High temperature — induced changes in germination,seedling vigour and the metabolic activities in rice seeds

The effects of temperature treatments on rice seeds in the early imbibitional phase were studied with respect to changes in germination percentage, seedling growth in terms of root and shoot lengths, water uptake, respiration and hydrolytic enzymes,viz. α-amylase, adenosine triphosphatase (ATPase) and phytase. As compared with the control, the treatment for 30 min at 50 °C caused a variable degree of increase in all these characters and a positive correlation existed between seedling vigour and hydrolase activities. The treatment for 30 min at 60 °C, on the other hand, elicited a retarding influence on these characters. As regards the enzyme activities, the damaging effect of 60 °C could, however, be visualized only after 72 h of germination which was preceded by an enhancement during the early hours.     

Endo-β-mannanase isoforms are present in the endosperm and embryo of tomato seeds, but are not essentially linked to the completion of germination

A current hypothesis is that endo--mannanase activity in the endosperm cap of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seeds is induced by gibberellin (GA) and weakens the endosperm cap thus permitting radicle protrusion. We have tested this hypothesis. In isolated parts, the expression of endo--mannanase in the endosperm after germination is induced by GAs, but the expression of endo--mannanase in the endosperm cap prior to radicle protrusion is not induced by GAs. Also, abscisic acid (ABA) is incapable of inhibiting endo--mannanase activity in the endosperm cap, even though it strongly inhibits germination. However, ABA does inhibit enzyme activity in the endosperm and embryo after germination. There are several isoforms in the endosperm cap and embryo prior to radicle protrusion that are tissue-specific. Tissue prints showed that enzyme activity in the embryo spreads from the radicle tip to the cotyledons with time after the start of imbibition. The isoform and developmental patterns of enzyme activity on tissueprints are unaffected when seeds are incubated in ABA, even though germination is inhibited. We conclude that the presence of endo--mannanase activity in the endosperm cap is not in itself sufficient to permit tomato seeds to complete germination.Abbreviations ABA cis/trans-abscisic acid - GA(s) gibberellin(s) - IEF isoelectric focussing - pI(s) isoelectric point(s) We thank Dr. Bruce Downie for the seemingly endless but inspiring discussions.     

Assessment of changes in physiological and biochemical traits in four pistachio rootstocks under drought,salinity and drought + salinity stresses

In this study, 7-month-old UCB-1, Badami, Ghazvini and Kale-Ghouchi pistachio rootstocks were exposed to control, drought, salinity and drought + salinity environments for 60 d. Total chlorophyll and total carotenoid contents decreased in all cultivars under drought, salinity and drought + salinity stresses. Under drought and salinity stresses, alone or in combination, Na⁺ and Cl⁻ ions increased in all four pistachio rootstocks, while K⁺ ion decreased only in Ghazvini and Kaleh-Ghouchi cultivars. The enzyme activities of ascorbate peroxidase, polyphenol oxidase, catalase and guaiacol peroxidase increased in all cultivars when subjected to all three stresses with the exception of the ascorbate peroxidase activity in Kale-Ghouchi cultivar during drought stress. Oxidative stress parameters including electrolyte leakage, malondialdehyde, other aldehydes and hydrogen peroxide increased under all three stress conditions in all genotypes. The content of proline, total free amino acids and total soluble carbohydrates were enhanced under drought, salinity and drought + salinity stresses, whereas the protein content decreased in all pistachio rootstocks. In all evaluated traits, except for the K⁺ ion content and APX activity, the highest impacts was seen for drought + salinity > salinity > drought stresses, respectively. For the first time, we have proven that K⁺ ion content has a positive correlation with the ascorbate peroxidase, polyphenol oxidase, catalase and guaiacol peroxidase enzymes activities under drought + salinity stress. Finally, based on the bi-plot and cluster analyses, we have selected the UCB-1 > Badami > Ghazvini > Kale-Ghouchi cultivars as the most tolerant pistachio rootstocks under drought + salinity stress, respectively.     

