Proline-associated antioxidant enzyme response in cool-season turfgrasses under abiotic stress
In the northern United States, substantial turfgrass loss occurs due to severe and prolonged cold stress during winter. Cool-season turfgrass is generally have higher cold tolerance characteristic, however large energy inputs are required for preparation and recovery of turfgrass from cold stress. Freezing injury of turfgrass can have an economic and environmental impact as well as reduced aesthetic values of commercial turfgrass. Although maximum damage occurs during late winter to early spring, during deacclimation, but the biological process during acclimation (late fall to early winter) governs significant role for cold tolerance mechanism. Stimulation of the antioxidant response system, phenolic synthesis, biosynthesis of other protective metabolites, and shifts in overall metabolic pathways are common responses in plants during biotic and abiotic stresses.
Genetic heterogeneity is major drawback for induction of phenolic production for higher fitness in specific varieties during stress in cross-pollinated species like seeded creeping bentgrass (Agrostis stolonifera L.). Therefore, one major aim of this dissertation was screening and selection of single seed origin high phenolic creeping bentgrass clonal lines from a heterogeneous seed source and evaluation of these lines under different stress conditions. Further, the performance of other cool-season turfgrasses (perennial ryegrass, Kentucky bluegrass and tall fescue) under cold and UV-B stress, was evaluated to understand the role of antioxidant enzyme response and proline-associated pentose phosphate pathway in these species during abiotic stress.
Results indicated a significant genetic heterogeneity among single seed origin creeping bentgrass clonal lines. High phenolic clonal lines showed higher antioxidant activity and greater fitness during cold stress. Exogenous application of natural antioxidant stimulator significantly improved the fitness of these clonal lines by stimulating antioxidant enzyme response and higher phenolic biosynthesis. Significant biochemical adjustments were observed in cool-season turfgrasses during cold acclimation which may govern their fitness during winter injury. A strong association between proline synthesis and pentose phosphate pahway stimulation was found in cool-season turfgrasses under stress-induced conditions. Higher pentose phosphate pathway stimulation along with proline accumulation and enhanced phenolic synthesis were most significant responses observed in the investigated turfgrass species during cold and UV-B stress. Among different antioxidant enzymes, guaiacol peroxidase activity was consistently higher in these turfgrasses, while superoxide dismutase and catalase activity varied widely with species and clonal lines. Stimulation of phenolic biosynthesis coupled with proline-associated pentose phosphate pathway was also reflected in higher photochemical efficiency and higher visual quality of turfgrasses under cold and UV-B stress.