Asthir, BavitaKaur, Balraj2017-06-032017-06-032015http://krishikosh.egranth.ac.in/handle/1/5810016052The present study was conducted to evaluate the effect of application of nitrogen (N) under field conditions on six wheat genotypes (GLU 1356, HD 2967, PBW 621, PBW 636, PBW 550 and PBW 343) at three levels of N optimal N dose (120 Kg N/ha), sub-optimal N dose (90 Kg N/ha) and supra-optimal N dose (150 Kg N/ha). Enzymes involved in N metabolism (viz. nitrate reductase , glutamine synthetase, glutamate synthase, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase); and carbon metabolism [viz. sucrose synthase (synthesis), sucrose phosphate synthase, Sucrose synthase cleavage, acid invertase, neutral invertase, phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and isocitrate dehydrogenase (ICDH)] along with various metabolites were studied in roots, flag leaf and grains at different developmental stages. Results indicated that supra-optimal dose upregulated N and carbon metabolizing enzymes, whereas sub-optimal N dose indicated that aminotransferases enhanced the protein content while increased activities of invertases provide carbon skeleton for amino acid. Apparently, PEPC, ICDH and MDH resulted in assimilating ammonium ions thereby reducing its toxicity. Interestingly at sub-optimal N dose, higher activity of polyamine catabolizing enzymes results in speeding up oxidation of various polyamines to cope up with N deficiency in plant. Putrescine was found to be higher at early stage whereas spermidine and spermine were found to be higher towards mature stages of grain indicating the role of putrescine in grain filling process. Using, hydroponic culture technique in lab providing N sources viz. 4mM KNO3, NH4Cl and NH4NO3 for 12 days, the size of shoot and root system decreased significantly when plants were supplied with NH4Cl as exclusive N source. NH4Cl speed up amino acid content by elevated glutamate dehydrogenase, aminotransferases and PEPC activities and thereby decreasing NH4+ toxicity. Whereas under NH4NO3 treatment, N and carbon metabolism were elevated as compared to NH4Cl and control conditions but less than KNO3 source indicating inhibition of NH4+ toxicity by NO3- uptake. Tiller culturing technique also supported the above findings of grain filling processes, soluble sugars/starch were strongly correlated to invertase activities whereas proteins to aminotransferases. GLU 1356, HD 2967 showed highest value of nitrogen use efficiency followed by PBW 621, PBW 636, PBW 550 and PBW 343, therefore, categorized as N efficient genotypes.enenzymes, developmental stages, nitrogen, amino acids, planting, wheats, grain, genotypes, organic acid salts, acidityThesis