. In isolated intact microsomes a series of oligoglycans was recovered but neither subfraction I nor II. In in vitro assays using glucose 1-phosphate and recombinant cytosolic (Pho 2) phosphorylase both SHG(S) and subfraction I acted as glucosyl acceptor whereas subfraction II was essentially inactive. Rabbit muscle phosphorylase a did not utilize any of the plant glycans indicating a specific Pho 2-glycan interaction. As revealed by in vivo labeling experiments using 14CO2 carbon fluxes into subfraction I and II differed. Furthermore, in leaves the pool size of subfraction I varied during the light-dark regime.

Daily growth lines in some living Pectens (Mollusca: Bivalvia), and some applications in a fossil relative: Time and tide will tell

Laboratory experiments on two species from the Pecten (Pecten) subgroup of pectinids indicated that they form growth lines with a true (solar) daily periodicity. Experimental subjects that formed growth lines in numbers equal to their days of growth were consistently those with uniform, apparently continuous shell growth, and subjects that formed fewer lines than days were those with stress marks, or disturbance lines. No subjects formed more growth lines than days. Furthermore, those specimens forming stress marks had those marks spaced out in very similar patterns, apparently in response to stressful events in their aquarium, such that the patterns could be correlated, not only between the specimens with interrupted growth, but with the others as well. In the original experiments, a natural light–dark stimulus had been present (transparent aquaria near an outside window). To test whether the subjects were responding to this stimulus, another experiment was conducted in which several individuals were subjected to an accelerated light–dark regime. These subjects responded by increasing production of their growth lines to approach the number of cycles to which they had been exposed. An opportunity to extend this work into the fossil record came with the collection of a number of Pliocene pectinids, closely related to one of the species used in the experiments, from a thin horizon that almost certainly represents a catastrophic event. Measurements of the intervals between growth lines were made across hundreds of increments on many paired (and presumably untransported) valves. Comparison of these growth rate records suggested that many, and perhaps all of these individuals died at the same time. Moreover, frequency analysis of these records revealed a regular fluctuation of about 15 days, suggesting a tidal cycle marked off by solar increments. When the growth rate patterns were compared with nearby tidal regimes, the best fit was for a regime matching the currently accepted paleogeography of the collecting site in Pliocene time. This strongly supports the experiments on the living species, for tidal patterns in the fossil group could not have been revealed without an accurate solar marker.

Effect of light period on egg-discharge of gametophyte clones of Undaria pinnatifida (Phaeophyta)

A sporeling culture method using gametophyte clones developed in the early 1990s led to egg discharge occurring in the dark 5 min after the start of the dark period under growth under a 11:13 L-D photoperiod. The course of egg discharge could be disturbed by light, with irradiance as low as 5-6 mu mol photon m(-2) s(-1) causing 75-80% of the discharged eggs to detach from the oogonia and consequently to die within several hours. In order to enhance outgrowth rate of young sporophytes, a study was conducted to test the effect of controlling darkness in the period 2-3 h after dusk. When the slides were transferred from the standard 11:13 L-D regime to continuous light, eggs were discharged 5 min after the end of the light phase and peaked 5-l5 min later on first day after transfer, indicating that the female gametes "remember" the light-dark regime. This suggests the existence of an endogenous circadian rhythm. During the second and third days, very few eggs were discharged throughout the 11 h of the normal light phase of the L-D regime, indicating the inhibitory effect of continuous light and that the rhtyhm is easily damped by light.

Modulation of pigment profiles of Calothrix elenkenii in response to environmental changes

Cyanobacteria are versatile tetrapyrrole synthesizers that can regulate their tetrapyrrole content and composition in response to environmental signals. The present investigation analyses the interplay between light and dark regimes (continuous light, light–dark cycles (16:8) and continuous darkness) and aerobic, air-tight, and anaerobic environments (argon-enriched), on the relative composition of various pigments and growth attributes of Calothrix elenkenii as a prelude to exploiting C. elenkenii's bioindustrial potential as a source of pigments. Incubation in an anaerobic environment stimulated hormogonia formation and induced colouration/thickening of cells. Aerobically grown cultures of Calothrix, under continuous illumination produced the maximum amount of total phycobiliproteins and sugars, although chlorophyll accumulation and nitrogenase activity were highest in the light–dark environment. However, the β-carotene content was observed to vary under anaerobic conditions with different light–dark regimes. This C. elenkenii strain can be a valuable source of pigments under optimized environmental conditions.

