Abstract：Abstract Coix (Coix lachryma-jobi) is a kind of medicine and food crop, while drought is the most main factor limiting its growth. To explore the applicative effects of uniconazole (S3307) on coix seedlings under drought stress, the growth parameters, anti-oxidant enzyme activities, chlorophyll content and chloroplast ultrastructure in Yiliao No. 5 under drought stress were investigated through nutrient solution cultivation in greenhouse. The results showed that the stem diameter and ground biomass were significantly improved with 9 mg/L S3307 under drought stress (P＜0.05). Compared with the S0 (drought group), stem diameter were increased for 16.19%, and the above-ground and under-ground biomass increased for 19.56% and 22.75%, respectively. The activities of peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) were significantly enhanced (P＜0.05), while POD and CAT activities of roots were higher than those of leafs. Total chlorophyll content in the S3 (9 mg/L S3307 group) was the highest in all the treatments, which was increased by 7.35% compared to S0 (drought treatment group) (P＜0.05). Meanwhile, S3307 addition could improve chloroplast and root cell ultrastructure and lighten the damage to grana ultrastructure under drought stress, which was consistent with increasing chlorophyll content. All the analysis showed that 9 mg/L S3307 concentration was effective on alleviating the injury of coix seedlings under drought stress. This study can clarify physiological mechanism of coix drought resistance and provide a theoretical basis for S3307 in coix production and practice of drought resistance.
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