Tea plant often suffers from low temperature induced damage during its growth. How to improve the cold resistance of tea plant is an urgent problem to be solved. Nitric oxide (NO), γ-aminobutyric acid (GABA) and proline have been proved that can improve the cold resistance of tea plants, and signal transfer and biosynthesis link between them may enhance their function. NO is an important gas signal material in plant growth, but our understanding of the effects of NO on the GABA shunt, proline and NO biosynthesis are limited. In this study, the tea roots were treated with a NO donor (SNAP), NO scavenger (PTIO), and NO synthase inhibitor (L-NNA). SNAP could improve activities of arginine decarboxylase, ornithine decarboxylase, glutamate decarboxylase, GABA transaminase and Δ1-pyrroline-5-carboxylate synthetase and the expression level of related genes during the treatments. The contents of putrescine and spermidine under SNAP treatment were 45.3% and 37.3% higher compared to control at 24 h, and the spermine content under PTIO treatment were 57.6% lower compare to control at 12 h. Accumulation of proline of SNAP and L-NNA treatments was 52.2% and 43.2% higher than control at 48 h, indicating other pathway of NO biosynthesis in tea roots. In addition, the NO accelerated the consumption of GABA during cold storage. These facts indicate that NO enhanced the cold tolerance of tea, which might regulate the metabolism of the GABA shunt and of proline, associated with NO biosynthesis. Tea plant is an important economic crop which is widely planted in many regions of China. Adverse environmental conditions, mainly cold stress, impose major limitations on the suitable geographical locations for tea growth and impact both in tea production and quality 1. The GABA is a non-protein amino acid, C 4 H 9 NO 2 3 , and is widely distributed in nature among prokaryotes and eukaryotes as an important free amino acid. Some special treatments of fresh tea leaves, such as charging the nitrogen and removing oxygen can result in accumulation of GABA 2. It is widely known as a neurotransmitter in the sympathetic nervous system 4,5. Moreover, previous study also revealed its function on improving cold tolerance of tea plant 6. There are several GABA metabolism pathways, including glutamate catalyzed by glutamate decarboxylase (GAD) and the reversible conversion of GABA to succinic semialdehyde by GABA transaminase (GABA-T) followed by irreversible oxidization of succinic semialdehyde. Polyamines (PAs) include spermidine (Spd), spermine (Spm) and their diamine obligate precursor putrescine (Put) 3,7 , PAs catabolism can provide raw materials for GABA synthesis which means PAs degradation pathway is an important component of the GABA biosynthesis pathway 8. The Put and Spd are catalyzed by diamine oxidase and polyamine oxidase, respectively 3. PAs are widely present in plants, and the enzymes related to their biosynthesis have strong connections with environmental stresses such as cold, heat, salt and drought stress 9,10. The expression and a...