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Journal of Cell Science, Vol 4, 155-169, Copyright © 1969 by Company of Biologists
Submitted on March 20, 1968
1 Department of Botany, University of Wisconsin, Madison, Wisconsin, U.S.A.
The development of P-protein (slime) in the phloem of Coleus stem apices has been studied electron microscopically using material fixed in glutaraldehyde followed by osmium tetroxide. In phloem parenchyma cells the earliest-appearing groups of tubular P-protein commonly are seen as close association with clusters of ‘spiny’ vesicles similar to those reported in Phaseolus phloem (Newcomb, 1967). The vesicles break down as the P-protein masses enlarge, and are assumed to contribute to P-protein formation. Subsequently the groups of tubules are consolidated into a single spindle-shaped body aligned longitudinally in each phloem parenchyma cell or sieve element. The microtubules observed frequently in the vicinity of the young P-protein body may play a role in its consolidation or in the longitudinal alignment of its constituent tubules. Some P-protein bodies acquire a highly organized structure in which the tubules are arranged hexagonally around lightly staining centres.
Disaggregation of the P-protein body occurs during disintegration of the cytoplasm and nucleus, and results initially in the presence of swirls of packed fibrils. During disaggregation, the tubules of the mature P-protein body, which are about 200 Å in diameter, are converted to fibrils about 70 Å in diameter in a process apparently with several intermediate stages. In longitudinal view the fibrils exhibit alternate electron transparent and dense bands that impart a striated appearance to the mass. During maturation of the sieve element the swirls of fibrillar masses separate into individual fibrils which become dispersed through the cell lumen.
Submitted on March 20, 1968
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