Effects of UV-B on activities of enzymes of secondary phenolic metabolism in barley primary leaves |
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Authors: | Lan Liu Jerry W. McClure |
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Affiliation: | Dept of Horticulture, Ohio State Univ. Columbus, OH 43210, USA;Dept of Botany, Miami Univ., Oxford, OH 45056, USA. |
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Abstract: | Barley ( Hordeum vulgare L.) was grown in a glasshouse with 13.56 or 8.84 kJ m−2: biologically effective UV-B (280–320 nm: UV-BBE) simulating levels predicted to occur with 25 or 5% ozone depletion at 40°N latitude, with UV-A (320–400 mm), or with no supplemental irradiation. Activities of L-phenylalanine ammonia-lyase (PAL, EC 4.3.1.5). chalcone-flavanone isomerase (CFI, EC 5.5.1.6) and peroxidase (EC 1.11.1.7) were determined from the 5th through the 30th day after planting. PAL regulates diversion of L-phenylalanine into precursors for secondary phenolics. CFI regulates an early step of flavonoid biosynthesis, and peroxidase activates phenolic precursors for cross-linking and rigidifying cell walls. At all ages UV-B decreased soluble protein leaf−1 but had little effect on fresh weight or CFI activity. Exposure to UV-B decreased peroxidase activity only slightly in early growth stages but decreased it about 40% by day 30. PAL activity was highest 5 days after planting under all treatments, decreased thereafter, and was not detectable in control plants after day 10. UV-B prolonged PAL activity through day 15 in plants given the highest level of UV-B. This UV-B prolongation of PAL activity is correlated with, and is a likely underlying mechanism to explain, the UV-B- enhanced accumulation of flavonoids and ferulic acid in barley primary leaves. The results are discussed in terms of barley leaf adaptation to UV-B as developmental response dependent on conditions of plant growth. |
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Keywords: | Barley chalcone- flavanone isomerase Hordeum vulture peroxidase L-phenylalanine ammonia-lyase UV-B |
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