Abstract:cGMP (cyclic guanosine-3',5'-monophosphate) is a type of cyclic nucleotide and signaling molecule that can be responsive to plant abiotic stress. Using cGMP membrane permeability analog 8-Br-cGMP as a donor, this study investigated the effects of cGMP on seed germination and physiological indicators of ryegrass under salt stress. The effects of cGMP on the salt tolerance mechanism during the germination of ryegrass were determined through calculating the germination index and determining the physiological indicators in the process of seed germination. The results showed that a low concentration (50 mmol/L) of salt stress could promote the germination of ryegrass seeds. With increasing salt concentrations (100, 150, 200, and 250 mmol/L), the germination rate of ryegrass seeds gradually decreased and was even inhibited. Adding 20 μmol/L cGMP can relieve the damage caused by 100 mmol/L NaCl stress on ryegrass seed, increasing the germination rate, germination potential, germination index, and vigor index of ryegrass seed by 7.4%, 133.3%, 52.1%, and 104.2%, respectively. In addition, compared to the 100 mmol/L NaCl stress condition alone, the growth of roots of ryegrass could be promoted and the total length, root length, and leaf length of ryegrass plants increased, by 2.5, 2.8, and 2.6 times, respectively, when 20 μmol/L cGMP was added. The soluble sugar, soluble protein content, amylase activity, and proline content of seeds increased by 47.9%, 15.7%, 94.3%, and 117.4%, respectively, while starch content, MDA content, conductivity, and O2-. production rate were reduced by 40.9%, 128.7%, 88.6%, and 211.9%, respectively. The results showed that 20 μmol/L cGMP could increase the contents of soluble sugar, soluble protein, and proline, and reduce the production of MDA and O2-, so as to relieve the damage caused by salt stress on ryegrass seed and promote the hydrolysis of starch, which accelerated seed germination.
