Gasotransmitter ammonia accelerates seed germination, seedling growth, and thermotolerance acquirement in maize

Ammonia (NH3), as an intermediate product of nitrogen metabolism, is recognized as a novel gasotransmitter (namely gaseous signaling molecule), its signaling role being revealed in plants. NH3 exists in two different chemical forms, namely the weak base (free molecule: NH3) and the weak acid (ammonium: NH4 (+)), which are generally in equilibrium with each other in plants. However, the effect of NH3 on seed germination, seedling growth, and thermotolerance acquirement in maize remains unclear. Here, maize seeds were imbibed in the different concentrations of NH3 center dot H2O (NH3 donor), and then germinated and calculated seed germination rate at the various time points. Also, the 60-h-old seedlings were irrigated in the different concentrations of NH3 center dot H2O, and then subjected to heat stress and counted survival rate. The data implied that the appropriate concentrations (6, 9, and 12 mM) of NH3 center dot H2O accelerated seed germination as well as increased seedling height and root length compared with the control without NH3 treatment. Also, the suitable concentrations (2 and 4 mM) of NH3 center dot H2O improved tissue vitality, relieved an increase in malondialdehyde content, and enhanced survival rate of maize seedlings under heat stress compared with the control. These results firstly suggest that NH3 could accelerate seed germination, seedling growth, and thermotolerance acquirement in maize.