Stimulation of Proline-linked Antioxidant Response System in Cool-season Turfgrasses under UV-B Radiation.

The depletion of stratospheric ozone concentration and increase in UV-B radiation (UV-B 280 to 315 nm) in earth is likely to continue into foreseeable future with potential deleterious consequence for agriculture, forestry and horticulture. Ultraviolet-B radiation either alone or in combination with other abiotic stresses causes severe damages to turfgrasses, particularly during transportation and storages of the sods. Plants have several defense mechanisms, including antioxidant enzymes and secondary metabolites like phenolics to counter UV-B induced oxidative damages in cell. The objective of this research was to understand the antioxidant response system and metabolic regulation of cool-season turfgrasses under UV-B radiation. The experiment was carried out in growth chamber with five replications. Creeping bentgrass [Agrostis stolonifera L. (cv. Penncross)], perennial ryegrass [Lolium perenne L. (cv. Palmer II)], Kentucky bluegrass [Poa pratensis L. (cv. Baron)], and tall fescue [Festuca arundianaceae Schreb. (cv. Kentucky 31)] plugs (2.5 cm) were collected from the University of Massachusetts turf research facility. All turfgrass plugs were potted in 4.5 cm pots and grown under 20°C temperature with 10 h photoperiod. After one month of growth, turfgrass plugs were then subjected to artificial UV-B exposure (30 W tube, 70 µmol m^-2 s^-1) for 1 week with 10 h photoperiod. Control was carried out without UV-B exposure. Reduction of photosynthetic activity and bleaching of turfgrass leaves were observed in UV-B treated plants. Significant accumulation of total soluble phenolics and higher total antioxidant activity was found in all UV-B induced cool-season turfgrasses. Higher glucose-6-phosphate dehydrogenase activity along with low succinate dehydrogenase activity in response to UV-B exposure suggested a probable shift of carbon flux from tricarboxylic cycle to pentose phosphate pathway in these species. Stimulation of proline dehydrogenase activity and accumulation of proline was also observed in UV-B exposed turfgrasses. Among the antioxidant enzymes, guaicol peroxidase activity significantly increased in UV-B treated turfgrass plants, indicating the stimulation of anabolic pathways during UV-B treatment.