Accumulating pathways of γ-aminobutyric acid during anaerobic and aerobic sequential incubations in fresh tea leaves

The roles of the γ-aminobutyric acid (GABA) shunt and polyamine (PA) degradation pathway on GABA accumulation were investigated in fresh tea leaves under anaerobic and aerobic sequential incubations. The GABA accumulation was mainly completed in the first anaerobic incubation through the interaction of the GABA shunt with the PA degradation pathway. When treated with aminoguanidine, the diamine oxidase and polyamine oxidase activities were almost completely inhibited, and the GABA contents decreased by 40.7%, 46.4%, 41.0% and 37.5% in the tea leaves of the four cultivars 'Fuyun No. 6', 'Fudingdabai', 'Longjing No. 43' and 'Pingyangtezao', respectively. The glutamate decarboxylase activity decreased significantly, and the accumulation of GABA may increase or decrease because of varietal differences, which occurred mainly relying on the PA degradation pathway during the second anaerobic incubation. Thus, approximately 37%-47% of the GABA formed in fresh tea leaves under hypoxia was supplied by the PA pathway.