Abstract: By the method of hydroponic culture, this paper studied the effects of exogenous γ-aminobutyric acid (GABA) on the photosynthetic pigment contents,
photosynthesis, and chlorophyll fluorescence parameters of muskmelon seedlings under hypoxia stress. Hypoxia stress induced a significant decrease of photosynthetic pigment contents, resulting in the decrease of photosynthesis. Applying GABA could significantly increase the photosynthetic pigment contents, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), carboxylation efficiency (CE), maximal photochemical efficiency of PSⅡ(F_v/F_m), photochemical quenching (q_P), apparent photosynthetic electron transfer rate (ETR), and quantum yield of PSⅡelectron transport (Φ_PSⅡ), and decrease the stomatal limitation value (L_s), minimal fluorescence (F_o), and non-photochemical quenching (NPQ) under both hypoxic and normal conditions. The alleviation effect of GABA on photosynthetic characteristics was more obvious under hypoxia stress. However, simultaneously applying GABA and VGB could significantly decrease the alleviation effect of GABA under hypoxia stress.

Key words: hypoxia stress, γ-aminobutyric acid, muskmelon, photosynthesis, chlorophyll fluorescence parameters