Date of Award


Degree Type


Degree Name

Master of Science (MS)



Committee Chair

Avtar K. Handa

Committee Member 1

Lori A. Hoagland

Committee Member 2

Gurmukh S Johal

Committee Member 3

Peter M. Hirst


Plants response to various abiotic stress, including chilling injury, by differentially regulating genes responsible for protection against these stresses. Polyamines (PAs); putrescine (Put), spermidine (Spd), and spermine (Spm), are ubiquitous metabolite in all organisms and have been implicated in abiotic stresses in plants. Dr. Handa laboratory has previously developed high Spd/Spm tomato fruits genotypes by expressing yeast S-adenosylmethionine decarboxylase (SAMDC). In present investigation, the role of Spd/Spm in chilling injury was evaluated by using two independent transgenic lines with high Spd/Spm (556 and 579) and isogenic parental Ohio 8245 (WT) genotypes. Fruits at onset of ripening (Breaker, BR) and fully ripe (Breaker+8 days, BR+8) from both transgenic lines and WT were subjected to chilling by storing at 5°C or 8ºC. Results showed that the 556 and 579 fruits exhibit more chilling tolerance phenotype at BR+8 stage but performed poorly at BR stage compared to WT fruit. RNA-seq analyses of transcriptome showed differential expression of a large number of genes in response to chilling treatment of high Spd/Spm fruit compared to WT fruit, which suggesting a significant effect of PAs in chilling response mechanism. PAs are implicated in regulating genes related to redox homeostasis (Thioredoxin family protein), stress signaling pathway (MAPK cascade), various cold responsive genes, protein chaperon (heat shock proteins) and cellular antioxidant system (CAT, SOD and APX). It can be postulated that, being positive charged molecules, PAs bind to DNA, RNA and transcription factors and differentially regulate expression of genes associated with chilling tolerance in ripened fruits that help acclimate fruits to sub optimal chilling temperatures