Activities of peroxidase (soluble and cell wall bound) and of other H2O2 scavenging enzymes are markers of the flower bud development stage in lemon

Abstract

Specific activities of H₂O₂ scavenging enzymes, soluble peroxidase (G-POD), catalase (CAT) and ascorbate peroxidase (APX), and cell wall bound (CWB) G-POD, have been characterized in flower buds and leaves in potted lemon trees (Citrus limon L. Burm.) growing in a glasshouse in Tunisia. In leaves during the winter rest period (from September to December), enzyme activities did not change markedly. Then, leaf G-POD (soluble and CWB activity) increased 4-5 fold in January as the buds reached dormancy release. In growing buds, the activities of the three enzymes increased strongly (10-100-fold) between dormancy and full bloom and decreased slightly (3-fold) post-bloom (beginning of fruit-set). Along the shoots, the developmental stages of flower buds advanced from node 1 to node 5. G-POD activity increased from the shoot apex toward the base of the twig in both leaves and buds. A similar trend was observed for APX and CAT but their activities tended to decrease slightly far from the apex. Retardation of flowering by application of growth regulators strongly reduced leaf-specific activities of the H₂O₂ scavenging enzymes. Therefore, G-POD activity (APX and to a lesser extent CAT) appears to be a good marker of flower formation in lemon (from bud swelling to full bloom). The results also suggest a link between H₂O₂ production and flower bud development.