- Title
- Effect of hydrogen sulphide on the postharvest metabolism of the green leafy vegetables, pak choy (Brassica rapa.subsp. Chinensis)
- Creator
- Al Ubeed, Hebah Muhsien
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Postharvest senescence of leafy green vegetables is characterised by leaf yellowing and changes to a range of other physio-chemical factors, which together, limit market life. The plant hormone ethylene is traditionally associated with accelerating senescence in postharvest produce and its effects have been closely studied. In recent years, a range of other gases including hydrogen sulphide (H₂S), carbon monoxide and nitric oxide (NO) have been identified as plant signaling agents and have been shown to be associated with senescence processes in horticultural produce. This thesis examined the ability of H₂S to inhibit senescence in a range of leafy green vegetables, with pak choy the main target species. The initial study of the thesis determined that fumigation of pak choy with 250 μL/L H₂S for 4 hr was as the optimal concentration for extending postharvest life at 10°C. Fumigation was found to affect a range of physiological properties including endogenous ethylene production, rate of chlorophyll degradation, respiration, weight loss, ion leakage and antioxidant activity. It was considered that H₂S inhibited both the favourably affected exogenous ethylene action and endogenous action of ethylene. Studies involving fumigation with H₂S and 100 μL L-1 NO in the presence of 0.1μL/L ethylene were conducted and were found to successfully inhibit chlorophyll loss and decrease respiration in pak choy, with individual gas studies showing H₂S fumigation alone to be the more effective treatment. The inhibition of senescence of pak choy by H₂S was then studied in comparison with 1-MCP a known inhibitor of ethylene action. In the absence of exogenous ethylene both H₂S fumigation and 1-MCP treatment were found to be equally effective, while in the presence of exogenous ethylene, 1-MCP proved a more effective anti-senescence treatment. It was concluded that for pak choy, 1-MCP was a more effective inhibitor of ethylene action than H₂S. The interaction of exogenous H₂S fumigation with PAG, a known inhibitor of endogenous H₂S production in both plants and mammals, was examined. In these experiments, fumigation with H₂S gas significantly extended the postharvest life of pak choy, while treatment with PAG (as a spray) accelerated senescence. Sequential treatment involving application of H₂S followed by PAG produced varied responses in the individual senescence factors assessed. The findings suggest that the action of PAG was not solely limited to action on endogenous H₂S production pathways, presumably because of its known mode of action in inactivating pyridoxal phosphate, a cofactor form many biochemical processes. Potential commercial applications involving the use of H₂S gas a fumigant present significant logistical and regulatory barriers. D- and L-Cysteine are the exclusive metabolic precursors of endogenous H₂S in plants. L-cysteine has identified Generally Regarded as Safe (GRAS) status. Experiments assessing spray treatment of pak choy leaves with 10 mmol D-, L- or DL-cysteine were conducted and found to be equally effective in inhibiting senescence and are considered to have commercial potential.
- Subject
- hydrogen sulphide; ethylene; leafy vegetables; pak choy; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1393800
- Identifier
- uon:33610
- Rights
- Copyright 2018 Hebah Muhsien Al Ubeed
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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