Abstract: Pot experiments were conducted to compare the effects of drought on growth morphology, osmolyte content, and antioxidant enzyme activity of two citrus seedlings Sanhuhongju and Sanhuhuahong. Results showed that, plant heights were decreased, while root-shoot ratios were increased in both seedlings under drought. The taproot length was decreased in Sanhuhuahong while it was increased in Sanhuhongju under drought. Moreover, proline content was significantly increased in leaves and roots of the two citrus seedlings, and greater increase was found in leaves of Sanhuhongju than that of Sanhuhuahong. Except for soluble sugar in leaves of Sanhuhongju, contents of soluble sugar and soluble protein were increased in the treated seedlings. Enzyme analysis revealed that the activities of superoxide dismutase (SOD) and catalase (CAT) were decreased in leaves whereas increased in roots of both seedlings. The leaf peroxydase (POD) activity was firstly increased and then decreased in Sanhuhongju, and it was always increased in Sanhuhuahong. In roots, the POD activity was significantly increased in Sanhuhongju and was significantly decreased in Sanhuhuahong under drought. Overall, the higher drought tolerance shown by Sanhuhongju might be related to the longer taproot and higher root-top ratios, which could improve the water uptake ability of root. Additionally, the accumulation of osmolytes especially the proline and the increase of POD activities in roots might also help the Sanhuhongju to cope with drought stress.

Key words: citrus seedling, drought stress, growth morphology, osmolyte, antioxidant enzyme