Effects of UV‐B on flavonoids, ferulic acid, growth and photosynthesis in barley primary leaves

Abstract

Barley (Hordeum vulgare L.) was grown with UV‐B (280–320 nm) at levels simulating 25 nr 5% ozone depletion on the date of the summer solstice al 40°N latitude, with UV‐A (320–400 nm), or with no supplemental irradiation. In plant growth chambers providing 300 μmol m−2 s−1 photosynthetically active radiation (PAR). UV‐B‐grown leaves elongated more slowly than controls but reached the same final length 1 day later. Leal specific fresh weight (mass leaf area−1) was significantly increased by UV‐B after the 7th day of growth. IV‐B did not significantly affect leaf area, fresh weight, dry weight, total chlorophylls, total carotenoids or photosynthetic quantum efficiency. CO2 assimilation was decreased by UV‐B only at internal CO2 levels above 250 μl l−1. By the 8th day of growth, UV‐B increased flavonoid (saponarin and lutonarin) accumulation in both the lower epidermis and the mesophyll: about 40% of the saponarin and 20% of the lutonarin were in the lower epidermis under all experimental conditions. Glasshouse conditions proved too variable for reproducible determination of growth and photosynthesis but were reliable for determining developmental changes in flavonoid (saponarin and lutonarin) accumulation and provided up to 800 μmol m−2 s−1 PAR. In the glasshouse UV‐B‐grown leaves had more flavonoids than controls al all stages from 5 to 30 days after planting: ca 509 more saponarin and 100% more lutonarin. Levels of soluble (vacuolar) ferulic acid esters were similar under all conditions on day 5. and on day 20 or later, but were significantly higher in UV‐B‐grown plants on days 10 and 15. UV‐B decreased insoluble (cell‐wall‐bound) ferulic acid esters on a whole leaf basis but significantly increased this fraction in the lower epidermis. UV‐A had no significant effects on growth, photosynthesis or ferulic acid, but it slightly increased flavonoid accumulation. The results are discussed in terms of secondary phenolics as a tissue‐specific, developmentally regulated adaptive response to UV‐B.