Physiological changes during seed germination and seedling development in Karelinia caspia Less. under drought and salinity stress

In order to explore the physiological changes in Karelinia caspia during seed germination and seedling development under drought and salt stress, we used different concentrations of PEG-6000 or NaCl to simulate drought and salt stress, respectively. Germination rate, protective enzyme activity, relative conductivity and the Malondialdehyde (MDA)content during seed germination and in the seedling of K. caspia under stress (drought and salinity) were determined. The results show that: 1) With increasing amounts of PEG and NaCl, a gradual decrease in germination was observed, while there were no significant differences between the seeds treated with 15% PEG and 50 mmol·L-1 NaCl when compared to control. However, when PEG was above 20%, or when NaCl concentration was increased above 100 mmol·L-1, we observed significant differences between treated samples and control. 2) In the range of 5%~20% PEG or 200~400 mmol·L-1 NaCl, with a concentration gradient and increasing stress duration, a corresponding increase in MDA content, and elevated enzymatic activities for POD, SOD and CAT were observed. When plants were treated with 25% PEG and 500 mmol·L-1 NaCl, the relative conductivity and MDA content increased significantly with prolonged stress periods. Enzyme activities for POD, SOD and CAT also increased initially with prolonged stress before decreasing to normal levels. These preliminary results reveal that K. caspia Less has huge potential to adapt to adverse environmental conditions. Also, our study revealed that the drought threshold was equivalent to the PEG 25%, while the salinity threshold was the equivalent of 300 mmol·L-1 NaCl.