Abstract:
Phloridzin is a major flavonoid in apple (Malus x domestica) with positive health benefits for human health. It has been shown to reduce blood glucose level by blocking glucose absorption and reabsorption. Recent studies have shown phloridzin may be responsible for a range of functions in the plant from pathogen defence to growth regulation. However, these studies remain inconclusive.This is thesis a range of biotic and abiotic stresses were applied to apple leaves and their effects on phloridzin levels were analysed. No major changes in phloridzin content was detected by most abiotic stresses. However changes were detected after wounding and infection with the apple scab pathogen Venturia inaequalis. This suggests phloridzin may be involved in wounding and pathogen defence in plants. A fruit developmental series was conducted where phloridzin levels, and the transcripts of six key phloridzin biosynthetic genes were measured. Phloridzin level was observed to drop dramatically after early fruit development, while PAL and CHS expression correlated strongly with this reduction. Russeting is often considered a defect on fruit, where a brown-green crust is formed. Metabolite analysis showed rusetted patches have an elevated phloridzin content compared to non-russetted patches. A strong negative correlation was observed between phloridzin level and CHI expression. This suggests that CHI can channel metabolites away from phloridzin and could have a negative effect on phlroidzin synthesis. A tobacco (Nicotiana benthamiana) infiltration study was performed with MYB93, a russet-related transcription factor linked to suberin biosynthesis. Results showed elevated phloridzin levels in tobacco co-infiltrated with MYB10. This suggests MYB93 is a potential positive regulator for phloridzin accumulation.
