Michel Paynot

Wound-Induced Tyramine Hydroxycinnamoyl Transferase in Potato (Solanum tuberosum) Tuber discs

Summary The enzyme tyramine hydroxycinnamoyl transferase (THT) was induced by wounding in potato tuber discs ( Solanum tuberosum var. Bintje ). THT activity was barely detectable in the intact tuber but increased dramatically during two days in the outermost cell layers of the excised discs. Thereafter the activity declined but the enzyme remained induced for at least one week. The induction of THT, which was detectable 3 to 4 hours after wounding, was completely blocked by cycloheximide. The main products formed in vivo were identified as amides of ferulic acid with tyramine or octopamine. The concentration of these amides increased upon wounding but only about 6 days after preparation of the tuber slices. Mild alkaline hydrolysis of the suberin-enriched cell wall residue purified from healed tuber discs released feruloyltyramine and feruloyloctopamine together with free tyramine and octopamine. Moreover exogenously supplied [ 14 C]-feruloyltyramine was very rapidly integrated into the cell walls of the first layer of cells at the surface of wound healing tuber discs. Taken together our results suggest that the induction of THT and the integration of cinnamoyltyramines into cell walls could be part of the primary response of potato tuber tissues to wounding.

Separation of putrescine and spermidine hydroxycinnamoyl transferases extracted from tobacco callus

Abstract Putrescine and spermidine hydroxycinnamoyl transferase activities, which can both be detected in extracts of tobacco callus grown from leaf discs, were separated by ion exchange chromatography on DEAE Trisacryl. Spermidine hydroxycinnamoyl transferase (SHT) is ca 12-fold less active than putrescine hydroxycinnamoyl transferase (PHT). The two enzymes exhibit remarkable differences in specificity towards cinnamoyl-CoA derivatives, putrescine being preferentially conjugated to caffeic acid while spermidine is mainly conjugated to p-coumaric acid. After ion exchange chromatography the PHT fraction is not specific for putrescine and uses other diamines as substrates (mainly cadaverine and diaminopropane), contrary to the SHT fraction which was found to act only on spermidine. Agmatine is conjugated in neither of the two fractions but undergoes rapid hydrolysis to putrescine in the crude enzymic extract. Only N1-feruloylspermidine can be detected when the amide synthesized in vitro by SHT from feruloyl-CoA and spermidine is analysed by mass spectrometry.

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.

Action de molecules a proprietes hormonales sur l'activite phenylalanine ammoniac lyase

Abstract A comparative study has been made of phenylalanine ammonia lyase (PAL) activity in plants sensitive or resistant to various herbicides (piclorame, methylchloro-phenoxyacetic acid (MCPA), atrazine). Piclorame, a herbicide with hormonal activity caused a large decrease in PAL activity of sensitive plants ( Nicotiana tabacum ), even at low concentrations (5 × 10 -9 M) whilst in resistant plants ( Triticum aestivum ) its effect is negligible; MCPA, also a herbicide with hormonal activity, similarly affects the activity of PAL, but only at higher concentrations. On the contrary, the action of atrazine, which has no hormonal activity, is lower and weaker, probably being only a secondary effect. Determinations of PAL activity during the photoperiod following piclorame application indicate that this herbicide influences principally the photodependent enzyme activity.

Influence du piclorame sur l'activité phénylalanine-ammoniac lyase de Nicotiana tabacum induite par la réaction d'hypersensibilité au virus de la mosaïque du tabac

Abstract In Nicotiana tabacum var. Xanthi n.c. phenylalanine ammonia lyase (PAL) activity, which increases significantly during the hypersensitivity reaction to tobacco mosaic virus (TMV), is only partially affected when plants are treated with piclorame, which is known to be an inhibitor of PAL in vivo . Using piclorame together with TMV, it has been possible to distinguish between that increase in PAL activity due to the virus and that dependent on the photoperiod.