Prey location, recognition and ingestion by the phagotrophic marine dinoflagellate Oxyrrhis marina

The initial ingestion rates of Isochrysis galbana and Dunaliella primolecta by Oxyrrhis populations precultured separately on these phytoplanktonic prey were quantified and related to the chemosensory responses elicited in Oxyrrhis by the filtrate from live and heat killed prey cells. Despite evidence to suggest that Oxyrrhis shows specific distaste towards Isochrysis (but not Dunaliella) such that consumption of N-deplete Isochrysis halted in grazing experiments, positive chemotaxis was observed towards the cell-free filtrate from both species. These results suggest that while tactile cues encountered upon contact with Isochrysis and Dunaliella may enable Oxyrrhis to recognise differences between the two species, the chemosensory responses observed towards dissolved chemical cues derived from potential prey items are non-specific. That chemosensory and ingestion behaviours do not appear to be tightly coupled raises important questions concerning the ecological implications of chemotaxis in Oxyrrhis. Chemotaxis may enhance the overall efficiency of prey detection; however, when confronted with a variety of chemical stimuli (i.e. from a mixed-prey assemblage) Oxyrrhis may be unable to discern the difference between cues that originate from high quality, poor quality (or even toxic) prey items. The positive chemosensory responses observed towards a range of synthetic amino acid, amino sugar and ammonium solutions suggest that chemotaxis could facilitate the detection of solute gradients in prey deplete environments for direct exploitation via osmotrophy. Furthermore, the positive chemotaxis elicited by regenerated ammonium and compounds derived from heat killed conspecifics suggests that Oxyrrhis may release chemical cues which induce cannibalistic behaviour as a ‘life boat mechanism’ when no other suitable (non-self) prey items are available. Further work is required to explore the nature of the chemosensory apparatus and signal transduction pathways that mediate responses to dissolved chemical stimuli in Oxyrrhis and to investigate other sensory mechanisms that enable cells to recognise and differentiate between potential prey items.     

Predator-prey interactions between Isochrysis galbana and Oxyrrhis marina. III. Mathematical modelling of predation and nutrient regeneration

A mathematical model was derived to simulate ingestion, growthand nitrogen (N) regeneration for the phagotrophic dinoflagellateOxyrrhis marina. Two types of experimental study were undertaken:prey-deplete O.marina were supplied with lsochrysis galbanain continuous darkness (thus preventing growth of the prey),and predator-prey interactions were also followed in culturesmaintained in a light-dark cycle (allowing growth of the prey).During light-dark cycles, Oxyrrhis volume increased more inthe light phase than in the dark. Digestion of isochrysis lasted{small tilde}0.3 days. with an average maximum ingestion rateof 55 prey predator–1 day–1 During active predation,30% of Oxyrrhis-carbon (C) was lost from the particulate phase:per day, with this loss falling to 10%: per day at the cessationof herbivory when cannibalism became noticeable. Ingestion wasmodelled as a function of prey density, C-loss and divisionas functions of cellular predator C. with cannibalism by Oxyrrhisalso included. Two N-regeneration expressions were investigated:one proposed by D.A.Caron and J.C.Goldman (Journal of Protozoology.35, 247–249, 1988) and an alternative function which relatedN regeneration to intracellular carbon and N based on the conceptof an optimal Oxyrrhis C:N ratio. The latter was more successfulin simulating batch culture data and did not require a priorcalculation of Oxyrrhis gross growth efficiency. The model ofOxyrrhis numbers, C and N contained only nine parameters whosevalues were fully obtainable from batch culture experiments.By using this model, we were able to use a single parameterset to simulate the transient dynamics of Oxyrrhis ingestingN-replete and N-stressed prey. Further experiments in whichOxyrrhis grew on Isochrysis in light-dark cycles were simulatedby combining the Oxyrrhis model with the nutrient-processingmodel for Isochrysis of K.Davidson et al. (Journal of PlanktonResearch, 15, 351–359, 1993). The dynamics of the fullpredator-prey model were found to be sensitive to the levelof sophistication of the prey model; the Quota model was foundto be less successful than the nutrient-processing prey model.Theoretical model runs indicated the importance of being ableto simulate changes in both prey numbers and biomass, and alsoin including realistic equations for nutrient regeneration frompredators in microbial predator-prey models.     

