Mechanisms regulating effects of pre-harvest stress on rocket salad post-harvest quality

Alotaibi, Lama 2024. Mechanisms regulating effects of pre-harvest stress on rocket salad post-harvest quality. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Wild rocket (Diplotaxis tenuifolia) (Dt) is valued for its distinctive peppery taste and content of beneficial compounds such as glucosinolates. The UK growth environment subjects horticultural crops to a wide range of stresses, including periods of cold, heat and flooding. These are likely to be exacerbated as climate change makes weather patterns less predictable. These stresses will affect the growth and development of the plants, as well as their post-harvest performance. Wild rocket was grown at an optimal temperature for 30 days (the samples were collected on day 30, and the stress was applied before that, depending on the length of the stress period. For example, if the stress was three days of heat, the plants were subjected to the heat on days 28, 29 and 30, and the samples were collected immediately at the end of this period) and then subjected to short periods of cold (2 nights or 3 days), heat (1 or 3 days), or flooding (2 days). The samples were collected, and the profile of volatile organic compounds (VOCs) was assessed at harvest (day zero) and after a 7-day storage period (day seven) at 6 ◦C ±0.5oC to simulate the salad supply chain. Post-harvest storage significantly affected VOC profiles from leaves of both stressed and control plants. At harvest, the differences in VOC profiles were not as significant as after storage; however, the 3-day heat stress experiment showed a better separation in VOC profiles of the two treatments (stressed and non-stressed) compared to the other experiments according to random forest analysis. Expression of stress-induced NAC transcription factors and Dt epigenetics-related genes was differentially affected by storage and pre-harvest stresses. The experiment of pre-harvest heat stress (3 days) was further investigated to understand better its impact on VOC emission, metabolism, and transcriptome both at harvest and after storage. The experiment was repeated to examine the effects of earlier exposure to the stress, different sampling methods for day seven (cumulative VOCs rather than snapshots) on VOC profiles, and to track changes in VOC profiles within the storage period (adding sampling points day 2 and 5). Earlier exposure to heat stress still influences the post-harvest VOC profiles, and snapshot sampling was more effective in detecting differences in VOC profiles after storage than the cumulative VOCs. The impact of heat on VOC profiles was observed at all storage time points. The metabolomics analysis result was consistent with the outcomes of VOC profiles and showed a significant increase in proline and serine after storage in the heat-stressed leaves. Higher numbers of DEGs and transcriptional factors on day seven indicate that rocket leaves were more stressed by the later imposed stress by storage. The heat stress significantly enriched the circadian apparatus at harvest and the flavonoid biosynthesis pathway after storage. This work sheds light on stress mechanisms at harvest and after storage, revealing potential targets for improving the post-harvest quality of wild rocket leaves.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	27 August 2024
Last Modified:	30 Aug 2024 15:17
URI:	https://orca.cardiff.ac.uk/id/eprint/171586

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