18.1 I ntroduction 18.2 Physiology of flavonoid accumulation in plants J. B. Harborne et al. (eds.), The Flavonoids © Springer Science+Business Media Dordrecht 1975 Many reports detail the accumulation of 'anthocyanin' without identifying the pigment or mixture of pigments. Increased accumulation is assumed. Decreases attributable to light are designated by (decr), trace amounts by (tr). 2 Abbreviations as follows: Hl = High Intensity responses to either blue (B), green (G), red (R) or far red (FR) light of 1 J cm -2 or moretotal irradiation. Prr = low energy red, far-red reversible photoresponse. UV = ultraviolet light.

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.

i. Effecls of UV-B on Hayonoids. ferulic acid, growth and photosynthesis in barley primary leaves. -Physiol. Plant. 93: 725-733,Bailey {Hordeum vuli'ttre'L.) was grown with UV-B (280-320 nm) at levels simulating 25 or 5'fc ozone depletion on the date of tbe summer solstice at 40°N latitude, with UV-.A (320-^00 nm). or with no supplemental irradiation. In plant growth chambers providing 300 ^tmol m"-s"' photosynthetically aclive radiation (PARI. L'V-B-grown leaves elongated more slowly than controls but reached the same finai length I day later. Leaf specific fresh weight (mass leaf area"') was significantly increased hy UV-B after the 7th day of growth. UV-B did nol significantly affect leaf area, fresh weight, dry weight, total chlorophylls, total carotenoids or photosynthelic quantum efficiency. CO, asstailation was decreased by UV-B only at internal CO, levels above 250 (il V. By the 8th day of growih. UV-B increased flayonoid (saponarin and lutonarin I accumulation in both the Iciwcr epidermis and Ihe mesophyll: about 409r of tbe saponarin and 20'J of the lutonarin were in the lower epidermis under all experimental conditions. Glasshouse conditions proved too variable for reproducible delermination of growih and photosynthesis bul were reliable lor detennining developmcntul changes in flavonoid (saponarin and lulonarin) accumulation and provided up Ui SCO ^imol m'-s"' V.\K. In the glasshouse UV-B-grcmn lea\es had more flavonoids Ihan controls at all stages from 5 to 30 days after planting: ca 5()'7( 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, bul were significantly higher in UV-B-grown plants on days 10 and 15. UV-B decreased insoluble (cell-wa'H-bound) ferulic acid esters on a wbole leaf basis hut significantly increased this fraction in the lower epidermis. UV-A had no significant effects on growth, photosynthesis or ferulic acid, bul it slightly increased llavonoid accumulation. Tbe results are discussed in terms of secondary phenolics as a lissuc-specific. developmentally regulated adaptive response lo UV-B.

An intercellular washing solution containing about 1% of the soluble protein, 0.3% or less of the glucose-6-phosphate dehydrogenase activity, but up to 20% of the peroxidase and 6-Dglucosidase activity of barley (Hordeum vulgare L.) or oat (Avena sativa L.) primary leaves was obtained by vacuum infiltrating peeled leaves with pH 6.9 buffered 200 millimolar NaCI. After this wash, segments were homogenized in buffer, centrifuged, and the supernatant was assayed for soluble cytoplasmic enzymes. The pellet was washed and resuspended in 1 molar NaCI to solubilize enzymes strongly ionically bound to the cell wall. The final pellet was assayed for enzyme activity covalently bound in the cell wall. Apoplastic (intercellular washing solution, ionically bound, and covalently bound) fractions contained up to 76% of the ,6-D-glucosidase activity, 36% of the peroxidase activity, 11% of the nonspecific arylesterase activity, 4% of the malate dehydrogenase activity, but less than 2% of the glucose-6-phosphate dehydrogenase activity of peeled leaf segments. The partitioning and salt-solubility of the enzymes between the apoplast and symplast differed considerably between these two species. Intercellular washing fluid prepared by centrifuging unpeeled leaves had higher activity for glucose-6-phosphate dehydrogenase, less soluble protein, and less peroxidase activity per leaf than intercellular washing solution obtained by our peeling-infiltration-washing technique. The results are discussed in relation to the roles of these enzymes in phenolic metabolism in the cell wall.

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