ISHS Acta Horticulturae 381: International Symposium on Natural Phenols in Plant Resistance
METABOLISM OF SALICYLIC ACID IN TOBACCO NICOTIANA TABACUM. |
| Author: | R. Edwards |
| Abstract:
Tobacco leaf disks were treated with 4.5μM [14C-carboxy]-salicylic acid (SA) for 36h. The uptake and metabolism of the label was slow over the first 8h, with the radioactivity recovered from the disks as unchanged SA and it's Beta-D-glucoside (salicylic acid 2–O-glucoside; SAG) in approximately equal proportions. Subsequently the rate of uptake increased such that by 36h 64% of the label had been taken up by the leaf disks and metabolised by a combination of sugar conjugation and decarboxylation. In addition to SAG several glycosidic conjugates were observed though glucose esterification remained a minor route of metabolism. Glucosyltransferases (SOGTs) with activities toward SA were identified in tobacco leaves. Using UDP-glucose as cosubstrate two reaction products could be observed in crude preparations, corresponding to the ether and ester glucosides. In crude preparations two pH optima for glucosyltransferases were observed (pH7 and pH8). However only the activity at pH7 was specific for SA as substrate. SOGT activity was higher in cell cultures than in leaves and was stimulated by sulphydral reagents, EDTA and divalent cations (Mg, Mn). In leaf disks the specific activity of SOGT was induced 15-fold following a 24h treatment with 500μM SA, the optimal concentration for enzyme induction. In contrast the glucosyltransferase with activity toward endogenous substrates (pH optimum pH 8) was only induced twofold by this treatment. The results suggest that the inducibility of SOGT | |
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