Peroxidase activities and isoenzyme profiles associated with development of avocado (Persea americana,M.) leaves at different ontogenetic stages

Changes in four peroxidase activity fractions (soluble, membrane-bound, as well as ionically and covalently bound) were studied during development of juvenile and adult avocado leaves. Greater differences were found in the soluble fraction with an increase in total activity at the end of the growth phase. In relation to the ontogenetic stages, there were significant variations in the soluble peroxidase activity of both stages, especially in leaves which have already detained their growth, 263 U/g fresh wt in adult leaves vs. 70 U/g fresh wt juvenile leaves. Moreover, the isozyme profile of this fraction revealed the appearance of an anionic band, R_f 0.35, at much earlier stages in juvenile than in adult leaves. Concerning the other three fractions, there were no marked changes in total activity of either membrane-bound or ionically and covalently bound peroxidases. However, in the isoenzyme profiles of the ionically bound fraction of juvenile leaves, three highly cationic bands appeared at much earlier stages than in adult leaves. In avocado, attempts to use leaf peroxidase activity as marker of ontogenetic age must be taken with caution, since great fluctuations related with developmental stages occur in juvenile and adult leaves.