No abstract

The indirect defences of plants are comprised of herbivoreinduced plant volatiles (HIPVs) that among other things attract the natural enemies of insects. However, the actual extent of the benefits of HIPV emissions in complex co-evolved plant-herbivore systems is only poorly understood. The observation that a few Quercus robur L. trees constantly tolerated (T-oaks) infestation by a major pest of oaks (Tortrix viridana L.), compared with heavily defoliated trees (susceptible: S-oaks), lead us to a combined biochemical and behavioural study. We used these evidently different phenotypes to analyse whether the resistance of T-oaks to the herbivore was dependent on the amount and scent of HIPVs and/or differences in non-volatile polyphenolic leaf constituents (as quercetin-, kaempferol-and flavonol glycosides). In addition to non-volatile metabolic differences, typically defensive HIPV emissions differed between S-oaks and T-oaks. Female moths were attracted by the blend of HIPVs from S-oaks, showing significantly higher amounts of (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and (E)-b-ocimene and avoid T-oaks with relative high fraction of the sesquiterpenes a-farnesene and germacrene D. Hence, the strategy of T-oaks exhibiting directly herbivore-repellent HIPV emissions instead of high emissions of predator-attracting HIPVs of the S-oaks appears to be the better mechanism for avoiding defoliation.

A large number of simple sequence repeat (SSR) marker-containing genetic maps are available for several Populus species. For aspen however, no SSR-containing map has been published so far. In this study, genetic linkage mapping was carried out with an interspecific mapping pedigree of 61 full-sib hybrids of European × quaking aspen (Populus tremula L. × Populus tremuloides Michx.), using the two-way pseudo-testcross strategy. Amplified fragmentlength polymorphism (AFLP) and SSR markers were used for mapping, resulting in the first SSR-containing genetic linkage maps for aspen. The maps allow comparisons with a Populus consensus map and other published genetic maps of the genus Populus. The maps showed good collinearity to each other and to the Populus consensus map and provide a direct link to the Populus trichocarpa genomic sequence. Sex as a morphological trait was assessed in the mapping population and mapped on a non-terminal position of linkage group XIX on the male P. tremuloides map.

Summary The expression of single rol genes of the TL‐DNA of Agrobacterium rhizogenes strain A4 in transgenic tobacco (Nicotiana tabacum L.) and potato (Solanum tuberosum L.) plants alters the internal concentrations of, and the sensitivity to, several plant hormones. The levels of immunoreactive cytokinins, abscisic acid, gibberellins and indole‐3‐acetic acid were analysed in tissues of the apical shoots, stems, leaves, roots and undifferentiated callus tissue. The addition of the dominant and morphogenetically active rolA, rolB, or rolC genes resulted in alterations in the content of several hormones. rolC overexpression in particular led to an up to fourfold increase in the content of isopentenyladenosine, dihydrozeatin riboside and trans‐zeatin riboside‐type cytokinins in potato plants. This increase correlated well with different levels of expression of the rolC gene in different transgenic plants. Furthermore it was shown that the dwarfism of P35s‐rolC transgenic tobacco and potato plants is correlated with a 28–60% reduction of gibberellic acid A1 concentration in apical shoots. Exogenous addition of gibberellic acid completely restored stem elongation in P35s‐rolC transgenic plants. Apical shoots of dwarf rolA transgenic tobacco plants also contained 22% less gibberellic acid A1 than control plants, but growth cannot be restored completely by exogenously added gibberellic acid. Similarly, the sensitivity of transgenic tobacco seedlings or callus tissues towards different phytohormone concentrations can be altered by the expression of single rol genes. The overexpression of the rolC gene in seedlings led to an altered response to auxins, cytokinins, abscisic acid, gibberellic acid and the ethylene precursor 1‐aminocyclopropane‐carboxylic acid. The overexpression of the rolB gene in tobacco calli led to necrosis at lower auxin concentrations than in the wild‐type, while other parameters of auxin action, like the induction of cell growth, remained unchanged.

The phytopathogenic bacterium Erwina carotovora spp. which infects potato plants causes severe losses in agriculture. No protective means or resistance traits usable for plant breeding are known. Introduction of a new resistance gene into potato by gene technology leads to a reduced susceptibility of the transgenic plants towards Erwinia carotovora atroseptica infection. Bacteriophage T4 lysozyme is the most active member of a class of bacteriolytic enzymes also detected in several plant species. Secretion of the foreign T4 lysozyme into the intercellular spaces of transgenic potato plants effects a resistance against the phytopathogenic bacterium already at low expression levels.