Response of blue light in different proportions on the growth & flowering in sunflower

Due to the light sensitivity of sunflowers, regulating spectral composition holds significant potential for optimizing sunflower growth and flowering to meet market demands. In this study, sunflower plants were exposed to white light (W200, control) and three levels of blue light (B40R80Fr80 with blue light intensity of 40 µmol m⁻² s⁻¹; B67R67Fr67 with blue light intensity of 67 µmol m⁻² s⁻¹; B100R50Fr50 with blue light intensity of 100 µmol m⁻² s⁻¹) under an overall irradiance level of 200 µmol m⁻² s⁻¹ for 60 days. The aim was to investigate the effects on sunflower morphology regulation, leaf growth, and flowering. Results demonstrated that the growth of sunflowers under B40R80Fr80 treatment with 20 % blue light inhibited plant height compared with B67R67Fr67 and B100R50Fr50 treatments. The highest total leaf dry weight was observed in sunflower leaves under the B100R50Fr50 treatment. Leaves under B67R67Fr67 treatment enhanced activities of Glyceraldehyde 3-phosphate dehydrogenase, Fructose-1,6-bisphosphate aldolase, and soluble starch synthase, along with a 10.4 % increase in Rubisco activity compared with B100R50Fr50 treatment. The sucrose and starch content under B67R67Fr67 treatment increased by 41.0 % and 19.1 % than those of B100R50Fr50 treatment, respectively. Sunflower plants under B67R67Fr67 treatment significantly improved flower disk diameter and No. of petal per flower compared with W200 treatment. Phenotype-assisted transcriptome analysis revealed that B67R67Fr67 treatment on sunflower leaves had positive effects on circadian rhythm-related genes associated with flowering [CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and FLOWERING LOCUS T (FT)], compared with B100R50Fr50 treatment. Additionally, four genes related to GA metabolism were identified for flower development regulation; LOC110884159 and LOC110890361 (GID1B) were up-regulated under B67R67Fr67 treatment. Sunflower leaves under B67R67Fr67 treatment increased GA content and induced the GA pathway related to circadian rhythm, compared with those of B100R50Fr50 treatment. Consequently, the implementation of B67R67Fr67 treatment led to improved circadian rhythm and GA pathway activation, resulting in induced flowering to fulfill market demands for sunflowers.