EVIDENCE FOR A POLYAMINE-MEDIATED CONTROL OF SOLUBLE NITROGEN MOBILIZATION DURING POST-CLIPPING REGROWTH OF WHITE CLOVER (TRIFOLIUM-REPENS L)

A putative contribution of polyamines to the control of peptidase acti vity expression during re-growth was studied in source organs (roots a nd stolons) of defoliated white clover (Trifolium repens I,.). Endopep tidase activity increased in roots during the first 6 days following c omplete defoliation, while exopeptidase expression seemed to be restri cted to the early hours of re-growth. These changes correlated with an immediate 80% decline in the content of total free polyamines, mainly represented by the diamine cadaverine. The inhibitory capacities of c adaverine and spermine were tested on enzyme activity in vitro in orde r to elucidate whether the endogenous polyamine level was associated w ith the cut-induced endopeptidase expression. Cadaverine seemed to inh ibit endopeptidase activity of stolons but not root endopeptidase acti vity. These data support the view that polyamines may play a role in t he regulation of peptidase expression in source organs of white clover during post-clipping re-growth. The existence of different endopeptid ase isoforms in roots and stolons is discussed in relation to the mole cular mechanisms by which polyamines may regulate their activities.