Abstract
We used chlorophyll fluorescence imaging to examine the homogeneity of photosynthetic metabolism during CAM in the thick leaves of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie. Intense, persistent fluorescence from a DCMU treated thin leaf of Clematis sp placed beneath a K. daigremontiana leaf was readily detected through the thick leaf. Evidently reabsorption of fluorescence was qualitatively unimportant in the system used. Chlorophyll fluorescence images from 7 mm tissue discs excised from Kalanchoë leaves were collected at 60 s intervals during 20 min transients elicited by red excitation light. Information about patchiness and subsurface processes was gained by statistical factor analysis and Fourier transform. Although small, highly resolved rings of bright chlorophyll fluorescence surrounding discs of low fluorescence were observed from cells near the surface, no independent regional temporal variation in fluorescence was evident in the surface-biased images. Temporally independent chlorophyll fluorescence was present in images biased towards sub-epidermal sources, in most phases of CAM, and during endogenous rhythm. These asynchronous changes were several millimetres apart. This patchy fluorescence was confirmed when attached leaves were excited with blue light in a leaf chamber while CO2 and H2 O exchange was monitored. Large spatio-temporal variations in the efficiency of photosystem II were always observed during phases II and IV of CAM, when both CO2 fixation cycles are active, and during the maximum rate of CO2 fixation during the endogenous rhythm in continuous light. These data are discussed in terms of metabolic isolation in the thick but uniform tissues in which gas diffusion may be largely confined to wet cell walls, thereby rendering the tissue functionally heterobaric. Prolonged, but in some instances, reversible alterations in PSII efficiency could be produced by injection of metabolic inhibitors, confirming that patchy fluorescence may reflect the differing energy costs of photosynthesis in different CAM phases.
Abbreviations
CAM: Crassulacean acid metabolism
DCDP: 3,3-dichloro-2-dihydroxyphosphinoyl-methyl-2-propenoate
DCMU: 3,4-dichlorophenyl-1,1-dimethylurea
DTT: 1,4-dithiothreitol
ML: maximum likelihood
NPQ: non-photochemical quenching
PC: principal components
PEPCase: phosphoenolpyruvate-carboxylase
Rubisco: ribulose-1,5-bisphosphate-carboxylase-oxygenase
ΦPSII : effective quantum efficiency of photosystem II
Key words
Chlorophyll a fluorescence - Crassulacean acid metabolism (CAM) - effective quantum yield of photosynthesis - factor analysis - fluorescence imaging - fluorescence heterogeneity -
Kalanchoë daigremontiana
- Fourier image processing - spatio-temporal pattern formation
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1 Dedicated to the memory of the late George G. Laties.
B. Osmond
Biosphere 2 Center Columbia University
PO Box 689 Oracle, AZ 85623 USA
eMail: osmond@bio2.columbia.edu
Section Editor: H. Rennenberg