Philippe Barthe

Regulation of bud dormancy by manipulation of ABA in isolated buds of Rosa hybrida cultured in vitro

In vitro cultures showed that the proximal buds isolated from a rose (Rosa hybrida L. cv. Ruidriko Vivaldi®) stem were endodormant. Growth and a high percentage of bud break could be observed when cultures were treated with fluridone, an inhibitor of carotenoid synthesis. Flow cytometry determination of nuclear DNA content revealed that cell cycle activity of endodormant buds was arrested in the G 1 phase. Upon culture, the large decrease in bud ABA content was responsible for the progress from G1 to G2 phase whatever the culture medium. However, in control culture, neither cell division nor leaf primordium initiation could be observed and cells appeared stably arrested in G2 . By contrast, with fluridone, an additional ABA decrease was observed resulting from an inhibition of its synthesis inside the bud. New leaf primordia were initiated and many figures of mitosis could be observed, indicating that intense activity of cell division occurred after DNA replication. Therefore, the results indicate that, as long as ABA was synthesized inside the buds, cell cycle was arrested in G2 phase and buds remained dormant. Continued in situ ABA biosynthesis appears, therefore, to be required for the maintenance of bud dormancy.

Endogenous cytokinins in rose petals and the effect of exogenously applied cytokinins on flower senescence

In extracts from rose petals cytokinin activity was detected by Amaranthus bioassay in HPLC eluates corresponding to the standards: Z, ZR, 2iP and 2iPA; subsequently, the presence of two groups of endogenous cytokinins was confirmed by ELISA.Measurements of senesence indicators (cell sap osmolarity and conductivity) and observations of flower vase-life indicated that when the above cytokinins were applied as holding solutions they delayed flower senescence by 34–56% and prolonged rose longevity.

Metabolism of (+) abscisic acid to dihydrophaseic acid-4′-β-d-glucopyranoside by sunflower embryos

Abstract (+)-[2- 14 C]Abscisic acid [(+) ABA], prepared from ±-[2- 14 C] ABA by HPLC on a chiral column, at an initial concentration of 10 μM, was absor

Maternal abscisic acid transport in developing embryos of sunflower

Summary When [2- 14 C] abscisic acid (ABA) was applied to «blocks» excised from sunflower heads, containing achenes and leaving a layer of head tissue below the base of the achenes, its uptake by the embryo was about 2 times higher than when achenes were placed on the surface of the culture medium; this suggested that in the mother plant, preferential anatomical connections allowed maternal (exogenous) ABA to be transported to the embryo. This transport of ABA through the head tissue was possible even during late embryogenesis. Changes, with embryo age, in [2- 14 C] ABA uptake by isolated embryos proved that the regulation of external ABA accumulation took place at the level of the embryo itself. During the first part of embryo development, an increasing intracellular pH of cotyledonary cells contributed to the increasing accumulation of unmetabolized ABA. Thereafter, an increasing catabolism played a major role in the decrease of ABA level. The importance of this catabolism and its particular orientation towards the formation of alkaline non-hydrolysable compounds presented the problem of the physiological significance of these conjugates.

ABA CONTENTS AND THE REGENERATION ABILITY OF FRITILLARIA IMPERIALIS L. CULTURED IN VITRO

Correlation between ABA content in “mother” tissue and subsequent regeneration ability of Fritillaria imperialis cultured in vitro was investigated. In every experiment regeneration was always most efficient from plant material containing the lowest amount of free ABA: a leafy stem part, bulbs used for micropropagation in October and those stored two months at 30 °C prior to in vitro culture. However, no direct correlation between the absolute amounts of ABA and percentage of regeneration was found.

Séparation et Identification des Bétalaines Synthétisées par les Tissus de Tige de Myrtillocactus geometrizans Cultivés «in vitro»

Summary Sephadex gel column chromatography enabled us to separate betalains present in stem tissue cultures as well as in fruits of Myrtillocactus geometrizans. The identification of the isolated fractions was attempted by means of paper chromatography, electrophoresis, spectrum analysis and Sephadex gel chromatography. Three pigments — one betaxanthin and two betacyanins -, have been identified in both materials. Indicaxanthin and betanin were characterized with relative certainty. Another betaxanhin was tentatively identified as phyllocactin.

ABA Dynamics During the Growth Cycle of Amaranthus tricolor: Release of Low and High Molecular Weight ABA Conjugates in the Culture Medium

Summary During the growth cycle of Amaranthus tricolor cell suspensions, endogenous ABA accumulated transiently inside cells and reached a maximum level during the logarithmic phase. ABA levels remained low in the culture medium throughout the culture. Long-term (+)[ 3 H]-ABA feeding experiments showed that ABA was strongly metabolized according two classic pathways, oxidation and conjugation. Study of immunoreactive endogenous compounds showed that ABA was present under free, alkali- hydrolysable and non-alkali-hydrolysable forms both in the cells and in the culture medium. Conjugates that could not be cleaved by alkaline hydrolysis were separated by alcoholic precipitation. Both the high molecular weight conjugates, present in the pellet, and the low molecular weight conjugates, present in the supernatant, exhibited a non-negligible immunoreactivity and were able to release ABA upon enzymatic hydrolysis.