Heat stress has been proved to increase the content of melatonin in plants. In the present study, a combination of methods including physiological and biochemical, gene transcription and proteomic were used to investigate the melatonin accumulation mechanisms in mustard sprouts under heat treatment during the germination period. It was revealed that the heat treatment can significantly affect sprout growth, antioxidant enzyme activity and melatonin content in mustard sprouts. Meanwhile, the expression of melatonin key synthase genes, such as tryptophan decarboxylase genes (BjTDC 1, BjTDC 2) and serotonin N-acetyltransferase genes (BjSNAT 1), were significantly induced by heat stress, which coincided with the trend of melatonin content. Under the heat stress, a total of 172 differential abundance proteins were confidently identified in mustard sprouts and participated in many physiological processes. Functional classification analysis showed that the defense/pressure, energy and nucleotide metabolism, protein biosynthesis, signal transduction and transcription etc. were largely induced. Heat treatment stimulated a defense response at the protein level by regulating the growth and physiological metabolism in mustard sprouts. The results in this work provided novel deep insights into the proteins' response to heat stress, which will certainly promote further understanding of the heat-tolerance mechanism of mustard sprouts.

Glutamate decarboxylase (GAD) is the key enzyme in GABA shunt, which catalyzes the α-decarboxylation of glutamate to produce GABA. A specific inhibitor for GAD is convenient to study the dynamic balances of GABA metabolism in plants. The inhibitor of GAD in germinated fava beans was screened, and its inhibitory effect on the growth and GABA accumulation in fava beans during germination under hypoxia-NaCl stress was investigated. The inhibitory effect of aminoxyacetate for fava bean GAD was better than those of other chemicals, and it increased with the increase in concentration in vivo. After aminoxyacetate (5 mM) application for 4 days during germination, the GAD activity in germinating fava beans was significantly inhibited by more than 90% in both organs. Meanwhile, the growth of fava bean sprouts was also slightly suppressed. Moreover, the GABA contents decreased by 43.9% and 81.5% in a 4 day-old cotyledon and embryo, respectively, under aminoxyacetate treatment compared with that in the control. In summary, these results showed that aminoxyacetate can serve as a specific inhibitor of GAD in plants. At least 43.9% and 81.5% of GABA in germinating fava beans under hypoxia-NaCl stress were synthesized via GABA shunt.

ITRAQ-based quantitative proteomic analysis reveals the molecular mechanisms of dark-germinated soybeans in response to salt stress.