There are two ways of GABA synthesis and transformation in plants: one is that glutamate decarboxylase (GAD) catalyzes the decarboxylation of glutamate, which is called shunt; The other is the transformation of polyamine degradation products to form it, which is called polyamine degradation pathway.
In higher plants, its metabolism is mainly completed by three enzymes. Firstly, under the action of GAD, L-glutamic acid (Glu) in α- An irreversible decarboxylation reaction takes place at the position to produce it, and then it reacts with pyruvate and pyruvate under the catalysis of its transaminase α- Ketoglutarate reacts to produce succinic semialdehyde. Finally, succinic semialdehyde dehydrogenase (SSADH) catalyzes the oxidative dehydrogenation of succinic semialdehyde to form succinic acid and finally enters the Krebs cycle. This metabolic pathway constitutes a branch of the TCA cycle called its branch.
In plants, GAD in the cytoplasm and SSADH in mitochondria jointly regulate its pathway metabolism, in which GAD is the rate-limiting enzyme for its synthesis. Plant GAD contains a calmodulin (CAM) binding region. GAD activity is not only regulated by the concentration of Ca2 + and H + but is also affected by the concentration of GAD coenzyme pyridoxal phosphate (PLP) and substrate glutamate. This dual regulatory mechanism links the cellular accumulation of which with the nature and severity of environmental stress. Cold shock, heat shock, osmotic pressure, and mechanical injury can increase the concentration of Ca2 + in cell fluid. Ca2 + combines with cam to form Ca2 + / CAM complex, which can stimulate GAD gene expression and improve GAD activity under normal physiological pH conditions; The appearance produced by acidic pH is due to stress-reducing the pH of the pH cells and slowing down the damage of cells by acidity. branch in plants is considered the main pathway of its synthesis. Most studies focus on improving GAD activity and achieving it enrichment.
Polyamine (polyamine), putrescine (polyamine), and putrescine (polyamine), including putrescine (polyamine) and putrescine (polyamine). The polyamine degradation pathway refers to the process in which diamine or polyamine (PAS) is catalyzed by diamine oxidase (DAO) and polyamine oxidase (PAO) to produce 4-aminobutyric and then dehydrogenated by 4-aminobutyric dehydrogenase (made) to produce it. The polyamine degradation pathway finally intersects with the branch and participates in TCA cycle metabolism. Diamine oxidase and polyamine oxidase are the key enzymes that catalyze the degradation of put, SPD, and SPM in organisms, respectively. During the germination of Vicia faba, anaerobic stress can induce the increase of the critical enzyme activity of polyamine synthesis and promote the accumulation of polyamine. At the same time, the movement of polyamine oxidase also increases. The polyamine degradation pathway promotes the synthesis and assembly of it and improves the stress resistance of Vicia faba. The results showed that the content of free polyamines in soybean roots increased under salt stress, the activity of Dao increased, and the enrichment increased 11 ~ 17 times. Although the polyamine degradation pathway is considered another critical pathway for synthesis, its ability to synthesize in monocotyledonous plants is much lower than that of the branch.
Spraying (200 mg / L) during wheat flowering can adjust membrane stability, increase antioxidant capacity and reduce the loss of wheat under high temperature; The application of exogenous also had a noticeable effect on the growth of cucumber seedlings. Hyperthermia can inhibit the activity of central neurons, activate the cholinergic nervous system, and increase body temperature. Under high temperatures for a long time, the movement of neurons in the hypothalamus will increase to adapt to the environment and regulate body temperature. it will increase plasma and inhibit the catecholamine concentration in cold-sensitive nucleus plasma to reduce esophageal temperature.
Low temperature will reduce the biosynthetic ability of plants, interfere with essential functions and cause permanent damage. Animals can also cause injury or even more severe damage at low temperatures. The expression of biological which is upregulated under low temperature, related to the tolerance to low temperature. At low temperature, 75% of metabolites will increase, including amino acids, sugars, ascorbate, putrescine, and some tricarboxylic acid cycle intermediates. The amino acid metabolism involved in energy metabolism and the transcriptional abundance of enzymes will increase. It can produce ATP and accumulate GHB by enhancing the shunt pathway. In addition, the use of melatonin at low temperatures can accumulate spermine, spermidine, and proline and promote the expression of diamine oxidase. it is synthesized through the putrescine pathway, making H2O2 accumulation and phenylpropane pathway flux decrease to achieve anti-corrosion and cold resistance.
it has long been related to various stress and defence systems in plants.it increases with the stimulation of plants. It is considered an effective mechanism in plants responding to external changes, internal stimuli, and ionic environments, such as pH, temperature, and external natural enemy stimuli. it can also regulate the internal environment of plants, such as antioxidation, ripening, and keeping plants fresh. it has also been found in plants as a signal molecule to transmit expanded information in recent years. it has been found in soybean, Arabidopsis, jasmine, strawberry, and other plants. Low concentrations of it have
it also responds to external acidification: it increases rapidly in cells at low pH, and this accumulation also exists in microorganisms and animals. Under acidic pH, intracellular H + grown, and intracellular content increased. The synthesis consumes H +, which alleviates intracellular acidification. This rapid reaction mechanism also exists in microorganisms. While producing it, it will increase the expression of the proton respiratory chain complex and promote ATP synthesis. It also upregulates the activity of F1F0-ATP hydrolase and facilitates the ATP-dependent H + excretion process under acidic conditions. In animals, cells also excrete glutamate to change the pH of the extracellular environment. More importantly, it is zwitterionic in the physiological environment, playing a specific role in acid-base regulation. GABA is conducive to plant growth and development, and it will play the opposite role at high concentrations.