Seasonal Modulation of the 8‐and 24‐Hour Rhythms of Ondansetron Tolerance in Mice

Ondansetron (Zophren®) is a serotonin 5HT₃-receptor antagonist used primarily to control nausea and vomiting caused by cytotoxic chemo‐and radio‐therapy. Tolerance to this drug shows both 24 and 8 h periodicities. In this framework, this study aimed to determine whether these ondansetron tolerance rhythms are modulated by season. The chronotoxic effect of a fixed dose (3.5 mg/kg, i.p.) of the drug was investigated with reference to both time of the day and year dependencies. Season‐related studies were performed on 560 male Swiss mice, 10 to 12 wks old, synchronized with L:D=12:12 for three weeks. During a 1 yr span (2005), four 24 h studies were performed with a single dosing time at 1, 7, 13, and 19 hours after light onset (HALO), respectively. Tolerance was assessed daily during a 40‐day span after acute ondansetron treatment. Both χ² test and cosinor methods were used to analyze the time series data. Statistically significant dosing time‐dependent changes were validated in both yearly and daily time scales. The 24 h mean survival rate peaked in spring (92%) compared to fall (72%), the 20% difference being statistically significant (χ² test with p<0.05 and cosinor with p<0.0001 for seasonal rhythm detection and with a peak time, Ø,=April 3±6.6 days). A 24 h rhythm was also detected in each of the seasonal time points. However, the curve pattern was monophasic in fall as well as spring. In fall, a large amplitude (A) circadian rhythm was detected that peaked at 19 HALO, while in the spring, a small circadian rhythm was detected that peaked at 1 HALO. The curve pattern was biphasic in summer (with large A) and in winter (with a small A). The existence of two peaks of equal magnitude in winter (100% survival rate) and in summer (100% and 90%) suggests the presence of both circadian and ultradian rhythms rather than an ultradian component of the 24 h period. The seasonal modulation of ondansetron circadian chronotolerance seems to involve several rhythm parameters: season‐related changes in the 24 h mean (M), amplitude (A), acrophase location (Ø), as well as bimodal curve patterns including the coexistence of rhythms with respectively 24 and 8 h periods in winter and summer. In conclusion, tolerance to ondansetron varies not only according to the 24 and 8 h periods but also according to seasons, which suggests the complexity of ondansetron toxicity rhythms. Seasonal modulation of ondansetron tolerance may also influence the strategies of chemo‐and chrono‐therapy, and it is therefore necessary to take it into account in clinical drug‐delivery protocols to minimize side effects of cytotoxic anticancer and antiemetic agents.     

Seasonal changes in eelgrass functions: current velocity reduction,prevention of sediment resuspension,and control of sediment–water column nutrient flux in relation to eelgrass dynamics

We assessed seasonal changes in eelgrass (Zostera marina) functions, i.e., reduction of current velocity, buffering of sediment resuspension, and control of dissolved inorganic nitrogen flux between the sediments and the water column, using field observations and experiments in the Akkeshi-ko estuary, Hokkaido, Japan. We also analyzed the relationships between eelgrass traits and functions. The efficiency of the reduction in current velocity increased with the development of the eelgrass canopy. Sediment resuspension was inhibited from May to August, during which time the eelgrass canopy developed. Eelgrass controlled the NH₄ ⁺ concentration of sediment porewater through root nutrient uptake, affecting NH₄ ⁺ flux between the sediments and the water column. Fluctuations in eelgrass functions and coincident changes in dynamics resulted in seasonal changes in the eelgrass environment, which may in turn affect the dynamics of organisms inhabiting eelgrass beds, e.g., mysids and epiphytic algae. Moreover, the developed eelgrass canopy trapped a large amount of material during spring and summer, which was resuspended into the surrounding ecosystem in autumn when the canopy and its functions (i.e., reduction of current and sediment resuspension) diminished. These results suggest that seasonal changes in eelgrass functions also affect communities within marginal coastal ecosystems through the control of allochthonous resources. Handling editor: P. Viaroli     

Seasonal and interannual cycles of endemic cholera in Bengal 1891–1940 in relation to climate and geography

The temporal distribution of chlorophyll a (chl a), suspended matter (SM), and vertical flux of chl a and organic carbon (OC) has been investigated at three sites along the north-eastern coast of the Gulf of Aqaba during the period from January 1991 through December 1992. Highly significant temporal and interannual variations were found in chl a, and in the vertical flux of chl a and OC. The SM and its OC content did not show any significant temporal or interannual variations. The recorded levels of the forementioned variables were generally low. The temporal distribution of chl a in the water column was polymodal in 1991 with peaks in March, June, August and December, and bimodal in 1992 with peaks in May–June, and October. Maximum values of SM and its OC content occurred in July of 1991 and September of 1992. The temporal variations in the vertical flux of total particles, chl a, and OC followed those of chl a in the water column. The bulk of the sediment material was of inorganic nature, derived from desert sand carried from Wadi Araba by the prevailing northerly winds, and dust of exported raw phosphate. The temporal changes described appear to be related to the temporal variations in water stability, horizontal advection, and winds.     

