Abstract: This paper studied the effects of different concentration 5-aminolevulinic acid (ALA) on the growth and alkaloids (indigo and indirubi) content of Isatis indigotica seedlings under shading condition. Shading decreased the root length and diameter, plant biomass, chlorophyll content, photosynthetic gas exchange parameters, and alkaloid content of the seedlings significantly, while exogenous ALA could alleviate the inhibition effect of shading on the vegetative growth, photosynthesis, and alkaloid accumulation of the seedlings. Spraying 13.3-25 mg·L^-1 of ALA was most effective to promote the vegetative growth and photosynthesis, and spraying 100 mg·L^-1 of ALA was most effective to promote alkaloids accumulation. It was suggested that under low light condition, spraying low concentrations (13.3-25 mg·L^-1) ALA at the early growth stage of I. indigotica- could promote its biomass production, and spraying higher concentration (100 mg·L^-1) ALA could promote the alkaloid production of I. indigotica for medical purpose.

Key words: winter wheat sowed in spring, sowing date, photosynthetic efficiency, chlorophyll fluorescence parameter, grain yield.