Plasma membrane NADH oxidase of maize roots responds to gravity and imposed centrifugal forces

NADPH Oxidases: The Vital Performers and Center Hubs during Plant Growth and Signaling

NADPH oxidases (NOXs), mostly known as respiratory burst oxidase homologs (RBOHs), are the key producers of reactive oxygen species (ROS) in plants. A lot of literature has addressed ROS signaling in plant development regulation and stress responses as well as on the enzyme's structure, evolution, function, regulation and associated mechanisms, manifesting the role of NOXs/RBOHs as the vital performers and center hubs during plant growth and signaling. This review focuses on recent advances of NOXs/RBOHs on cell growth, hormone interaction, calcium signaling, abiotic stress responses, and immunity. Several primary particles, including Ca2+, CDPKs, BIK1, ROPs/RACs, CERK, FER, ANX, SnRK and SIK1-mediated regulatory mechanisms, are fully summarized to illustrate the signaling behavior of NOXs/RBOHs and their sophisticated and dexterous crosstalks. Diverse expression and activation regulation models endow NOXs/RBOHs powerful and versatile functions in plants to maintain innate immune homeostasis and development integrity. NOXs/RBOHs and their related regulatory items are the ideal targets for crop improvement in both yield and quality during agricultural practices.

Early axis growth during seed germination is gravitropic and mediated by ROS and calcium

In plant establishment, seed germination is characterized by the emergence of a radicle for secured anchorage to the soil and nutrient and water uptake. Early growth of germinating axes appears to be gravisensitive, and the regulation of this process is largely uncharacterized, particularly in case of epigeally germinating species. Our previous work on the germination of Vigna radiata seeds demonstrated the role of apoplastic reactive oxygen species (ROS) in germination-associated axis growth. This study attempts to explore a possibly similar role of ROS in the gravitropic bending of germinating axes. Pharmacological and histological studies correlated the curvature growth of the axis (due to cell elongation in the cortical region of the upper side) with apoplastic superoxide accumulation. The superoxide was produced by diphenylene iodonium chloride (DPI)-insensitive NADH oxidase, which was different from the DPI-sensitive NADPH oxidase active in the apical elongation zone of the radicle. This NADH oxidase was differentially controlled by IAA, and its activation required influx of apoplastic Ca²⁺. This study shows that the early axis growth in germinating seeds is gravisensitive, which is distinct spatially as well as temporally from the elongation growth of the axis (radicle) and controlled by auxin and cytosolic Ca²⁺ through NADH oxidase-dependent ROS production.