Physio-biochemical, agronomical, and gene expression analysis reveals different responsive approach to low nitrogen in contrasting rice cultivars for nitrogen use efficiency.

BACKGROUND: Nitrogen (N) is an essential macronutrient for plant growth and development as it is an essential constituent of biomolecules. Its availability directly impacts crop yield. Increased N application in crop fields has caused environmental and health problems, and decreasing nitrogen inputs are in demand to maintain crop production sustainability. Understanding the molecular mechanism of N utilization could play a crucial role in improving the nitrogen use efficiency (NUE) of crop plants. METHODS AND RESULTS: In the present study, the effect of low N supply on plant growth, physio-biochemical, chlorophyll fluorescence attributes, yield components, and gene expression analysis were measured at six developmental stages in rice cultivars. Two rice cultivars were grown with a supply of optimium (120 kg ha-1) and low N (60 kg ha-1). Cultivar Vikramarya excelled Aditya at low N supply, and exhibits enhanced plant growth, physiological efficiency, agronomic efficiency, and improved NUE due to higher N uptake and utilization at low N treatment. Moreover, plant biomass, leaf area, and photosynthetic rate were significantly higher in cv. Vikramarya than cv. Aditya at different growth stages, under low N treatment. In addition, enzymatic activities in cultivar Vikramarya were higher than cultivar Aditya under low nitrogen, indicating its greater potential for N metabolism. Gene expression analysis was carried out for the most important nitrogen assimilatory enzymes, such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT). Expression levels of these genes at different growth stages were significantly higher in cv. Vikramarya compared to cv. Aditya at low N supply. Our findings suggest that improving NUE needs specific revision in N metabolism and physiological assimilation. CONCLUSION: Overall differences in plant growth, physiological efficiency, biochemical activities, and expression levels of N metabolism genes in N-efficient and N-inefficient rice cultivars need a specific adaptation to N metabolism. Regulatory genes may separately or in conjunction, enhance the NUE. These results provide a platform for selecting crop cultivars for nitrogen utilization efficiency at low N treatment.

An Insight into Animal Glutamate Receptors Homolog of Arabidopsis thaliana and Their Potential Applications-A Review.

Most excitatory impulses received by neurons are mediated by ionotropic glutamate receptors (iGluRs). These receptors are located at the apex and play an important role in memory, neuronal development, and synaptic plasticity. These receptors are ligand-dependent ion channels that allow a wide range of cations to pass through. Glutamate, a neurotransmitter, activates three central ionotropic receptors: N-methyl-D-aspartic acid (NMDA), -amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), and kainic acid (KA). According to the available research, excessive glutamate release causes neuronal cell death and promotes neurodegenerative disorders. Arabidopsis thaliana contains 20 glutamate receptor genes (AtGluR) comparable to the human ionotropic glutamate (iGluRs) receptor. Many studies have proved that AtGL-rec genes are involved in a number of plant growth and physiological activities, such as in the germination of seeds, roots, abiotic and biotic stress, and cell signaling, which clarify the place of these genes in plant biology. In spite of these, the iGluRs, Arabidopsis glutamate receptors (AtGluR), is associated with the ligand binding activity, which confirms the evolutionary relationship between animal and plant glutamate receptors. Along with the above activities, the impact of mammalian agonists and antagonists on Arabidopsis suggests a correlation between plant and animal glutamate receptors. In addition, these glutamate receptors (plant/animal) are being utilized for the early detection of neurogenerative diseases using the fluorescence resonance energy transfer (FRET) approach. However, a number of scientific laboratories and institutes are consistently working on glutamate receptors with different aspects. Currently, we are also focusing on Arabidopsis glutamate receptors. The current review is focused on updating knowledge on AtGluR genes, their evolution, functions, and expression, and as well as in comparison with iGluRs. Furthermore, a high throughput approach based on FRET nanosensors developed for understanding neurotransmitter signaling in animals and plants via glutamate receptors has been discussed. The updated information will aid in the future comprehension of the complex molecular dynamics of glutamate receptors and the exploration of new facts in plant/animal biology.

Low nitrogen stress regulates chlorophyll fluorescence in coordination with photosynthesis and Rubisco efficiency of rice.

Nitrogen (N) is the basis of plant growth and development and, is considered as one of the priming agents to elevate a range of stresses. Plants use solar radiations through photosynthesis, which amasses the assimilatory components of crop yield to meet the global demand for food. Nitrogen is the main regulator in the allocation of photosynthetic apparatus which changes of the photosynthesis (Pn) and quantum yield (Fv/Fm) of the plant. In the present study, dynamics of the photosynthetic establishment, N-dependent relation with chlorophyll fluorescence attributes and Rubisco efficacy was evaluated in low-N tolerant (cv. CR Dhan 311) and low-N sensitive (cv. Rasi) rice cultivars under low-N and optimum-N conditions. There was a decrease in the stored leaf N under low-N condition, resulting in the decreased Pn and Fv/Fm efficiency of the plants through depletion in the activity and content of Rubisco. The Pn and Fv/Fm followed the parallel trend of leaf N content during low-N condition along with depletion of intercellular CO2 concentration and overall conductance under low-N condition. Photosynthetic saturation curve cleared abrupt decrease of effective quantum yield in the low-N sensitive rice cultivar than the low-N tolerant rice. Also, the rapid light curve highlighted the unacclimated regulation of photochemical and non-photochemical quenching in the low-N condition. The low-N sensitive rice cultivar triumphed non-photochemical quenching, whereas the low-N tolerant rice cultivar rose gradually during the light curve. Our study suggested that the quantum yield is the key limitation for photosynthesis in low-N condition. Regulation of Rubisco, photochemical and non-photochemical quenching may help plants to grow under low-N level.