Chemical defence in chrysomelid eggs and neonate larvae

ABSTRACT. Eggs and neonate larvae of chrysomelid beetles (sub-tribes Chrysomelina and Phyllodectina) were investigated for the presence of defensive substances.
The two isoxazolinone glucosides (compounds 1 and 2), characteristic of the adult defence secretion, were detected in the eggs of all studied species. Compound 2, containing a nitropropionate, is always present in concentrations (above 10^-2 M), which are highly deterrent to the ant Myrmica rubra. This compound is not at all or only slightly toxic to ants at 10^-2 M. Compound 1, devoid of nitropropionate, is a minor constituent, and is neither deterrent nor toxic to ants.
The five Chrysomela species studied and Phratora vitellinae also sequester salicin in their eggs in amounts highly deterrent and toxic to ants. A single Chrysomela egg often contains enough salicin to kill an ant. While the isoxazolinones are discarded with the egg shells, salicin is used by neonate larvae as a precursor for the production of salicylaldehyde in the thoracic defence glands, already functional at hatching. No salicin could be detected in the eggs of those species whose larvae produce cyclopentanoid monoterpenes, even if they feed on Salicaceae. No larva of any species seems to be able to produce detectable amounts of monoterpenes at birth. A very early defence, possible only in those species using salicin as the precursor for their defensive secretion, could be highly advantageous in protecting the clustered larvae during the long process of hatching and in avoiding cannibalism between siblings.
Only trace amounts of oleic acid were found in the eggs of Gastrophysa viridula , in contrast to previous reports on its presence in large quantities in the American G. cyanea.     

Leaf thionins, a novel class of putative defence factors

Leaf thionins of barley have been identified as a novel class of highly abundant polypeptides with antifungal activity, which are present in walls and vacuoles of barley leaf cells. Similar thionins occur not only in monocotyledonous but also in various dicotyledonous plants. The leaf thionins of barley are encoded by a complex multigene family, which consists of at least 50–100 members per haploid genome. The toxicity of these thionins for plant pathogenic fungi and the fact that their synthesis can also be triggered by pathogens strongly suggest that leaf thionins are involved in the mechanism of plant defence against microbiol infection.     

Consequences of herbivory in the mountain birch (Betula pubescens ssp tortuosa): importance of the functional organization of the tree

Summary Three types of experiments indicate that the functional organization of the mountain birch may influence the ways in which the tree responds to simulated or natural herbivory. The first experiment showed that herbivory to both short and long shoot leaves affects plant development but, because growth largely proceeds by resources of the previous year, is manifested only in the year following the damage. The second experiment showed that even partial damage to a single long shoot leaf caused the axillary bud of that leaf to produce a shorter shoot the next year. Therefore, the value of a leaf depends also on the organ which it is subtending. In the third experiment we manipulated the apical dominance of shoots in ramets and caused improvement to leaf quality in extant shoots. Ramets within a tree responded individually, probably mediated by disturbance of the hormonal control because removal of apical buds elicited the response although removal of the same number of basal buds did not. Induced amelioration is a different response to induced resistance. The two responses are triggered by different cues and may occur in the same plant. By altering hormonal balance of shoots it is potentially possible for herbivores to induce amelioration of food quality. The ways in which herbivory is simulated may explain variability of results obtained when herbivory-induced responses in plants have been studied.     

Colony orientation and successful defence behaviour in the conifer aphid, Schizolachnus pineti

We studied colony structure and body orientation behaviour of Schizolachnus pineti, a specialised aphid feeding on needles of Scots pine. Aphids feeding at the margin of a colony always face towards the centre of the colony, bounding the colony with their legs. This behaviour increased the defence success aginst the specialised parasitoid (Pauesia unilachni) and the specialised predator (Scymnus nigrinus). Both enemies had less success when attacking S. pineti from the abdominal site when compared to the front. We assume that the defence orientation displayed by marginally feeding aphids has an adaptive nature and is particularly effective when feeding in a row on linear plant structures such as needles.     

Host-plant relationships of lycaenid butterflies: large-scale patterns, interactions with plant chemistry, and mutualism with ants

The Lycaenidae are the second-largest family of butterflies. From host-plant data collated for more than 1200 species worldwide, large-scale taxonomic, geographical and ecological patterns emerge which suggest that phytochemical similarities and barriers, coupled with phylogenetic conservatism and constraints are key factors governing hostplant use. More than two thirds of the lycaenid species are restricted to one plant family or genus. Affiliations with toxic plants are rare in the Lycaenidae, and excretion rather than sequestration of plant toxins appears to be their usual way of detoxifying host-plant compounds. Flavonoids are frequently sequestered by lycaenid larvae and are subsequently concentrated as pigments in the adults' wings, where they might play a role in visual communication. Mutualistic associations with ants occur in the larvae of more than 50% of the extant Lycaenidae species. Because of a conflict between the nutrient demands of the larvae and the proportion of plant-derived resources allocated to maintain the mutualism with ants, variation in resource quality often translates into variation of mutualistic capacities of the caterpillars, in particular under nutrient stress.     

Bacterial expression of an active class Ib chitinase from Castanea sativa cotyledons

Ch3, an endochitinase of 32 kDa present in Castanea sativa cotyledons, showed in vitro antifungal properties when assayed against Trichoderma viride. The characterization of a cDNA clone corresponding to this protein indicated that Ch3 is a class Ib endochitinase that is synthesized as a preprotein with a signal sequence preceding the mature polypeptide. Bacterial expression of mature Ch3 fused to the leader peptide of the periplasmic protein ompT resulted in active Ch3 enzyme. A plate assay was adapted for semi-quantitative determination of chitinase activity secreted from cultured bacteria, which should facilitate the identification of mutants with altered capacity to hydrolyse chitin.     

Plant defence systems induced by ozone

Recent advances in the understanding of the molecular basis of plant response to ozone attack are reviewed. Plants grown in elevated atmospheric ozone are known to undergo several biochemical changes before any actual damage can be detected. These reactions include increases in the activities of enzymes associated with general plant defence mechanisms. Ozone exposure often causes a surge in the production of the plant hormone ethylene, as well as changes in polyamine metabolism and increases in the activities of several phenylpropanoid and flavonoid pathway enzymes. The activities of superoxide dismutase and peroxidases that protect cells from the oxidative damage caused by hydroxyl radicals, H₂O₂ and superoxides also increase. However, ozone-induced changes in plant cells at the gene level are almost unknown. The limited data available suggest close similarities between ozone-induced and pathogen-induced defence responses in plants. Several general defence genes that have been cloned in other studies will soon be applied to studies of gene expression in ozone-exposed plants. The use of molecular biological tools in ozone research should enable the development of highly specific and sensitive molecular markers for biomonitoring ozone-induced injuries in plants.     

Developments in tomographic methods for biological trace element research

Neutron-induced γ-ray emission tomography for quantitative determination of the concentration and distribution of elements in a selected plane through a biological specimen is briefly explained and applied by way of illustration to the analysis of gallstones. A system capable of carrying out studies of the binding site of⁷⁵Se in different matrices using time differential perturbed angular correlation spectroscopy is also briefly described. Developments in the detector technology of positron emission tomography have allowed small-diameter imaging devices to be built for in vivo preclinical evaluation of new tracers in small animals and are discussed in the context of a proposed experiment combining the techniques mentioned above.