Physiological responses of Scaevola aemula seedlings under high temperature stress

Global climate change is expected to result in a relative high frequency of a short period of extreme high temperature (HT) on plant ecosystems and can have an adverse impact on plant growth and development, yet the response of plants to such damage is not fully understood. In this study, physiological responses of Scaevola aemula seedlings to a short-term (a 3-day period) HT stress were investigated in order to examine the adaptation of S. aemula to the thermal environment. The S. aemula seedlings were cultivated under four temperature treatments of 25/20, 35/27, 40/30, 46/35 °C (day/night). The HT stress-induced injure symptoms in leaves were recorded and several selected important physiological variables were measured. The results showed that the leave injuries were not apparent under HT (35/27 °C), but serious damages were observed at days two and three post-treatment under severe HT (40/30 and 46/35 °C). For adapting the thermic environments, S. aemula seedlings exhibited a rapid increase of photosynthetic pigments, soluble sugar contents, and superoxide dismutase activity, and simultaneously a decrease of soluble protein contents, proline contents and catalase activity. The HT tolerance of S. aemula species depends upon both the elevated temperature and the period of time under the increased temperature. Our study suggests that S. aemula could grow well under 35/27 °C. The results provide evidence for the introduction and resource assessment of S. aemula species.