Involvement of NO and ROS in sulfur dioxide induced guard cells apoptosis in Tagetes erecta.

Abstract Both nitric oxide (NO) and reactive oxygen species (ROS) are very important signal molecules, but the roles they play in signal transduction of sulfur dioxide (SO 2 ) induced toxicities on ornamental plants is not clear. In this study, the functions of NO and ROS in SO 2 -induced death of lower epidermal guard cells in ornamental plant Tagetes erecta were investigated. The results showed that SO 2 derivatives (0.4–4.0 mmol L −1 of final concentrations) could reduce the guard cells' viability and increase their death rates in a dose-dependent manner. Meanwhile, the significant increase of cellular NO, ROS, and Ca 2+ levels ( P −1 of SO 2 derivatives combined with either NO antagonists (NO scavenger c-PTIO; nitrate reductase inhibitor NaN 3 ; NO synthase inhibitor L-NAME), ROS scavenger (AsA or CAT) or Ca 2+ antagonists (Ca 2+ scavenger EGTA or plasma membrane Ca 2+ channel blocker LaCl 3 ) can effectively block SO 2 -induced guard cells death and corresponding increase of NO, ROS and Ca 2+ levels. In addition, addition of L-NAME or AsA in 2.0 mmol L −1 of SO 2 derivatives led to significant decrease in the levels of NO, ROS and Ca 2+ , whereas addition of LaCl 3 in them just resulted in the decrease of Ca 2+ levels, hardly making effects on NO and ROS levels. It was concluded that NO and ROS were involved in the apoptosis induced by SO 2 in T. erecta , which regulated the cell apoptosis at the upstream of Ca 2+ .