摘要We investigated the diurnal dependence of the hypocotyl-growth responses to shade under sunlight-night cycles in Arabidopsis thaliana.Afternoon shade events promoted hypocotyl growth,while morning shade was ineffective.The Ihy-D,elf3,lux,pif4 pif5,toc1,and quadruple della mutants retained the response to afternoon shade and the lack of response to morning shade while the Ihy cca 1 mutant responded to both morning and afternoon shade.The phyB mutant,plants overexpressing the multidrug resistance-like membrane protein ABCB19,and the iaa17/axr3 loss-of-function mutant failed to respond to shade.Transient exposure of sunlight-grown seedlings to synthetic auxin in the afternoon caused a stronger promotion of hypocotyl growth than morning treatments.The promotion of hypocotyl growth by afternoon shade or afternoon auxin required light perceived by phytochrome A or cryptochromes during the previous hours of the photoperiod.Although the ELF4-ELF3-LUX complex,PIF4,PIF5,and DELLA are key players in the generation of diurnal hypocotyl-growth patterns,they exert a minor role in the control of the diurnal pattern of growth responses to shade.We conclude that the strong diurnal dependency of hypocotyl-growth responses to shade relates to the balance between the antagonistic actions of LHY-CCA1 and a light-derived signal.