Different endogenous cytokinins between male and female Mercurialis annua L.

The endogenous pool of cytokinin metabolites during sexual differentiation of Mercurialis annua L. was studied with a computerized gas-chromatography-mass spectrometry system. Certain metabolites were common to both sexes: ribosides (isopentenyl-adenosine, ribosylzeatin) and the nucleotide of I₆-Ade. Zeatin could be detected only in females while its nucleotide was present in males. The results were obtained with differentiating apices and whole plants. The high Z concentration and the low level of its nucleotide are related to the absence of two dominant complementary genes, determining maleness. Study of the regulation of cytokinin metabolism now seems possible.Abbreviations IPA isopentenyl adenosine - I₆-Ade isopentenyl adenine - Z zeatin - RZ ribosylzeatin     

Temporal dynamics of host-marking in the tropical tephritid fly, Anastrepha ludens

Abstract. The temporal dynamics of host-marking behaviour in the tropical tephritid fly, Anastrepha ludens (Loew), is described and used to formulate a model of control of marking behaviour. The following temporal patterns in host-marking behaviour were observed. Time spent marking increased as Aludens females deposited clutches in a given fruit previously marked zero, one, two or three times. This trend was paralleled by an increase in the number of pauses in marking behaviour within the host-marking bout (and hence an increase in the number of sub-bouts separated by such pauses). Finally, within any given marking bout, the length of a sub-bout diminished progressively. The length of a pause, by contrast, showed no significant trend. Based on these results, we propose that host-marking pheromone, or HMP, while deterrent to females prior to egg-laying, actually stimulates continued host-marking behaviour after egg-laying. We argue that host-marking is regulated by sensory adaptation or habituation to HMP in conjunction with a dosage-dependent restoration of inhibition of the motor pattern. Functional aspects of this pattern of motor control are discussed.     

Repeated exposure reduces the response to impulsive noise in European seabass

Human activities have changed the acoustic environment of many terrestrial and aquatic ecosystems around the globe. Mounting evidence indicates that the resulting anthropogenic noise can impact the behaviour and physiology of at least some species in a range of taxa. However, the majority of experimental studies have considered only immediate responses to single, relatively short‐term noise events. Repeated exposure to noise could lead to a heightened or lessened response. Here, we conduct two long‐term (12 week), laboratory‐based exposure experiments with European seabass (Dicentrarchus labrax) to examine how an initial impact of different sound types potentially changes over time. Naïve fish showed elevated ventilation rates, indicating heightened stress, in response to impulsive additional noise (playbacks of recordings of pile‐driving and seismic surveys), but not to a more continuous additional noise source (playbacks of recordings of ship passes). However, fish exposed to playbacks of pile‐driving or seismic noise for 12 weeks no longer responded with an elevated ventilation rate to the same noise type. Fish exposed long‐term to playback of pile‐driving noise also no longer responded to short‐term playback of seismic noise. The lessened response after repeated exposure, likely driven by increased tolerance or a change in hearing threshold, helps explain why fish that experienced 12 weeks of impulsive noise showed no differences in stress, growth or mortality compared to those reared with exposure to ambient‐noise playback. Considering how responses to anthropogenic noise change with repeated exposure is important both when assessing likely fitness consequences and the need for mitigation measures.     

Cytokinin oxidase/dehydrogenase in Pisum sativum plants during vegetative development. Influence of UV-B irradiation and high temperature on enzymatic activity

Cytokinin oxidase/dehydrogenase (EC 1.5.99.12) specific activity was determined in leaves and roots of two P. sativum cultivars (cv. Scinado and cv. Manuela) during vegetative development and the effect of UV-B irradiation or elevated temperature was assessed. The measurement of CKX activity during development showed localisation of this enzyme to roots. The reduction in CKX activity in leaves after UV-B irradiation and the increased levels of the enzyme in high temperature-treated plants suggests that the enzymes from the CKX gene family have a different expression during stress responses provoked by different factors and probably are tissue specific. Differences regarding cytokinin oxidase/dehydrogenase activity stress response were observed between the two pea cultivars.     

