Drought stress is a major constraint for crop production in arid and semiarid regions, such as Iran. In this study the effect of 5-aminolevolinic acid (ALA), the new plant growth regulator, on Coriander (Corianderum sativum L.) plants under drought stress was studied. The layout was factorial experiment in randomized complete block design (RCBD) with 3 levels of drought stress including stress-free conditions (irrigation within the field capacity), mild stress (humidity of soil about 60% of field capacity) and severe stress (humidity of soil about 30% of field capacity) and 4 concentrations of ALA (including 0 (as a control), 0.25, 0.5 and 1 mM) as main factors and 4 replication. The experiment was conducted in the greenhouse of agricultural faculty of Ilam University. Statistical analysis showed significant effects of the drought and ALA on plant growth parameters, chlorophyll index and antioxidant activity. Result showed that drought stress imposed negative effects on plant growth and productivity. In drought conditions, plant height, leaf area, plant and leaf dry and fresh weight and chlorophyll index reduced but antioxidant activity increased. ALA application significantly caused increasing of plant height, leaf area, plant and leaf dry and fresh weight, chlorophyll index and antioxidant activity. ALA treatment with increasing of chlorophyll and antioxidant activity decreased adverse effects of drought stress on coriander plants. These results suggest that ALA has plant growth regulating properties at low concentrations and may enhance agriculture productivity under drought condition.

Keywords: Medicinal plants, Drought, Chlorophyll, Antioxidant activity.

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