Marie-Thérèse Le Page-Degivry

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.

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

The influence of light quality on rose flower senescence: involvement of abscisic acid

The aim of this work was to study the impact of light applied during preharvest culture on the subsequent senescence of cut rose flower and to analyse the possible involvement of abscisic acid (ABA). The longevity of cut rose flowers was longer when rose plants were previously grown under high pressure sodium lamps than under metal halide lamps. A change in light source did not lead to a change in leaf ABA content but significantly affected the petal ABA content. The relationship between ABA level and flower longevity, previously reported for differences of genetic origin, was again observed for culture-induced differences: the higher the ABA level at harvest, the shorter the vase-life observed.

Alteration of hormonal levels and hormone sensitivity by ri T-DNA-transformation of apple cuttings

Summary Changes in hormone levels and sensitivity to hormones were studied in the apple rootstock M 26 and in the clone transformed by Agrobacterium rhizogenes strain A4. The transformation of apple microcuttings by insertion of both TL-DNA and TR-DNA led to changes in leaf levels of all plant hormones studied (auxin, cytokinins and abscisic acid). An important increase in auxin and a decrease in cytokinin levels were observed. The ABA level was substantially lowered by transformation, whatever the water status of the leaves. The sensitivity to hormones of both transformed and untransformed cuttings was compared on the basis of their root induction efficiency. No significant difference in auxin sensitivity could be observed on this long-term response. However, the transgenic clone was less sensitive to cytokinin-induced rooting inhibition and more sensitive to ABA-induced rooting inhibition than the untransformed clone. The consequences of the changes in both hormone levels and sensitivity to hormones are discussed.

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 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.