Distinct regulation of sucrose: sucrose-1-fructosyltransferase (1-SST) and sucrose: fructan-6-fructosyltransferase (6-SFT), the key enzymes of fructan synthesis in barley leaves: 1-SST as the pacemaker.

• Previously we have cloned sucrose: fructan-6-fructosyltransferase (6-SFT) from barley (Hordeum vulgare) and proposed that synthesis of fructans in grasses depends on the concerted action of two main enzymes: sucrose: sucrose-1-fructosyltransferase (1-SST), as in other fructan producing plants, and 6-SFT, found only in grasses. • Here we report the cloning of barley 1-SST, verifying the activity of the encoded protein by expression in Pichia pastoris. As expected, the barley 1-SST is homologous to invertases and fructosyltransferases, and in particular to barley 6-SFT. • The gene expression pattern of 1-SST and 6-SFT, along with the corresponding enzyme activities and fructan levels, were investigated in excised barley leaves subjected to a light-dark regime known to sequentially induce fructan accumulation and mobilization. The turnover of transcripts and enzyme activities of 1-SST and 6-SFT was compared, using appropriate inhibitors. • We found the 1-SST transcripts and enzymatic activity respond quickly, being subject to a rapid turnover. By contrast, the 6-SFT transcripts and enzymatic activity were found to be much more stable. The much higher responsiveness of 1-SST to regulatory processes, as compared with 6-SFT, clearly indicates that 1-SST plays the role of the pacemaker enzyme of fructan synthesis in barley leaves.

Day/night pattern of arterial blood gases in the cow.

Both metabolic rate and pulmonary ventilation change throughout 24h with a circadian pattern. Because their changes occur almost in synchrony and by a similar amount, blood gases may remain steady within a narrow range. We tested this possibility in five cows (Bos taurus, Bruna Italiana breed), maintained in a stable at 29 degrees C, under natural light-dark (LD) regime, by measuring arterial blood gases every 3h for 2 days. All cows presented a clear day/night pattern of body temperature (T(b)), with an average peak-trough difference (PTD) of 0.5 degrees C. Breathing rate oscillated significantly in three out of five animals, with a group-mean PTD of 2 breaths per minute, and it was time-advanced with respect to the oscillation of T(b). Significant oscillations in arterial pH, bicarbonate, partial pressure of oxygen and partial pressure of carbon dioxide (Pa(CO2) ) were observed in, respectively, 1 cow out of 5, 1/5, 3/5 and 5/5. Of all these variables, group-mean analysis revealed a significant day/night pattern only for Pa(CO2), and even in this case the average PTD was less than 1 mmHg. We conclude that, in the cow, blood gases remain remarkably stable throughout the 24 h. Hence, the daily oscillations of body temperature, breathing rate, and probably of many other factors affecting metabolic rate and pulmonary ventilation do not preclude an excellent homeostasis of blood gases.

The stem-loop region of the tobacco psbA 5'UTR is an important determinant of mRNA stability and translation efficiency.

Regulation of chloroplast gene expression involves networked and concerted interactions of nucleus-encoded factors with their target sites on untranslated regions (UTRs) of chloroplast transcripts. So far, only a few cis-acting elements within such 5'UTR sequences have been identified as functional determinants of mRNA stability and efficient translation in Chlamydomonas in vivo. In this study, we have used chloroplast transformation and site-directed mutagenesis to analyse the functions of the 5'UTRs of tobacco psbA and rbcL fused to the coding region of the reporter gene uidA. Various mutant versions of the psbA leader, as well as rbcL/psbA hybrid leader elements, were investigated. Our results showed a 1.5- to 3-fold decrease in uidA mRNA levels and a 1.5- to 6-fold reduction in uidA translation efficiency in all psbA 5'UTR stem-loop mutants generated by sequence deletions and base alterations. This indicates that the correct primary sequence and secondary structure of the psbA 5'UTR stem-loop are required for mRNA stabilisation and translation. The 5'-terminal segment of the rbcL 5'UTR did not enhance the stability or translational activity of chimeric uidA mRNA under the standard light-dark regime of 16 h light and 8 h dark. Stabilising effects were, however, observed when the cells were kept continuously in the dark. Possible reasons for the influence of the 5'UTR of the tobacco psbA on mRNA stability and translation efficiency are discussed.

