Comparative Analyses of Physiological Responses of Cynodon dactylon Accessions from Southwest China to Sulfur Dioxide Toxicity

Sulfur dioxide (SO2), a major air pollutant in developing countries, is highly toxic to plants. To achieve better air quality and landscape, planting appropriate grass species in severe SO2 polluted areas is very critical. Cynodon dactylon, a widely used warm season turfgrass species, has good SO2-tolerant ability. In this study, we selected 9 out of 38 C. dactylon accessions from Southwest China as representatives of high, intermediate SO2-tolerant and SO2-sensitive accessions to comparatively analyze their physiological differences in leaves under SO2 untreated and treated conditions. Our results revealed that SO2-tolerant C. dactylon accessions showed higher soluble sugar, proline, and chlorophyll a contents under both SO2 treated and untreated conditions; higher chlorophyll b and carotenoid under SO2 treated condition; lower reactive oxygen species (ROS) level, oxidative damages, and superoxide dismutase (SOD) activities under SO2 treated condition; and higher peroxidase (POD) activities under SO2 untreated condition. Further results indicated that SO2-tolerant C. dactylon accessions had higher sulfur contents under both SO2 treated and untreated conditions, consistent with higher SO activities under both SO2 treated and untreated conditions, and higher SiR activities under SO2 treated condition. Taken together, our results indicated that SO2 tolerance of C. dactylon might be largely related to soluble sugar, proline and chlorophyll a contents, and SO enzyme activity.