Chytridiomycosis of marine diatoms : the role of stress physiology and resistance in parasite-host recognition and accumulation of defense molecules

Little is known about the role of chemotaxis in the location and attachment of chytrid zoospores to potential diatom hosts. Hypothesizing that environmental stress parameters affect parasite-host recognition, four chytrid-diatom tandem cultures (Chytridium sp./Navicula sp., Rhizophydium type I/Nitzschia sp., Rhizophydium type IIa/Rhizosolenia sp., Rhizophydium type IIb/Chaetoceros sp.) were used to test the chemotaxis of chytrid zoospores and the presence of potential defense molecules in a non-contact-co-culturing approach. As potential triggers in the chemotaxis experiments, standards of eight carbohydrates, six amino acids, five fatty acids, and three compounds known as compatible solutes were used in individual and mixed solutions, respectively. In all tested cases, the whole-cell extracts of the light-stressed (continuous light exposure combined with 6 h UV radiation) hosts attracted the highest numbers of zoospores (86%), followed by the combined carbohydrate standard solution (76%), while all other compounds acted as weak triggers only. The results of the phytochemical screening, using biomass and supernatant extracts of susceptible and resistant host-diatom cultures, indicated in most of the tested extracts the presence of polyunsaturated fatty acids, phenols, and aldehydes, whereas the bioactivity screenings showed that the zoospores of the chytrid parasites were only significantly affected by the ethanolic supernatant extract of the resistant hosts

Drought stress affects constitutive but not induced herbivore resistance in apple plants

Plant-herbivore interactions are influenced by chemical plant traits, which can vary depending on the plants' abiotic and biotic environment. Drought events, which are predicted to become more frequent and prolonged due to climate change, may affect primary and secondary plant metabolites contributing to constitutive resistance. Furthermore, the ability of plants to respond to herbivore attack in terms of induced resistance may be altered under drought conditions. We assessed the effects of drought stress on constitutive and induced apple plant resistance to a generalist insect herbivore by quantifying plant and herbivore responses in concert. Plants were exposed to different drought stress intensities (constitutive resistance) and subsequently to herbivore damage treatments that included different damage durations (induced resistance). As drought stress intensified, plant growth and concentrations of the leaf phenolic phloridzin decreased, whereas leaf glucose concentrations increased. Changes in fructose concentrations and in herbivore feeding preferences indicated a non-monotonic shift in constitutive resistance. Moderately stressed plants showed reduced fructose concentrations and were consumed least, while severely stressed plants were fructose-enriched and consumed most compared to well-watered control plants showing intermediate fructose concentrations and palatability. We found no evidence for effects of drought stress on induced resistance, as herbivore feeding preferences for undamaged over damaged plants were independent of drought intensity. Our results suggest a strong role of primary metabolites for drought-dependent variation in constitutive plant resistance and offer novel experimental insights into the effects of drought stress on induced plant resistance across a gradient of water deprivatio

Iso-duration determination of D´ and CS under laboratory and field conditions

Whilst Critical Speed (CS) has been successfully translated from the laboratory into the field, this translation is still outstanding for the related maximum running distance (D´). Using iso-duration exhaustive laboratory and field runs, this study investigated the potential interchangeable use of both parameters, D´ and CS. After an incremental exercise test, ten male participants (age: 24.9±2.1 yrs; height: 180.8±5.8 cm; body mass: 75.3±8.6 kg; V ̇O2peak 52.9±3.1 mL∙min-1∙kg-1) performed three time-to-exhaustion runs on a treadmill followed by three exhaustive time-trial runs on a 400 m athletics outdoor track. Field time-trial durations were matched to their respective laboratory time-to-exhaustion runs. D´ and CS were calculated using the inverse-time model (speed=D´/t+CS). Laboratory and field values of D´ and CS were not significantly different (221±7 m vs. 225±72 m; P = 0.73 and 3.75±0.36 m∙s-1 vs. 3.77±0.35 m∙s-1, P = 0.68), and they were significantly correlated (r = 0.86 and 0.94). The 95% LoA were ±75.5m and ±0.24 m∙s-1 for D´ and CS, respectively. Applying iso-durations provides non-significant differences for D´ and CS and a significant correlation between conditions. This novel translation testing method can consequently be recommended to coaches and practitioners, however a questionable level of agreement indicates to use D´ with caution