Germination of Sclerotinia minor and S. sclerotiorum Sclerotia Under Various Soil Moisture and Temperature Combinations

ABSTRACT Sclerotial germination of three isolates each of Sclerotinia minor and S. sclerotiorum was compared under various soil moisture and temperature combinations in soils from Huron and Salinas, CA. Sclerotia from each isolate in soil disks equilibrated at 0, -0.03, -0.07, -0.1, -0.15, and -0.3 MPa were transferred into petri plates and incubated at 5, 10, 15, 20, 25, and 30 degrees C. Types and levels of germination in the two species were recorded. Petri plates in which apothecia were observed were transferred into a growth chamber at 15 degrees C with a 12-h light-dark regime. All retrievable sclerotia were recovered 3 months later and tested for viability. Soil type did not affect either the type or level of germination of sclerotia. Mycelial germination was the predominant mode in sclerotia of S. minor, and it occurred between -0.03 and -0.3 MPa and 5 and 25 degrees C, with an optimum at -0.1 MPa and 15 degrees C. No germination occurred at 30 degrees C or 0 MPa. Soil temperature, moisture, or soil type did not affect the viability of sclerotia of either species. Carpogenic germination of S. sclerotiorum sclerotia, measured as the number of sclerotia producing stipes and apothecia, was the predominant mode that was affected significantly by soil moisture and temperature. Myceliogenic germination in this species under the experimental conditions was infrequent. The optimum conditions for carpogenic germination were 15 degrees C and -0.03 or -0.07 MPa. To study the effect of sclerotial size on carpogenic germination in both S. minor and S. sclerotiorum, sclerotia of three distinct size classes for each species were placed in soil disks equilibrated at -0.03 MPa and incubated at 15 degrees C. After 6 weeks, number of stipes and apothecia produced by sclerotia were counted. Solitary S. minor sclerotia did not form apothecia, but aggregates of attached sclerotia readily formed apothecia. The number of stipes produced by both S. minor and S. sclerotiorum was highly correlated with sclerotial size. These results suggest there is a threshold of sclerotial size below which apothecia are not produced, and explains, in part, why production of apothecia in S. minor seldom occurs in nature.

Modeling of photobioreactors: Application to bubble column simulation

Photobioreactors using algae, plant cells, or photosynthetic bacteria have received considerable attention from biochemical engineers. Industry is presently engaged in developing new products and testing a new generation of algal-derived natural products such as natural dyes, polyunsaturated fatty acids and polysaccharides. The present paper is a review of some of the recent findings of the authors in the field. A mathematical representation of the growth of a photosynthetic system in an alternating light-dark regime is presented. This model integrates fluid dynamics and maintenance into the three-state "Photosynthetic Factories" model by Eilers and Peeters. The model was solved analytically and the constants were fitted to experimental data obtained in a thin film tubular reactor. The theoretical prediction that the introduction of light-dark cycles may enhance the growth was confirmed by the experimental results. The model allows predicting the collapse of cultures in photobioreactors either under light-deficit or light-excess conditions, as well as the influence of mixing on these critical phenomena. This paper presents an approach to modeling the kinetics of photosynthetic systems for photobioreactor design. Under conditions of simultaneous occurrence of photoinhibition in one region of the reactor, and photo-limitation in another, it takes into account the movement of the cells from one region to the other. The model was applied to the mathematical modeling of a 13-liter bubble column photobioreactor. Experimental data were satisfactorily fit, using the kinetic data obtained independently in the thin-film experiments. The model was extended to simulate a "farm" of photobioreactors and the results presented defining Ground Productivity, which expresses the rate of biomass production of a farm of relatively small photobioreactors per area of ground required for the installation.

Behavioral and electrophysiological evidence for volatile sex pheromones in Parcoblatta wood cockroaches.

