Résumé
Ethephon, an ethylene generator, is applied to the bark of rubber trees to increase rubber production by stimulating latex regeneration and flow. Studies on ethylene biosynthesis and its regulation were needed to gain a better understanding of the mechanisms involved in latex production and avoiding its negative effects like oxidative burst that can result in tapping panel dryness that leading to a loss of production. Ethylene biosynthesis is catalyzed by 2 main enzymes ACC synthase (ACS) andACCoxidase (ACO). Given ACO genes were well-characterized [1], ACS genes were isolated from the rubber tree and their expression studied by semi-quantitative RT-PCR in response to ethylene stimulation and wounding. A full length of HbACS1 gene was isolated. This HbACS1 encoded 380 amino acids and its genomic structure comprised 3 introns and 4 exons. The BLAST-X analysis showed that the peptide sequence of HbACS1 had a homology of 75-79% to many ACS of other species like P. euphratica, C. papaya, C. sinensis, M. domestica. While phylogenetic analysis showed that it was in the same group with P. euphratica, C. papaya, and A. thaliana. The expression of HbACS1 was induced by ethylene treatment in both leaves and bark. This induction earlier and higher in leaves than in bark. The kinetic expression showed that there was a transient effect with a pick at 4h in leaves and 8h in bark. The treatment of 1-MCP, an ethylene action inhibitor, and prior to ethylene stimulation showed that the expression of HbACS1 was under positive feed back control.Wound induced rapid expression of HbACS1 within 15 minutes after treatment to reach a maximum in one hour both in leaves and bark. The induction was higher in leaves than in bark. Hence there was a different response of plant tissues. In conclusion, these results showed that ethylene stimulation and wounding induces the expression of HbACS [1]. This was consistent with the endogenous ethylene biosynthesis measured in rubber tree [2], and the general physiological knowledge on autocatalytic ethylene production [3]. The ACS was a multigene family. Several partial sequences were isolated and the isolation of full lengthcDNAwas in progress.The prospect was to know the effect of treatment to the expression of each member and grouping them according to their expression in relation to ethylene stimulation and wounding, and understanding their role in rubber biosynthesis. (Résumé d'auteur)