Changes in the plastid ultrastructure duringSedum rotundifolium leaf development |
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Authors: | Sun Kim |
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Institution: | (1) Department of Biological Science Education, College of Education, Chosun University, Gwangju, 501-759, Republic of Korea |
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Abstract: | The ultrastructure of plastids was investigated in succulent leaves ofSedum rotundifolium to examine their changes during development. Leaves were categorized as etiolated, immature, young, and mature, based on
their developmental stage and size. Of particular interest were the features of the tubular inclusion bodies (TIBs) and starch
grains. These, along with vacuole size, showed remarkable changes over time. Etioplasts of unexposed leaves had prolamellar
bodies, abundant starch grains, large TIB, few plastoglobuli, and thylakoid systems. Membranes of the thylakoids were still
continuous with those of the prolamellar body. The plastids were often influenced by the presence and profile of inclusion
bodies and starch grains throughout the early stages. Morphology was highly variable in the etioplasts but consistently hemispherical
or ovoid in mature chloroplasts. TIB was most abundant in the etiolated leaves, but disappeared completely with development.
Starch grains also became significantly reduced in size. Both young and mature mesophyll cells exhibited a normal chloroplast
ultra-structure and huge central vacuoles, with an extremely thin peripheral cytoplasm. Grana were extensive and comprised
a large portion of the chloroplasts. Traces of peripheral reticulum were also discovered in the chloroplasts of expanded leaves.
The implications of these ultrastructural changes in the tubular inclusions and starch grains are discussed with relevance
to Crassulacean acid metabolism (CAM). |
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