Species within the cockroach genus Parcoblatta are sexually dimorphic for wing length; females have reduced wings and are flightless, while males have long wings that are used in flight. We predicted that Parcoblatta females would release a volatile sex pheromone to attract the more mobile males. Nymphs of the broad wood cockroach, P. lata, and the Caudell's wood cockroach, P. caudelli, were collected in forested areas in North Carolina, USA, and reared in the laboratory for observations of sexual behavior and for pheromone analysis. After several days of sexual maturation, virgin females of both species exhibited distinct calling behaviors. In females of P. lata, calling commenced 6 days after adult emergence. Under a light-dark photoperiod regime, calling behavior in both species was restricted to the scotophase. Calling consisted of a repeated pattern of raising and lowering the abdomen with occasional exposure of the genital vestibulum. To test whether calling behavior is associated with the release of pheromone, volatiles from calling and noncalling females were collected on Super-Q and tested by electroantennogram (EAG) and behavioral assays. Volatile collections from calling females elicited higher male-specific EAG responses than collections from noncalling females of the same physiological stage. In an olfactometer choice test (Y-tube), males preferred volatiles from calling females over those from noncalling females. To determine the anatomical source of the pheromone, solvent extracts of various body parts were analyzed by EAG. The first through seventh tergites were the only body parts that elicited male-specific EAG responses in both species. In P. lata, the activity of the extract increased from 1- to 7-day-old females, but was lower in mated than in virgin females of the same age. The putative pheromone gland appears to consist of numerous class-3 secretory units, each composed of a secretory cell connected to a cuticular pore via a tubular duct. We conclude that female P. lata and P. caudelli produce ex-specific volatile pheromones that are emitted during calling behavior.

Recent Outbreak of Soybean Stem Canker Caused by Diaporthe phaseolorum var. caulivora in the Main Soybean-Producing Region of Argentina.

The first report of soybean stem canker (SSC) caused by Diaporthe phaseolorum var. caulivora in South America was published in 2001, and was based on an isolate obtained in 1999 at Oliveros, Santa Fe (32°33'S, 60°51'W), Argentina (2). During the 2001 to 2002 growing season, isolates of D. phaseolorum var. caulivora were obtained from stems of field-grown soybeans (Glycine max L.) exhibiting SSC symptoms. Isolates were collected in three localities of the main soybean-producing region of Argentina: Marcos Juárez, Córdoba (32°66'S, 62°10'W); Salto, Buenos Aires (34°20'S, 60°33'W); and Diego de Alvear, Santa Fe (34°21'S, 62°10'W), and disease incidence in the fields was 10 to 60%, 5 to 15%, and 10 to 20%, respectively. The pathogen was isolated on potato glucose agar acidified with 0.2% lactic acid cultured in the dark at 25 ± 1°C. White colonies with compact and tufted mycelium were produced and turned yellow and light tan after 6 days. Appressed and fluffy mycelia were observed in old cultures. Stromata (2 mm diameter) were produced but pycnidia were not detected. After 20 days in culture at 25 ± 1°C under a 12-h light and 12-h dark regime, clustered perithecia developed on stem segments. For each isolate, 10 perithecia, 90 asci, and 30 bicellular, biguttulate ascospores were measured. Averages of asci length and width were 28.3 ± 2.3 and 5.9 ± 0.7 μm, respectively. Averages of ascospores mean length and width were 8.4 ± 0.6 and 2.5 ± 0.4 μm, respectively. These measures were similar to the measures obtained previously (2). Based on these features, the new isolates were classified as D. phaseolorum var. caulivora (Athow & Caldwell). Clustered perithecia, smaller asci and ascospores, and the development of fluffy mycelia with age were the main characteristics that distinguished D. phaseolorum var. caulivora from D. phaseolorum var. meridionalis (1). Pathogenicity trials were performed on cvs. Tracy M, Crockett, Hutchenson, and RA 702 in the greenhouse by placing a small amount of mycelium in soybean seedling hypocotyls wounds made with a scalpel. The pathogen was reisolated from stem portions of the symptomatic plants. Control plants remained healthy. The results reported here show that D. phaseolorum var. caulivora is widely disseminated in the main soybean-producing region of Argentina, where it coexists with D. phaseolorum var. meridionalis (2). The coexistence of both varieties indicates pathogen variability in the region is higher than previously recognized.

