Degree Type


Date of Award


Degree Name

Doctor of Philosophy





First Advisor

Rajeev . Arora


This dissertation constitutes two main research projects :1) salicylic acid (SA)-induced freezing tolerance, and 2) the effect of short versus prolonged freezing on freeze-thaw injury. Both studies used spinach (Spinacia oleracea L.) as the model. Regarding the SA study, freezing tolerance and metabolome changes were investigated for spinach seedlings sub-fertigated with 0.5 mM SA. Experiments included seedlings sub-fertigated with SA at both the ambient (non-acclimation; NA) and cold acclimation (CA) temperatures, i.e. NASA and CASA, respectively. SA-fed plants exhibited, in general, similar growth performance as non-treated controls. SA application improved freezing tolerance of spinach at both warm- and cold temperatures; CASA-plants were the most freezing tolerant followed by CA-, NASA-, and NA-plants. Metabolite profiling revealed that SA-feeding differentially alters plant metabolism at warm or cold. SA-induced freezing tolerance may be due to improved tolerance to oxidative stress and freeze-desiccation, as indicated by accumulation of antioxidants, compatible solutes, and osmolytes. Additionally, SA-induced FT appears to be mediated cooperatively by NO and H2O2 signaling since removal of H2O2 or NO reduced beneficial effect of SA on freezing tolerance. This study proposed that exogenous SA application could be an important strategy to improve plant freezing tolerance. In the second study, we conducted metabolite profiling to gain metabolic insight into the differential response by spinach leaves to a short (0.5 and 3.0-h freezing) versus prolonged freezing (5.5 and 10.5-h freezing) at a sub-lethal temperature (-4.5 °C) causing a reversible versus irreversible injury, respectively. Some of the key findings from this study are that: 1) SA may induce tolerance/recovery response in leaves exposed to short-term freezing whereas trigger programmed cell death in irreversibly injured leaves following prolonged freezing, 2) GABA accumulation in freeze-thaw stressed tissues serves as a ‘pH-stat’ against cytoplasmic acidification in leaves exposed to short-term freezing, 3) chloroplast functions may be less sensitive to prolonged freezing than mitochondria, 4) increased accumulation of fatty acids and policosanols with increasing freezing duration indicates incremental injury to membrane lipids and epicuticular waxes, respectively, and 5) ascorbic acid and α–tocopherol accumulation during short-term freezing may facilitate recovery by removal of free radicals. This study provided insight into several cellular events/alterations potentially associated with reversible versus irreversible injury following a short-term or prolonged freezing, respectively, and thereby advance our fundamental understanding of plant response to freezing.

Copyright Owner

Kyungwon Min



File Format


File Size

174 pages

Included in

Agriculture Commons