Effect of regurgitant from Leptinotarsa decemlineata on wound responses in Solanum tuberosum and Phaseolus vulgaris

The effect of regurgitant from Leptinotarsa decemlineata Say larvae on wound-induced responses was studied using two plant species, Solanum tuberosum L. and Phaseolus vulgaris L. Wounding of one leaf of intact S. tuberosum plants differentially affected ethylene production and activities of peroxidase and polyphenol oxidase. Only polyphenol oxidase activity was stimulated by wounding in both wounded and systemic leaves. Peroxidase activity was not affected by wounding. Wounding caused only a transient increase of ethylene production from wounded leaves. The application of regurgitant to wound surfaces stimulated ethylene production as well as activities of peroxidase and polyphenol oxidase in both wounded and systemic leaves. Wounding significantly enhanced ethylene production and polyphenol oxidase activity in wounded and systemic leaves of P. vulgaris . The application of regurgitant caused an amplification of ethylene production, peroxidase activity, and polyphenol oxidase activity, in both wounded and systemic leaves of bean plants. Several substances were tested for their role as possible endogenous signals in P. vulgaris . Hydrogen peroxide and methyl jasmonate appeared as potential local and systemic signals of ethylene formation in wounded bean plants. Local ethylene production in leaf discs was differentially affected by the regurgitant application in potato versus bean plants. While all tested concentrations of regurgitant caused stimulation of ethylene formation from potato leaf discs, ethylene production was completely inhibited by increasing concentrations of the regurgitant in bean leaf discs. Our data present evidence that ethylene may play an important role in the interaction between plants and herbivores at the level of recognition of a particular herbivore leading to specific induction of signalling cascades.     

Changes of morphogenic competence in mature Pinus sylvestris L. buds in vitro

The effects of season and cold storage on morphogenic competence in mature Pinus sylvestris buds were investigated. Peroxidase and polyphenol oxidase activity were measured as markers of oxidative metabolism. No growth in vitro was observed on explants detached from the end of January until the beginning of March. Brachioblasts, each with a couple of needles, formed on 11% of the buds without macrostrobili that were detached in early April and introduced immediately into culture. Of the explants detached in late July, 15% formed shoots with brachioblasts and needles. The lowest activity of peroxidase and polyphenol oxidase in pine buds was observed from the end of April until the beginning of June when morphogenic competence of tissues started to increase. Development of bud explants detached in January was achieved by cold storage for 5 months. Low polyphenol oxidase and peroxidase activity coincided with increased morphogenic potential. Results suggest that reduced or stable activity of peroxidase and polyphenol oxidase is associated with an increased ability of tissues to start growth in vitro.     

Endogenous rhythmicity of ethylene production in growing intact cereal seedlings

Ethylene evolution from etiolated barley (Hordeum vulgare), wheat (Triticum aestivum), and rye (Secale cereale) seedlings during coleoptile growth followed a rhythmic pattern, with a period of about 16 h for barley and wheat and 12 h for rye seedlings. Leaf emergence disturbed the established rhythm of ethylene evolution.     

Critical tests for determination of microbiological quality and biological activity in commercial vermicompost samples of different origins

The aim of the present paper was to show that differences in biological activity among commercially produced vermicompost samples can be found by using a relatively simple test system consisting of microorganism tests on six microbiological media and soilless seedling growth tests with four vegetable crop species. Significant differences in biological properties among analyzed samples were evident both at the level of microbial load as well as plant growth-affecting activity. These differences were mostly manufacturer- and feedstock-associated, but also resulted from storage conditions of vermicompost samples. A mature vermicompost sample that was produced from sewage sludge still contained considerable number of Escherichia coli. Samples from all producers contained several potentially pathogenic fungal species such as Aspergillus fumigatus, Pseudallescheria boidii, Pseudallescheria fimeti, Pseudallescheria minutispora, Scedosporium apiospermum, Scedosporium prolificans, Scopulariopsis brevicaulis, Stachybotrys chartarum, Geotrichum spp., Aphanoascus terreus, and Doratomyces columnaris. In addition, samples from all producers contained plant growth-promoting fungi from the genera Trichoderma and Mortierella. The described system can be useful both for functional studies aiming at understanding of factors affecting quality characteristics of vermicompost preparations and for routine testing of microbiological quality and biological activity of organic waste-derived composts and vermicomposts.     

