## 1 Introduction  
Cold atmospheric-pressure plasma carries charged particles (i.e., electrons, ions), reactive oxygen species--ROS (such as hydroxyl radicals [OH], hydrogen peroxide [H\({}_{2}\)O\({}_{2}\)], singlet oxygen [O], ozone [O3], superoxide [O\({}_{2}\)*-]), reactive nitrogen species--RNS (such as nitrite [NO\({}_{2}\)], nitrate [NO\({}_{3}\)] and nitric oxide [NO]), and UV radiation, which can interact and have substantial effects on living organisms. In recent decades, cold plasma has been extensively studied and is widely applied in various fields, from skin cancer treatment [1], wound healing [2], surface and solution disinfection and decontamination [3], to sustainable agriculture [4, 5]. In the latter application, cold plasma can be used to induce progressive changes in developmental and physiological processes in seeds, including improving seed resistance to stress and diseases [6], modifying and increasing the permeability of seed coats [7], reducing microbial population [8], and stimulating seed germination and seedling growth [9, 10].  
Mung bean (_Vigna radiata_) is a common economical crop in Southeast Asia. Diseases and abiotic stresses can lead to a considerable loss in nutritional quality and economic yield of mung beans, and are traditionally addressed through genetic engineering and the use of growth-inducing chemicals, such as antibiotics [11]. However, not only can these chemicals be a danger to both humans and the environment, but excessive antibiotic treatments can also induce the development of antibiotic resistance, which makes them less effective. Therefore, a replacement of these chemicals with alternative treatments is beneficial.  
Both the dormancy and germination of seeds are regulated by the balance of two endogenous natural plant hormones: abscisic acid (ABA) and gibberellic acid (GA\({}_{3}\)) [12]. ABA (C\({}_{15}\)H\({}_{20}\)O\({}_{4}\)) is known as the plant hormone responsible for the establishment of seed dormancy and prohibits germination, while higher levels of GA\({}_{3}\) (C\({}_{19}\)H\({}_{22}\)O\({}_{6}\)) are required to promote the release from dormancy, plant cell growth, and stem elongation. The activity of these hormones counteracts each other, and can depend on the concentration of reactive species such as hydrogen peroxide, nitrates, and nitric oxide [13]. However, their mechanisms are still far from being fully understood. Among reactive species generated by cold atmospheric-pressure gas-phase plasma, nitric oxide (NO) has been proven to induce the rapid decrease of ABA and promote GA\({}_{3}\) biosynthesis via competitive pathways, which in turn leads to breaking seed dormancy [14; 15]. Recently, NO from cold plasma has been proposed to be able to regulate GA\({}_{3}\) in treated seeds [10; 16], resulting in enhanced seed germination.  
Although enhancing seed germination by cold plasma has been investigated in various plant species with different plasma configurations (dielectric barrier discharge--DBD, gliding arc, plasma jet) and a wide range of treatment protocols [10; 17], the optimal parameters for enhancement effect have not been well established. Moreover, there is a lack of study on the phytochemistry pathway of how cold plasma treatment can enhance seed germination and growth of mung beans (_Vigna radiata_).  
This work studied the effect of plasma duration and different reactive species ratios (RNS/ROS) of cold plasma treatment on both physical and endogenous hormone changes in enhancing seed germination and radiate growth of mung beans. While the physical changes on the seed's surface are dose-dependent, there are optimal \"windows\" for plasma energy dosage, and the NO concentration in the plasma induces the highest amount of up-regulated gibberellic acid, leading to better growth in the treated seeds. We believe that our findings can serve as a guide for plasma energy dosage, as well as the crucial NO concentration, to achieve the optimal effect of enhancing seed germination and plant growth, regarding any cold plasma setup.