A transient increase in apoplastic peroxidase activity precedes decrease in elongation rate of B73 maize (Zea mays) leaf blades

Peroxidase (EC 1.11.1.7) activity From homogenized tissue or in apoplastic fluid was analyzed along the developmental gradient of expanding B73 maize (Zea mays L.) leaf blades. Soluble plus ionically bound peroxidase activity from homogenized tissue was present in high levels at the leaf base, which includes the region of cell division, and decreased as tissue was displaced away from the base by growth. A different pattern of change in peroxidase activity was seen in apoplastic fluid extracted From segments of intact tissue, where an increase in peroxidase activity preceded a rapid decrease in leaf elongation rate. Similar patterns in peroxidase activity from homogenized and intact tissue have been found in leaf blades of tall fescue (Festuca arundinacea Schreb.), suggesting a common phenomenon. At the location within the elongation zone where the increase in apoplastic peroxidase activity occurred, the activities of neutral and acidic (pI 4.6) peroxidase isoforms were also elevated in both the homogenate and in apoplastic fluid. The coincidence of these isoforms with the decline in leaf elongation rate suggests they may contribute to cessation of growth. At the distal end of the elongation zone, the activities of other acidic peroxidases (pI 5.6 and 5.7) increased in the homogenate and in apoplastic fluid, and remained elevated as tissue was displaced into the maturation region. The location of their appearance and their relatively high activity in the maturation region suggest the involvement of these isoforms in lignification.