Nitrate Starvation Induced Changes in Root System Architecture, Carbon:Nitrogen Metabolism, and miRNA Expression in Nitrogen-Responsive Wheat Genotypes.

Improvement of nutrient use efficiency in cereal crops is highly essential not only to reduce the cost of cultivation but also to save the environmental pollution, reduce energy consumption for production of these chemical fertilizers, improve soil health, and ultimately help in mitigating climate change. In the present investigation, we have studied the morphological (with special emphasis on root system architecture) and biochemical responses (in terms of assay of the key enzymes involved in N assimilation) of two N-responsive wheat genotypes, at the seedling stage, under nitrate-optimum and nitrate-starved conditions grown in hydroponics. Expression profile of a few known wheat micro RNAs (miRNAs) was also studied in the root tissue. Total root size, primary root length, and first- and second-order lateral root numbers responded significantly under nitrate-starved condition. Morphological parameters in terms of root and shoot length and fresh and dry weight of roots and shoots have also been observed to be significant between N-optimum and N-starved condition for each genotypes. Nitrate reductase (NR), glutamine synthatase (GS), and glutamate dehydrogenase (GDH) activity significantly decreased under N-starved condition. Glutamine oxoglutarate amino transferase (GOGAT) and pyruvate kinase (PK) activity was found to be genotype dependent. Most of the selected miRNAs were expressed in root tissues, and some of them showed their differential N-responsive expression. Our studies indicate that one of the N-responsive genotype (NP-890) did not get affected significantly under nitrogen starvation at seedling stage.