Isoperoxidase Patterns in Tobacco Pith and their Alteration Following Tissue Excision

Previous work has shown that young tobacco pith cells containlow peroxidase activity resolvable into two anodic iso-zymesby electrophoresis at pH 8.3 on starch gel. During normal cellenlargement and ageing in situ, these two isoenzymes increaseslowly in activity. By contrast, within 24 h after excisionof pith, high activities appear in several apparently new anodicand cathodic isoperoxidases. This development of new isoperoxidasesis prevented by physiological levels of IAA and by inhibitorsof RNA and protein synthesis. The present work describes additional quantitative isoperoxidasegradients, both vertical and horizontal, in the pith. Severaladditional isoenzymes, some of which are excreted into the mediumduring incubation, have been detected by improved electrophoretictechniques. Enzyme leakage can be prevented by incubation inmoist chambers and by auxin application through terminally placedagar blocks. With such techniques, new peroxidases form preferentiallynear cut surfaces within 12 h under aerobic conditions. Tissuesperipheral to the pith retard the development of new peroxidaseactivity. IAA in agar blocks applied terminally to a cut pithcylinder retards peroxidase formation mainly at the base. Theregulation of the quantity and quality of isoperoxidases seemsto be correlated with certain morphogenetic phenomena.