Abstract: The phytotoxicical effects of gold nanoparticles on Phaseolus radiatus and the underlying physiological mechanism were examined in a seed germination and seedling cultivation experiment. The results showed that gold nanoparticles inhibited seed germination and seedling growth of P. radiatus. Seed germination characteristics (including seed germination potential, germination rate, germination index, and vigor index) and seedling growth indices (including seedling height, root length, and fresh weight) significantly decreased with the increasing concentration of gold nanoparticles. The decrease in root length and root fresh weight was more significant than that in seedling height and shoot fresh weight. An increased mortality rate of seedlings was associated with an elevated concentration of gold nanoparticles. The physiological characteristics of P. radiatusseedlings were significantly affected by gold nanoparticles. With the increasing concentration of gold nanoparticles, chlorophyll and nitrogen contents in leaves decreased, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in both shoot and root increased first and then decreased, and malondialdehyde (MDA) contents increased. The activities of those three anti-oxygen enzymes in shoot were higher than those in root, while the MDA content in shoot was lower than that in root. In conclusion, the phytotoxicity of gold nanoparticles was stronger in root tissues than in shoot issues, and this effect was concentration-dependent. Decreased chlorophyll and nitrogen contents in leaves and altered oxidative stress levels contributed to the morphological changes of seedlings. Our findings provide an important insight for the safe application and potential ecological risk assessment of gold nanoparticles.  

Key words: melon, hypoxia stress, γ-aminobutyric acid, GABA metabolism, amino acid.