Physiological Response of the Plant with Extremely Small Population Firmiana kwangsiensis to Drought Stress and Rehydration

The growth, photosynthetic gas exchange and physiological and biochemical response characteristics of Firmiana kwangsiensis seedlings under drought rehydration were investigated by weighing the soil and pots. The result showed that the length of the plant, base diameter, and root number( > 5 cm) decreased significantly, and could not recover to CK after rehydration. The chlorophyll content of seedlings firstly decreased and then increased under drought stress and rehydration. The photosynthetic activity and the relative water content of leaves in seedlings decreased under drought stress but could recover to CK level after rehydration. The relative electrical conductivity(RFC) and malondialdehyde(MDA) content of leaves were significantly increased under drought stress. After rehydration, the RFC decreased and could recover to CK level, but the MDA content was still higher than CK. Under the drought stress, the free proline content of leaves increased significantly , and decreased after rehydration. The soluble protein content had no significant difference under drought stress but had a significant difference after rehydration. The soluble sugar content first increased and then decreased under drought stress and could be recovered to CK level after rehydration. Under the drought stress, the activity of SOD and POD was lower than CK level but increased after rehydration. The CAT activity increased under drought stress and rehydration but was still lower than the CK level. In summary, F. kwangsiensis seedlings growing inhibited under drought stress. Although the protective enzyme system and osmatic adjustment substance could adjust themselves to avoid drought harms after rehydration, the growth indexes were hard to recover to the CK level, which indicated the weak tolerant ability of F. kwangsiensis seedlings to drought stress.