Elongation, rooting and acclimatization of micropropagated shoots from mature material of hybrid larch

Factors were defined for elongation, rooting and acclimatization of micropropagated shoots of Larix x eurolepis Henry initiated from short shoot buds of plagiotropic stecklings serially propagated for 9 years from an 8-year-old tree. Initiation and multiplication were on Schenk and Hildebrandt (SH) medium supplemented with 5 μM 6-benzyladenine (BA) and 1 μM indole-butyric acid (IBA). Stem elongation was obtained in 36% of the shoots on SH medium containing 0.5 μM BA and 63% of the remaining non-elongated shoots initiated stem elongation after transfer on SH medium devoid of growth regulators. Rooting involved 2 steps: root induction on Campbell and Durzan mineral salts and Murashige and Skoog organic elements, both half-strength (CD-MS/2), supplemented with 1 μM of both naphthaleneacetic acid (NAA) and IBA, and root elongation following transfer to CD-MS/2 medium devoid of growth regulators. Repeating this 2-step sequence yielded up to 67% rooted shoots. Acclimatization of plantlets ranged from 83% to 100%. Over 300 plants were transferred to the greenhouse; some showed plagiotropic growth

IRS-2 Deficiency Impairs NMDA Receptor-Dependent Long-term Potentiation

The beneficial effects of insulin and insulin-like growth factor I on cognition have been documented in humans and animal models. Conversely, obesity, hyperinsulinemia, and diabetes increase the risk for neurodegenerative disorders including Alzheimer's disease (AD). However, the mechanisms by which insulin regulates synaptic plasticity are not well understood. Here, we report that complete disruption of insulin receptor substrate 2 (Irs2) in mice impairs long-term potentiation (LTP) of synaptic transmission in the hippocampus. Basal synaptic transmission and paired-pulse facilitation were similar between the 2 groups of mice. Induction of LTP by high-frequency conditioning tetanus did not activate postsynaptic N-methyl-D-aspartate (NMDA) receptors in hippocampus slices from Irs2−/− mice, although the expression of NR2A, NR2B, and PSD95 was equivalent to wild-type controls. Activation of Fyn, AKT, and MAPK in response to tetanus stimulation was defective in Irs2−/− mice. Interestingly, IRS2 was phosphorylated during induction of LTP in control mice, revealing a potential new component of the signaling machinery which modulates synaptic plasticity. Given that IRS2 expression is diminished in Type 2 diabetics as well as in AD patients, these data may reveal an explanation for the prevalence of cognitive decline in humans with metabolic disorders by providing a mechanistic link between insulin resistance and impaired synaptic transmission

Micropropagation and rejuvenation of Sequoia sempervirens (Lamb) Endl: a review

This article describes the botanical, biological and forest-tree characteristics of Sequoia sempervirens, the reasons for interest in its in vitro vegetative multiplication, the difficulty in achieving this from old and remarkable trees, and reviews means of overcoming this limitation. Among such means are the repeated culture of stem fragments on media containing appropriate hormonal combinations, the micrografting of buds originating from old trees onto juvenile rootstocks, and regeneration of buds from previously rejuvenated material. The value and limitations of these protocols and of morphological, physiological and biochemical markers of rejuvenation are discussed. The experimental conditions required for the formation of somatic embryos are described. Increased knowledge of in vitro micropropagation will be essential to enhance the use of clonal selection and offer practical outlets to studies concerning somatic hybridization and somatic embryogenesis.Micropropagation et rajeunissement du Sequoia sempervirens (Lamb) Endl : revue. Cet article présente les principales caractéristiques botaniques, biologiques et forestières du Sequoia sempervirens. Il analyse l'intérêt de la multiplication végétative réalisée in vitro soit par micropropagation sensu stricto (figs 1, 2 et 3), soit par régénération (figs 6, 7 et 9); il discute les raisons de la difficulté à la réaliser à partir d'arbres âgés et remarquables ainsi que les moyens de la contourner. Parmi ces moyens figurent la réitération des cultures de fragments de tige sur des milieux contenant un équilibre hormonal adéquat (tableaux I et II), le microgreffage de bourgeons appartenant à des plantes âgées sur des porte-greffes juvéniles (figs 4 et 5), la régénération de bourgeons à partir de matériel préalablement rajeuni selon l'un des protocoles précédents (figs 10 et 11). L'intérêt et les limites de ces protocoles sont discutés, en considérant les marqueurs morphologiques (figs 12 et 13), physiologiques et biochimiques du rajeunissement. Les conditions d'obtention de l'embryogenèse somatique chez cet arbre sont décrites (fig 8). Finalement, l'accroissement de nos connaissances en micropropagation in vitro apparaît essentiel pour augmenter la qualité de la sélection clonale et offrir des débouchés pratiques aux travaux concernant l'hybridation somatique et l'embryogenèse somatique. L'acquisition de telles connaissances de base devrait permettre une meilleure utilisation de cet arbre

Réflexion sur les modalités d'appréciation du rajeunissement in vitro chez le Sequoia sempervirens

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