Photosynthetic capacity and temperature responses of photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) acclimate to changes in ambient temperatures

The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V _cmax, and maximal light driven electron flux, J _max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A–C _i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T _opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A _opt), V _cmax and J _max at a reference temperature of 25°C (V _cmax25 and J _max25) as well as activation energy of V _cmax and J _max (E _aV and E _aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V _cmax and J _max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J _max25/V _cmax25 was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V _cmax25/N _a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.     

Function of muscle-type lactate dehydrogenase and citrate synthase of the Galápagos marine iguana, Amblyrhynchus cristatus, in relation to temperature

The Galápagos marine iguana, Amblyrhynchus cristatus, is unique among lizards in foraging subtidally, leading to activity across a broad range of ambient temperatures ( approximately 14-40 degrees C). To determine whether the marine iguana shows any biochemical changes consistent with maintaining enzyme function at both warm and cold body temperatures, we examined the function of the aerobic enzyme citrate synthase (CS) and the muscle isoform of the anaerobic enzyme lactate dehydrogenase (A(4)-LDH) in A. cristatus and a confamilial species, Iguana iguana, from 14 to 46 degrees C. We also deduced amino acid sequences from cDNA of each enzyme. In CS, despite two amino acid substitutions, we found no difference in the apparent Michaelis-Menten constant K(m) of oxaloacetate at any temperature, indicating that the substrate affinity of CS in A. cristatus has not adapted to changes in thermal environment. In A(4)-LDH, we used site-directed mutagenesis to show that the substitutions T9A and I283V (A. cristatus --> I. iguana) individually have no effect on kinetics, but together significantly decrease the K(m) of pyruvate and catalytic rate constant (k(cat)) of the A. cristatus ortholog. Thus, our data show that A. cristatus A(4)-LDH has not become cold adapted in response to this species' aquatic foraging behavior, and instead may be consistent with moderate warm adaptation with respect to the I. iguana ortholog.     

‘Safe sites’ for the seed germination ofRhus javanica: A characterization by responses to temperature and light

Germination responses ofRhus javanica L. seeds to temperature and light were investigated with special reference to their gap-detecting mechanisms in germination, i.e., responses to elevated and/or fluctuating temperatures and sensitivity to leaf-canopy transmitted light. The seeds, which have water-impermeable coats to prevent imbibition, were shown to become permeable and germinable after exposure to higher temperatures of 48–74°C for a brief period depending on the temperature. Once the coat impermeability had been removed by such heat treatment, the seeds became readily germinable over a wide range of temperature and light conditions. The lower and higher temperature limits for germination were around 8° and 36°C, respectively, with an optimal temperature of around 25°C. Simple linear relationships were observed between the temperature and germination rates, i.e., the reciprocals of the time taken by the seed subpopulations to show 10–70% germination in the sub-optimal temperature range, where the required ‘thermal time’ for germination was 2300–3600 Kh. The presence or absence of light or a simulated ‘canopy light’ had little effect on the germination of this species. It was concluded that the seeds ofR. javanica are furnished with a gap-detecting mechanism in the form of a heat requirement for the breakage of water-impermeable seed dormancy, which may be fulfilled by either daytime elevation of the surface temperature of exposed soil, or more effectively by fire.     