Differential effects of cannabinoid exposure and stress on plasma prolactin, growth hormone and corticosterone levels in male mice

Plasma prolactin (PRL) levels were reduced in stressed and non-stressed male mice after a single dose of Δ⁹-tetrahydrocannabinol (THC), the main psychoactive constituent of marihuana, while growth hormone (GH) levers were reduced only in non-stressed animals. Chronic treatment with THC did not affect PRL or GH levels under either condition. Neither acute nor repeated exposure to THC affected plasma corticosterone levels.In contrast to the affects of THC, acute exposure to cannabinol (CBN), a non-psychoactive ingredient in marihuana, increased plasma GH levels in non-stressed mice, while repeated CBN treatments reduced GH levels in stressed animals. Moreover, chronic CBN exposure resulted in decreased peripheral levels of corticosterone in both stressed and non-stressed mice, and reduced plasma PRL levels in stressed mice.Psychoactive and non-psychoactive components of marihuana can exert different effects on endocrine function and on responsivity to stress in male mice.     

Effect of pitcher age on trapping efficiency and natural prey capture in carnivorous Nepenthes rafflesiana plants

Background and Aims

Nepenthes pitchers are sophisticated traps that employ a variety of mechanisms to attract, capture and retain prey. The underlying morphological structures and physiological processes are subject to change over the lifetime of a pitcher. Here an investigation was carried out on how pitcher properties and capture efficiency change over the first 2 weeks after pitcher opening.

Methods

Prey capture, trapping efficiency, extrafloral nectar secretion, pitcher odour, as well as pH and viscoelasticity of the digestive fluid in N. rafflesiana pitchers were monitored in the natural habitat from pitcher opening up to an age of 2 weeks.

Key Results

Pitchers not only increased their attractiveness over this period by becoming more fragrant and secreting more nectar, but also gained mechanical trapping efficiency via an enhanced wettability of the upper pitcher rim (peristome). Consistently, natural prey capture was initially low and increased 3–6 d after opening. It was, however, highly variable within and among pitchers. At the same time, the pH and viscoelasticity of the digestive fluid decreased, suggesting that the latter is not essential for effective prey capture.

Conclusions

Prey capture and attraction by Nepenthes are dynamic processes strongly influenced by the changing properties of the pitcher. The results confirm insect aquaplaning on the peristome as the main capture mechanism in N. rafflesiana.Key words: Carnivorous plants, pitcher development, prey attraction, prey capture, insect aquaplaning, extrafloral nectar, Nepenthes rafflesiana     

Patterns of resistance and resilience of the stress-tolerant coral Siderastrea radians (Pallas) to sub-optimal salinity and sediment burial

