Abstract:

The effects of full light and 50% shading on sepal color and pigment composition in different blooming periods of Hydrangea macrophylla‘Hanatemari’were studied. The color phenotype was determined by the Royal Horticultural Society colorimetric card and colorimeter. Anthocyanin composition was qualitatively and quantitatively analyzed by high-performance liquid chromatography and mass spectrometry（LC-MS）. Physiological indexes，such as the biosynthetic enzyme activities and metal ion contents，were determined. The correlation between sepal color and physiological indexes was analyzed through multiple linear regression analysis. Results showed that shading considerably affected the sepal color of H. macrophylla. The sepal color under 50% shading had lower redness value（a^*），higher yellowness value（b^*），and presented to be more pinkish（greyed-purple group）than that under full light. Fading speed of sepal color was retarded under 50% shading. From the full blooming to the withering period of flowers，the redness value a^* under full light decreased by 88.90%，whereas it only decreased by 65.67% under 50% shading. Five anthocyanidins（cyanidin，pelargonidin，delphinidin，malvidin，and petunidin）were detected in the sepal，and 11 anthocyanins were formed through glycosylation modification. Delphinium-3-O-glucoside，accounting for 92.12% of anthocyanin components，was the main reason for the coloration of hydrangea sepal. Later，50% shading was beneficial for anthocyanin accumulation，and the total anthocyanin content（1 286.96 µg · g^-1FW）was significantly increased by 36.32% compared with full light（944.10 µg · g^-1FW）. The activities of phenylalanine ammonia-lyase （PAL）and chalcone isomerase（CHI）were higher at the initiation stage，and the PAL activity was significantly higher under 50% shading at the budding stage than under full light. However，shading did not cause considerable changes in Al，Fe，Ca，and Mg contents. Multiple regression analysis showed that delphinidin，malvidin，and petunidin accumulations were beneficial to the redness of sepal color. Total anthocyanins played a dominant role in the coloration of H. macrophylla sepal under different treatments，and through synergistic effects of flavonoids，total phenols，PAL，and CHI enzyme activities，jointly affected the sepal color presentation.

Key words: Hydrangea macrophylla, anthocyanins, flower color, shade