Josette Martin-Tanguy

Polyamines and their biosynthetic enzymes in dormant embryos of the spindle tree (Euonymus europaeus L.) and in dormancy break obtained after treatment with gibberellic acid

Abstract Dormancy break of spindle tree embryos after gibberellic acid treatment was followed by an increase in polyamine levels and the activities of their biosynthetic enzymes, especially arginine decarboxylase (ADC). Increasing levels of putrescine, spermidine and ADC activity occurred during the first hours of culture (before the emergence of the radicle). Dormancy break was also correlated with a decrease of tyramine. Treatment with α- dl -difluoromethylarginine (DFMA), a specific and irreversible inhibitor of the putrescine-synthesizing enzyme, arginine decarboxylase (ADC), led to the maintenance of embryo dormancy in a GA 3 -medium. Application of agmatine or putrescine to the inhibited system resulted in a reversal of inhibition. With α- dl -difluoromethylornithine (DFMO), a specific and irreversible inhibitor of putrescine biosynthesis by ornithine decarboxylase (ODC), embryo dormancy in a GA 3 -medium was completely broken and germination was complete within 36 h. Our results suggest that polyamines (via ADC pathway) mediate hormone-induced growth responses in spindle tree embryos.

Effect of cinnamoyl putrescines on in vitro cell multiplication and differentiation of tobacco explants.

Hydroxycinnamoyl putrescines promote the cell multiplication of leaf discs of a tobacco mutant, RMB7, cultivatedin vitro on the Murashige and Skoog medium. This mutant never accumulates these molecules during its development and does not enter in floweirng. Maximal effect is obtained at 2.5·10−4M. The same molecules inhibit bud formation ofNicotiana tabacum var. Xanthi nc, at 5·10−5 M but promote callus formation. From 10−4 M to 5·10−3 M they strongly inhibit cell multiplication and bud formation without toxic effect. Their possible role in plant metabolism is discussed.

Stimulation of root and somatic embryo production in Euonymus europaeus L. by an inhibitor of polyamine biosynthesis

In vitro formation of roots and somatic embryos is obtained from cotyledon explants of a Spindle tree (Euonymus europaeus L.) cultured on two different media: a medium inducing callus formation and the production of roots, and a medium inducing callus formation, root and somatic embryo production. We studied the effects of α-difluoromethylornithine (DFMO), a specific, irreversible inhibitor of ornithine decarboxylase (ODC) on root and somatic embryo production, growth and titers of putrescine in Euonymus explants and explant-derived calli. Early changes in putrescine levels were detected in both cultures before the visible emergence of roots or somatic embryos. DFMO rapidly inhibited putrescine accumulation and growth in non-embryogenic calli and highly stimulated rooting activity. DFMO partially inhibited putrescine accumulation in embryogenic calli. This inhibition had no effects on callus growth but significantly reduced the time of emergence of roots and highly stimulated somatic embryo production. The relationship among putrescine, putrescine metabolism, growth, root and somatic embryo formation is discussed.

Polyamine metabolism in normal and sterile Chrysanthemum morifolium

Abstract In normal and sterile Chrysanthemum plants ( Chrysanthemum morifolium ) polyamine conjugate appeared in the apical meristem before the first observable transformation of the meristem into floral structures. These compounds accumulated upon floral initial and well before floral evocation. In fertile plants ( C. morifolium v. Epidote) spermidine conjugates were predominant during floral initiation whereas in male-sterile plants ( C. morifolium v. Jericho) only putrescine conjugates were detected. In both cases ornithine decarboxylase (ODC) is involved in regulating floral initiation in normal and male-sterile plants. The male-sterile flowers can be distinguished by their lack of free aromatic amines and aromatic amine conjugates. In fertile flowers diamine oxide (DAO) followed the same pattern as ODC. In male-sterile flowers DAO activity did not parallel the increase in ODC activity.

Polyamine metabolism during seedling development in rice

The main free amines identified during growth and development of rice seedlings were agmatine, putrescine, spermidine, diaminopropane and tyramine. Amine composition differed according to tissue and stages of development. Conjugated amines were only found in roots. We present evidence that arginine decarboxylase (ADC) regulates putrescine during the development of rice seedlings. When ADC action was blocked by DFMA (α-DL-difluoromethylarginine, a specific irreversible inhibitor of ADC), polyamine titers and seedling development were diminished; when agmatine or putrescine was added, normal polyamine titers and growth were restored. The effects of DFMA were concentration dependent. DFMO (α-DL-difluoromethylornithine, a specific irreversible inhibitor of ornithine decarboxylase or ODC) promoted growth and development at concentrations below 2 mM. This effect was probably related to its unexplained, but consistently observed slight enhancement of rice ADC. When the increase in the concentration of spermidine was prevented by CHA (cyclohexylammonium sulfate), the number of roots increased and the increase in length of leaves and roots was strongly inhibited. The addition of exogenous spermidine at the time of treatment with CHA reversed the inhibition by CHA.

Control of Root System Architecture through Chemical and Genetic Alterations of Polyamine Metabolism

Plant growth is plastic, responding to a variety of environmental cues and conditions; and plant growth has been altered using genetics, biochemistry, horticulture and agronomy. However, efforts to modify growth have been mostly been aimed at the aerial parts of the plant. In the present paper we will retrace and discuss our efforts to alter root system architecture, first through genetic transformation, then through chemical and physiological means.

Diurnal modulation of polyamine content in seedlings of Lycopersicum esculentum Mill.cv. Ace 55 by temperature and light

Abstract Polyamine composition is investigated in Lycopersicum esculentum Mill.cv. Ace 55 seedlings under constant and alternating temperature and lighting conditions. Growth of tomato seedlings is correlated with several changes in polyamine composition. Polyamine levels vary rhythmically. The diurnal rhythm of polyamine levels is primarily controlled by the temperature cycle and less influenced by the light program. Polyamine accumulation persists when the same temperature program is applied under continuous darkness. The endogenous rhythm in polyamine levels and composition is maintained under continous light at 25°C. These results suggest that polyamine changes are regulated endogenously, irrespective of immediate environmental conditions. It seems that under normal diurnal conditions of photo and thermoperiod with high polyamine levels during the night and low levels during the day, there is an optimal stabilization of chloroplast membranes.