Role of NADPH oxidase-derived reactive oxygen species in Melanoxylon brauna germination under heat stress

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Abstract In plasma membranes, the generation of reactive oxygen species (ROS) is primarily mediated by the activation of NADPH oxidases (NOXs). This study investigated the role of NOX-derived ROS in the germination of Melanoxylon brauna under optimal (25 °C) and heat stress (40 °C) conditions. Seeds were treated with diphenyleneiodonium (DPI), a NOX inhibitor, and evaluated after 48 and 96 h for germination rate, germination speed index, internal anatomy, hydrogen peroxide (H 2 O 2 ) content, and the activity of amylases and antioxidant enzymes. Internal anatomical changes were examined by light microscopy, whereas H 2 O 2 levels and enzyme activities were determined spectrophotometrically. Under optimal conditions, DPI treatment reduced germination rate and speed by 27% and 35.4%, respectively, and hindered seed coat loosening. In addition, DPI lowered H 2 O 2 content and suppressed both amylase and antioxidant enzyme activities. Under heat stress, seeds failed to germinate regardless of treatment; however, ROS inhibition further decreased H 2 O 2 levels and reduced the activities of superoxide dismutase and ascorbate peroxidase. Collectively, these results indicate that in M. brauna , heat stress is the dominant factor impairing germination, and inhibition of NOX-derived ROS does not mitigate—and may even aggravate—the deleterious effects of elevated stress.

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