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Additional index words. alpha-tocopherol, antioxidant enzyme activity, ascorbic acid, ascorbate peroxidase, catalase, chlorophyll fl uorescence, photochemical effi ciency, superoxide dismutase, turf injury Abstract. High ultraviolet-B (UV-B; 290-320nm wavelength) may signifi cantly contribute to kentucky bluegrass (Poa pratensis L.) sod death at harvest and transplanting. As terrestrial UV-B levels continue to increase due to a depletion of the stratospheric ozone layer this problem may worsen. Epidermal attenuation from pigments and detoxifi cation of reactive oxygen species by antioxidant metabolites and enzymes are involved in plant defense against oxidative stress caused by UV-B. Our objective was to determine whether the attenuation and detoxifi cation systems of kentucky bluegrass could be artifi cially boosted by exogenous applications of ascorbic acid (AA), alpha-tocopherol (AT), or a colorant before exposure to high levels of UV-B. Ascorbic acid, AT, and the colorant Green Lawnger (GL), were ap- plied to plugs of mature kentucky bluegrass alone or in combination, and then subjected to artifi cial, continuous UV-B exposure (70 µmol·m -2 ·s -1 ); three greenhouse experiments were conducted. By 3 to 5 days after UV-B initiation, visual quality and photochemical effi ciency, as measured by chlorophyll fl uorescence were signifi cantly reduced. However, in Expt. 1, AA alleviated decline of visual quality, delayed loss of photochemical effi ciency, and increased recovery relative to the control. In Expt. 3, decreased endogenous AT and antioxidant enzyme activities were measured due to UV-B stress. Application of AA, AA + AT, or GL partially alleviated photochemical effi ciency decline from 4 to 12 days after initiation of UV-B. In addition, application of the chemical treatments increased leaf tissue AT concentrations by 32% to 42%, increased SOD activity by 30% to 33% and increased catalase activity by 37% to 59%, relative to the control as measured 10 days after UV-B initiation. Greater AT concentration and SOD and catalase activities were associated with greater visual quality under UV-B stress. The results of these studies indicate that kentucky bluegrass UV-B toler- ance may be increased by supplementing its pigment and antioxidant defense systems with foliar applications of AA, AT or GL.

Ultraviolet-B Radiation Damage on Kentucky Bluegrass. I. Antioxidant and Colorant Effects