Reactive oxygen and ethylene are involved in the regulation of regurgitant-induced responses in bean plants

Application of regurgitant from Leptinotarsa decemlineata Say on wound surfaces of one wounded leaf of intact bean (Phaseolus vulgaris L.) plants resulted in activation of ethylene biosynthesis followed by an increase of both peroxidase and polyphenol oxidase activity. The aim of the present investigation was to study the source of increased oxidative enzyme activities in regurgitant-treated bean leaves and to determine if hydrogen peroxide and ethylene biosynthesis is responsible for regurgitant-induced amplification of wound responses in bean plants. As the regurgitant contained relative high activities of both peroxidase and polyphenol oxidase, there is a possibility that increased enzyme activities in bean leaves following regurgitant treatment is an artifact of insect-derived enzymes. Localisation experiments and electrophoretic analysis revealed that only part of the increased enzyme activities could be attributed to regurgitant-derived enzymes. Both increase of ethylene production and oxidative enzyme activities depended on protein synthesis. To demonstrate if the increase of oxidative metabolism was ethylene-dependent, seedlings were pretreated with aminooxyacetic acid, an inhibitor of ethylene biosynthesis, and 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene action. Increase of both peroxidase and polyphenol oxidase activity in wounded and subsequently regurgitant-treated leaf was abolished by both aminooxyacetic acid and 1-MCP. Inhibitor studies indicated that H2O2 generated through NADPH oxidase and superoxide dismutase is necessary for regurgitant-induced increase of ethylene production and oxidative enzyme activities.     

Coleoptile removal-induced ethylene production in winter rye seedlings

Coleoptile removal-induced ethylene production was investigated in light-grown winter rye seedlings. Removal of the coleoptile induced 1-aminocyclopropane-l-carboxylic acid (ACC) synthesis and ethylene production by primary leaves and caused an inhibition of elongation growth of the leaves. The activity of ethylene-forming enzyme (EFE) was associated with the increase in ethylene evolution. Both rise in ethylene and ACC production, as well as EFE activity were inhibited by cycloheximide. Wounding the tissue 40 min after the initial treatment resulted in the second increase in ethylene evolution. Derooting of the seedlings without coleoptile removal did not induce ethylene production. It is suggested that the coleoptile represents a barrier for wound-induced ethylene production from actively growing leaf tissue.     

Neodiprion sertifer defoliation causes long-term systemic changes of oxidative enzyme activities in Scots pine needles

The aim of the experiments reported here was to study possible long-term effects of Neodiprion sertifer Geoff. (Hymenoptera: Diprionidae) herbivory, or artificial defoliation, on oxidative enzyme activities in Scots pine (Pinus sylvestris L.) needles as a consequence of induced defense responses. During year 1 (the first season), defoliation by N. sertifer, which feeds on previous season’s needles, did not result in statistically significant changes in polyphenol oxidase activity in the current year’s needles. In contrast, defoliation did lead to increased peroxidase activity in those needles. In the second season (year 2) N. sertifer defoliation of pine seedlings, also defoliated in the previous season either by larvae or artificially, resulted in a decrease of peroxidase activity in the current year’s needles. No significant differences between treatments carried out in year 1 were found in year 2 for peroxidase activity in the previous year’s needles. However, defoliation in year 1 by N. sertifer resulted in decreased needle consumption, and higher mortality of larvae, in year two. These results indicate the existence of long-term changes in needle oxidative enzyme activities as a consequence of N. sertifer feeding.     

Changes of 1-Aminocyclopropane-1-Carboxylic Acid Oxidase Activity in Stressed Pinus Sylvestris Needles

Stimulation of ethylene biosynthesis in pine needles by hydrogen peroxide and sodium bisulfite coincided with the activation of ACC oxidase at the level of protein synthesis. Decrease in ethylene production at high concentrations of sodium bisulfite (above 7 mM) was apparently due to inhibition of ACC oxidase activity. Treatment of pine needles with aminotriazole caused an inhibition of both ethylene production and ACC oxidase activity. Both methylviologen and methyl jasmonate stimulated ACC oxidase activity in a concentration-dependent manner with no parallel changes in ethylene production. The presented results suggest that ACC oxidase plays an important role in regulation of ethylene formation in pine needles in response to different stimuli.