[Cell-wall and peroxidase-isoenzyme synthesis in isolated protoplasts of Nicotiana tabacum L]

Abstract

Mesophyll-protoplasts of tobacco show increasing peroxidase-activity immediately after isolation. This is due to an enhancement of activity of the constitutive isoenzymes of GIII (=slow migrating cathodic group) and to a new formation of GII-isoenzymes (=slow migrating anodic group). (GII is not present in intact leaves.) As both processes are inhibited by actinomycin and actidion it is assumed that there is a new synthesis of peroxidase enzymes -The peroxidase reaction is independent of the further development of the protoplasts, as was evidenced by culturing protoplasts in different media which regulate the development of the protoplasts. Peroxidase reaction is always the same whether or not there is cell-wall synthesis and cell division. This leads to the conclusion that peroxidases in this case have no relation to synthesis of primary cell-walls. On the other hand they could be related to the dedifferentiation processes that always take place in isolated protoplasts.In the protoplasts GII is localized in the cytoplasma as GIII is, because GII appears before cell walls are synthesised and there is no lack of GII isoenzymes when protoplasts are remazerated after having formed new cell walls.GI (fast migrating anodic group), which is not detectable in isolated protoplasts, appears again after small calluses have developed out of protoplasts. Therefore as far as function is concerned GI is quite different from GII and GIII. The results confirm the hypothesis that GI is localized in intercellular spaces only. It is discussed whether all of the isoenzymes of peroxidase detectable in crude extracts are cytoplasmic ones.