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

• The signaling functions of NO and ROS in SO2-induced guard cells death in ornamental plant T. erecta were proposed.
• SO2 induced guard cells death showed typical apoptosis characteristics.
• Cross talk of NO, ROS and Ca2+ were found.
• NO and ROS regulate the cell apoptosis at the upstream of Ca2+, via NO–Ca2+ or ROS–Ca2+ or NO and ROS–Ca2+ signal pathway.

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 (SO2) induced toxicities on ornamental plants is not clear. In this study, the functions of NO and ROS in SO2-induced death of lower epidermal guard cells in ornamental plant Tagetes erecta were investigated. The results showed that SO2 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 Ca2+ levels (P<0.05) and typical apoptosis features including nucleus condensation, nucleus break and nucleus fragmentation were observed. However, exposure to 2.0 mmol L−1 of SO2 derivatives combined with either NO antagonists (NO scavenger c-PTIO; nitrate reductase inhibitor NaN3; NO synthase inhibitor L-NAME), ROS scavenger (AsA or CAT) or Ca2+ antagonists (Ca2+ scavenger EGTA or plasma membrane Ca2+ channel blocker LaCl3) can effectively block SO2-induced guard cells death and corresponding increase of NO, ROS and Ca2+ levels. In addition, addition of L-NAME or AsA in 2.0 mmol L−1 of SO2 derivatives led to significant decrease in the levels of NO, ROS and Ca2+, whereas addition of LaCl3 in them just resulted in the decrease of Ca2+ levels, hardly making effects on NO and ROS levels. It was concluded that NO and ROS were involved in the apoptosis induced by SO2 in T. erecta, which regulated the cell apoptosis at the upstream of Ca2+.

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