PETUNIA PEROXIDASE-A IS LOCALIZED IN THE EPIDERMIS OF AERIAL PLANT ORGANS

The distribution of soluble peroxidase activity in tissues from petals, leaves and stems of petunia (Petunia hybrida) was investigated. In petals, the upper epidermis contained nearly 20 % of the soluble peroxidase activity, but no peroxidase activity was recovered from protoplasts isolated from this tissue. In contrast, protoplasts from the remaining tissue contained about 45 % of the total peroxidase activity in the form of the isoenzyme PRXb. The extracellular peroxidase activity present in the epidermis was mainly PRXa. In leaves, the lower epidermis contained 14-40 % of the soluble peroxidase activity, depending on their stage of development. In fully expanded leaves about half of the activity in the lower epidermis was located extracellularly. In stems, nearly 80 % of the soluble peroxidase activity was present in the epidermis, and about 30 % of this activity was localized extracellularly. Since the extracellular extracts contained merely PRXa, these results suggested that PRXa is localized mainly in the epidermis of the aerial organs of petunia. When leaves and stems were cut transversely and pressed on membrane filters, the resulting dip-blots were employed for in situ localization of peroxidase by activity staining and of PRXa by immunodetection. Both peroxidase activity and immunoreactive PRXa were present mainly in the epidermis of stems and leaves, particularly at the site of the midrib and veins. With respect to this distribution, the function of PRXa is discussed. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.