DenNit – Experimental analysis and modelling of soil N2O efflux in response on changes of soil water content, soil temperature, soil pH, nutrient availability and the time after rain event

To quantify the effects of soil temperature (T_soil), and relative soil water content (RSWC) on soil N₂O emission we measured N₂O soil efflux with a closed dynamic chamber in situ in the field and from soil cores in a controlled climate chamber experiment. Additionally we analysed the effect of soil acidity, ammonium, and nitrate concentration in the field. The analysis was performed on three meadows, two bare soils and in one forest. We identified soil water content, soil temperature, soil nitrogen content, and pH as the main parameters influencing soil N₂O emission. The response of N₂O emission to soil temperature and relative soil water content was analysed for the field and climate chamber measurements. A non-linear regression model (DenNit) was developed for the field data to describe soil N₂O efflux as a function of soil temperature, soil moisture, pH value, and ammonium and nitrate concentration. The model could explain 81% of the variability in soil N₂O emission of all individual field measurements, except for data with short-term soil water changes, namely during and up to 2 h after rain stopped. We validated the model with an independent dataset. For this additional meadow site 73% of the flux variation could be explained with the model.     

Seasonal changes of resistance to fenvalerate and cypermethrin in the larval parasitoid Cotesia plutellae （Hymenoptera： Braconidae）

The seasonal changes of insecticide resistance and stability in hymenopteran Cotesia plutellae, collected from Jianxin, Fuzhou-City, and Shangjie, Minhou-County, Fujian, China, were assessed by using a dry residual film method. The resistance to two insecticides in the field populations of C. plutellae was not stable under insecticide-free conditions in the insectarium. Compared with susceptible F11 progeny of C. plutellae in the insectarium, the resistance ratios （RR） in F0 parents were 18.4 for fenvalerate and 11.4 for cypermethrin based on LC50 at 9 hours, and 32.8 for fenvalerate and 28.5 for cypermethrin based on LC50 at 24 hours when the parasitoids were left in contact with the insecticides for 1 hour and mortalities were recorded at 9 and 24 hours, respectively. However, the RR in a field population of C. plutellae were 9.2 for fenvalerate and 12.7 for cypermethrin, if the parasitoids were left in contact with the insecticides for 24 hours. The resistances to the two pyrethroids in other field populations collected from Jianxin and Shangjie from November 2000 and July 2004 were also determined. Significant seasonal variations of resistance to the two insecticides in the field populations of C. plutellae were found. The RR were 3.0-18.4 for fenvalerate and 4.8-20.6 for cypermethrin in Jianxin populations from November 2000 to April 2002 based on LC50 at 9 h, and 2.3-13.6 for fenvalerate and 3.6-16.0 for cypermethrin in Shangjie populations from May 2002 to July 2004 based on LC50 at 24 hours. The resistance levels were high in spring and autumn and decreased sharply in summer. In addition, significant recovery from the knocked-down caused by the insecticides was found in the F0 and field populations of C. plutellae which were resistant to fenvalerate and cypermethrin if the parasitoids were left in contact with the pyrethroids for 1 hour. However, no recovery was found in susceptible F11 progeny.     

Populations of ducks and trout of the River Laxá, Iceland, in relation to variation in food resources

We examined annual variation in production, recruitment and density of the three most abundant vertebrate species of the River Laxá at Lake Myvatn, Iceland: Barrow’s goldeneye, Bucephala islandica, harlequin duck, Histrionicus histrionicus, and brown trout, Salmo trutta, in relation to food resources and other environmental variables. The study is largely based on correlations from long-term monitoring series in the period 1975–2002. Production of young in the harlequin duck was significantly correlated with food resources (the blackfly, Simulium vittatum) of the river, as was the recruitment of brown trout to the angling stock. In Barrow’s goldeneye, which uses both the lake and the river, dispersion of adults in spring and young in August was influenced by the availability of aquatic insects in each habitat. The dispersion of Barrow’s goldeneye tracks the availability of aquatic insects in each of these two main habitats. Introduced Amercian mink, Mustela vison, may have affected spring numbers and dispersion of harlequin ducks, but the evidence was not conclusive. Numbers of both duck species and the trout (as CPUE) were relatively stable, although a sharp drop in numbers followed by slow recovery was observed in Barrow’s goldeneye, and an increase was observed in harlequin ducks in the first year of study.     

Amounts of winter or summer rain triggering germination and ‘the point of no return’ of seedling desiccation tolerance,of some Hordeum spontaneum local ecotypes in Israel.

