Physiological Mechanism Of Tolerance To Nicosulfuron In Sweet Maize

To investigate the effect of nicosulfuron on the sugar metabolism pathway of sweet maize and to reduce its harmful effects.In this study,a pair of sweet maize sister lines（HK301 and HK320）with different tolerances to nicosulfuron were used as test material and sprayed at a concentration of 36 g/hm2 with water as control.Samples were taken at 1,3,5 and 7 d after spraying to investigate the effects of nicosulfuron stress on photosynthetic characteristics,chlorophyll fluorescence parameters and gene expression of sugar metabolism pathways and their related enzymes in sweet maize.the results show that:1.Net photosynthetic rate（P_n）,stomatal conductance（G_s）,transpiration rate（E）,maximum photochemical efficiency（F_v/F_m）,actual photochemical efficiency(Φ_PSII),non-cyclic photosynthetic electron transfer rate（ETR）and photochemical burst coefficient（q P）values of HK320 were significantly lower than HK301,and intercellular carbon dioxide concentration（C_i）and non-photochemical burst factor（NPQ）values of HK320 were significantly higher than HK301 under nicosulfuron stress.2.Straight-chain starch,fructose（FUR）,sucrose（SUC）and Fuctose-1,6-diphosphate（FDP）contents and sucrose synthase（SS-Ⅱ）,sucrose phosphate synthase（SPS）,fructose-1,6-bisphosphate kinase（FBA）,soluble starch synthase（SSS）,and binding-state starch synthetase（GBSS）activities were significantly increased;branched chain starch content was significantly reduced.This indicates that stress affected the carbohydrate content and enzyme activities associated with the selfed sweet maize line,resulting in reduced dry matter accumulation under nicosulfuron treatment.3.Glucose（GLU）,glucose 6-phosphate（6PG）and pyruvate（PA）contents were significantly increased and malic acid（MDH）,citric acid（CA）,oxaloacetate（OAA）,adenosine triphosphate（ATP）contents,phosphoenolpyruvate carboxylase（PEPC）and pyruvate kinase（PK）activities were significantly reduced under nicosulfuron stress in the sensitive autotrophic sweet corn HK320 compared to the resistant autotrophic sweet corn HK301.This indicates that nicosulfuron enhanced glycolytic translocation and slowed respiration rate in HK320 and HK301.4.The relative gene expression of SS-Ⅱ,HK,PFK,PEPC and PK gene families was altered under nicosulfuron treatment.It indicates that nicosulfuron affects the activity of enzymes related to the sugar metabolism pathway.