Glycerol effects both carbohydrate metabolism and cytoskeletal rearrangements during the induction of somatic embryogenesis in chicory leaf tissues

In leaf tissue of the chicory hybrid '474' (Cichorium intybus L. var. sativum x Cichorium endivia L. var. latifolia), induction and expression of somatic embryogenesis can be separated into a two-step procedure by the presence of glycerol during the induction step. This effect of glycerol is caused by the inhibition of the initiation of the first divisions of the embryogenic cells by a so far unknown mechanism. In an attempt to unravel this mechanism, the effects of glycerol on carbohydrate metabolism and cytoskeletal rearrangements were studied. When the induction medium was supplemented with [C-14]-glycerol for 24 h, about 25 % of [C-14]-glycerol were converted to other soluble carbohydrates. Activity of glycerol kinase was very high during the induction phase of somatic embryogenesis and decreased after transfer. Glycerol supplementation was of no avail on glycerol 3-phosphate dehydrogenase activity. A nuclear magnetic resonance study showed that glycerol 3-phosphate had accumulated in leaf tissue. Microscopic studies using alpha- and beta -tubulin antibodies revealed that cytoskeletal rearrangements were greatly affected by the presence of glycerol. Immunobloting using antibodies against alpha- and beta -tubulins revealed that this effect of glycerol was not caused by alteration in the quantity of either type of tubulin monomers. We describe the progress made in the analysis of the effects of glycerol on somatic embryogenesis in chicory. New evidences are given on the occurrence of an active glycerol metabolism during the inhibitory treatment. Moreover, the effect of glycerol was correlated with a defect in the pre-mitosis cytoskeleton organization. (C) 2001 Editions scientifiques et medicales Elsevier SAS.