The coastal lagoons of south Florida, U.S., experience fluctuating levels of sedimentation and salinity and contain only a subset of the coral species found at the adjacent reefs of the Florida Reef Tract. The dominant species within these habitats is Siderastrea radians, which can reach densities of up to 68 colonies m^- 2 and is commonly exposed to salinity extremes (< 10 psu to > 37 psu) and chronic sediment burial. In this study, we document the patterns of resistance and resilience of S. radians to sub-optimal salinity levels and sediment burial in a series of short-term, long-term, acute, chronic, single-stressor, and sequential-stressor experiments.S. radians displayed remarkable patterns of resistance and resilience and mortality was documented only under prolonged (≥ 48 h) continuous exposure to salinity extremes (15 and 45 psu) and chronic sediment burial. A reduction in photosynthetic rates was documented for all salinity exposures and the decrease in photosynthesis was linearly related to exposure time. Negative impacts on photosynthetic rates were more severe under low salinity (15 psu) than under high salinity (45 psu). Corals exposed to intermediate, low-salinity levels (25 psu), exhibited initial declines in photosynthesis that were followed by temporary increases that may represent transient acclimatization patterns. The impacts of sediment burial were influenced by the duration of the burial period and ranged from a temporary reduction in photosynthesis to significant reductions in growth and tissue mortality. The maintenance of P/R ratios > 1 and the rapid (< 24 h) recovery of photosynthetic rates after burial periods of 2-24 h indicates that S. radians is able to resist short-term burial periods with minor physiological consequences. However, as burial periods increase and colonies become covered at multiple chronic intervals, sediment burial resulted in extended photosynthetic recovery periods, reduced growth, and mortality. Under normal conditions (i.e., no salinity stress), S. radians was very effective at clearing sediments, and > 50% of the colonies' surface area was cleared within 1 h. However, clearing rates were influenced by physiological status, and prior exposure to sub-optimal salinity significantly reduced the clearing rates of stressed colonies.The response of S. radians to disturbance documented in this study characterizes this species as highly stress-tolerant and provides an explanation for its present high abundance in both reef and marginal environments. Moreover, the key life-history attributes of S. radians, such as brooding reproductive strategy, small colony size, high stress-tolerance, and high recruitment rates, suggest the potential for this species to replace reef-building taxa under increased disturbance scenarios in Florida and elsewhere in the region.     

Silicon Application to Rice Root Zone Influenced the Phytohormonal and Antioxidant Responses Under Salinity Stress

Silicon (Si) application shows beneficial effects on plant growth; however, its effects on the phytohormone and enzymatic antioxidant regulation have not been fully understood. We studied the effects of short-term (6, 12, and 24 h) silicon (0.5, 1.0, and 2.0 mM) application on salinity (NaCl)-induced phytohormonal [abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA)] and antioxidant regulation in Oryza sativa. The results showed that Si treatments significantly increased rice plant growth compared to controls under salinity stress. Si treatments reduced the sodium accumulation resulting in low electrolytic leakage and lipid peroxidation compared to control plants under salinity stress. Enzymatic antioxidant (catalase, peroxidase and polyphenol oxidase) responses were more pronounced in control plants than in Si-treated plants under salinity stress. Stress- and defense-related phytohormones like JA were significantly downregulated and SA was irregular after short-term Si applications under salinity stress compared to control. Conversely, ABA was significantly higher after 6 and 12 h but insignificant after 24 h in Si-treated plants under salinity stress. After 6 and 12 h, Si and salinity stress resulted in upregulation of zeaxanthin epoxidase and 9-cis-epoxycarotenoid dioxygenase 1 and 4 (NCED1 and 4), whereas 24-h treatments significantly downregulated the expressions of these genes compared to those in the control. NCED3 expression increased after 6 and 24 h but it was insignificant after 12 h of Si application compared to control. The current findings indicate that increasing the Si concentrations for longer periods of time can regulate the salinity-induced stress by modulating phytohormonal and enzymatic antioxidants’ responses.     

Abscisic Acid Accumulation by in Situ and Isolated Guard Cells of Pisum sativum L. and Vicia faba L. in Relation to Water Stress

Isolated guard cells, prepared by sonication of epidermal peels, were used to investigate the endogenous level of abscisic acid (ABA) in the guard cells of turgid and stressed leaves of Vicia faba L. and the argenteum (arg) mutant of Pisum sativum L. The guard cells of V. faba and arg were found to contain 18 and 8 times more ABA, respectively, when isolated from stressed leaves than from turgid leaves. Isolated guard cells of V. faba were also directly stressed with the osmoticum Aquacide III. These guard cells were capable of producing stress-induced ABA to at least 3 times their ABA level when non-stressed.     

Associations between APOE variants and metabolic traits and the impact of psychological stress

Objective

In a previous study, we observed that associations between APOE rs439401 and metabolic traits were moderated by chronic stress. Thus, in a population of stressed and non-stressed Danish men, we examined whether associations between APOE rs439401 and a panel of metabolic quantitative traits, all metabolic traits which may lead to T2D and CVD were moderated by psychological stress.

