Sustained source-activity is imperative for vigor plant growth and yield. In present study, physio-biochemical responses of wheat plant contributing to source-activity were measured after application of salicylic acid-chitosan nanoparticles (SA-CS NPs). SA-CS NPs slowly release SA for sustained availability to plant. In seedling bioassay, as compared with salicylic acid (SA), SA-CS NPs incurred up to ~1.5 folds increased activities of seed reserve food remobilizing enzymes for substantial mobilization of reserve food to growing seedlings and enhanced seedling vigor index (SVI) by 1.6 folds. At booting stage, foliar application of SA-CS NPs (0.01-0.08%; w/v) enhanced the activities of superoxide dismutase (1.94 folds), catalase (1.33 folds), peroxidase (1.99 folds) and polyphenol oxidase (1.04 folds) in flag leaf. SA-CS NPs further contrived cellular homeostasis by comforting reactive oxygen species (ROS), malondialdehyde (MDA) and proline contents in flag leaf. SA-CS NPs (0.08%; w/v) significantly increased chlorophylls (a-b) contents (1.46 folds), spike length without awns, spike lets per spike and grain weight per pot as compared with SA. Study categorically explicates that slow release of SA from SA-CS NPs could exert significant effect on source-activity by maneuvering various physio-biochemical responses of wheat plant.