Quantification of endogenous levels of IAA, IAAsp and IBA in micro-propagated shoots of hybrid chestnut pre-treated with IBA

Endogenous levels of indole-3-acetic acid (IAA), indole-3-acetylaspartic acid (IAAsp) and indole-3-butyric acid (IBA) were measured during the first 8 d of in vitro rooting of rootstock from the chestnut ‘M3’ hybrid by high performance liquid chromatography (HPLC). Rooting was induced either by dipping the basal ends of the shoots into a 4.92-mM IBA solution for 1 min or by sub-culturing the shoots on solid rooting medium supplemented with 14.8- μM IBA for 5 d. For root development, the induced shoots were transferred to auxin-free solid medium. Auxins were measured in the apical and basal parts of the shoots by means of HPLC. Endogenous levels of IAA and IAAsp were found to be greater in IBA-treated shoots than in control shoots. In extracts of the basal parts of the shoots, the concentration of free IAA showed a significant peak 2 d after either root inductive method and a subsequent gradual decrease for the remainder of the time course. The concentration of IAAsp peaked at day 6 in extracts of the basal parts of shoots induced with 14.8-μM IBA for 5 d, whereas shoots induced by dipping showed an initial increase until day 2 and then remained stable. In extracts from basal shoot portions induced by dipping, IBA concentration showed a transient peak at day 1 and a plateau between day 2 and 4, in contrast to the profile of shoots induced on auxin-containing medium, which showed a significant reduction between 4 and 6 d after transferred to auxin-free medium. All quantified auxins remained at a relatively low level, virtually constant, in extracts from apical shoot portions, as well as in extracts from control non-rooting shoots. In conclusion, the natural auxin IAA is the signal responsible for root induction, although it is driven by exogenous IBA independently of the adding conditions

Effects of type of carbohydrate during proliferation and rooting of microcuttings of Malus Jork 9

The type of carbohydrate used in the medium influenced the proliferation of Malus Jork 9. The microcuttings obtained showed marked differences in rooting ability. During proliferation, sorbitol (0.176 M) gave the best results. The plants grown on fructose (either directly added or resulting from the hydrolysis of sucrose) showed a definite tendency to become an unorganised structure. This abnormal growth showed similarities with the "cancerisation" of microcuttings in the presence of very high cytokinin levels ! This BAP toxicity could be caused by a higher contact surface due to softer gel, this in turn being caused by lowering of pH after autoclaving. During rooting, it seems that both the sugar used during proliferation and that present in the rooting medium influenced the criteria chosen. The best results were obtained with sucrose (0.088 M) during proliferation and glucose (0.088 M) during rooting. Statistically, however, they did not differ from sorbitol (0.176 M) used during both phases of culture.Effet du type de glucide utilisé durant la prolifération et l'enracinement de microboutures de Malus Jork 9. Le type de glucide utilisé dans les milieux de culture in vitro influence la capacité de prolifération intensive de Malus Jork 9. Les microboutures obtenues montrent de nettes différences dans leur capacité rhizogène exprimée par le pourcentage d'enracinement et par le nombre de racines formées par bouture. En phase de prolifération, le sorbitol (0, 176 mol.l-1) donne des résultats statistiquement supérieurs à tout autre traitement. Les plantes se développant sur un milieu de culture contenant du fructose (apporté directement ou résultant de l'hydrolyse du saccharose) montrent une tendance marquée de passage de l'état «touffes» à celui de structure inorganisée. La capacité de récupération d'une croissance normale est inversement proportionnelle au nombre de subcultures et à la quantité de fructose présente dans le milieu. Les perturbations de croissance en présence de fructose montrent des analogies avec la «cancérisation» des microplants rencontrée lors d'apports excessifs de cytokinine ! Cette intoxication par la BAP pourrait trouver son origine dans une augmentation des surfaces de contact à la suite d'une dureté du gel plus faible consécutive à un abaissement accru du pH au cours de l'autoclavage. En phase d'enracinement, il apparaît que le sucre utilisé durant la prolifération comme dans le milieu de rhizogenèse influence les 2 critères susmentionnés. Les meilleurs résultats obtenus en utilisant le saccharose (0,088 mol.l-1) en phase de prolifération et le glucose (0,088 mol.l -1) en phase d'enracinement ne diffèrent pas statistiquement de ceux obtenus avec l'emploi du sorbitol (0, 176 mol.l-1) pendant les 2 phases de culture

Effect of endomycorrhizal infection on root system development in the apple rootstock (Malus domestica Borkh.) M26

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