Methods

Obese young men (n = 475, BMI≥31.0 kg/m²) and a randomly selected control group (n = 709) identified from a population of 141,800 men were re-examined in two surveys (S-46: mean age 46, S-49: mean age 49 years) where anthropometric and biochemical measures were available. Psychological stress factors were assessed by a self-administered 7-item questionnaire. Each item had the possible response categories “yes” and “no” and assessed familial problems and conflicts. Summing positive responses constituted a stress item score, which was then dichotomized into stressed and non-stressed. Logistic regression analysis, applying a recessive genetic model, was used to assess odds ratios (OR) of the associations between APOE rs439401 genotypes and adverse levels of metabolic traits.

Results

The APOE rs439401 TT-genotype associated positively with BMI (OR = 1.09 [1.01; 1.17]), waist circumference (OR = 1.09 [1.02; 1.17]) in stressed men at S-46. Positive associations were observed for fasting plasma glucose (OR = 1.42 [1.07; 1.87]), serum triglycerides (OR = 1.41 [1.05; 1.91]) and with fasting plasma insulin (OR = 1.48 [1.05; 2.08]) in stressed men at S-49. Rs439401 TT-genotype also associated positively with surrogate measures of insulin resistance (HOMA-IR; OR = 1.21 [1.03; 1.41]) and inversely with insulin sensitivity (Stumvoll index; OR = 0.90 [0.82; 0.99], BIGTT-S_I; OR = 0.60 [0.43; 0.85]) in stressed men. No significant associations were observed in non-stressed men, albeit the estimates showed similar but weaker trends as in stressed men.

Conclusion

The present results suggest that the APOE rs439401 TT-genotype is associated with an adverse metabolic profile in a population of psychologically stressed Danish men.     

Flatworms like it round: nematode consumption by <Emphasis Type="Italic">Planaria torva</Emphasis> (Müller 1774) and <Emphasis Type="Italic">Polycelis tenuis</Emphasis> (Ijima 1884)

To identify the mechanisms whereby substrate embeddedness and water velocity influence Nooksack dace (Rhinichthys cataractae subsp. cataractae) prey capture efficiency, we stocked dace in foraging arenas with varying substrate types over a range of velocities (0, 25, 35 cm s^?1) and measured their efficiency of prey capture. We stocked a known number of mayfly (Ephemeroptera), black fly (Simuliidae), and chironomid (Chironomidae) larvae in each foraging arena and measured the number of invertebrates remaining after 12 h. Foraging efficiency for mayflies was significantly reduced over unembedded substrate, and capture efficiency for all taxa decreased at higher velocities in all substrate treatments. Decreased foraging efficiency indicates that higher velocities may degrade the accuracy of prey strikes, that dace may alter their foraging behavior to reduce energy expenditures at higher velocities, that there is less available foraging habitat within their velocity tolerances, or that invertebrates become more interstitial at higher velocities. Although it is difficult to unambiguously discriminate among these mechanisms with our experimental design, our results suggest that dace are adapted to foraging in low-velocity micro-habitats within the boundary layer, and that their foraging efficiency may be sensitive to both the refuging ability of their prey and velocity and turbulence at their focal point.     

Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis

Backround and Aims

It has been suggested that the rate of net photosynthesis (A_N) of carnivorous plants increases in response to prey capture and nutrient uptake; however, data confirming the benefit from carnivory in terms of increased A_N are scarce and unclear. The principal aim of our study was to investigate the photosynthetic benefit from prey capture in the carnivorous sundew Drosera capensis.

Methods

Prey attraction experiments were performed, with measurements and visualization of enzyme activities, elemental analysis and pigment quantification together with simultaneous measurements of gas exchange and chlorophyll a fluorescence in D. capensis in response to feeding with fruit flies (Drosophila melanogaster).

