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2012 - 20162
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Subject: Biochemistry × Author: Gurpreet Kaur × End date: 2018 × Start date: 2012 × Thesis Type: Ph.D ×
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    BIOCHEMICAL CHARACTERIZATION OF WHEAT GENOTYPES WITH RESPECT TO NITROGEN USE EFFICIECNY
    (PAU Ludhiana, 2012) Gurpreet Kaur; Bavita, Asthir
    Increased use of nitrogen (N) fertilizer has raised concerns because N surplus causes environmental contamination and also high cost associated with its production. Thus, improving nitrogen use efficiency (NUE) through identification of efficient genotypes is becoming a necessity. In this two years study (2009-10 and 2010-11), 18 wheat genotypes (PBW 621, PBW 636, PBW 590, DBW 17, HD 2967, PBW 509, BW 9178, BW 9183, BW 8989, BW 9022, PBW 343, PBW 550, GLU 1101, GLU 1356, GLU 2001, GLU 700, PH132-4836, PH132-4840) selected on the basis of their commercial relevance or distinct genetic background were used for studying N metabolism at four N doses including the presently recommended N dose (RDN) (120 Kg N/ha), suboptimal N doses [RDN-50% (60 Kg N/ha) and RDN-25% (90 Kg N/ha)] and supraoptimal N dose [RDN+25% (150 Kg N/ha)]. Enzymes involved in N assimilation [nitrate reductase (NR), nitrite reductase (NIR), glutamine synthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH)] in relation to deposition of amino acids and proteins were studied at tillering (30 days after sowing; DAS), anthesis (about 90-100 DAS) and post-anthesis (15 days post anthesis) stages. PBW 621 showed higher activities of NR, NIR and GS at RDN-25%. At RDN-50%, PBW 636 and GLU 1356 showed highest GS activity. HD 2967 and PBW 590 revealed maximum activities of these enzymes at RDN and RDN+25%. Widely grown cultivar PBW 343 and advanced breeding lines BW 9178, BW 9183, BW 8989 and BW 9022 showed low efficiency for N assimilating enzymes. GLU 1356 showed high grain protein content indicating higher translocation of assimilates from flag leaf to sink. Sugar and starch content was higher in the PBW 343, BW 9178, BW 8989 and BW 9022 genotypes in which amino acid and protein content was less. PBW 621 showed higher NUE and yield compared to other genotypes. NR and GS enzymes were positively correlated with NUE and yield indicating that these might be the rate limiting steps in N metabolism. Biochemical similarity between PBW 621, PBW 636 and GLU 1356 was authenticated from cluster analysis. Tiller culture technique did not reveal much difference with respect to PBW 621 and PBW 343 in N metabolism. However, hydroponically raised seedlings showed complementary results with field studies in identifying genotypes with maximum NUE. Due to stable performance of PBW 621, PBW 636 and GLU 356 at suboptimal doses over two years, these genotypes hold future potential for developing new cultivars with improved NUE.
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    Genotypic variation for water and salt stress induced proline dynamics in wheat
    (Punjab Agricultural University, Ludhiana, 2016) Gurpreet Kaur; Asthir, Bavita
    The present study was conducted to evaluate the proline metabolism and its cross talk with various biochemical parameters in nineteen wheat genotypes viz. C 306, C 273, C 591, C 518, Type 11, Excalibar, Krichauff, Babax, Gladius, Drysdale, Kharchia, Krl 1-4, Krl 19, PBW 175, HD 2967, PBW 621, WH 1105, HD 3086 and PBW 660 raised under water deficit (8% PEG – 6000), water withholding and salt stress (300 mM NaCl) conditions. Enzymes involved in proline synthesis [glutamate dehydrogenase (GDH), pyrroline-5-carboxylate synthetase (P5CS) and δ-pyrroline-5-carboxylate reductase (P5CR)] and degradation [proline dehydrogenase (PDH)] were studied in the roots and shoots of seven day old seedlings. Based on various biochemical parameters, these genotypes were categorized into four groups i.e tolerant towards water stress (Excalibar, Krichauff, Babax, Drysdale, Gladius and C 306), tolerant towards salinity stress (Kharchia, Type 11, Krl 1-4 and Krl 19), intermediate tolerant (C 273, C 518 and C 591) and susceptible towards water and salinity stress (HD 2967, PBW 621, WH 1105, HD 3086, PBW 660 and PBW 175). Genotypes tolerant to water and salt stress revealed increased proline content and 1,1 diphenyl-picryl hydrazyl radical scavenging activity alongwith reduced content of thiobarbituric acid reactive species in parallel with decreased H2O2 content. Correspondingly, higher activities of GDH, P5CS and P5CR were also observed in these genotypes. However, the declining trend of PDH activity and low contents of TBARS and H2O2 were recorded in all studied genotypes except for HD 2967, PBW 621, HD 3086, PBW 175 and WH 1105. Results were further strengthened by studying the effect of ABA and its cross talk with various parameters under different stresses in selected five genotypes viz. Gladius, Drysdale, Kharchia, PBW 660 and PBW 175. Exogenous ABA application triggered the upregulation of proline synthesis in tolerant genotypes (Kharchia, Gladius and Drysdale) which indicated a predominant role of this osmolyte in maintaining root/shoot elongation and thereby, ameliorating the deleterious effect of ROS on membrane stability both under water and salt stress conditions. Overall, results indicated that increased proline content might have contributed in upregulating proline synthesizing enzymes and thereby overcoming oxidative stress more in tolerant genotypes than susceptible ones. In crux, results indicated that GDH activity was particularly responsible in proline synthesis pathway via enhancing P5CS activity and would trigger abiotic stress tolerance. Proline metabolizing enzymes particularly P5CS and GDH could be used as a marker for enhancing tolerance to these stresses by breeders and plant biotechnologists.