Renu PandeyPRIYA PAUL2019-02-122019-02-122018http://krishikosh.egranth.ac.in/handle/1/5810094645t-9933To dissect the mechanism governing dual-nutrient (nitrogen and phosphorous) stress tolerance in already identified contrasting wheat (Triticum aestivum) genotypes (Mishra, 2017), a study was planned interlinking nutrient stress and recovery with hormonal (ABA and ethylene) regulation. Under abiotic stress, ABA and ethylene are the two well-studied phytohormone and nitric oxide (NO) is the signalling molecule in plants acting upstream of ethylene. Physiological and biochemical analysis of various traits involved in N and P metabolism and remobilization were carried out in 21 days old seedlings. Plants were subjected to low nutrient stress (P -5 μM, N- 10 μM and dualnutrient) and restoration treatment in combination with exogenous supply of ABA (0.5 μM), ACC (1 μM), SNP (2.5 μM), and Fluridon (0.001 μM). Results revealed that the dual-nutrient stress tolerant genotype, HD-2781 showed most desirable growth parameters, root morphology, P uptake and activity of enzymes involved in N assimilation and P remobilization from root cell wall pectin under different nutrient treatments in combination with ABA. Addition of ABA caused reduction in uronic acid content in pectin. In HD-2781, the uronic acid content in pectin, which is responsible for remobilizing root cell wall P, was higher under both low P and low NP and dualnutrient recovery. Production of ethylene in roots under low P was significantly higher in HD-2781 but under dual-nutrient stress, it was similar in both genotypes. It was observed that production of ethylene was independent of endogenous ABA synthesis. Further, production of NO was also found to be independent of ABA in HD-2781 but similar effect was not seen inC-306. Endogenous root ABA content was higher in C306 as compared to HD-2781. The ABA content in root was independent of ethylene and NO in HD-2781 while in C-306, it was indirectly influenced after addition of ethylene precursor. The genes involved in P uptake, translocation (PT2, PT8) and N uptake (NRT1.1) showed upregulation in HD-2781 under dual-nutrient stress. Under low P, the expression level of TaACS2 and TaACO was higher in HD-2781. In both genotypes, the expression level of TaACS2, TaACO and TaNOS were not significantly influenced by adding ABA to control or nutrient starved plants. Considering all the above-mentioned traits, HD-2781 exhibited superior mechanism in terms of nutrient uptake and remobilization under nutrient stress and inhibitory effect of ABA and this pathway was found to be independent of ethylene and NO. Further study involving other hormones and their effect on N and P uptake and remobilization can provide better understanding of hormonal cross-talk and nutrient deficiency. Above all, HD-2781 can be used as a donor in breeding programme to develop varieties tolerant to dual-nutrient stress. Keywords : ABA, Ethylene, NO, Uronic acid, P uptake and remobilization, N uptakeen-USnullThesis