Key Results

Red coloration of tentacles did not act as a signal to attract fruit flies onto the traps. Phosphatase, phophodiesterase and protease activities were induced 24 h after prey capture. These activities are consistent with the depletion of phosphorus and nitrogen from digested prey and a significant increase in their content in leaf tissue after 10 weeks. Mechanical stimulation of tentacle glands alone was not sufficient to induce proteolytic activity. Activities of β-D-glucosidases and N-acetyl-β-D-glucosaminidases in the tentacle mucilage were not detected. The uptake of phosphorus from prey was more efficient than that of nitrogen and caused the foliar N:P ratio to decrease; the contents of other elements (K, Ca, Mg) decreased slightly in fed plants. Increased foliar N and P contents resulted in a significant increase in the aboveground plant biomass, the number of leaves and chlorophyll content as well as A_N, maximum quantum yield (F_v/F_m) and effective photochemical quantum yield of photosystem II (Φ_PSII).

Conclusions

According to the stoichiometric relationships among different nutrients, the growth of unfed D. capensis plants was P-limited. This P-limitation was markedly alleviated by feeding on fruit flies and resulted in improved plant nutrient status and photosynthetic performance. This study supports the original cost/benefit model proposed by T. Givnish almost 30 years ago and underlines the importance of plant carnivory for increasing phosphorus, and thereby photosynthesis.     

Low salinity stress experienced by larvae does not affect post-metamorphic growth or survival in three calyptraeid gastropods

Marine larvae that experience some sub-lethal stresses can show effects from those stresses after metamorphosis, even when they seem to recover from those stresses before metamorphosis. In this study we investigated the short and long-term effects of exposing the larvae of three calyptraeid gastropods (Crepidula fornicata, Crepidula onyx, and Crepipatella fecunda) to temporary reductions in salinity. Larvae of all three species showed slower larval growth rates, longer time to metamorphic competence, and substantial mortality after being stressed in seawater at salinities of 10, 15, and 20 for less than 48 h. Larval tolerance to low salinities varied widely within and among species, but longer stresses at lower salinities were generally more harmful to larvae. However, larvae in nearly all experiments that were able to metamorphose survived and grew normally as juveniles; there were no documented “latent effects.” For all three species, starving larvae in full-strength seawater was not as harmful as exposing larvae to low salinity stress, indicating that detrimental effects on larvae were caused by the salinity stress per se, rather than by an indirect effect of salinity stress on feeding. C. fornicata that were stressed with low salinity as juveniles were more tolerant of the stress than larvae: all stressed juveniles lived and showed reduced growth rates for no more than 3 days. Our data suggest that even though reduced salinity is clearly stressful to the larvae of these 3 gastropod species, metamorphosis seems to generally provide individuals with a fresh start.     

Diurnal Fluctuations in Relative Water Content, Nitrate Reductase and Proline Content in Water-stressed and Non-stressed Wheat

Diurnal variations in relative water content (RWC), nitrate reductase (NR) and proline content (PC) were studied at 3 h intervals during a 24 h cycle in the flag leaf of wheat (Triticum vulgare, v. Kalyansona) grown under stressed and non-stressed conditions. RWC was lower in stressed plants than in non-stressed ones throughout the 24 h period. Although it was lowest at 12 h, it recovered by 15 h. Non-stressed plants maintained higher NR activity compared to those under stress. The enzyme activity during night was about the same as during day time in both types of plants. Compared to non-stressed plants, stressed ones had lower NO₃^? content. Proline accumulation occurred under stress conditions and had a maximum at 12–15 h. Non-stressed plants exhibited higher PC during night than day time. Changes in temperature and relative humidity were noted during the period and their influence on RWC, NR and proline was discussed.     

