Polyphenol Increases in Safflower and Cucumber Seedlings Exposed to Strong Visible Light with Limited Water

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  To assess effects of the environmental stress on polyphenol compounds (polyphenols) in plants, the polyphenol contents were investigated in the seedlings of safflower (Carthamus tinctrius L.) and cucumber (Cucumis sativus L.) grown under three types of growth conditions: control; light stress, irradiated with strong light in the visible wavelength range; and light/water stress, irradiated with strong visible light with a limited water supply. The total polyphenol contents and the amounts of the major polyphenols, especially luteolin 7-O- glucoside in safflower cotyledons, and luteolin 7-O-glucoside and luteolin in safflower foliage leaves, increased in response to both stresses. The polyphenol increasing effect of light/water stress was clearly observed in safflower compared to cucumber, suggesting that plants that are resistant to these stresses can accumulate substantial amounts of polyphenols compared to the plants which respond weakly to the stresses.