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Title: The improvement of chilling tolerance in chilling sensitive basil (Ocimum basilicum var Marian)
Author: Begum, Firdous
ISNI:       0000 0004 8499 972X
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2017
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Basil is the most popular culinary herb in the UK but sensitive to chilling temperatures. Chilled basil leaves wilt and become discoloured, thus, become unappealing to consumers. Therefore, herbs are rarely maintained as part of the 'cool-chain', and this can increase the risk of microbial contamination. The aim of the project was to modify the growing conditions of basil to improve its tolerance towards chilling temperatures. Basil's sensitivity towards chilling temperatures was assessed by quantifying cell damage in several ways. Damage to membranes (membrane leakage), photosystems (chlorophyll fluorescence) and a decline in antioxidant content was 33%, 50%, and 33%, respectively after exposure of 24 h at 4oC. Basil also showed an increased lipid peroxidation (66%) and accumulation of reactive oxygen species (ROS) (85%). 3000 transcripts from the RNA sequencing experiment of basil treated with or without chilling temperature were analysed. 1206 (40.2%) of the genes were differentially regulated among which 138 (11.44%) were upregulated and 1062 (88%) downregulated in response to cold. Genes involved in metabolite and ion transport and those involved in primary metabolism (lipid, carbohydrate and ascorbate-glutathione system) were downregulated and were associated with either the chloroplast or the plasma membrane. Suppression of important metabolic pathways and defense against the generation of toxic ROS to the cell is considered a possible mechanism in basil's susceptibility towards chilling temperatures. Light is required for the activation of cold regulated genes (COR) and the phytochromes are known to be involved in a plant's response to chilling temperatures. In this project, basil was treated with low R:FR light on four consecutive days and then exposed to 24 h of chilling stress that resulted in basil showing reduced damage to membranes, accumulation of ROS and damage to the light absorbing photosynthetic apparatus. LR:FR light treated plants also induced expression of genes coding for phyA, abscisic ABA signalling and jasmonate JA signalling or involved in scavenging of ROS that may promote basil cells survival under chilling stress.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Ocimum basilicum ; Chilling temperature ; RNA sequencing ; Electrolyte leakage ; ROS accumulation ; cell membrane damage ; Antioxidants ; Low red to far red light ; High red to far red light ; Chilling sensitivity ; Chilling tolerance