Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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EVALUATION OF PROLINE-LINKED PENTOSE PHOSPHATE PATHWAY IN
CREEPING BENTGRASS. D. Sarkar, P. Bhowmik, Y.I. Kwon, and K. Shetty, Univ. of
Massachusetts, Amherst.
ABSTRACT
Creeping bentgrass (Agrostis palustris Huds.) is an important cool-season
turfgrass species in North America. It is used widely in putting greens, tees, bowling
greens, and in grass tennis courts. Abiotic and biotic stresses are major hindrances for
normal performance of the cool-season turfgrass. Under stress conditions plants produce
reactive oxygen intermediates (singlet oxygen, etc.) within cells. Antioxidant defense
systems scavenge reactive oxygen species and protect cells against oxidative stress
injury. Plant phenolics play important role in this defense mechanism by providing UV
protection, antifungal, antiviral, antibacterial, antifeedant and antimitotic activity. Phenolic
antioxidants can either trap the free radicals or scavenge them through series of coupled
antioxidant enzyme defense system. Proline plays a significant role in plant under stress
condition by regulating redox and hydride ion-mediated stimulation of pentose phosphate
pathway. Shetty (1997) proposed a role for proline-linked pentose phosphate pathway
(PLPPP) in stimulating phenolic metabolites in plants. Proline is synthesized from
glutamate through series of reduction reactions, and in this process pyrroline-5-
carboxylate (P5C) and proline function as a redox couple and are known to be metabolic
regulators. The proline, through reactions of proline dehydrogenase (PDH), can enter
mitochondria and support oxidative phosphorylation (instead of NADH). The reduction of
P5C provides NADP+, which is the co-factor for glucose-6-phosphate dehydrogenase
(G6PDH), an enzyme that catalyzes the rate-limiting step of the pentose phosphate
pathway. Proline-linked pentose phosphate pathway can stimulate both shikimate and
phenylpropanoid pathways. Since, genetic heterogeneity in cross pollinated plant causes
inconsistency in phenolic profiles, and related antioxidant enzyme response, screening of
single seeded clonal lines is important to select an elite clonal line with superior phenolic
profile and protective response. The objectives of this study are i) to understand the role
of proline-linked pentose phosphate pathway for phenolic antioxidant production in
creeping bentgrass, and ii) to evaluate overall antioxidant response system of creeping
bentgrass. Single seeded creeping bentgrass plants (20 lines) were grown in 4.5 cm
plastic pots with sand based soils and kept in growth chamber at 27 C (day/night), and
12-h photoperiod conditions. Turf was watered daily, mowed, and fertilized weekly.
Shoots were collected and analyzed repeatedly for G6PDH, PDH, SDH (succinate
dehydrogenase), CAT (catalase), GPX (guaiacol peroxidase), SOD (superoxide
dismutase), DPPH (antioxidant activity), total phenolic, total protein, and chlorophyll.
HPLC analyses of proline and phenolic profile were also undertaken. Results showed
significant differences in PLPPP related enzymes such as G6PDH, and PDH among
twenty creeping bentgrass lines. Similar trends were observed in case of antioxidant
enzymes, like SOD, and GPX. Antioxidant activity (DPPH), and chlorophyll content also
varied, but total phenolic, SDH, and CAT showed similar results in all twenty lines.
Differences in activity of G6PDH, PDH, SOD, and GPX among the clonal lines provide
clues to the significance of proline-linked pentose phosphate pathway in selected
creeping bentgrass clonal lines.
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