The lower oxygen limit (LOL) in plants marks the oxygen (O2) level where the
metabolism shifts from being predominantly aerobic to anaerobic; recent work has shown
that respiratory-based indicators of this metabolic shift are well-correlated with changes
in chlorophyll a fluorescence signals. The physiological and biochemical changes at the
root of this relationship have not been well-described in the literature. The processes
involved are spatially separated: chlorophyll fluorescence is associated with the lightdependent
reactions and emanates from the chloroplasts whereas aerobic respiration and
fermentation occurs in the mitochondria and cytosol, respectively. Evidences outlined in
this thesis are used to suggest the mechanistic link between these three regions of the cell
is a fluid exchange of cellular reductant. When mitochondrial respiration is inhibited as a
result of inadequate O2, used as a terminal electron acceptor, glycolytic reductant in the
form of NADH accumulates in the cytosol. Reductant imbalances between the cytosol
and organelles can be adjusted indirectly using translocators. Excess chloroplastic
reductant is used to reduce the plastoquinone (PQ) pool via NADPH-dehydrogenase, a
component of the chlororespiratory pathway, effectively decreasing the photochemical
quenching (qP) capacity thereby inducing a switch from minimum fluorescence (Fo) to a
higher relative fluorescence (F) value where qP < 1. Subjecting dark-adapted
photosystems to low-intensity light increased Fo to a slightly higher F value due to a lightinduced
reduction of the oxidized PQ pool when the O2 was above the LOL, but
decreased F as a result of a PSI-driven oxidation of the already over-reduced PQ pool
when the O2 was below the LOL. Low O2 was also shown to increase violaxanthin deepoxidation
and non-photochemical quenching (qN), likely a reflection of the overreduced
state of the photosystems and associated pH decrease.
Dynamic controlled atmosphere (DCA) is a fluorescence-based controlled atmosphere
(CA) system that sets the optimum atmosphere for fruits and vegetables based on a
product’s fluorescence response. Experiments in this thesis on the relationship between
O2, temperature, light, metabolism, pigmentation and chlorophyll fluorescence were used
to interpret the physiology behind fluorescence changes, suggest improved DCA
techniques and outline potentially profitable avenues for future research.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/13979 |
| Date | 09 June 2011 |
| Creators | Wright, Harrison |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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