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Changes in growth and pigment concentrations with leaf age in pea under modulated UV-B radiation field treatments

Day, T.A., Howells, B.W., Ruthland, C.T.
Plant, cell and environment 1996 v.19 no.1 pp. 101-108
chlorophyll, dosage, height, dry matter accumulation, leaf area, flavonoids, chemical constituents of plants, Pisum sativum, mesophyll, ultraviolet radiation, leaves, ozone depletion
We assessed whether growth of garden pea (Pisum sativum mutant Argenteum) was reduced under ecologically relevant enhancements of ultraviolet-B radiation (UV-B, 280-320 nm) by employing modulated field lampbanks which simulated 0,16 or 24% ozone depletion. In addition, we determined whether enhanced UV-B altered the concentration and distribution of chlorophyll and UV-B-absorbing compounds in leaves, and whether this was dependent on leaf age. There were no significant UV-B effects on the four whole-plant parameters we examined (height, above-ground biomass, total leaflet area or average leaflet area). Of the 12 leaf-level parameters we examined, UV-B had a significant effect (P<0.05) on only one parameter: the ratio of UV-B-absorbing compounds to chlorophyll, which was greatest at the highest UV-B level. Total chlorophyll concentrations tended to be lower under enhanced UV-B (P=0.11), while the proportion of UV-B-absorbing compounds in the adaxial epidermis tended to be higher (P=0.11). Total leaf concentrations of UV-B-absorbing compounds were unaffected by UV-B level. Cooler, suboptimal growing conditions during this late summer/early autumn experiment may have masked some potential UV-B effects. In contrast to the UV-B effects, we found strong leaf-age effects on nearly all parameters that we assessed. On an area basis, concentrations of total chlorophyll and UV-B-absorbing compounds increased with leaf age, while chlorophyll a/b ratios decreased. One of the few parameters unaffected by leaf age was the ratio of UV-B-absorbing compounds to total chlorophyll, which remained constant within a given UV-B treatment. Pea was much less sensitive to enhanced UV-B than in previous growth-chamber and greenhouse studies, and in nearly all cases UV-B treatment effects were overshadowed by leaf-age effects. In view of the large effect leaf age had on concentrations of UV-B-absorbing compounds, as well as their distribution within leaves, researchers may need to consider leaf age in UV-B experimental designs.