In this study we observed an important interrelationship between the ability of Hordeum spontaneum C. Koch (Poaceae) seeds to germinate after a small rainfall in winter and the dehydration tolerance of young seedlings after one, two or three weeks in dry conditions. In winter, local ecotypes of H. spontaneum started to germinate after only 10 mm of rain, when temperatures were mild, daily evaporation rates were low, and soil water content was 5.8%. In summer, however, germination was not triggered until at least 50 mm of rain was received, at higher temperatures, evaporation rates and soil water content. The point of no return is the earliest stage of germination or after germination at which dehydration will cause the death of the seedling and it depends on the duration in a dry environment, root length before desiccation and on the ecotype. Seedlings were stored in dry conditions for one, two or three weks and then rewetted. A higher percentage of seedlings which had developed roots of 5–20 mm long before desiccation, developed adventitious roots than that of seedlings with roots 1–4 or 40–50 mm long before desiccation. The strategy of regulating germination according to different amounts of rainfall, depending on the season, and seedling drought tolerance, are important survival adaptations in arid and semi-arid regions. These adaptations may enable the young seedlings to overcome drought periods between rainfalls.     

Seasonal variation of amino acids in the xylem sap of “Populus x canadensis” and its relation to protein body mobilization

Summary The seasonal changes in the pattern of 21 amino acids occurring in the xylem vessels of Populus twigs have been studied in connection to the mobilization of protein bodies in ray parenchyma cells at the electron microscopic level. Hydrolysis of protein bodies in spring and movement of amino acids into vessels are found to be closely linked. Comprising more than 75% of total amino acid content, glutamine (Gln) is by far the dominant N-constituent of the sap. Gln reaches up to 11 mol ml^-1 in the spring sap while other amino acids only show 1/20 to 1/100 of this amount. From the measured Gln accumulation rates in the vessels in nature and in the vessels of isolated shoots, a minimum flux rate for Gln of 5.6 pmol cm^-2 min^-1 is calculated for the ray contact cell/vessel interface. Furthermore, because Gln constitutes 75% of the amino acid content of the sap but only 1.3% of the amino acids in the 32 kDa storage protein of the ray cells in the wood (Clausen and Apel 1991), it becomes evident that most amino acids originating from protein body mobilization do not enter the vessels but are used for Gln synthesis preceding Gln release into the vessels.     

Chromosome elimination and chromosome pairing in tetraploid hybrids of Hordeum vulgare × H. bulbosum

Summary The C₀ tetraploid counterparts of diploid hybrids of Hordeum vulgare × H. bulbosum were meiotically analysed, and were found to be chromosomally less stable than the same genotypes had been as diploids. The 14 bulbosum chromosomes present in the tetraploid cytotypes were probably eliminated as pairs rather than randomly or one genome at the time. Development of the vulgare and bulbosum genomes was asynchronous in some hybrids, the bulbosum chromosomes appearing less advanced than the vulgare chromosomes in the same cell. This appeared to reduce pairing between bulbosum homologues and also suppressed homoeologous pairing.     

Long-term changes in Krill biomass and distribution in the Barents Sea: are the changes mainly related to capelin stock size and temperature conditions?

Krill plays a significant role in the Barents Sea ecosystem, providing energy transport between different trophic levels. The current paper presents the results of a long-term study (1980–2009) based on pelagic trawl catches from August to September. Our investigations show that the krill species were distributed widely in the Barents Sea and that the largest krill concentrations were restricted to the west-central and eastern parts of the Barents Sea. The current paper presents the relative biomass indices, and the estimates must be interpreted as minimum biomass. The mean annual krill biomass was estimated to be 22 million tonnes in wet weight, with the highest values being as much as 48 million tonnes. Capelin is the largest pelagic stock, and in some years, their biomass can amount to 4–7 million tonnes, which can impose high predation pressure on krill. When their biomass is high, capelin may consume close to 26 million tonnes annually. The predation from pelagic (herring and blue whiting) and bottom (cod and haddock) fish species was much lower, being 9 and 1 million tonnes, respectively. A negative relationship between krill biomass and capelin stock size above 74°N was observed during the study period. However, during the last decade, the krill biomass has increased despite heavy predation from capelin in some years. A positive significant linear relationship between the mean annual Kola temperature and the krill biomass seems to indicate that the recent warming conditions have favourable impacts on the krill populations in the Barents Sea.