Abstract: Nitric oxide (NO) has emerged as a key molecule involving in the regulation of various abiotic stresses that induces physiological responses in plants. NO acts as an antioxidant to protect chloroplast from oxidative damages by maintaining chloroplast membrane intactness, thus keeps high activity of PS II. The experiment was conducted under PEG stress of -0.5 MPa, while we chose 0.1 mmol L^-1 sodium nitroprusside (SNP) as NO donor. The effects of SNP on the content of photosynthetic pigments and the ability of utilizing the light in PS II of winter wheat (Triticum aestivum L.) under drought stress were studied through chlorophyll fluorescence kinetic technique. The results showed that the content of photosynthetic pigment increased, but the pro-portion of opened PSII reaction centers (indicated by qP) decreased under drought stress, thus drought restricted the utilization of light-energy in PS II (F’_v/F’_m) and the exertion of photosynthetic function (L_PFD). SNP could help to increase photosynthetic pig-ment content, and decrease the cell permeability, thus avoided decreasing the confined value of photosynthetic function (L_PFD) by drought. Furthermore, SNP increased the proportion of opened PS II reaction centers (indicated by qP), leading to transference of the more excited light-energy to PS II function center, decreased the dissipation of excited energy in antenna pigments (NPQ), which increased the more absorbed light to participate in photochemical reaction (F’_v/F’_m). In addition, SNP alleviated the excited pressure in PS II reaction center imposed by drought and lowered the deoxidization of Q_A (1 - qP). Therefore, exogenous nitric oxide donor (SNP) may participate in the synthesis of photosynthetic pigments and the utilization of light-energy in PS II of wheat under drought stress.

Key words: Sodium nitroprusside (SNP), Water stress, Photosynthetic pigment, PS II, Light use capability, Wheat