Some Effects of Amo-1618 on Growth, Peroxidase and α-Amylase Which Cannot Be Easily Explained by Inhibition of Gibberellin Biosynthesis

Growth and peroxidase activity of roots and stems of lentil seedlings were compared after treatment with Amo-1618, alone or in combination with gibberellic acid (GA) at varying concentrations. The peroxidase enhancement in Amo-1618 treated stems could not be attributed to a decrease in the gibberellin content since GA alone had no effect on this enzyme. In other experiments, AMO, at low concentrations, was able to induce α-amylase production in barley aleurone layers; the lag period needed for this induction, was longer than for GA. These facts seem to indicate that some growth retardants might act at least in some cases by mechanisms other than inhibition of gibberellin biosynthesis and reversal of GA action.     

A matter of timing: heat wave impact on crustacean zooplankton

1. Climate change has affected zooplankton phenology and abundance in many freshwater ecosystems. The strong temperature anomalies that characterise summer heat waves make these events particularly suitable to study the effects of different seasonal warming patterns on zooplankton. Since heat waves are expected to occur more frequently under continuing climate change, they may also allow us to investigate how freshwater systems will be affected in the future. 2. Using a long‐term data set (1991–2007) from a shallow, eutrophic lake in Germany, we identify time periods in spring and summer during which cyclopoid copepods and bosminids are particularly sensitive to changes in water temperature. Based on this knowledge, we consider why summer populations responded differently to recent heat wave events that occurred at different times in the season. 3. Linear regressions of moving averages suggested that water temperatures shortly before and shortly after the clear‐water phase (CWP) were crucial for summer development of bosminids and cyclopoid copepods, respectively. Algal food availability (diatoms and cryptophytes) in the first weeks after the CWP also strongly influenced the summer populations of the two zooplankton groups. 4. Inter‐annual differences in water temperature during the critical time periods at least partly explained the contrasting responses of cyclopoid copepods and bosminids to heat wave events. 5. Our findings indicate that the zooplankton response to climate warming, particularly to heat wave events, is critically dependent on the temporal pattern of elevated water temperatures. Beyond that, we show that the summer zooplankton populations react to periods of warming in relation to events in the plankton annual cycle (such as the CWP in eutrophic lakes) rather than to warming at a fixed time in the season.     

Intra‐specific body size variation in Polistes paper wasps as a response to social parasite pressure

1. Like avian brood parasites, obligate insect social parasites exploit the parental care of a host species to rear their brood, causing an evident loss of host reproductive success. This fitness cost imposes selective pressure on the host to reduce the parasite effect. A possible outcome of an evolutionary arms race is the selection of host morphological counter‐adaptations to resist parasite attacks. 2. We studied host–parasite pairs of Polistes wasps in which the fighting equipment of the parasite's body allows it to enter the host colony. 3. We searched for host morphological traits related to fighting ability that could be considered counter‐adaptations. As a host–parasite co‐evolutionary arms race can only occur where the two lineages co‐exist, we compared morphological traits of hosts belonging to populations with or without parasite pressure. We report that host foundresses belonging to populations under strong parasite pressure have a larger body size than those belonging to populations without parasite pressure. 4. Behavioural experiments carried out to test if an increase in host body size is useful to oppose parasite usurpation show that large body size foundresses exhibit a greater ability of nest defence.     

The chemical strategies used by Polistes nimphus social wasp usurpers (Hymenoptera Vespidae)

Polistes foundresses can behave as facultative social parasites when, instead of founding their own nest, they usurp colonies of the same or a different species and temporary use the host workforce to raise their own brood. Conspecific usurpation appears to be common among Polistes wasps, but nothing is known about the mechanisms that these facultative social parasites use to have themselves accepted within usurped colonies. Using behavioural tests, we studied the chemical strategies employed by females of Polistes nimphus when they behave as facultative social parasites in colonies of the same or of a different species. We hypothesized that usurpers would mark host nests with their own odours and/or acquire host nest odours in order to camouflage their real identity from host workers. Our results indicated that P. nimphus usurpers used different chemical strategies depending on host nest species: they acquired conspecific host odours but marked heterospecific host combs with their own odours.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 505–512.     

Manipulation of sink-source relations in transgenic plants

Since 1980, the use of transgenic plants in modern plant science has become a powerful tool to study whole plant physiology. In this review, we try to summarize the data obtained in the field of photoassimilate partitioning. Attempts to study sink-source interactions concern factors which might limit sink strength and source capacity. Transgenic plants have been used to manipulate the sucrose to starch ratio in order to produce plants with higher sucrose levels in their source leaves. Alterations in partitioning were achieved by manipulating Calvin cycle enzymes, transport proteins and sucrose biosynthetic enzymes. The ability of sink tissues to attract photoassimilates has been altered by either increasing or decreasing sucrose hydrolytic activities. The increase of sucrose hydrolysis was achieved by creating transgenic potato plants with tuber specific yeast-derived invertase. Decreased sucrose utilization was achieved by antisense inhibition of sucrose synthase in potato tubers.     

