γ-Aminobutyric acid (GABA) is an important neurotransmitter in mammals whose receptor is reported to be regulated by flavonoids. In plants, it is considered to be at the intersection of carbon and nitrogen metabolism, but its relationship with flavonoid metabolism remains unclear. Our recent RNA-seq analysis showed that expression of flavonoid biosynthetic genes was influenced in poplar by the blockage of α-ketoglutarate dehydrogenase (α-KGDH) activity and the application of GABA under NaCl stress, accompanied by the changes in GABA shunt activity. Here, we further found that the flavonoid accumulation was significantly affected by blocking the activities of α-KGDH and GABA transaminase as well as applying exogenous GABA, coupled with the changes of endogenous GABA contents. Key genes involved in the flavonoid biosynthetic pathway were also significantly influenced, including two PALs, 4CL, and two CHSs. Our results suggest that the GABA shunt is closely associated with the metabolism of flavonoids, which would benefit future understanding of GABA's roles in carbon allocation by regulating the pathway of flavonoid biosynthesis under normal or stress conditions.
Seedling-rot is a term applied to all troubles causing death of rice seedlings, involving both non-parasitic and parasitic diseases.The kind of seedling-rot which causes the most damage in the early crop of non-glutinous rice in Northern Kiangsu,where seedling-rot is often serious,is due primarily to physiologic disorders,but it can often be complicated with Saprolegniaceous molds infections. Such disease usually occurs at times with a cold spell accompanied by a period of cloudy or rainy weather.Young seedlings already weakened by unfavorable growth conditions succumb.The use of immature or improperly stored seeds, exposed site or carelessly prepared seed-bed,the use of unfermented green ma- nure,an overgrowth of filamentous algae in the seed bed,too high a temperature during the soaking and sprouting of rice seeds—all these are contributory to the weakening of the seedlings.However,the chief cause seems to be the suffocation of the seedlings which sink into the suspended mud,or are lying free and flat under a deep layer of irrigation water without rooting.Prolonged submergence induces seedling-rot even under a less unfavorable weather condition.This relationship of seedling-rot to suffocation is substantiated by the ready occurrence of the rot in seedlings subjected to conditions leading to poor aeration and by the fact that seedlings exposed to air or submerged under water containing a small amount of hydrogen peroxide (0.03%) are considerably more resistant to low temperatures than those submerged under water,when they are kept at 4-7℃ in a refrigerator. Seedlings weakened by low temperature or partial suffocation may readily be attacked by water molds such as Achlya or other Saprolegniaceous fungi which are but weakly parasitic,killing them while they may otherwise recover when the unfavorable factor is removed. Covering the sprouted rice seeds,after sowing,with charred rice chaff,and controlling the irrigation water to an amount just enough to keep the bed moist, is a measure recommended to combat seedling-rot.The charred chaff keeps the sprout moist but does not prevent aeration which is essential to the well-being of the seedlings.It also keeps away mud and fixes the seeds to a position to faci- litate rooting.Pot test showed that seedlings thus raised have a higher percentage of emergence,though shorter in height than those submerged under the water, and that they are deeper green in color,with a larger number of roots,a higher green weight,and what is more,they offer a greater resistance to low temperatures.How- ever,when a cold wave is forecasted,the field should be temporarily flooded to protect the seedlings,and it will be especially helpful if warmer water from a river or canal is employed.
Nitrogen (N) deficiency adversely affects tree growth. Additionally, γ-aminobutyric acid (GABA) is closely associated with growth and stress responses because of its effects on carbon (C) and N metabolism. However, little is known about its roles related to plant adaptations to N-deficient conditions. In this study, we analyzed the effects of GABA (0, 2 and 10 mM) applications on the growth traits and physiological responses of poplar (Populus alba × P. glandulosa '84K') seedlings under high N (HN) and low N (LN) conditions. We found that the added GABA interacted with N to affect more than half of the studied parameters, with greater effects in LN plants than in HN plants. Under LN conditions, the GABA application tended to increase poplar growth, accompanied by increased xylem fiber cell length and xylem width. In stems, exogenous GABA increased the abundance of non-structural carbohydrates (starch and sugars) and tricarboxylic acid cycle intermediates (succinate, malate and citrate), but had the opposite effect on the structural C contents (hemicellulose and lignin). Meanwhile, exogenous GABA increased the total soluble protein contents in leaves and stems, accompanied by significant increases in nitrate reductase, nitrite reductase and glutamine synthetase activities in leaves, but significant decreases in those (except for the increased glutamate synthetase activity) in stems. A multiple factorial analysis indicated that the nitrate assimilation pathway substantially influences poplar survival and growth in the presence of GABA under LN conditions. Interestingly, GABA applications also considerably attenuated the LN-induced increase in the activities of leaf antioxidant enzymes, including peroxidase and catalase, implying that GABA may regulate the relative allocation of C and N for growth activities by decreasing the energy cost associated with stress defense. Our results suggest that GABA enhances poplar growth and adaptation by regulating the C and N metabolic flux under N-deficient conditions.
Peach fruit was treated with 5 mM γ-aminobutyric acid (GABA) to further investigate the mechanism by which GABA induced chilling tolerance. Here, we found that GABA not only inhibited the occurrence of chilling injury in peach fruit during cold storage but also maintained fruit quality. Most of the ascorbic acid (AsA) and glutathione (GSH) biosynthetic genes were up-regulated by GABA treatment, and their levels were increased accordingly, thus reducing chilling damage in treated peaches. Meanwhile, the increased transcript of genes in the AsA-GSH cycle by GABA treatment was also related to the induced tolerance against chilling. GABA treatment also increased the expression levels of several candidate ERF transcription factors involved in AsA and GSH biosynthesis. In conclusion, our study found that GABA reduced chilling injury in peach fruit during cold storage due to the higher AsA and GSH contents by positively regulating their modifying genes and candidate transcription factors.
Understanding the migration and transformation of nitrogen during biomass pyrolysis and the influence of cellulose components on the nitrogen-containing components of biomass is important for the clean and efficient utilization of biomass. In this study, we performed pyrolysis-photoionization time-of-flight mass spectrometry (Py-PI-TOF-MS), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and closed U-tube pyrolysis to analyze phenylalanine, glutamic acid, and their mixtures, the product composition of the primary and secondary reactions of amino acids, and the effect of glucose on the pyrolysis products of the two amino acids. The experimental results were combined with density functional theory calculations to reveal the pyrolysis path of the two amino acids and the mechanism of the effect of glucose on amino acid pyrolysis. The results revealed that phenylalanine undergoes deamination and decarboxylation reactions during pyrolysis. The hydrogen on the carboxyl group is transferred during this process to release CO 2 and generate phenethylamine. Phenylalanine generates a large amount of N-phenethylpropane-2-imine through a secondary reaction. Glucose may play a role in the hydrogen supply and promote the deamination of phenylethylamine to produce styrene. The primary reaction product of glutamic acid is a nitrogen-containing heterocyclic ring. The pyrolysis product, L-pyroglutamic acid, generates 2-pyrrolidone through a decarboxylation reaction. Glucose can reduce the reaction energy barrier for the formation of 2-pyrrolidone.
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