Leaf inner structure and immunogold localization of some key enzymes involved in carbon metabolism in CAM plants |
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Authors: | Kondo A; Nose A; Ueno O |
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Institution: | Faculty of Agriculture, Saga University, Honjo, Saga 840-8502, Japan; Department of Plant Physiology, National Institute of Agrobiological Resources, Tsukuba, Ibaraki 305-8602, Japan; Corresponding author e-mail: uenoos@abr.affrc.go.jp |
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Abstract: | There are relatively few reports on the leaf structure and in
situ immunolocalization of carbon metabolism enzymes in
crassulacean acid metabolism (CAM) plants, compared with reports on C4
plants. The leaf inner structure and the subcellular location of some key
CAM enzymes for a phosphoenolpyruvate carboxykinase (PCK) CAM species,
Ananas comosus, and three malic enzyme (ME) CAM
species, Mesembryanthemum crystallinum, Kalanchoe
daigremontiana, and K. pinnata, was
investigated by immunogold labelling and electron microscopy in this study.
The leaves of these species had few intercellular air spaces in the
mesophyll. A large vacuole occupied the mesophyll cells, and many vesicles
of various sizes occurred in the cytosol. Immunocytochemical study revealed
that labelling was present for phosphoenolpyruvate carboxylase in the
cytosol and for ribulose-1,5-bisphosphate carboxylase/oxygenase in the
chloroplasts of the mesophyll cells in all species. No specific labelling
for pyruvate orthophosphate dikinase (PPDK) was observed in the PCK-CAM
species. In the ME-CAM species, the patterns of labelling for PPDK
differed. In M. crystallinum labelling for PPDK was
present only in the chloroplasts, whereas in the two
Kalanchoe species it occurred in the cytosol
as well as in the chloroplasts. These results suggest that the subcellular
localization of PPDK varies with ME-CAM species, in contrast to the
conventional belief that it is localized in the chloroplasts.Key
words: Crassulacean acid metabolism, immunolocalization, leaf
inner structure, phosphoenolpyruvate carboxylase, pyruvate orthophosphate
dikinase.
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