Profiling of urinary testosterone and luteinizing hormone in exercise-stressed male athletes,using gas chromatography-mass spectrometry and enzyme immunoassay techniques

Knowledge of the effects of episodic or short-term exercise-stress on endogenous testosterone and luteinizing hormone levels still remains fragmentary and inconclusive. In this study, an approach based on the absolute concentrations of urinary total testosterone (T), luteinizing hormone (LH) and the T/LH concentration ratios, was used to profile short-term exercise-stress responses in healthy drug-free male athletes. Testosterone and luteinizing hormone concentrations were measured using gas chromatography-mass spectrometry (GC-MS) and microparticle enzyme immunoassay (MEIA) techniques, respectively. Stress profiles derived from exercise-stress at VO₂max, 68.1% VO₂max and 51.6% VO₂max were plotted using the concentrations of T, LH and the ratios of T/LH found under non-stressed and stressed conditions. Significant changes in LH concentrations (p<0.005) and T/LH ratios (p<0.005) levels were observed between the pre-stress and post-exercise conditions during acute exercise-stress at VO₂max but the T concentration did not show any marked change relative to the non-stressed condition. Whilst exercise-stress appeared to reduce the change in T concentrations between the pre- and post-exercise states compared to that in the non-stressed control condition, the change in LH concentrations showed a moderate increase at submaximal oxygen uptake values. The stress profiles derived from this study facilitated an assessment of the relationship between the endogenous T, LH and T/LH ratio stress-responses over a short period of applied exercise-stress.     

Harmful effects of Dinophysis to the ciliate Mesodinium rubrum: Implications for prey capture

Toxigenic Dinophysis spp. are obligate mixotrophic dinoflagellates that require a constant supply of prey—Mesodinium rubrum—to achieve long-term growth by means of kleptoplasty. Mesodinium rubrum is, however, a fast moving, jumping ciliate exhibiting an effective escape response from suspensivorous predators. In the present study, a series of laboratory experiments evaluating the motility and survival of M. rubrum in the presence of Dinophysis cells and/or substances contained in their culture medium was designed, in order to assess the mechanisms involved in prey capture by Dinophysis spp. Cell abundance of M. rubrum decreased in the presence of Dinophysis cf. ovum cells producing okadaic acid (OA; up to 7.94 ± 2.67 pg cell⁻¹) and smaller amounts of dinophysistoxin-1 (DTX-1) and pectenotoxin-2 (PTX-2). Prey capture was often observed after the ciliate had been attached to adhesive “mucus traps”, which only appeared in the presence of Dinophysis cells. Before being attached to the mucus traps, M. rubrum cells reduced significantly their swimming frequency (from ∼41 to 19 ± 3 jumps min⁻¹) after only 4 h of initial contact with D. cf. ovum cells. M. rubrum survival was not affected in contact with purified OA, DTX-1 and PTX-2 solutions, but decreased significantly when the ciliate was exposed to cell-free or filtered culture medium from both D. cf. ovum and D. caudata, the latter containing moderate concentrations of free eicosapentaenoic acid and docosahexaenoic acid. The results thus indicate that Dinophysis combines the release of toxic compounds other than shellfish toxins, possibly free PUFAs, and a “mucus trap” to enhance its prey capture success by immobilizing and subsequently arresting M. rubrum cells.     

A forceful upper jaw facilitates picking-based prey capture: biomechanics of feeding in a butterflyfish,Chaetodon trichrous

Biomechanical models of feeding mechanisms elucidate how animals capture food in the wild, which, in turn, expands our understanding of their fundamental trophic niche. However, little attention has been given to modeling the protrusible upper jaw apparatus that characterizes many teleost species. We expanded existing biomechanical models to include upper jaw forces using a generalist butterflyfish, Chaetodon trichrous (Chaetodontidae) that produces substantial upper jaw protrusion when feeding on midwater and benthic prey. Laboratory feeding trials for C. trichrous were recorded using high-speed digital imaging; from these sequences we quantified feeding performance parameters to use as inputs for the biomechanical model. According to the model outputs, the upper jaw makes a substantial contribution to the overall forces produced during mouth closing in C. trichrous. Thus, biomechanical models that only consider lower jaw closing forces will underestimate total bite force for this and likely other teleost species. We also quantified and subsequently modeled feeding events for C. trichrous consuming prey from the water column versus picking attached prey from the substrate to investigate whether there is a functional trade-off between prey capture modes. We found that individuals of C. trichrous alter their feeding behavior when consuming different prey types by changing the timing and magnitude of upper and lower jaw movements and that this behavioral modification will affect the forces produced by the jaws during prey capture by dynamically altering the lever mechanics of the jaws. In fact, the slower, lower magnitude movements produced during picking-based prey capture should produce a more forceful bite, which will facilitate feeding on benthic attached prey items, such as corals. Similarities between butterflyfishes and other teleost lineages that also employ picking-based prey capture suggest that a suite of key behavioral and morphological innovations enhances feeding success for benthic attached prey items.     

