Effects of Exogenous Nitric Oxide on Photochemical Activity of Photosystem in Potato Leaf Tissue Under Non-stress Condition

Abstract: Under non-stress condition, effects of exogenous nitric oxide (NO) on chlorophyll fluores-cence parameters in detached leaves and leaf discs of potato (Solanum tuberosum L.) were surveyed. Results showed that the maximal quantum efficiency (Fv/Fm) and the effective quantum efficiency (F PS) of photosystem (PS) were reduced by exogenous NO under illumination (150 mmol.m-2.s-1, 25 ℃). This influence was related not only to the concentration of sodium nitroprusside (SNP, a NO donor) solution, but also to the active duration of NO on leaf tissue. Results with leaf discs showed that the effects of SNP on F PS could be prevented by bovine hemoglobin (a powerful NO scavenger), while a mixture of NO2- and NO3- (the decomposition product of NO or its donor SNP) had much less influence on F PS than SNP, indicating that effects of exogenous SNP on PS photochemical activity was mainly due to NO generation. Under light (150 mmol.m-2.s-1, 25 ℃) for 4 h or longer period, the non-photochemical quenching (NPQ) in SNP-soaked leaves was statistically similar to that in H2O-soaked control, but F PS and the proportion of open reaction centers (measured as qP) were lower than control, respectively. After 25 min dark-adaptation, the maximal fluorescence (Fm) in SNP treatment (8 and 12 h illumination duration) was significantly lower than the control, while the initial fluorescence (Fo) in SNP and H2O-treated leaves had no significant difference. Therefore this indicated that under the present experimental condition, th