Effects of Temperature on the Growth and Development, Osmolytes Accumulation and Antioxidant Activity of Sesuvium portulacastrum L

Sesuvium portulacastrum L. is a perennial halophyte, and most studies have focused on its salt tolerance, while there is limited literature on its temperature adaptability. In this study, we conducted experiments to investigate the impact of varying temperatures (15, 18, 21, 24, 27 °C) on the physiological and biochemical responses of S. portulacastrum. The results showed that the appearance features such as leaf number, relative growth of stem segments and root length were significantly higher in the group of 24 and 27 °C that of the group from 15 to 21 °C (P < 0.05). The root activity was positively correlated with temperature. Regarding the chlorophyll content within photosynthetic pigments, as follows: 27 °C > 24 °C > 21 °C > 18 °C ≥ 15 °C for chlorophyll a, and 27 °C ≥ 24 °C > 21 °C > 18 °C ≥ 15 °C for total chlorophyll and chlorophyll b. The activity of antioxidant enzymes, SOD and APX, was significantly higher in the 15 °C group than in the 27 °C group, registering approximately 2.5-fold and 3.5-fold increases, respectively. The accumulation of total soluble sugars was significantly higher in the 15 and 18 °C groups compared to 24 and 27 °C groups. The proline concentration in the plants grown in the 15 °C group was significantly higher (2.77 ± 0.18 mg/g) than in the 24 and 27 °C groups, approximately 4-fold that of these two groups. In summary, when the stem segments of S. portulacastrum are subjected to stress at 15 °C, the process of photosynthesis is initially inhibited. Concurrently, self-protective mechanisms are activated, including the enhancement of the antioxidant system and osmoregulatory substances. As the stress duration prolongs, especially at 15 and 18 °C, root development is hindered, which consequently leads to delayed plant growth.