Date of Award

Spring 2023

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Subhash Minocha

Second Advisor

Rakesh Minocha

Third Advisor

Anissa Poleatewich

Abstract

The importance of nitrogen metabolism in plants in response to abiotic stress is widely known. Plant growth is severely hampered by abiotic stress, and appropriate nitrogen supply helps in plant growth and improves stress tolerance. At the same time, the regulation of nitrogen metabolism depends on the stress intensity. Abiotic stress can occur due to natural calamities, improper use of hazardous chemicals from industries, and careless environmental dumping of these chemicals. Hence, soils contaminated with hazardous chemicals are a significant threat to the development and yield of plants. Plants are affected by various abiotic stresses, i.e., salt, drought, and heavy metal stress. In the presence of these stresses, plants respond via complex mechanisms that include morphological, physiological, biochemical, and molecular changes. Small aliphatic amines like polyamines regulate plant growth and development, including plant metabolism. Polyamines like putrescine, spermidine, and spermine regulate several critical biochemical pathways, including the biosynthesis of amino acids and plant growth regulators. Under abiotic stress, polyamines protect plants from various detrimental effects. The interplay of polyamine and nitrogen is a critical factor in plant response to abiotic stress, as it connects nitrogen metabolism, carbon fixation, and other metabolic pathways. Some of these responses are short-lived and others long-term, affecting not only the physiology but also growth and biomass. However, little information about how polyamines interact with plants to maintain normal growth in response to abiotic stress is available. So, it is essential to investigate the biochemical responses in cellular polyamines and amino acids in abiotic stress. The goal of the study was to understand the physiological and biochemical effects of salt and cadmium, and their interactions with polyamines sprayed on the leaves in Populus nigra x maximowiczii, (clone NM6) young plants. The two specific objectives of the study were: (1) to analyze the effects of two concentrations of NaCl on the physiology and biochemistry of poplar NM6 plants and potential mitigation of these effects by spray with putrescine; and (2) to analyze the effects of two concentrations of cadmium chloride on the physiology and biochemistry of poplar NM6 plants and potential mitigation of these effects by spray with spermidine. The results showed that plants had chlorosis, necrosis, slower growth because of abiotic stress. Exogenous putrescine application increased gas exchange & altered several metabolites under salt stress. The results also suggest a close relationship between amino acids, polyamines, and phytochelatins and their involvement in the cadmium detoxification mechanisms. Finally, it can be said that timely applications of exogenous spermidine via foliar spray could ameliorate the adverse effect of heavy metal stress in poplar NM6 plants. In conclusion, overall finding addressed multi-dimensional effect of the foliar spray of polyamines on poplar NM6 plants in response to abiotic stress.

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