EN
Festuca arundinacea Schreb. (tall fescue) is a turfgrass desired for planting in transition-zones. To determine the major processes associated with drought tolerance in this crop, four cultivars were analyzed for enzymatic and non-enzymatic antioxidant activity as well as SGR transcript level under drought stress. These cultivars were selected from larger set of eleven tall fescue cultivars based on genetic relationships delineated via inter-simple sequence repeat (ISSR) analysis. This analysis divided the cultivars into 6 groups, according to Jaccard’s similarity coefficient (65 %), and identified Jaguar, h–d, Pixie, and Mini-mustang as representing diversity within the samples. These cultivars were thus subjected to drought stress treatment by withholding irrigation for up to 8 days. By the end of the treatment, two of the four cultivars had decreased chlorophyll content; Jaguar and h– d, moderately drought-tolerant cultivars did not display significant differences. Notably, the FaSGR transcript increased drastically over the course of the drought stress in Pixie and Mini-Mustang, in contrast to Jaguar and h–d, supporting the notion of SGR-mediated chlorophyll degradation in the less drought-tolerant cultivars. Biochemical adaptation to drought stress includes accumulation of solutes such as proline to maintain turgor, and detoxification of drought-associated reactive oxygen species. Pixie, Jaguar, and Mini-mustang exhibited drastic changes in proline content as compared to h–d, possibly due to their dependency on proline in order to maintain cellular homeostasis against drought stress. The droughttolerant h–d may accumulate only slightly more proline due to other drought-tolerance adaptations. Water scarcity during drought stress significantly increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) activity in all cultivars, though the extent of induction was correlated with drought susceptibility. This suggests that most of the superoxide that was produced as a result of drought stress was converted to H2O2 by SOD and subsequently detoxified by APX into H2O. Collectively, these data indicate that the cultivars Pixie and Mini-mustang protect critical cellular enzymes and structures during severe drought stress through drastically increased proline and SOD activity, while the more drought-tolerant h–d and jaguar do not require such extreme biochemical modifications.