Effects of exogenous Putrescine on plant growth and photosynthesis of perennial ryegrass under drought stress

Putrescine is crucial for plant growth and abiotic stress resistance. Here, the effects of exogenous Putrescine and its synthetic inhibitors on seedlings growth and photosynthesis response were examined in perennial ryegrass (Lolium perenne, Pinnacle III) under drought stress. The results showed that drought stress inhibited the growth of perennial ryegrass, and exogenous 0.1 and 1 mmol·L⁻¹ Putrescine could alleviate the inhibition of drought stress on the seedlings of perennial ryegrass and 0.1 mmol·L⁻¹ putrescine treatment has a better effect. Compared with those of the control, exogenous Putrescine improved net photosynthetic rate (P_n), water use efficiency (WUE), and PSII potential photochemical efficiency (F_V/F_o) and maximum photochemical quantum yield (F_v/F_m) of ryegrass, but decreased stomatal conductance (G_s), transpiration rate (T_r), intercellular carbon dioxide concentration (C_i) , and relative conductivity (REC) under drought stress. Putrescine synthetic inhibitor ornithine decarboxylase inhibitor (DFMO) decreased the alleviation effect of Putrescine. Summarily, our results indicate that 0.1 mmol·L⁻¹ exogenous Putrescine could alleviate the inhibition of drought stress on perennial ryegrass seedling growth, and improve its photosynthetic capacity and water use efficiency, thus enhancing the drought resistance of ryegrass.