Cold atmospheric plasma as a testable redox input in plants: Chemistry, biological dose and evidence requirements

Cold atmospheric plasma (CAP) and plasma-activated water (PAW) provide chemically diverse inputs that can modify plant establishment, physiology, and defense. Their effects remain difficult to transfer because exposure duration does not specify the chemistry reaching responsive tissues. This critical narrative review develops redox programming as a testable input–response framework, rather than an established precision technology. We connect plasma generation and post-discharge chemistry with tissue accessibility, endogenous buffering, calcium dynamics, protein redox regulation, and agricultural outcomes. A biological redox dose is operationalized as a multidimensional exposure-and-context descriptor with separately reported chemical amounts, concentration–time integrals, delivery geometry, and plant-state measurements. A published wheat dataset illustrates both its measurable components and the information that cannot be reconstructed retrospectively. The signaling window is explicitly related to established oxidative-window and hormesis concepts; the added contribution is a measurement and causal-validation workflow, not a new universal dose–response law. Selected primary studies are compared using mechanistic evidence grades and separate application-readiness categories. Chemistry-matched comparisons show why nitrate nutrition, acidity and physical surface modification must be distinguished from redox signaling. We specify analytical controls, plant-compatible biosensors, and a crop-specific optimization example. CAP is therefore a promising experimental redox input, but its programmability requires prospective chemical, mechanistic, agronomic, and economic validation.