Chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant physiologists and ecophysiologists. This review aims to provide an introduction for the novice into the methodology and applications of chlorophyll fluorescence. After a brief introduction into the theoretical background of the technique, the methodology and some of the technical pitfalls that can be encountered are explained. A selection of examples is then used to illustrate the types of information that fluorescence can provide.
Chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant physiologists and ecophysiologists. This review aims to provide an introduction for the novice into the methodology and applications of chlorophyll fluorescence. After a brief introduction into the theoretical background of the technique, the methodology and some of the technical pitfalls that can be encountered are explained. A selection of examples is then used to illustrate the types of information that fluorescence can provide.
The occurrence, activity and plasticity of the CAM pathway is described from an introductory viewpoint, framed by the use of the four "Phases" of CAM as comparative indicators of the interplay between environmental constraints and internal molecular and biochemical regulation. Having described a number of "rules" which seem to govern the CAM cycle and apply uniformly to most species, a number of key regulatory points can then be identified. These include temporal separation of carboxylases, based on the circadian expression of key genes and their control by metabolites. The role of a circadian oscillator and interplay between tonoplast and nuclear control are central to maintaining the CAM cycle. Control of reserve carbohydrates is often neglected, but the importance of daily partitioning (for growth and the subsequent night-time CAM activity) and use at night is shown to drive the CAM cycle. Finally, it is shown that the genotypic and phenotypic plasticity in patterns of CAM expression is mediated partly by environmental conditions and molecular signalling, but also by diffusive constraints in succulent tissues. A transformation system is now required to allow these key areas of control to be elucidated.
Leaf internal conductance to CO2
(gi) from substomatal cavity to
the carboxylation sites of Rubisco was measured in the leaf succulent CAM
species, Kalanchoe daigremontiana Hamet et Perr.
Measurements were made during Rubisco-mediated atmospheric
C3 carboxylation in phase IV photosynthesis. Using
simultaneous gas exchange and chlorophyll fluorescence techniques, internal
conductance was calculated to be 0.05 mol m-2
s-1 bar-1 , when measured at both
saturating and limiting light. This is one of the lowest recorded values for
gi as compared to a range of
C3 species with comparable Rubisco content and indicates
a large diffusion limitation to atmospheric CO2 fixation
through the C3 pathway in
K. daigremontiana. In ambient air,
CO2 partial pressure at the carboxylation sites of
Rubisco was 109 µbar. Internal diffusion is limited by a thick leaf
consisting of densely packed, succulent mesophyll with a small portion of
airspace. We speculate that a low internal conductance to
CO2 diffusion results from the compromise between a
succulent mesophyll required for C4 acid storage and
access for CO2 diffusion to both PEPC in the cytoplasm
and Rubisco in the chloroplasts. Restricted diffusion of
CO2 within the leaf makes CO2
assimilation less efficient during the transient phases of crassulacean acid
metabolism.
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