Light is one of the most important environmental factors affecting flavonoid biosynthesis in plants. The absolute dependency of light to the plant development has driven evolvement of sophisticated mechanisms to sense and transduce multiple aspects of the light signal. Light effects can be categorized in photoperiod (duration), intensity (quantity), direction and quality (wavelength) including UV-light. Recently, new information has been achieved on the regulation of light-controlled flavonoid biosynthesis in fruits, in which flavonoids have a major contribution on quality. This review focuses on the effects of the different light conditions on the control of flavonoid biosynthesis in fruit producing plants. An overview of the currently known mechanisms of the light-controlled flavonoid accumulation is provided. R2R3 MYB transcription factors are known to regulate by differential expression the biosynthesis of distinct flavonoids in response to specific light wavelengths. Despite recent advances, many gaps remain to be understood in the mechanisms of the transduction pathway of light-controlled flavonoid biosynthesis. A better knowledge on these regulatory mechanisms is likely to be useful for breeding programs aiming to modify fruit flavonoid pattern.

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Light-controlled flavonoid biosynthesis in fruits.

The growth conditions in different latitudes vary markedly with season, day length, light quality and temperature. Many plant species have adapted well to the distinct environments through different strategies, one of which is the production of additional secondary metabolites. Flavonoids are a widely spread group of plant secondary metabolites that are involved in many crucial functions of plants. Our understanding of the biosynthesis, occurrence and function of flavonoids has increased rapidly in recent decades. Numerous studies have been published on the influence of environmental factors on the biosynthesis of flavonoids. However, extensive long-term studies that examine the effect of the characteristics of northern climates on flavonoid biosynthesis are still scarce. This review focuses on the current knowledge about the effect of light intensity, photoperiod and temperature on the gene-environment interaction related to flavonoid biosynthesis in plants.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2010.02154.x

Effect of latitude on flavonoid biosynthesis in plants.

Light signaling and plant responses to blue and UV radiations—Perspectives for applications in horticulture

Shifts in the geographic distribution of species caused by climate change could detrimentally affect ecosystems and biodiversity. This Perspective highlights the importance of adaptations to day length in predicting the latitudinal range shifts of different species under global warming.

Climate change-driven species' range shifts filtered by photoperiodism

The objective of this study was to evaluate the significance of blue light (B) in the growth and photosynthetic capacity of cucumber. Gas exchange, chlorophyll (Chl) fluorescence kinetics, chloroplast ultrastructure, and leaf growth were investigated to explore the influence of three different light qualities of light emitting diodes (LEDs) on plant morphogenesis and the development of photosynthetic apparatus in cucumber (Cucumis sativus) leaves from emergence to full expansion under weak light [50 μmol(photon) m−2 s−1]. We found that B could significantly increase the leaf area (LA), shoot elongation, Chl a/b, net photosynthetic rate, and stomatal conductance (gs). In addition, the comparisons of maximal quantum yield of PSII photochemistry and the photosynthetic performance index between B-, W (white light)-, and R (red light)-grown leaves suggested that B was essential for the development of photosynthetic apparatus under weak light. B-grown leaves had the lowest Chl content under weak light, however, they had well-developed chloroplasts with the highest degree of stacked lamellae and the lowest starch accumulation. This could explain to a considerable extent the highest net photosynthetic rate per Chl unit. The results demonstrated that B optimized photosynthetic performance by improving the photosynthetic rate, increasing LA, and prolonging active photosynthesis duration under low irradiance. Therefore B is necessary to ensure healthy development of chloroplasts and highly efficient photosynthetic functions in cucumbers under a weak light environment. More importantly, our study also provided theoretical and technical support for the development of light environmental control technology.

The importance of blue light for leaf area expansion, development of photosynthetic apparatus, and chloroplast ultrastructure of Cucumis sativus grown under weak light

Background: Light is one of the most significant environmental factors affecting to the accumulation of flavonoids in fruits. The composition of the light spectrum has been shown to affect the production of phenolic compounds during fruit ripening. However, specific information on the biosynthesis of flavonoids in fruits in response to different wavelengths of light is still scarce. In the present study bilberry (Vaccinium myrtillusL.)fruits,whichareknowntoberichwithanthocyanin compounds, were illuminated with blue, red, far-red or white light during the berry ripening process. Following the illumination, the composition of anthocyanins and other phenolic compounds was analysed at the mature ripening stage of fruits. Results: All the three monochromatic light treatments had significant positive effect on the accumulation of total anthocyanins in ripe fruits compared to treatment with white light or plants kept in darkness. The elevated levels of anthocyanins were mainly due to a significant increase in the accumulation of delphinidin glycosides. A total of 33 anthocyanin compounds were detected in ripe bilberry fruits, of which six are novel in bilberry (cyanidin acetyl-3-O-galactose, malvidin acetyl-3-O-galactose, malvidin coumaroyl-3-O-galactose, malvidin coumaroyl-3-Oglucose, delphinidin coumaroyl-3-O-galactose, delphinidin coumaroyl-3-O-glucose). Conclusions: Our results indicate that the spectral composition of light during berry development has significant effect on the flavonoid composition of ripe bilberry fruits.