Species-specific responses of herbivores to within-plant and environmentally mediated between-plant variability in plant chemistry

Allocation of resources to growth and defense against herbivores crucially affects plant competitiveness and survival, resulting in a specific distribution of assimilates and defense compounds within plant individuals. Additionally, plants rarely experience stable environmental conditions, and adaptations to abiotic and biotic stresses may involve shifts in resistance to herbivores. We studied the allocation of phytochemicals in Brassica oleracea (Brussels sprouts) due to leaf age, drought stress and herbivore damage and assessed effects on two lepidopteran herbivores differing in diet breadth: the generalist Spodoptera littoralis and the specialist Pieris brassicae. Glucosinolates as secondary defense compounds and total nitrogen and carbon were quantified and linked to plant palatability, i.e., herbivore feeding preference. Herbivore responses were highly species-specific and partially related to changes in phytochemicals. Spodoptera littoralis preferred middle-aged leaves with intermediate levels of glucosinolates and nitrogen over young, glucosinolate and nitrogen rich leaves, as well as over old leaves, poor in glucosinolates and nitrogen. In contrast, P. brassicae preferred young leaves. Both species preferred severely drought-stressed plants to the well-watered control, although analyzed glucosinolate concentrations did not differ. Both S. littoralis and P. brassicae feeding induced an increase of indole glucosinolate levels, which may explain a reduced consumption of damaged plants detected for S. littoralis but not for P. brassicae. By revealing distinct, sometimes contrasting responses of two insect herbivores to within-plant and stress-mediated intraspecific variation in phytochemistry of B. oleracea, this study emphasizes the need to consider specific herbivore responses to understand and predict the interactions between herbivores and variable plant

Within-plant distribution of induced resistance in apple seedlings: rapid acropetal and delayed basipetal responses

Induction of plant resistance by herbivory is a complex process, which follows a temporal dynamic and varies spatially at the within-plant scale. This study aimed at improving the understanding of the induction process in terms of time scale and within-plant allocation, using apple tree seedlings (Malus×domestica) as plant model. Feeding preferences of a leaf-chewing insect (Spodoptera littoralis) for previously damaged and undamaged plants were assessed for six different time intervals with respect to the herbivore damage treatment and for three leaf positions. In addition, main secondary defense compounds were quantified and linked to herbivore feeding preferences. Significant herbivore preference for undamaged plants (induced resistance) was first observed 3days after herbivore damage in the most apical leaf. Responses were delayed in the other leaf positions, and induced resistance decreased within 10days after herbivore damage simultaneously in all tested leaf positions. Chemical analysis revealed higher concentrations of the flavonoid phloridzin in damaged plants as compared to undamaged plants. This indicates that herbivore preference for undamaged apple plants may be linked to phloridzin, which is the main secondary metabolite of apple leaves. The observed time course and distribution of resistance responses within plants contribute to the understanding of induction processes and patterns, and support the optimal defense theory stating young tissue to be prioritized. Moreover, induced resistance responses occurred also basipetally in leaves below the damage site, which suggests that signaling pathways involved in resistance responses are not unidirectiona

Methodological Approaches and Related Challenges Associated With the Determination of Critical Power and Curvature Constant