Conditions for assessing cortisol in sheep: the total form in blood v. the free form in saliva

Cortisol is often used as a stress indicator in animal behaviour research. Cortisol is commonly measured in plasma and can also be measured in saliva. Saliva contains only the free form of cortisol, which is biologically active, and saliva sampling is not invasive and may therefore be less stressful. Our study aims to guide the choice between the measurements of cortisol in plasma v. saliva depending on experimental conditions. We analysed the effect of the level of cortisol in plasma on the concentration of cortisol in saliva compared to plasma and the effect of saliva sampling v. jugular venepuncture on the cortisol response. In Experiment 1, blood and saliva were collected simultaneously under conditions in which the expected cortisol release in blood varied: in an undisturbed situation or after the isolation of lambs from their pens or the administration of exogenous ACTH (six animals per treatment). In Experiment 2, we subjected lambs to saliva sampling, venepuncture or neither of these for 8 days to evaluate how stressful the sampling method was and whether the animals habituated to it by comparing the responses between the first and last days (four animals per treatment). All animals were equipped with jugular catheters to allow regular blood sampling without disturbance. Samples were collected 15 min before any treatment was applied, then at various time points up to 135 min in Experiment 1 and 45 min in Experiment 2. In Experiment 1, we observed a strong correlation between salivary and plasma cortisol concentrations (r = 0.81, P < 0.001). The ratio between salivary and plasma cortisol concentrations was 0.106 on average. This ratio was higher and more variable when the cortisol concentration in plasma was below 55 nmol/l. In Experiment 2, venepuncture induced a larger cortisol response than saliva sampling or no intervention on day 1 (P < 0.02); this difference was not observed on day 8, suggesting that sheep habituated to venepuncture. We recommend the measurement of cortisol in saliva to avoid stressing animals. However, when the expected concentration in plasma is below 55 nmol/l, the cortisol in saliva will reflect only the free fraction of the cortisol, which may be a limitation if the focus of the experiment is on total cortisol. In addition, if cortisol is measured in plasma and blood is collected by venepuncture, we recommend that sheep be habituated to venepuncture, at least to the handling required for a venepuncture.     

Learning in Stentor

SYNOPSIS. When placed in a vertical capillary tube of 0.5 mm inner diameter opening at the bottom end into a reservoir, Stentor coeruleus learns to escape; that is, on the 1st trial it takes a long time to find its way out and much less time on the 2nd and succeeding trials. It was found that learning did not occur in a horizontal tube, or in a vertical tube with the open end above, or in tubes of 1 or 2 mm inner diameter. To explain the results it is suggested that the response is actually a delayed geotaxis released only after a definite period of mechanical stimulation from bumping into the walls of the tube. Possibly the phenomenon is related to the process of habituation to mechanical stimuli which has been elucidated by other authors.     

Adventitious bud development in embryonic tissue ofPinus caribaea andPseudotsuga menziesii

Summary Adventitious bud formation was induced on detached cotyledons and on cotyledons attached to excised embryos ofPinus caribaea andPseudotsuga menziesii. The embryonic tissue was exposed to the cytokinin 6-benzyl amino purine contained within an agar medium. This exposure resulted in the formation of a meristematic zone, involving both epidermal and sub-epidermal cells, and then nodules on the tissue surface. Some of these nodules were induced to differentiate into bud primordia, and thence shoots, following exposure to a combination of auxin (IAA) and cytokinin. Shoots were produced over the entire surface of detached cotyledons ofPs. menziesii but predominantly on the adaxial surfaces of detached cotyledons ofPi. caribaea and the tips and adaxial surfaces of the cotyledons on the entire embryos of both species. Thus, inter-specific differences in the distribution of competent areas for adventitious bud production were detected in embryos.