Biological differences that distinguish the 2 major stages of wound healing in potato tubers.

The two stages of potato tuber wound healing, closing layer formation (CLF) and wound periderm formation (WPF), have critical biological differences. The first stage, CLF, involves early induction of DNA synthesis and nuclear division in the absence of cell division. The transition phase from CLF to the second stage, WPF, is marked by a transient decrease in expression of suberin-specific genes. The second stage involves cell division. Although biologically active cytokinins (CKs) are not present in quantifiable amounts during this stage, the presence of precursor and catabolic products suggest the presence of trace amounts of active CKs that, in conjunction with increased auxin (indole acetic acid), provide necessary signals for meristematic activity. Augmenting these putative trace amounts with exogenous biologically active CK inhibits WPF; this suggests that the CK requirements for meristematic activity are finely controlled and sensitive to extremely low concentrations. Evidence is discussed for separate biological processes and signals that distinguish the 2 stages of wound healing.