Adenosine 3':5'-Cyclic Monophosphate in Normal and Habituated Helianthus Callus

A compound with properties identical to adenosine 3’:5′-cyclic monophosphate (cAMP) has been isolated from callus of Helianthus annuus. The compound accompanied cAMP during an extensive purification procedure and co-chromatographed with cAMP in three solvent systems. The compound stimulated cAMP-dependent protein kinase and was active in a cAMP protein-binding assay. Its activity was abolished by cAMP phosphodiesterase. It is concluded that the compound is cAMP. The variation in cAMP content in the callus during its development was determined. In 1974 when the stock callus was grown on auxin-containing medium the content was c. 2 pmol cAMP/g when the cells were vigorously dividing and c. 125 pmol cAMP/g two weeks after the transfer. In 1976 the callus had attained hormone autotrophy. Its cAMP content was generally low during the whole developmental cycle. The results might indicate that cAMP played a role in the development of the normal callus of 1974, while it has no regulatory function in the tumour-like tissues of 1976. The results are discussed on the basis of recent literature.     

Characteristics of Root-to-Shoot Transport of Cytokinin 6-Benzylaminopurine in Intact Seedlings of Citrus aurantium

Transport of the cytokinin 6-benzylaminopurine-8-¹⁴C in the root and shoot of intact Citrus aurantium L. seedlings was studied by “replacing” the 0.5 cm root tip with the uptake solution. The cytokinin was transported basipetally in the root and was distributed in an acropetal direction in the stem and into the leaves. Kinetic analysis of the transport for periods of up to 96 h revealed a characteristic advancing front of the label along the axis of the seedling. The estimated velocity of transport of 6-benzylamino-purine-8-¹⁴C in various regions of the intact root was 2.6 to 5.1 mm/h. The transport of 6-benzylaminopurine was predominantly in the transpiration stream, in stelar tissues of the root. Conditions of high transpiration favored enhanced transport to the shoot and an overall greater accumulation of the label. The total accumulation of 6-benzylaminopurine in roots of intact seedlings after 48 h of transport was 354% of that in roots of shoot-less seedlings. Root girdling and treatment of the root with KCN did not reduce the basipetal transport of the label in the root and into the shoot. Radiochromalogram scanning of root extracts and analysis of the ethanol insoluble-NaOH soluble fraction revealed considerable metabolic changes in the translocated cytokinin. Only 51% of the radioactivity remained in the original 6-benzylaminopurine peak after 24 h of incubation. Two other, unidentified, metabolites were detected. It is suggested that all the factors that affect the ascent of sap are involved in the long-distance transport of cytokinins, and that the rate and mode of transport of cytokinins from the root system to the shoot may be a major factor in the expression of their physiological activity.     

EFFECTS OF ORALLY AND DERMALLY APPLIED METALDEHYDE ON MUCUS CELLS OF SLUGS (DEROCERAS RETICULATUM) DEPENDING ON TEMPERATURE AND DURATION OF EXPOSURE

Using light and electron microscopy in combination with histochemicaland immunocytochemical techniques, the impact of orally anddermally applied metaldehyde on mucus cells in the digestivetract, the skin, and the salivary gland of the slug Derocerasreticulatum (Müller) was investigated. The studies showedthat metaldehyde induces severe alterations and damages in mycocyteseven under low temperature and humid conditions when sufficientlyhigh doses were applied. After metaldehyde application, notonly the quantity of mucus produced by slugs but also its qualityis modified. Structural, enzymehistochemical and immunocytochemicalinvestigations revealed metaldehyde-induced effects in mucocytesto be related to influences of the molluscicide on serotoninand on energy metabolism. (Received 29 September 1997; accepted 8 December 1997)     

Ecohydrological effects of grazing‐induced degradation in the Patagonian Monte,Argentina

Water‐limited ecosystems have undergone rapid change as a consequence of changing land use and climate. The consequences of these changes on soil quality and vegetation dynamics have been documented in different regions of the world. In contrast, their effects on soil water, the most limiting resource in these environments, have received less attention, although in recent years increasing efforts have been made to relate grazing, soil water and vegetation functioning. In this paper, we present the results of field observations of plant phenology and soil water content carried out during two successive years at four sites along a degradation gradient caused by grazing in the Patagonian Monte, Argentina. We also developed a simplified soil water balance model to evaluate how changes in plant cover could affect water balance. Our field observations showed that the soil water content in the soil layer where roots of grasses are abundant (0–25 cm) was higher and the growing cycles were longer in degraded than in preserved sites. Similarly, our modelling approach showed that the deep soil (depth > 10 cm) was wetter in the degraded than in the preserved situation. Simulation also suggested a switch from transpiration to a direct evaporation dominance of water losses with degradation. Although reductions in plant cover related to grazing degradation were associated with a decrease in annual transpiration, the simulated soil water loss by transpiration was higher during summer in the degraded than in the well preserved situation. Thus, our field observations seem to be a consequence of ecohydrological changes causing an accumulation of water in the soil profile during the cold season and its transpiration during summer. In conclusion, our results showed that changes in plant cover caused by grazing disturbance can alter the soil water balance, which in turn can affect vegetation function.