CHANGES IN PROTEOLYTIC ACTIVITIES IN GLUCOSE-STARVED MAIZE ROOT-TIPS - REGULATION BY SUGARS

Excised maize (Zea mays L.) root tips were used to monitor the changes in different proteolytic activities during a four-day period of gluco se starvation. Starvation-induced protein degradation was correlated w ith a transient increase (up to 48 h) of free amino acids and a rise i n global autoproteolytic activities (up to 96 h). This rise in autolyt ic activities was Linked with an increase in acidic endopeptidase and carboxypeptidase activities, whereas aminopeptidase activities continu ously decreased during starvation. The endopeptidase activities involv ed in the response to starvation appear to be different from those pre sent in non-starved root tips: (a) the sensitivity to protease inhibit ors and the change of optimum pH show the involvement of a new set of serine and cysteine protease activities in the course of starvation; ( b) the addition of cycloheximide and cordycepin in the sugar-depleted incubation medium maintained the proteolytic activity at base level, s uggesting that new proteases are induced and synthesized during starva tion. Glucose-depleting or supplying experiments show that the level o f endoproteolytic activities is strictly controlled by the level of su gars at any moment during the starvation period.