Volatile cinnamaldehyde induces systemic salt tolerance in the roots of rice (Oryza sativa)

Cinnamaldehyde (CA) is a volatile plant secondary metabolite that exhibits strong anti-pathogenic activities. Nonetheless, less is known about the effect of CA on plant tolerance to abiotic stresses. In this study, we delineated the effects of CA fumigation on rice roots (Oryza Sativa L cv. TNG67) under salinity stress (200 mM NaCl). Our result showed that CA vapor significantly alleviated salinity-induced ROS accumulation and cell death. This CA-induced alleviation appears to be mediated primarily by the upregulation of proline metabolism genes, the rapid proline accumulation, and the decrease of Na⁺/K⁺ ratio as early as 3 h after NaCl treatment. Of note, the activities of peroxidase (POD; EC 1.11.1.7) isozymes a and b were decreased by CA fumigation, and the activities of catalase (CAT; EC 1.11.1.6) and superoxide dismutase (SOD; EC 1.15.1.1) were not significantly affected. Our findings suggest that CA vapor might be useful for priming rice roots to withstand salinity stress, which is more prevalent due to the ongoing global climate change. To the best of our knowledge, this is the first study to show modulation of macro- and micro-elements as well as antioxidative factors after CA fumigation of salinity-stressed rice roots.