Research On The Mechanism Of Different Supplemental Blue Light Frequencies On Metabolism Of Carotenoids In Tomatoes

Tomato,a favorite fruit vegetable consumed in high volume around the world,is considered a superb source of dietary antioxidants because of its rich content in carotenoids.Among all sorts of carotenoids,lycopene is of great importance to contribute to tomato color and is also proved to be one of the most extraordinary antioxidant properties in tomato.Light is well known to not only improve the nutrient qualities and contents of health-promoting compounds,but also heighten the flavor and product appearance of tomato fruit.More important,light has the ability to work as an environmental stimuli affecting the biosynthesis of lycopene.The role of blue light in lycopene synthesis,however,remains unclear and therefore our research on the effects of supplementary blue light on lycopene metabolism in tomato fruit is crucial in production.In this paper,tomatoes（Solanum lycopersicum L.cv.Micro-Tom）were grown under natural light during the vegetative period.When reached anthesis,the plants began to supplement with blue light.There were four frequencies of supplemental blue light treatments:S6（30 min blue light 30 min pause）,S8（30 min blue light and 15 min pause）,S10（30min blue 8 min pause）,S12（continuous blue light for 12h）,and control（CK,natural light）.Photosynthetic photon flux density（PPFD）of supplemental blue light was set at 100μmol m^–1 s^–1and photoperiod was from 6:00 to 18:00 every day.Agronomic traits and nutritional qualities of tomato fruits were measured at 30,34,38,42 and 46 days after anthesis（DAA）,respectively.And the effects of different frequencies of supplemental blue light treatments on the metabolism of lycopene were studied by real-time fluorescent quantitative PCR.The main findings were as follows:1.Different frequencies of supplemental blue light could accelerate flowering of tomato plants and promote fruit ripening about 3 to 4 days ahead,which significantly facilitate the processes of color change and maturity in tomato fruits.2.Different frequencies of supplemental blue light had significant effects on nutritional qualities and antioxidant properties of tomato fruits.All light treatments could significantly increase the contents of total phenolic compounds,total flavonoids,soluble sugar and the lycopene in fruits,and also enhance the overall antioxidant activity of the fruit.3.Real-time quantitative PCR analysis showed that the expression of S1PIFs at DAA30 was significantly higher under all blue light treatments than that in CK.The expression of Sl HY5 at DAA30 and DAA38 were also upregulated by all light treatments,but both were downregulated at DAA34,DAA42 and DAA46.The expression of S1RIN at DAA38 was significantly higher in all blue light treatments.The S1ACS2 only expressed at DAA30,and the expression level was significantly higher under all supplemental blue light treatments than CK.The ethylene receptor genes,such as Sl ETR3 and Sl E8,were upregulated by all blue light treatments at DAA38.The expression level of fruit lycopene synthesis gene Sl PSY1 was significantly increased by all blue light treatments and reached the peak value at DAA38.Among those,the expression of Sl PSY1 at DAA30 was significantly higher than that in other treatments.The above results indicated that different frequencies of supplemental blue light had the ability to influence gene expressions involving in fruit ripening and lycopene metabolism in tomato fruits.To sum up,different frequencies of supplemental blue light could promote the early color change and maturation of tomato fruits by regulating the transcriptional levels of light transcription factors,such as Sl PIFs,Sl HY5 gene and mature promoter gene Sl RIN,thus affecting the process of fruit lycopene metabolism.different frequencies of supplemental blue light significantly reinforced the antioxidant levels and nutritional qualities of tomato fruits,especially lycopene.Among them,S10 treatment was optimal for tomato fruits production.