Development of the Kranz structure during leaf growth in C4
Euphorbia maculate |
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Authors: | InSun Kim Jae -Hong Pak Bong -Bo Seo Seung -Dal Song |
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Institution: | (1) Department of Biology, Keimyung University, 704-701 Taegu, Korea;(2) Department of Biology, Kyungpook National University, 702-701 Taegu, Korea |
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Abstract: | The development of the Kranz structure was investigated in leaves of C4
Euphorbia maculata using electron microscopy. Four leaf stages, i.e., primordial, immature, young, and mature, were examined, based on the photosynthetic
tissue that surrounded the veins. The examination revealed how cells differentiated into distinct bundle sheath cells (BSCs)
and mesophyll cells (MCs). Specialization of the BSCs was invariably associated with the development of the veins as well
as the MCs. Precursors for BSC and MC were recognizable fairly early, at the immature stage, according to their position and
differential enlargement Once these precursors were delimited from the procambial area, differentiation into each cell type
occurred synchronously, in a coordinated manner. All cells enlarged as they were displaced from the Kranz precursor area,
but the BSC precursors were initially larger and remained relatively larger than the other cell types throughout leaf development
The developmental changes sharply distinguished BSCs from the adjacent MCs at the onset of Kranz formation and continued until
maturity. Chloroplast enlargement also occurred during cell displacement, but the rate of enlargement was greater in BSCs,
resulting in larger chloroplasts at later stages. However, no significant structural differences were detected among the chloroplasts
of BSC and MC in the early stages. Most of the specialized features appeared at the young-leaf stage; structural dimorphism
became prominent at the later stages. This enhanced development of the BSC chloroplasts was correlated with asymmetric distribution
of cellular components. In addition, the BSC formed thin primary pit fields with numerous plasmodesmata. Peripheral reticulum
was present, but generally was not conspicuous. We also discuss the characteristics of leaf anatomy and ultrastructure inE. maculata as they relate to the C4 photosynthetic pathway. |
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Keywords: | C4 species cell differentiation Euphorbia maculate Kranz development ultrastructure |
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