Relationship between boron and phenolic metabolism in tobacco leaves

Tobacco plants (Nicotiana tabacum var. Sevilla) were treated with boron (B) as H3BO3 in the following concentrations B1: 0.5 mu M, B2: 5 mu M, B3: 10 mu M and B4: 20 mu M, and we analysed: total B, total phenols, orthodiphenols, phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) and dry weight. The effect of the B treatments were differentiated by: (1) foliar accumulation of phenols induced by the minimum B treatment (B1) and maximum (B4); and (2) oxidation of the phenols induced by the intermediate treatments (B2 and B3). The two predominant forms in which B is found in leaves (forming complexes with pectins and phenols, or in the free form) appears to determine and explain the effect of this element on the metabolism of the phenols. (C) 1998 Elsevier Science Ltd. All rights reserved.