Different effects of the combined stress of nitrogen depletion and high temperature than an individual stress on the synthesis of biochemical compounds in <Emphasis Type="Italic">Arthrospira platensis</Emphasis> C1 (PCC 9438)

In nature, several abiotic stresses occur simultaneously, leading to retarded growth and biochemical changes in microalgae, including the commercial cyanobacterium, Arthrospira platensis. To gain more understanding of stress response, we investigated the integrative effects of nitrogen depletion and high temperature stress on physiological changes of A. platensis C1. The results revealed that photosynthetic activities of the stressed cells were markedly reduced by more than a half in comparison to the non-stressed cells. Moreover, a reduction of biomass was observed within 24 h after prolonged exposure to combined stress of nitrogen depletion and high temperature. The total protein contents, including phycocyanin (PC), in the stressed cells, decreased rapidly within 8 h of incubation. This finding was concomitant with the increase in carbohydrate content. However, the accumulation of carbohydrates in the nitrogen depletion-treated cells was greater than that in the cells under the combined stress. Furthermore, the levels of polysaccharides increased only under long-term incubation under nitrogen depletion but not under the combined stress. In addition, the combination of nitrogen depletion and high temperature stress resulted in an increase in the proportion of linoleic acid but a decrease in γ-linolenic acid within 24 h. These results suggest that the response of A. platensis to the combined stress was different from the responses of cells to individual stress. The PC degradation, the increased carbohydrates, and the alteration in fatty acids profiles were required for physiological response to combined nitrogen depletion and high temperature stress of A. platensis C1.     

Effects of bacterial single inoculation and co-inoculation on growth and phytohormone production of sunflower seedlings under water stress

The purpose of the study was to measure shoot and root dry matter (DM) and production of auxins, salicylic acid, abscisic acid, and jasmonic acid in sunflower (Helianthus annuus L.) seedlings cultivated under water stress and singly inoculated or co-inoculated with Achromobacter xylosoxidans (SF2) and Bacillus pumilus (SF3 and SF4) bacterial strains. Shoot DM was higher in non-stressed seedlings than in stressed seedlings for all inoculation treatments. Water stress resulted in decreased relative water content and reduction of shoot DM. Root DM was higher in stressed seedlings than in non-stressed seedlings. Salicylic acid was the most abundant phytohormone in shoots of stressed, singly inoculated and co-inoculated seedlings. High salicylic acid content in stressed seedlings suggests that this hormone plays a key role in abiotic stress. Abscisic acid was higher in stressed and co-inoculated seedlings than in non-stressed seedlings but was lower than that of salicylic acid. Auxin profile was similar to that of abscisic acid in co-inoculated seedlings. Shoot jasmonic acid content was increased in stressed seedlings co-inoculated with SF2/SF3 or SF2/SF4. Shoot hormonal profiles were different from those of root, suggesting a differential effect of bacterial inoculation on these plant organs. Our findings will be useful in future strategies to mitigate drought effects on crop plants through bacterial inoculation treatments.     