Diurnal Oscillations in Gas Production (O2, CO2, CH4, and N2) in Soil Monoliths

Soil cores (35 cm long, 7 cm diameter) from the Macaulay Land Use Research Institute's Sourhope Research Station in the Scottish Borders were kept and monitored at constant temperature (18± 1°C) for gas production using a 1.6 mm diameter stainless steel probe fitted with a membrane inlet and connected to a quadrupole mass spectrometer. This provided a novel method for on-line, real time monitoring of soil gas dynamics. In closed-system headspace experiments, O2 and CO2 (measured at m/z values 32 and 44, respectively) showed anti-phase diurnal fluctuations in low-intensity simulated daylight and under a light-dark (LD, 12:12 h) regime. O2 increased during periods of illumination and decreased in the dark. The inverse was true for CO2 production. Ar (m/z = 40) concentration and temperature (°C) remained constant throughout the experiments. The same phase-related oscillations, in CO2 and O2 concentrations, were observed at 2 and 5 cm depth in soil cores. The O2 concentration did not oscillate diurnally at 10 cm depth. In below-ground experiments, CH4 (m/z = 15) concentration showed diurnal cycles at 2, 5 and 10 cm depth. The CH4 production had the same diurnal phase cycle as CO2 but with lower amplitude. Evidence of below-ground diurnal oscillations in N2 (m/z = 28) concentration was provided at 5 cm depth. The scale of production and consumption of gases associated with soil-atmosphere interactions and below-ground processes, are shown to be a multifaceted output of several variables. These include light, circadian-controlled physiological rhythms of plants and microbes, and the interactions between these organisms.

First plant circadian phase mutant identified

Circadian rhythms exhibited by plants include leaf movements, CO2 fixation, stomatal conductance and gene expression. They have evolved in response to, and are entrained by, environmental periodicities (zeitgeber), primarily daily changes in light intensity, such that the endogenous oscillation adopts the 24 h periodicity of the zeitgeber and a particular phase relationship to it. The phytochrome (PHY) and cryptochrome (CRY) photoreceptor families mediate light input to the clock and the importance of several of these proteins in establishing period length has recently become apparent. However, how the phase of plant rhythms is determined is unknown. Indeed, the Arabidopsis Genome Initiative revealed no plant orthologues to clock proteins involved in phase determination in animal and prokaryote circadian systems.‘…this study identifies PHYB as an important regulator of white light-mediated phase determination…’In a new study, Patrice A. Salome and colleagues [1xThe out of phase 1 mutant defines a role for PHYB in circadian phase control in Arabidopsis. Salome, P.A. et al. Plant Physiol. 2002; 129: 1674–1685Crossref | PubMed | Scopus (61)See all References][1] describe a new allele of PHYB, out of phase 1 (oop1), which confers an altered circadian phase phenotype. The Arabidopsis thaliana mutant was isolated by exploiting a rhythm of sensitivity to the air pollutant sulfur dioxide, selecting plants exhibiting damaged leaves at a time when wild-type plants were resistant. After 7 days entrainment in a 12-h:12-h (white) light–dark regime, the peaks of leaf movement and CO2 assimilation rhythms in oop1 plants occurred 3.6 and 3.4 h earlier, respectively, than in wild-type plants. Period lengths were unaltered. Sequencing revealed two mutations in PHYBoop1; one introducing an early stop codon such that a truncated protein lacking most of the C-terminal kinase domain is expressed. Because oop1 seedlings displayed light-induced inhibition of hypocotyl elongation under blue or far- red light but not red light, the authors propose that the altered phase phenotype results primarily from impaired red-light photoreception through PHYB. Indeed, when phyB-9, a previously identified complete loss-of-function allele, was crossed into plants harbouring a transcriptional fusion of the LIGHT-HARVESTING CHLOROPHYLL a/b BINDING PROTEIN promoter and luciferase (LHCB::LUC), LHCB::LUC rhythms were coincident with those exhibited by the corresponding oop1 cross. However, the data suggest that the oop1 mutation also interferes with other light-signalling pathways because the elongated hypocotyl phenotype was also observed when oop1 seedlings were illuminated by white light or combinations of red light with high fluence blue light. This implies a red light-dependent alteration of blue-light signalling, presumably through CRY1, the primary blue-light photoreceptor at high fluence rates.In characterizing oop1, the first circadian phase mutant of a plant, this study identifies PHYB as an important regulator of white light-mediated phase determination, and, as such, represents an important milestone in circadian biology. Observations that oop1 plants exhibit wild-type period length and do not show the altered phase phenotype when entrained to temperature cycles indicate that oscillator function itself is not affected. However, whether impaired PHYB signalling affects light input to the clock or components of the output pathway downstream of the oscillator remains to be determined. Future studies on PHY INTERACTING FACTOR 3, a target of PHYB signalling, which activates transcription of two known clock components in plants should help resolve this question and provide further insight into the molecular basis of phase determination in plants.