EFFECT OF HUMIC-ACID ON INVERTASE SYNTHESIS IN ROOTS OF HIGHER-PLANTS

Humic acid (HA) stimulated the development of invertase activity in beetroot storage tissue discs washed in water and also in pea root segments, excised from the 2-4 mm region behind the root tip, during their most active growth phase when cultured in sucrose media. In contrast HA had no effect on the incorporation of [14C]leucine into proteins in either tissue. Inhibitors of protein synthesis (d-threo-chloramphenicol, cyclohexamide and puromycin) and RNA synthesis (actinomycin d) inhibited invertase development and the incorporation of [14C]leucine into proteins in both tissues, while also abolishing the stimulation of invertase development in the presence of HA. Similar effects were produced by the amino acid analogues, p-fluorophenylalanine, cis-4-hydroxy-l-proline and azetidine-2-carboxylic acid but, with the exception of p-fluorophenylalanine in beet discs, the inhibitory effects of the analogues were prevented in the presence of the corresponding natural amino acid. The results show that HA stimulated the synthesis of de noro invertase during the period when it also enhanced cell elongation and the effect was dependent on continuous RNA and protein synthesis. © 1979.