Physiological response of anthocyanin synthesis to different light intensities in blueberry

Abstract

Fruit color is an important economic character of blueberry, determined by the amount of anthocyanin content. Anthocyanin synthesis within the blueberry fruits is significantly affected by light. To reveal the physiological response mechanism of anthocyanin synthesis in blueberry fruits in different light intensities, four light intensities (100% (CK), 75%, 50% and 25%) were set for the 'O'Neal' southern highbush blueberry as the experimental material in our study. The relationship between endogenous hormones content, associated enzyme activities, and variations with the anthocyanin content in blueberry fruits under various light intensities during the white fruit stage (S1), purple fruit stage (S2), and blue fruit stage (S3) were studied. The results showed that adequate light could significantly promote anthocyanin synthesis in blueberry fruits (P < 0.05). Blueberry fruits had an anthocyanin content that was 1.76~24.13 times higher under 100% light intensity than it was under non-full light intensity. Different light intensities significantly affected the content of endogenous hormones and the activity of associated enzymes in anthocyanin synthesis pathway (P < 0.05). Among them, the JA (jasmonic acid) content and PAL (phenylalanine ammonia lyase) activity of fruits under 100% light intensity were 2.49%~41.83% and 2.47%~48.48% higher than those under other light intensity, respectively. And a significant correlation was found between the variations in anthocyanin content in fruits and the content or activities of JA, ABA (abscisic acid), ETH (ethylene), GA3 (gibberellin 3), IAA (indoleacetic acid), PAL, CHI (chalcone isomerase), DFR (dihydroflavonol reductase) and UFGT (UDP-glucose: flavonoid 3-glucosyltransferase) (P < 0.05). It indicated that 100% light intensity significantly promoted anthocyanin synthesis in blueberry fruits by affecting endogenous hormones content and associated enzyme activities in the anthocyanin synthesis pathway. This study will lay a foundation for further research on the molecular mechanism of light intensity regulating anthocyanin synthesis in blueberry.

Fig 1. Blueberry fruits at different development stages under different light intensities.

Note: CK: 100% light intensity, 75%: 75% light intensity, 50%: 50% light intensity, 25%: 25% light intensity; S1: white fruit stage, S2: purple fruit stage, S3: blue fruit stage.

Fig 2. Effect of light intensity on endogenous hormones content in blueberry fruits.

Note: In the figure, different uppercase letters indicate significant differences in the same light intensity during different stages, and different lowercase letters indicate significant differences in different light intensity treatments during the same stage (P < 0.05). Bars show standard deviation.

Fig 3. Effect of light intensity on associated enzyme activities in the anthocyanin biosynthesis pathway of blueberry fruits.

Note: In the figure, different uppercase letters indicate significant differences in the same light intensity during different stages, and different lowercase letters indicate significant differences in different light intensity treatments during the same stage (P < 0.05). Bars show standard deviation.

Fig 4. Effect of light intensity on anthocyanin content in blueberry fruits.

Note: In the figure, different uppercase letters indicate significant differences in the same light intensity during different stages, and different lowercase letters indicate significant differences in different light intensity treatments during the same stage (P < 0.05). Bars show standard deviation.

Fig 5. Correlation analysis of anthocyanin content with light intensity, endogenous hormones and enzyme activities in blueberry fruits at different developmental stages under light intensity treatment.

Note: AC: anthocyanin content, LI: light intensity; a: white fruit stage (S1), b: purple fruit stage (S2), c: blue fruit stage(S3); * indicates significant correlation at 0.05 level, ** indicates highly significant correlation at 0.01 level.