Abstract: ObjectiveEffects of 28-homobrassinolide(28-HBR)on photosynthetic characteristics and fluorescence characteristics of pepper seedlings under low temperature with dim light were explored in order to provide reference for culture of pepper seedlings in winter and spring seasons.MethodThe pepper variety Yazhouxiongfeng was used as mate-rial.The seedlings were sprayed with clear water and 150.0 mg/L 28-HBR under normal temperature and lightnight/day temperature 24℃/18℃,light 500.0 μmol/(m2·s)and low temperature with dim lightnight/day temperature 12℃/6℃, light 100.0 μmol/(m2·s)respectively. Biomass,chlorophyll content,gas exchange parameters and chlorophyll fluores-cence parameters of pepper seedlings were measured 1,5,9 and 13 d after treatments.ResultUnder low temperature with dim light,biomass,net photosynthesis rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),regulated energy dissipation of the quantum yield Y(NPQ),non photochemical quenching coefficient(NPQ),qN of the pepper seedlings 9 d after spraying 150.0 mg/L 28-HBR 9 d significantly increased(P<0.05,the same below),but intercellular CO2concen-tration(Ci)significantly decreased.After 13 d of treatment,the results showed that the biomass,Pn,Y(NPQ),NPQ and qN significantly decreased,but chlorophyll a/b(Chla/b)and Cisignificantly increased.The correlation analysis indicated that,biomass had significant positive correlation with chlorophyll a(Chla)content,chlorophyll b(Chlb)content,Pn, Gs,Tr,qN and qP.ConclusionSpraying 150.0 mg/L 28-HBR can improve photosynthesis of pepper seedlings under low temperature with dim light,thereby protects photosynthetic system,and reduces the damage on pepper seedlings caused by low temperature with dim light.