The significance of non-foliar photosynthesis on development and nutritional value in tomato fruit
Publication Date
July 30, 2026
Creator
Williams, Alexander
Abstract
The primary aim of this study was to investigate whether the targeted manipulation of CBB cycle enzymes and chlorophyll partitioning could be used to improve photosynthetic performance, biomass accumulation, and metabolic composition in tomato fruit. During the early stages of fruit development, many fruits contain high quantities of chlorophyll along with the apparatus required to successfully photosynthesise. In species such as Solanum lycopersicum (tomato), 29% of all photosynthetic electron transport activity occurs in non-foliar organs such as the green fruit, supporting tissues and calyces. This form of photosynthesis is called non-foliar photosynthesis (NFP). Recent studies have shown that NFP, like leaf photosynthesis, significantly contributes to the production of photoassimilates. Studies have shown that improving photosynthetic efficiency in leaves can have a significant impact on biomass and nutritional quality. Similar improvements to NFP may have a comparable effect. However, NFP remains an underexplored area, despite the numerous potential benefits.
The Calvin-Benson-Bassham (CBB) cycle and light-harvesting apparatus could be targeted within fruit to improve their photosynthetic capacity, efficiency, and rate. In doing so, it will aid in determining the significance of NFP.
Through genetic modification, fruit-specific promoters were introduced that allow for selective differential expression of my genes of interest, Sedoheptulose-1,7-bisphosphatase (SBPase) and Fructose 1,6-bisphosphate aldolase (FBPa), to generate novel tomato lines. My genes of interest are enzymes that catalyse a critical step in the regeneration of ribulose-1,5-bisphosphate (RuBP), necessary for continuous CO₂ fixation. Additionally, I silenced the expression of Chlorophyll a Oxygenase (CAO) in fruit via RNAi. This enzyme is essential for the conversion of chlorophyll a to chlorophyll b; its silencing reduces the antenna size within the light-harvesting complex. This reduction allows for photosynthetically active radiation (PAR) to penetrate further into the fruit pericarp. This potentially allows more light-harvesting complexes to participate, enhancing light use efficiency by reducing non-photochemical quenching (NPQ). These studies aided me in assessing how fruit photosynthesis contributes to developmental processes and quality traits.
This project identified that the significance of fruit photosynthesis cannot be directly inferred from leaf studies, as tomato fruit are a complex and unique regulatory environment with distinct metabolic constraints. It was identified that silencing the enzyme led to increased sugar accumulation in fruit, while overexpressing the enzyme did not enhance compositional traits and reduced PSII efficiency. While FBPA overexpression did not alter fruit photosynthetic efficiency, a decoupling between biomass accumulation and sugar content occurred as the fruit biomass increased at the expense of soluble sugar concentration. I identified that silencing CAO in fruit has a measurable effect on carotenoid partitioning, PSII function (under specific conditions) and causes a shift in carbon partitioning away from sugar accumulation. The suggestions proposed towards further studies are of interest to the fruit industry and consumers alike.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Simkin Andrew J
Subjects (LC)
Associated Schools / Departments
UoN Repository URI
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Corrected PhD Thesis Alexander Williams (14298425).pdf
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