Phosphatidic acid and hydrogen peroxide coordinately enhance heat tolerance in tall fescue

Phosphatidic acid (PA) and hydrogen peroxide (H2 O2 ) play roles in regulating plant responses to abiotic stress. The objective of this study was to determine effects of H2 O2 or PA, individually and interactively, with a H2 O2 scavenging molecule, N,N'-dimethylthoiurea (DMTU), on plant tolerance to heat stress in tall fescue (Festuca arundinacea). Plants were treated with PA (25 µm), H2 O2 (5 mm) and PA (25 µm) + DMTU (5 mm) by foliar application and then exposed to heat stress (38/33 °C) or optimal temperature (23/18 °C, day/night) for 28 days. Foliar application of PA and H2 O2 alone resulted in increases in leaf fresh weight, chlorophyll content, photochemical efficiency and cellular membrane stability in plants exposed to heat stress, whereas addition of DMTU suppressed the positive effects of PA. Expression levels of genes encoding the PA synthesizing enzyme, FaPLDδ, were significantly up-regulated by H2 O2 . Phosphatidic acid- or H2 O2 -enhanced heat tolerance was associated with the activation of stress signalling components (FaCDPK3, FaMPK6, FaMPK3), transcription factors (FaMBF1 and FaHsfA2c) and heat shock proteins (FaHSP18, FaHSP70 and FaHSP90). Phosphatidic acid and H2 O2 may work in coordination to further improve heat tolerance, involving up-regulation of transcription factors in stress signalling cascades and heat protection systems.