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Monochromatic light increases anthocyanin content during fruit development in bilberry

Carotenoids are important pigments and precursors for central signaling molecules associated in fruit development and ripening. Carotenoid metabolism has been studied especially in the climacteric tomato fruit but the content of carotenoids and the regulation of their metabolism have been shown to be highly variable between fruit species. Non-climacteric berries of the genus Vaccinium are among the best natural sources of health-beneficial flavonoids but not studied previously for carotenoid biosynthesis. In this study, carotenoid biosynthetic genes, PSY, PDS, ZDS, CRTISO, LCYB, LCYE, BCH and CYP450-BCH, as well as a carotenoid cleavage dioxygenase CCD1 were identified from bilberry (V. myrtillus L.) fruit and their expression was studied along with carotenoid composition during fruit development under different photoperiod and light quality conditions. Bilberry was found to be a good source of carotenoids among fruits and berries. The most abundant carotenoids throughout the berry development were lutein and β-carotene, which were accompanied by lower amounts of 9Z-β-carotene, violaxanthin, neoxanthin, zeaxanthin, antheraxanthin and β-cryptoxanthin. The expression patterns of the biosynthetic genes in ripening fruits indicated a metabolic flux towards β-branch of the carotenoid pathway. However, the carotenoid levels decreased in both the β-branch and e,β-branch towards bilberry fruit ripening along with increased VmCCD1 expression, similarly to VmNCED1, indicating enzymatic carotenoid cleavage and degradation. Intense white light conditions increased the expression of the carotenoid biosynthetic genes but also the expression of the cleavage genes VmCCD1 and VmNCED1, especially in unripe fruits. Instead, mature bilberry fruits responded specifically to red/far-red light wavelengths by inducing the expression of both the carotenoid biosynthetic and the cleavage genes indicating tissue and developmental stage specific regulation of apocarotenoid formation by light quality. This is the first report of carotenoid biosynthesis in Vaccinium berries. Our results indicate that both transcriptional regulation of the key biosynthetic genes and the enzymatic degradation of the produced carotenoids to apocarotenoids have significant roles in the determination of the carotenoid content and have overall effect on the metabolism during the bilberry fruit ripening.

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Carotenoid metabolism during bilberry ( Vaccinium myrtillus L.) fruit development under different light conditions is regulated by biosynthesis and degradation

Currently, climate is warming at a considerable rate. The warming climate shifts the vegetation toward the poles. This causes competition between southern and northern plant species and ecotypes. Light environment obviously has an important role in controlling the competition. The controlling factors include daylength, spectral composition (especially the ratio of red/far-red light, blue light and UV-radiation), and the amount of photosynthetically active radiation.

Growth Responses of Trees to Arctic Light Environment

Taulavuori, K., Sarala, M., Karhu, J., Taulavuori, E., Kubin, E., Laine, K., Poikolainen, J. & Pesonen, E. 2005. Elongation of Scots pine seedlings under blue light depletion. Silva Fennica 39(1): 131–136.The effect of blue light (400–500 nm) removal on the elongation of Scots pine (Pinus sylvetris L.) seedlings was investigated in a ﬁeld experiment in Northern Finland during two growing seasons. The seedlings were grown in plexiglass chambers and ambient control plots. The blue wavelengths were removed from the light spectrum by using chambers made of orange plexiglass. The results of nearly daily measurements showed that the elongation of Scots pine seedlings was increased by the removal of blue light only at high latitudes.Keywords blue light, elongation, high latitude, Scots pineAuthors´ addresses Taulavuori K. & E., Sarala & Laine: Department of Biology, University of Oulu, PO Box 3000, FIN-90014, Oulu, Finland; Karhu, Kubin & Poikolainen: Muhos Research Station, Finnish Forest Research Institute, Kirkkosaarentie 7, FIN-91500 Muhos, Finland; Pesonen: Vantaa Research Centre, Finnish Forest Research Institute, PO Box 18, FIN-01301, Vantaa, FinlandE-mail ktaulavu@cc.oulu.ﬁReceived 10 June 2004 Revised 15 September 2004 Accepted 24 January 2005

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Marian Sarala

Papers

Monochromatic light increases anthocyanin content during fruit development in bilberry

Carotenoid metabolism during bilberry ( Vaccinium myrtillus L.) fruit development under different light conditions is regulated by biosynthesis and degradation

Growth Responses of Trees to Arctic Light Environment

Elongation of Scots Pine Seedlings under Blue Light Depletion

Elongation of Scots pine seedlings under blue light depletion is independent of etiolation