Dark-Induced Leaf Senescence

: Environmental Regulation, Manipulation and Application

Abstract

Leaf senescence is the final stage of leaf development and is characterised by the
transition from nutrient assimilation to nutrient remobilisation. The most notable visual
symptom of leaf senescence is leaf yellowing resulting from chlorophyll degradation and
chloroplast dismantling, as seen in autumnal foliage. The initiation and progression of
leaf senescence are tightly controlled by external and developmental cues and are
essential for plant fitness. Premature leaf senescence can be induced by biotic or abiotic
stress, such as prolonged darkness. This can reduce the shelf life and nutritional quality
of harvested crops, so is of key agricultural importance. As such, extensive efforts have
been made to dissect the regulatory mechanisms controlling leaf senescence and develop
strategies for inhibiting the premature onset of this process. This thesis investigates the
effectiveness of low-irradiance UV-B treatments in the suppression of dark-induced leaf
senescence (DIS) in Arabidopsis thaliana. Low-irradiance UV-B light, perceived by the UV
RESISTANCE LOCUS 8 (UVR8) photoreceptor, is an essential photomorphogenic cue
regulating plant development, yet studies describing the regulation of DIS by UV-B are
limited. Here, a UVR8-dependent role for low-irradiance UV-B in the transient inhibition
of DIS in both cotyledons and mature leaves is presented. The basic helix-loop-helix
transcription factors PHYTOCHROME INTERACTING FACTOR4 (PIF4) and PIF5 have
previously been identified as key promoters of DIS. This thesis presents a novel role for
PIF7 in regulating DIS and a potential regulatory mechanism by which PIF7 function is
controlled by UV-B. Laboratory methods for studying DIS developed in this thesis are also
applied to agriculturally relevant trials to assess whether vitamin B12 biofortification
affects the shelf life of Pisium sativum shoots.

Date of Award	30 Sept 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Keara A Franklin (Supervisor) & Alistair Hetherington (Supervisor)