Test for l-glutamate inhibition of growth of Alternaria alternata by inducing resistance in tomato fruit

- This is the first report that glutamate could suppress the alternaria rot in tomato fruit.
- The defence mechanism of glutamate may be related to the activation of energy-generated metabolism.
- The SA signalling pathway might be involved in glutamate-induced disease resistance.

Although numerous studies have reported the involvement of glutamate in plant abiotic stress, relatively little is known about the role of glutamate in plant defence against pathogens. To gain further knowledge, we investigated the effect of glutamate on Alternaria alternata in tomato fruit. A multidisciplinary approach was pursued, combining exogenous glutamate applications, enzymatic activity measurements and real-time quantitative PCR analysis. The results showed glutamate significantly reduced the disease incidence in tomato caused by A. alternata, by inducing resistance (Duncan's test, p < 0.05). A large variety of defence-related enzymes and genes involved in the glutamine synthetase/glutamate synthase cycle, energy-generated metabolism, such as the γ-aminobutyric acid shunt, glycolysis and the tricarboxylic acid cycle, and the salicylic acid signalling pathway were activated by glutamate. The activation of these pathways as mentioned above might play a potential role in the resistance mechanisms underpinning glutamate-induced plant immunity.