Studies on the secretion of maize root-cap slime : III. Histochemical and autoradiographic localization of incorporated fucose
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1Department of Botany, University of California, 94720, Berkeley, California, USA.
Abstract:
Autoradiography was used to localize the sites of incorporation of L-[(3)H]fucose into root tips of maize (Zea mays L. cv. S.X. 17). By light microsocpy, accumulation of label from [(3)H]fucose could be seen in the peripheral cells of the root cap. Extraction of sections prepared by freeze-substitution showed that most of the label in the cytoplasm of peripheral root-cap cells is water-soluble whereas label associated with the wall is sodiumhydroxide-soluble. In the electron microscope, glutaraldehyde-fixed peripheral cells of maize root caps are characterized by the presence of numerous dictyosomes and vesicles. The distended dictyosome cisternae and vesicles have large deposits of silver after staining with periodic acid-silver methanamine. An accumulation of material similar to that found in dictyosomes and vesicles is observed between the cell membrane and wall in glutaraldehyde-formaldehyde-fixed tissue. At the electron-microscope level label in peripheral root cap cells incubated in [(3)H]fucose for periods from 10 to 120 min was found primarily over dictyosomes and dictyosome vesicles. In pulse-chase experiments label was chased from the dictyosomes and vesicles to the exterior of the cell in 20-30 min. Less than 19% of the label in pulse-chase experiments was associated with organelles other than dictyosomes or dictyosome vesicles.
Insights
Researchers traced L-fucose incorporation in maize root tips using autoradiography. The study found that this sugar is primarily processed by dictyosomes and vesicles in root cap cells before secretion.
Area of Science:
- Plant Biology
- Cell Biology
- Biochemistry
Background:
- Root cap cells play a crucial role in plant growth and protection.
- Understanding cell wall synthesis and secretion is vital for plant development.
Purpose of the Study:
- To investigate the cellular localization and transport pathway of L-fucose in maize (Zea mays L.) root tips.
- To elucidate the role of dictyosomes and vesicles in L-fucose metabolism and secretion.
Main Methods:
- Autoradiography with L-[(3)H]fucose to trace sugar incorporation.
- Light and electron microscopy for cellular localization.
- Freeze-substitution and chemical fixation techniques.
- Pulse-chase experiments to track label movement.
Main Results:
- L-fucose incorporation was primarily observed in peripheral root cap cells.
- Label accumulated in dictyosomes and associated vesicles within these cells.
- Pulse-chase experiments demonstrated rapid transport from dictyosomes to the cell exterior within 20-30 minutes.
- Most of the incorporated L-fucose was water-soluble in the cytoplasm and NaOH-soluble in the cell wall.
Conclusions:
- Dictyosomes and vesicles are the primary sites for L-fucose processing and packaging in maize root cap cells.
- L-fucose is rapidly secreted from these cells, likely contributing to the root cap's extracellular matrix.
- This pathway highlights the dynamic role of the Golgi apparatus in plant cell wall component synthesis and secretion.
