DROUGHT INFLUENCES THE ACTIVITY OF ENZYMES OF THE CHLOROPLAST HYDROGEN-PEROXIDE SCAVENGING SYSTEM

The effect of drought on the activity of ascorbate peroxidase (AP), glutathione reductase (GR) and monodehydroascorbate reductase (MDAR) in leaves of barley (Hordeum vulgare) and tef (Eragrostis tef) was studied. These enzymes are components of the chloroplast hydrogen peroxide scavenging system. Severe leaf water deficit (> -3.0 MPa) resulted in increased activity (leaf dry weight basis) of GR and MDAR in barley and of AP and MDAR in tef. The specific activity of all the scavenging enzymes was greater in droughted plants. The activities (dry weight basis) of two ''control'' enzymes, malate dehydrogenase (barley) and phosphoenolpyruvate carboxylase (tef), not directly involved in the scavenging system, were not affected by drought. These data suggest that drought may cause an increase in the capacity of the hydrogen peroxide scavenging system and that it may, therefore, increase the rate of hydrogen peroxide formation in chloroplasts.