Role of nitrogen metabolites on the regulation of nitrate uptake in maize seedlings

The ability of individual amino acids to regulate nitrate uptake was studied in Zea mays L. seedlings. The amino acids were applied to the root media or supplied by immersion of the tip-cut leaves before the induction of inducible high-affinity transport system with 0.1 mM KNO3. NO3- uptake was measured by its depletion in amino acid – free medium. Glutamine and glutamate applicated via roots, were found to be the most effective inhibitors of uptake processes. The treatment with Gln via leaves also resulted in a strong inhibition of nitrate uptake rate accompanied with the significant enrichment of root tissue by amino compounds. Exclusion of conversion of glutamine to glutamic acid and to other amino acids by aminooxalacetic acid has showed, that with high probability the glutamine is responsible for the observed nitrate uptake inhibition. Since the lag-phase in inhibitory effect of glutamine was shorter than 2 hours, we suppose the direct inhibition of glutamine on the nitrate carrier itself, rather than on the corresponding gene expression

Modulation of phenolic metabolism under stress conditions in a Lotus japonicus mutant lacking plastidic glutamine synthetase

This paper was aimed to investigate the possible implications of the lack of plastidic glutamine synthetase (GS2) in phenolic metabolism during stress responses in the model legume Lotus japonicus. Important changes in the transcriptome were detected in a GS2 mutant called Ljgln2-2, compared to the wild type, in response to two separate stress conditions, such as drought or the result of the impairment of the photorespiratory cycle. Detailed transcriptomic analysis showed that the biosynthesis of phenolic compounds was affected in the mutant plants in these two different types of stress situations. For this reason, the genes and metabolites related to this metabolic route were further investigated using a combined approach of gene expression analysis and metabolite profiling. A high induction of the expression of several genes for the biosynthesis of different branches of the phenolic biosynthetic pathway was detected by qRT-PCR. The extent of induction was always higher in Ljgln2-2, probably reflecting the higher stress levels present in this genotype. This was paralleled by accumulation of several kaempferol and quercetine glycosides, some of them described for the first time in L. japonicus, and of high levels of the isoflavonoid vestitol. The results obtained indicate that the absence of GS2 affects different aspects of phenolic metabolism in L. japonicus plants in response to stress.España FEDER-Ministerio de Economía y Competitividad AGL2014-54413-REspaña Junta de Andalucía,Consejería de Economía, Innovación y Ciencia, P1O-CVI-6368España Junta de Andalucía,Consejería de Economía, Innovación y Ciencia, BIO-16

Biosynthesis and role of isoflavonoids in legumes under different environmental conditions

Isoflavonoids represent an important group of phenolic compounds in legumes that have significant health benefits for humans. In plants, they play crucial roles in adaptation to the biological environment both as defensive compounds and signaling molecules in symbiotic nitrogen fixation and rhizobia. Moreover, increasing evidence is available about the accumulation of isoflavonoids upon abiotic stress. The present review focuses on the induction of isoflavonoid biosynthesis under different types of abiotic stress factors. Isoflavonoids are likely involved in antioxidant defence, UV-radiation absorbence and metal chelation. Emphasis is put on their possible functions and cross-reactions between biotic and abiotic stress responses. The variety of functions of isoflavonoids predestines them for use in improving the defence capacity of legume species in changing climatic conditions