Summary
Portions of the hypocotyls of 16-day-old Cucurbita maxima plants, from which the cotyledons and first foliage leaves had been removed 2 days earlier, were fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. In well over 90% of the mature sieve elements examined the P-protein was entirely parietal in distribution in both the lumina and sieve-plate pores. In addition to the parietal P-protein, the unoccluded sieve-plate pores were lined by narrow callose cylinders and the plasmalemma. Segments of endoplasmic reticulum also occurred along the margins of the pores.
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Evert, R.F., Eschrich, W. & Eichhorn, S.E. P-protein distribution in mature sieve elements of Cucurbita maxima . Planta 109, 193–210 (1972). https://doi.org/10.1007/BF00387084
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DOI: https://doi.org/10.1007/BF00387084