Effects of low temperature stress on physiological-biochemical indexes and photosynthetic characteristics of seedlings of four plant species

Low temperature stress is one of the major environmental factors affecting the process of physiology and photosynthesis of plants, which is known to cause many physiological and biochemical changes in plant metabolism such as protein denaturation, lipid liquefaction, the increased activity of antioxidant enzymes or perturbation of membrane integrity. Also low temperature decreases capacity and efficiency of photosynthesis. Therefore, the above physiological and biochemical indexes and photosynthetic characteristics are often used as an indicator of stress injury in plants. In response to low temperature stress, plants naturally have developed diverse mechanisms which can mitigate the effect of stress and lead to the adjustment of plant tolerance. Effects of low temperature stress on physiological-biochemical indexes and photosynthetic characteristics were studied in the seedlings of Rhus chinensis, Duranta repens, Thunbergia erecta and Pueraria lobata. Results showed that (1) with increasing time of low temperature, the chlorophyll content of D. repens seedlings increased initially and then decreased, whereas that of the other three seedling types continuously decreased, and it rebounded significantly after removal of low-temperature stress for the four seedling types. The free proline content of the four seedling types gradually increased or fluctuated; the soluble protein content of P. lobata seedlings increased followed by an decrease, whereas the other three seedling types continuously increased, and that of the seedling types except for P. lobata rebounded significantly after low-temperature stress relieving; the contents of soluble sugar and MDA of the four seedling types tended to increase, their SOD activity continuously rose or rose initially and then fell, and SOD activity of the seedling types except for R. chinensis declined significantly after low-temperature stress relieving. (2) With increasing low temperature time, the net photosynthetic rate (P sub(n)), stomatal conductance (G sub(s)) and transpiration rate (T sub(r)) continuously decreased for the four seedling types, and the intercellular CO sub(2) concentration (C sub(i)) of D. repens continuously increased, whereas that of the other seedling types decreased followed by an increase. The P sub(n), G sub(s) and T sub(r) of the four seedling types increased to some extent, whereas their C sub(i) decreased to some extent after low-temperature stress relieving. Increase in contents of free p