The relationship between exercise intensity and time to task-failure (P-T relationship) is hyperbolic, and characterised by its asymptote (critical power, CP) and curvature constant (W’). The determination of these parameters is of interest for researchers and practitioners, but the testing protocol for CP and W’ determination has not yet been standardised. Conventionally, a series of constant work-rate tests (CWR) to task-failure have been used to construct the P-T relationship. However, the duration, number, and recovery between predictive CWR, and the mathematical model (hyperbolic or derived linear models) are known to affect CP and W’. Moreover, repeating CWR may be deemed as a cumbersome and impractical protocol. Recently, CP and W’ have been determined in field and laboratory settings using time-trials, but the validity of these methods has raised concerns. Alternatively, a 3-min all-out test (3MT) has been suggested, as it provides a simpler method for the determination of CP and W’, whereby power output at the end of the test represents CP, and the amount of work performed above this end-test power equates to W’. However, the 3MT still requires an initial incremental test, and may overestimate CP. The aim of this review is, therefore, to appraise current methods to estimate CP and W’, providing guidelines and suggestions for future research where appropriate

Comparison of two equated resistance training weekly volume routines using different frequencies on body composition and performance in trained males

The present study compared the effects of two weekly-equalized volume and relative load interventions on body composition, strength and power. Based on individual baseline maximal strength values, eighteen recreationally trained men were pair-matched and consequently randomly assigned to one of the following experimental groups: a low volume per session with a high frequency (LV-HF, n = 9) group who trained 4-days (Mondays, Tuesdays, Thursdays and Fridays) or a high volume per session and low frequency (HV-LF, n = 9) group who trained 2-days (Mondays and Thursdays). Both groups performed two different routines over 6 weeks. Participants were tested pre- and post- intervention for maximal strength, upper body power, fat-free mass, limb circumferences and muscle thickness. Compared to baseline values, both groups increased their fat-free mass (HV-LF +1.19 ± 1.94; LV-HF +1.36 ± 1.06 kg, p<0.05) and vastus medialis thickness (HV-LF +2.18±1.88, p<0.01; LV-HF +1.82±2.43 mm, p<0.05), but only the HV-LF group enhanced arm circumference (1.08±1.47cm, p<0.05), elbow flexors thickness (2.21±2.81 mm, P<0.01) values and decreased their fat mass (-2.41 ± 1.10, P<0.01). Both groups improved (p<0.01) the maximal loads lifted in the bench press (LV-HF +0.14 ± 0.01; HV-LF +0.14 ± 0.01 kg.body mass-1) and the squat (LV-HF +0.14 ± 0.06; HV-LF 0.17 ± 0.01 kg.body mass-1) exercises as well as in upper body power (LV-HF +0.22 ± 0.25; HV-LF +0.27 ± 0.22 watts.body mass-1) Although both training strategies improved performance and lower body muscle mass, only the HV-LF protocol increased upper body hypertrophy and improved body composition

Methoden für die Unterscheidung von ökologisch und konventionell erzeugten Lebensmitteln

Bioprodukte werden heute immer stärker international und über komplexe Wertschöpfungsketten produziert und gehandelt. Dadurch werden Kontrollen, welche die Authentizität der Bio-Produkte zuverlässig gewähren, immer schwieriger. Höhere Preise für Bioprodukte waren in der Vergangenheit zudem Motivation hinter einzelnen Betrugsfällen in der Biobranche. Aus diesem Grund braucht es weitere Methoden, welche die Kontrollen der Zertifizierungsstellen unterstützen und ergänzen. Außer dem analytischen Nachweis von chemisch-synthetischen Pestizidrückständen, der bereits seit geraumer Zeit in der Praxis etabliert ist, gibt es weitere analytische und ganzheitliche Methoden, welche biologische und konventionelle Lebensmittel differenzieren können. Vor diesem Hintergrund war es das Ziel der Studie, die bestehenden oder in der Entwicklung befindlichen differenzierenden Methoden zur Unterscheidung biologisch von herkömmlich erzeugten Nahrungsmitteln zu beschreiben und ihre Praxistauglichkeit zu bewerten. Hierfür wurden eine umfangreiche Literaturstudie sowie ergänzende Expertengespräche durchgeführt

Effects of environmental parameters on chytrid infection prevalence of four marine diatoms : a laboratory case study

Acknowledgements: The Icelandic Research Fund (grant reference 141423-051) is gratefully acknowledged for its support to BS.Peer reviewedPublisher PD