A Herbivorous Mite Down-Regulates Plant Defence and Produces Web to Exclude Competitors

Herbivores may interact with each other through resource competition, but also through their impact on plant defence. We recently found that the spider mite Tetranychus evansi down-regulates plant defences in tomato plants, resulting in higher rates of oviposition and population growth on previously attacked than on unattacked leaves. The danger of such down-regulation is that attacked plants could become a more profitable resource for heterospecific competitors, such as the two-spotted spider mite Tetranychus urticae. Indeed, T. urticae had an almost 2-fold higher rate of oviposition on leaf discs on which T. evansi had fed previously. In contrast, induction of direct plant defences by T. urticae resulted in decreased oviposition by T. evansi. Hence, both herbivores affect each other through induced plant responses. However, when populations of T. evansi and T. urticae competed on the same plants, populations of the latter invariably went extinct, whereas T. evansi was not significantly affected by the presence of its competitor. This suggests that T. evansi can somehow prevent its competitor from benefiting from the down-regulated plant defence, perhaps by covering it with a profuse web. Indeed, we found that T. urticae had difficulties reaching the leaf surface to feed when the leaf was covered with web produced by T. evansi. Furthermore, T. evansi produced more web when exposed to damage or other cues associated with T. urticae. We suggest that the silken web produced by T. evansi serves to prevent competitors from profiting from down-regulated plant defences

Role of sucrose in microspore embryo production in Brassica napus ssp. oleifera

One cultivar of winter oil seed rape (Brassica napus ssp. oleifera) and three cultivars of spring rape were used in a study of the effects of sucrose on microspore survival and embryo induction in cultured anthers. A preliminary study on the winter cultivar (Fiona) revealed that the osmotic pressure of the supernatant of anther homogenates was equivalent to a solution of 17% sucrose. A study of microspore survival and embryo induction in this cultivar on media containing either 8%, 12%, 16% or 20% sucrose revealed the highest survival (after 16 d) and the greatest number of anthers with induced embryos (after 42 d) occurred on the highest sucrose concentration. A subsequent study on three spring cultivars (Willi, Duplo and Tower) examined microspore survival at 8 d and embryo induction (42 d) on media containing either 8% or 16% sucrose and again revealed much higher survival and induction at the higher concentration. The variation in response between the cultivars was also reduced by culture at the higher sucrose concentration. The beneficial effect of the 16% level occurred regardless of the growth environment of the donor plants and of thestage of pollen development at the start of culture. However, macroscopic embryos emerged only from anthers on the 8% sucrose concentration, suggesting that transfer of anthers from a high to anormal sucrose concentration during culture would ensure that full advantage was taken of the much higher initial survival on the higher concentration

Cerebellar Cortex and Cerebellar Nuclei Are Concomitantly Activated during Eyeblink Conditioning: A 7T fMRI Study in Humans

There are controversies whether learning of conditioned eyeblink responses primarily takes place within the cerebellar cortex, the interposed nuclei, or both. It has also been suggested that the cerebellar cortex may be important during early stages of learning, and that there is a shift to the cerebellar nuclei during later stages. As yet, human studies have provided little to resolve this question. In the present study, we established a setup that allows ultra-high-field 7T functional magnetic resonance imaging (fMRI) of the cerebellar cortex and interposed cerebellar nuclei simultaneously during delay eyeblink conditioning in humans. Event-related fMRI signals increased concomitantly in the cerebellar cortex and nuclei during early acquisition of conditioned eyeblink responses in 20 healthy human subjects. ANOVAs with repeated-measures showed significant effects of time across five blocks of 20 conditioning trials in the cortex and nuclei (p < 0.05, permutation corrected). Activations were most pronounced in, but not limited to, lobules VI and interposed nuclei. Increased activations were most prominent at the first time the maximum number of conditioned responses was achieved. Our data are consistent with a simultaneous and synergistic two-site model of learning during acquisition of classically conditioned eyeblinks. Because increased MRI signal reflects synaptic activity, concomitantly increased signals in the cerebellar nuclei and cortex are consistent with findings of learning related potentiation at the mossy fiber to nuclear cell synapse and mossy fiber to granule cell synapse. Activity related to the expression of conditioned responses, however, cannot be excluded

Evaluation of a new approach for semi-automatic segmentation of the cerebellum in patients with multiple sclerosis

Cerebellar dysfunction is an important contributor to disability in patients with multiple sclerosis (MS), however, few in vivo studies focused on cerebellar volume loss so far. This relates to technical challenges regarding the segmentation of the cerebellum. In this study, we evaluated the semi-automatic ECCET software for performing cerebellar volumetry using high-resolution 3D T1-MR scans in patients with MS and healthy volunteers. We performed test-retest as well as inter-observer reliability testing of cerebellar segmentation and compared the ECCET results with a fully automatic cerebellar segmentation using the FreeSurfer software pipeline in 15 MS patients. In a pilot matched-pair analysis with another data set from 15 relapsing-remitting MS patients and 15 age- and sex-matched healthy controls (HC), we assessed the feasibility of the ECCET approach to detect MS-related cerebellar volume differences. For total normalized cerebellar volume as well as grey and white matter volumes, intrarater (intraclass correlation coefficient (ICC) = 0.99, 95 % CI = 0.98-0.99) and interobserver agreement (ICC = 0.98, 95 % CI = 0.74-0.99) were strong. Comparison between ECCET and FreeSurfer results likewise yielded a good intraclass correlation (ICC = 0.86, 95 % CI = 0.58-0.95). Compared to HC, MS patients had significantly reduced normalized total brain, total cerebellar, and grey matter volumes (p >/= 0.05). ECCET is a suitable tool for cerebellar segmentation showing excellent test-retest and inter-observer reliability. Our matched-pair analysis between MS patients and healthy volunteers suggests that the method is sensitive and reliable in detecting cerebellar atrophy in MS