Response of Split-Root Sour Orange Seedlings to NaCl and Polyethylene Glycol Stresses

Soil water cotent and salinity levels are seldom uniform inthe field, particularly with the use of micro-irrigation systemsthat may water only a portion of the root zone. For studyingnon-uniform salinity, a split-root experiment was designed toevaluate growth and water relations when half of the root systemof sour orange (Citrus aurantium) seedlings was stressed withsodium chloride (NaCl) or polyethylene glycol (PEG). This studyalso determined if non-stressed portions of the root systemcompensated for the decrease in water uptake by the stressedportions. One or both halves of the root system were treated for fourmonths with nutrient solution adjusted with NaCl or PEG to osmoticpotentials of –0.10, –0.20, or –0.35 MPa.Shoot dry weight was reduced by only 9% when half of the rootsystem was irrigated with saline solution at –0.10 MPa,but with both halves of the root system at –0.10 MPa,shoot and root dry weights were reduced as much as 45%. Similarly,leaf water and osmotic potentials were also more disturbed underuniform salinity than under non-uniform salinity conditions. Plant growth, leaf water potential, osmotic potential, stomatalconductance, and evapotranspiration decreased with increasingNaCl and PEG concentrations in the nutrient solution. Turgorpotential and leaf thickness increased in response to NaCl treatments.Microscopic examination showed that the increase in leaf thicknesswas due to the development of larger cells in the spongy mesophyll. Shoot growth did not correlate with the average osmotic potentialof the two root halves. Seedlings with one stressed half-rootsystem had shoot dry weight and leaf water potential valuescloser to those of the non-stressed control than to those withthe completely stressed root system. Key words: Non-uniform salinity, water relations, citrus     

Effect of calcium on water-stress-induced biochemical changes and yield of field-grown rice

Three different treatments by calcium (10²M), namely seed treatment, foliar spraying and their combination were applied on field-grown rice (Oryza sativa L. cv. Ratna) under both water stressed and non-stressed conditions in the course of plant development. The relative water content and leaf water potential decreased with increase in age of stressed and non-stressed plants. Pretreatment of seeds with Ca improved the water status of the plants most prominently at the vegetative stage but the effect gradually faded away with plant development. The foliar spraying by Ca was more effective in improving the water status of the plants at the reproductive stage. The combined Ca treatment significantly improved water status of the plants both at the vegetative and reproductive stages. The contents of chlorophyll and protein decreased and the activities of protease and RNase increased in the course of plant development in both non-stressed and even more in stressed plants. Ca treatments of seeds or plants or their combination inhibited the decline in chlorophyll and protein contents and the rising trends of protease and RNase activities, the combined treatment being most effective. During plant development free proline content increased significantly more in water stressed plants. In non-stressed plants there was a marked increase in the free proline content at the mature fruit stage. Ca treatment inhibited the rise of free proline in stressed plants. A significant reduction in yield components and yield of the crop in water stressed plants was increased by Ca treatment.     

NaCl-and Gibberellic Acid-induced Changes in the Content of Auxin and the Activities of Cellulase and Pectin Lyase During Leaf Growth in Rice (Oryza sativa)

The interactive effect of NaCl salinity and gibberellic acidin the activities of cellulase and pectin lyase, and on thecontent of auxin and chlorophyll, has been determined duringleaf growth (fifth from base) in rice. The linear growth, chlorophyllcontent, activity of cellulase, and the auxin level of leaveswere markedly decreased when plants were exposed to salt stress(12 dS m^–1). However pectin lyase activity did not registerany significant alteration in the leaves of salt-stressed plantscompared with the control. Treatment of plants with gibberellicacid (GA₃) (10 ppm) increased the leaf growth and chlorophyllcontent with a concomitant rise in the activity of cellulaseunder stressed as well as non-stressed conditions. A markedincrease in the content of auxin was discernible in the leavesof salt-stressed plants treated with GA₃ compared with non-treatedsalinized ones. An appreciable increment in the activity ofpectin lyase in response to GA₃ administration was detectedonly in the leaves of non-stressed plants. These results indicatethat enhancement of cellulase activity and the augmentationof endogenous auxin content may be involved in the stimulationof rice leaf growth by GA₃ under saline conditions. Oryza sativa, rice, leaf growth, NaCl salinity, gibberellic acid, cellulase, pectin lyase, auxin