The effect of Tetraneura ulmi L. galling process on the activity of amino acid decarboxylases and the content of biogenic amines in Siberian elm tissues.

Tetraneura ulmi (L.), a member of Eriosomatinae subfamily, is one of the gall-forming aphids occurring on elms. Sap-sucking behaviour of founding mothers results in the formation of new plant organs. This study documents the changes in the content of plant biogenic amines (putrescine, cadaverine, spermidine, tryptamine, spermine and histamine) and key enzymes of their biosynthesis: lysine decarboxylase (LDC), tyrosine decarboxylase and ornithine decarboxylase (ODC) in galls and other parts of Siberian elm (Ulmus pumila L.) leaves during the galling process. The direction and intensity of these changes for particular amines and enzymes were dependent on the stage of gall development and part of the galling leaf. Generally, the amine content tended to increase in gall tissues during the 1st and 2nd period of the galling process and decreased in later phases. LDC and ODC activities were markedly enhanced, especially in gall tissues at the initial stage of the galling process.

Influence of selected plant amines on probing behaviour of bird cherry-oat aphid (Rhopalosiphum padi L.).

The study aimed to quantify the influence of common plant polyamines and tyramine on probing behaviour in the bird cherry-oat aphid (Rhopalosiphum padi L.). Electrical penetration graphs (DC) were used to monitor the probing and feeding behaviour of R. padi exposed to the amines agmatine, cadaverine, putrescine, spermidine, spermine and tyramine. The study results showed that the analyzed amines tended to shorten the stylet activity of aphids in the gels (as indicated by the g-C pattern), prolong the duration of non-probing behaviour (g-np pattern) and decrease salivation into the gels (g-E1pattern) and ingestion from the gels (g-G pattern). The 10 mM concentration of the studied amines, especially cadaverine, reduced or completely inhibited aphid ingestion. The obtained results demonstrate that plant amines participate in plant defence responses to R. padi through disturbance of its probing behaviour and the intensity of such effects is concentration dependent.

Antimetabolic effect of phytohemagglutinin to the grain aphid Sitobion avenae fabricius.

The insecticidal activity of plant lectins against a wide range of insect species have been intensively studied. Understanding the mechanism of the toxicity of lectins is one of the studied aspects. In the present research, the first step was determine the effect of phytohemagglutinin (PHA) on the development, fecundity and mortality of grain aphid. Next, the effect of PHA lectin on the activity of such enzymes as: α- and ß-glucosidases, alkaline (AkP) and acid (AcP) phosphatases, aminopeptidase N and cathepsin L involved in the metabolism of sugar, phosphorus and proteins of an adult apterae aphids was investigated. The PHA lectin added into the liquid diet increased the pre-reproductive period, mortality of Sitobion avenae, the time of generation development and decreased its fecundity and the intrinsic rate of natural increase. In addition, activity of α-glucosidase, alkaline phosphatase and aminopeptidase N of adult apterae exposed to PHA were reduced. The results indicate that the insecticidal activity of PHA on S. avenae may involve changes in activity of the enzymes in the midgut and it may be part of its toxicity.

Induced proteolysis within the bird cherry leaves evoked by Rhopalosiphum padi L. (Hemiptera, Aphidoidea).

The objectives of this study were to elucidate the impact of bird cherry-oat aphid (Rhopalosiphum padi L.) feeding on functioning of the proteolytic machinery in bird cherry leaves. Biochemical analyses proved that R. padi feeding in tissues of primary host stimulated activity of the two major fractions of proteinases (extracted at the optimal pH values: 5.0 and 7.0). Additionally, it has been demonstrated that aphids' feeding on bird cherry led to a decline in levels of albumins and globulins (main protein fractions in P. padus leaves). The opposite tendency, regarding the amounts of these protein fractions was ascertained at the phase of disappearance of R. padi population on tested shoots. Furthermore, it is reported that an increase in activity of the analysed enzymes and a decline in the content of tested protein fractions, were proportional to density of aphid individuals developing on P. padus side shoots. It is hypothesized that long-term R. padi feeding may lead to intensifying the catabolic processing of proteins by the activated proteolytic machinery in bird cherry leaves. The multi-level biological functions of endogenous plant proteinases and their significance in triggering the defense reactions in aphid-infested plant tissues are discussed.